text:
Maximum terminal velocity of relativistic rocket
G. Vulpetti
The maximum terminal velocity problem of the classical propulsion is extended to a relativistic rocket assumed broken down into active mass, inert mass and gross payload. A fraction of the active mass is converted into energy shared between inert mass and active mass residual. Significant effects are considered. State and co-state equations are carried out to find the exhaust speed
Maximum Possible Transverse Velocity in Special Relativity.
ERIC Educational Resources Information Center
Medhekar, Sarang
Using a physical picture, an expression for the maximum possible transverse velocity and orientation required for that by a linear emitter in special theory of relativity has been derived. A differential calculus method is also used to derive the expression. (Author/KR)
Velocity Filtration (VF), Coronae and Winds
Jack Scudder
The approach of VF for coronal winds is not built on a presumption of an equation of state for the underlying coronal plasma; all moments are retained as VF addresses the classes of velocity space access of assumed non-thermal boundary distributions in the coherent forces of gravity, magnetic field, and electric field. The principal virtues of velocity filtration are: 1)
Maximum wind energy extraction strategies using power electronic converters
Quincy Qing Wang
This thesis focuses on maximum wind energy extraction strategies for achieving the highest energy output of variable speed wind turbine power generation systems. Power electronic converters and controls provide the basic platform to accomplish the research of this thesis in both hardware and software aspects. In order to send wind energy to a utility grid, a variable speed wind turbine
Satellite-tracked cumulus velocities. [for determining wind velocity
NASA Technical Reports Server (NTRS)
Fujita, T. T.; Pearl, E. W.; Shenk, W. E.
The research indicates that extreme caution must be exercised in converting cloud velocities into winds. The motion of fair-weather cumuli obtained by tracking their shadows over Springfield, Missouri revealed that the standard deviation in the individual cloud motion is several times the tracking error. The motion of over-ocean cumuli near Barbados clearly indicated the complicated nature of cumulus velocities. Analysis of whole-sky images obtained near Tampa, Florida failed to show significant continuity and stability of cumulus plumes, less than 0.3 mile in diameter. Cumulus turrets with 0.3 to 2 mile in size appear to be the best target to infer the mean wind within the subcloud layers. Cumulus or stratocumulus cells consisting of x number of turrets do not always move with wind. The addition and deletion of turrets belonging to a specific cell appear to be the cause of the erratic motion of a tracer cell. It may by concluded that the accuracy of wind estimates is unlikely to be better than 2m/sec unless the physical and dynamical characteristics of cumulus motion is futher investigated.
Maximum mass-loss rates of line-driven winds of massive stars
NASA Astrophysics Data System (ADS)
Aerts, C.; Lamers, H. J. G. L. M.
We develop a theoretical treatment that allows us to determine the maximum mass-loss rate of a hot rotating star with a wind that is accelerated by radiation pressure due to spectral lines, taking into account finite disk correction as well as the effect of photon tiring but neglecting multiple scattering. The maximum mass-loss rate of a star is obtained by subsequent numerical integrations of the momentum equation from an assumed position of the sonic point onwards for increasing values of the mass loss, until the wind can no longer escape. For stars rotating below 80% of the critical velocity the decrease in the velocity far out in the wind due to the maximisation of the mass loss is negligible. Stars rotating at >80% of the critical speed have a kinked velocity law connected with the highest possible mass-loss rate. In such cases the wind velocity increases up to typically a few stellar radii, and decreases subsequently almost ballistically outwards. In these cases the terminal wind velocity is much smaller than the maximum wind velocity. For O-type main-sequence stars, the maximum mass-loss rates derived from our formalism are somewhat smaller than those derived for self-regulated line-driven winds including multiple scattering. For B-type supergiants, however, the maximum mass-loss rate is higher by about a factor 1.5-2. Including rotation, but without gravity darkening, results in a maximum mass-loss rate that is twice as high as for a non-rotating star.
Maximum power tracking control scheme for wind generator systemsĀ
Mena, Hugo Eduardo
The purpose of this work is to develop a maximum power tracking control strategy for variable speed wind turbine systems. Modern wind turbine control systems are slow, and they depend on the design parameters of the turbine and use wind and/or rotor...
Maximum power tracking control scheme for wind generator systemsĀ
Mena Lopez, Hugo Eduardo
The purpose of this work is to develop a maximum power tracking control strategy for variable speed wind turbine systems. Modern wind turbine control systems are slow, and they depend on the design parameters of the turbine and use wind and/or rotor...
Sodar-derived structural functions of the wind velocity field
L. G. Shamanaeva
The structural functions of the wind velocity field reconstructed from the vertical profiles of the wind velocity vector measured with the Zvuk-2 three-channel monostatic Doppler sodar (1700 Hz) and a commercial minisodar of the Atmospheric Systems Corporation (4900 Hz) are presented in the report. The Doppler sodars allow long-term series of instantaneous values of the three wind velocity components in
An approximate, maximum terminal velocity descent to a point
Eisler, G.R.; Hull, D.G.
No closed form control solution exists for maximizing the terminal velocity of a hypersonic glider at an arbitrary point. As an alternative, this study uses neighboring extremal theory to provide a sampled data feedback law to guide the vehicle to a constrained ground range and altitude. The guidance algorithm is divided into two parts: 1) computation of a nominal, approximate, maximum terminal velocity trajectory to a constrained final altitude and computation of the resulting unconstrained groundrange, and 2) computation of the neighboring extremal control perturbation at the sample value of flight path angle to compensate for changes in the approximate physical model and enable the vehicle to reach the on-board computed groundrange. The trajectories are characterized by glide and dive flight to the target to minimize the time spent in the denser parts of the atmosphere. The proposed on-line scheme successfully brings the final altitude and range constraints together, as well as compensates for differences in flight model, atmosphere, and aerodynamics at the expense of guidance update computation time. Comparison with an independent, parameter optimization solution for the terminal velocity is excellent. 6 refs., 3 figs.
Velocity shear generation of solar wind turbulence
Roberts, D.A.; Goldstein, M.L.; Ghosh, S. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Matthaeus, W.H. [Univ. of Delaware, Newark, DE (United States)
The authors use a two-dimensional, incompressible MHD spectral code to establish that shear-driven turbulence is a possible means for producing many observed properties of the evolution of the magnetic and velocity fluctuations in the solar wind and, in particular, the evolution of the cross helicity ({open_quotes}Alfvenicity{close_quotes}) at small scales. They find that large-scale shear can nonlinearly produce a cascade to smaller scale fluctuations even when the linear Kelvin-Helmholtz mode is stable and that a roughly power law inertial range is established by this process. While the fluctuations thus produced are not Alfvenic, they are nearly equipartitioned between magnetic and kinetic energy. The authors report simulations with Alfvenic fluctuations at high wave numbers, both with and without shear layers and find that it is the low cross helicity at low wave numbers that is critical to the cross helicity evolution, rather than the geometry of the flow or the dominance of kinetic energy at large scales. The fluctuations produced by shear effects are shown to evolve similarly but more slowly in the presence of a larger mean field and to be anisotropic with a preferred direction of spectral transfer perpendicular to the mean field. The evolution found is similar to that seen in some other simulations of HMD turbulence, and thus seems in many respects to be an instance of a more generic turbulent evolution rather than due to specific conditions in the solar wind. 75 refs., 18 figs.
Estimating maximum global wind power availability and associated climatic consequences
NASA Astrophysics Data System (ADS)
Miller, Lee; Gans, Fabian; Kleidon, Axel
Estimating maximum global wind power availability and associated climatic consequences Wind speed reflects the continuous generation of kinetic energy and its dissipation, primarily in the atmospheric boundary layer. When wind turbines extract kinetic wind energy, less kinetic energy remains in the atmosphere in the mean state. While this effect does not play a significant role for a single turbine, it becomes a critical factor for the estimation of large-scale wind power availability. This extraction of kinetic energy by turbines also competes with the natural processes of kinetic energy dissipation, thus setting fundamental limits on extractability that are not considered in previous large-scale studies [1,2,3]. Our simple momentum balance model using ECMWF climate data illustrates a fundamental limit to global wind power extractability and thereby electricity potential (93TW). This is independent of engineering advances in turbine design and wind farm layout. These results are supported by similar results using a global climate model of intermediate complexity. Varying the surface drag coefficient with different simulations allows us to directly relate changes in atmospheric and boundary layer dissipation with resulting climate indices and wind power potential. These new estimates of the maximum power generation by wind turbines are well above the currently installed capacity. Hence, present day installations are unlikely to have a global impact. However, when compared to the current human energy demand of 17TW combined with plans by the US and EU to drastically increase onshore and offshore wind turbine installations [4,5,6], understanding the climatic response and ultimate limitations of wind power as a large-scale renewable energy source is critical. [1] Archer, C., and M.Z. Jacobson, (2005) Evaluation of global wind power, J. Geophys. Res. 110:D12110. [2] Lu, X., M.B. McElroy, and J. Kiviluoma, (2009) Global potential for wind-generated electricity, Proc Natl Acad Sci, 106. [3] Liu, W.T., W. Tang, and X. Xie, (2008) Wind power distribution over the ocean, Geophys. Res. Lett., 35 L13808. [4] IPCC, (2008) IPCC scoping meeting on renewable energy sources - proceedings, Intergovernmental Panel on Climate Change [5] U.S. Department of Energy, (2008) 20% wind energy by 2030: increasing wind energy's contribution to U.S. electricity supply, U.S. Dept. of Energy - Energy Information Administration. [6] EEA, (2009) Europe's onshore and offshore wind energy potential, European Environment Agency, ISSN 1725-2237.
Wind velocity profiles measured by the smoke-trail method at the Eastern Test Range, 1964
NASA Technical Reports Server (NTRS)
Manning, J. C.; Rhyne, R. H.; Henry, R. M.
Twenty-six detailed wind profiles measured by the smoke trail technique at the Eastern Test Range during the first seven months of 1964 are presented as plots of west-to-east and south-to-north velocity components at height intervals of 25 meters. The overall altitude ranges of the profiles vary from about 2.6 to 19.1 km. The wind measurements, which were made under a variety of conditions, include velocities in excess of the 90- and 95-percent highest values for the Eastern Test Range. The report also includes a listing of the wind profiles, their maximum velocities and direction of the maximum velocities, measured by the smoke trail method at the Eastern Test Range from 1962 to 1964.
TOWARDS VERTICAL VELOCITY AND HYDROMETEOR CLASSIFICATION FROM ARM WIND PROFILERS Scott Giangrande of Science ABSTRACT With support from the ARM Climate Research Facility infrastructure, two radar wind for studying deep convective clouds as part of larger ARM efforts towards the estimation of vertical velocity
Wind velocity effects on sampling rate of NO2 badge.
Lee, K; Yanagisawa, Y; Spengler, J D; Billick, I H
The effects of wind velocity on a sampling rate of a nitrogen dioxide (NO2) diffusive badge were experimentally determined using a turntable. The use of a turntable permits the collection of the large amounts of data that are needed for statistically reliable results at several wind velocities in one experiment. The regression model for the wind effect determined by these experiments was closely correlated with data previously gathered from experiments using wind tunnels. Experiments at two different relative humidities, 35% and 60%, were performed and analyzed by a simple least square regression model. A multi-regression model containing two independent variables, wind velocity and relative humidity, also was developed. The multi-regression model was useful at relative humidity between 20% and 60% and wind velocity between 0 and 7 meter per second (m/sec). PMID:1515772
Influence of sand grain diameter and wind velocity on lift-off velocities of sand particles.
Bo, Tian-Li; Zheng, Xiao-Jing; Duan, Shao-Zhen; Liang, Yi-Rui
In this paper, the velocities of sand particles near the sand bed in the saltation cloud were measured in a wind tunnel through an improved experimental scheme of the Particle Image Velocimetry (PIV) system. The influences of the diameter of sand particles in the saltation cloud and wind velocity on the probability distribution function (PDF) of lift-off velocities of sand particles were investigated. Results demonstrate that for the sand particles saltating above the sand bed with the mean grain diameter (d m = 0.3 mm), smaller and larger ones have the same velocity distribution, and wind velocity has no obvious influence on the distribution shape of the lift-off velocities, i.e., the PDFs of the horizontal and vertical lift-off velocities both follow a lognormal distribution, but the diameter of sand particles in the saltation cloud and wind velocity have an influence on the parameters of the PDF of horizontal and vertical lift-off velocities. Eventually, we present formulas to describe the PDF of lift-off velocities of sand particles with regard to the influence of wind velocity and the diameter of sand particles in the saltation cloud above the sand bed with d m = 0.3 mm. PMID:23695368
Velocity variations in the high-latitude solar wind
Neugebauer, M.; Goldstein, B.E. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States); McComas, D.J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Suess, S.T. [Marshall Space Flight Center, Huntsville, Alabama 35812 (United States); Balogh, A. [Imperial College, London (United Kingdom)
Velocity variations of the solar wind from a south polar coronal hole registered by the Ulysses spacecraft in 1994 are analyzed. Power spectra of hourly averages in the Hz range are presented. {copyright} {ital 1997 American Institute of Physics.}
The Helium Component of Solar Wind Velocity Streams
J. Hirshberg; J. R. Asbridge; D. E. Robbins
Systematic variations of the properties of the helium constituent of the solar wind in the velocity streams are described. It is found that the helium abundance na\\/n, varies by about a factor of 2 as the stream is crossed. The velocity of the helium differs from that of the hydrogen by a few kilometers per second throughout much of the
Velocity Distributions and Proton Beam Production in the Solar Wind
Pierrard, Viviane; Voitenko, Yuriy [Belgian Institute for Space Aeronomy, Ringlaan-3-Avenue Circulaire, B-1180 Brussels (Belgium)
Helios, Ulysses, and Wind spacecraft have observed the velocity distribution functions (VDFs) of solar wind particles deviating significantly from Maxwellians. We review recent models using different approximations and mechanisms that determine various observed characteristics of the VDFs for the electrons, protons and minor ions. A new generation mechanism is proposed for super-Alfvenic proton beams and tails that are often observed in the fast solar wind. The mechanism is based on the proton trapping and acceleration by kinetic Alfven waves (KAWs), which carry a field-aligned potential well propagating with super-Alfven velocities.
Spatiotemporal Dynamics of Wind Velocity from Mini-Sodar Measurements
NASA Astrophysics Data System (ADS)
Krasnenko, N. P.; Tarasenkov, M. V.; Shamanaeva, L. G.
Mini-sodar measurements of wind velocity profiles in the 20-200 m layer have demonstrated the high efficiency of the use of mini-sodars in monitoring the fine structure of the atmospheric boundary layer (ABL) and in detecting jets and wind shear. An analysis of measurements of vertical profiles of the wind velocity and its vertical and horizontal components has shown that analytical approximations of the vertical profile of the horizontal wind velocity are possible for both neutral and unstable stratifications of the atmosphere. They are well described by a logarithmic law. The approximation constants are found and the errors associated with their use are estimated. The established physical trends and the obtained constants for the horizontal and vertical components of the wind velocity allow a description of their hourly and daily dynamics and can be recommended for use in ABL models intended for prognostic calculations (forecasting). The vector representation makes it possible to visualize the spatiotemporal dynamics of the wind field in the atmospheric boundary layer, in particular to estimate the shape and size of jets and wind shear in them.
High-velocity tails on the velocity distribution of solar wind ions
Ogilvie, K.W. (Goddard Space Flight Center, Greenbelt, MD (United States)); Geiss, J. (Univ. of Bern (Swaziland)); Gloeckler, G. (Univ. of Maryland, College Park (United States)); Berdichevsky, D. (Highes-STX, Lanham, MD (United States)); Wilken, B. (Max-Plank-Institut fuer Aeronomie Katlenburg-Lindau (Germany))
Recent observations of the solar wind using the SWICS instrument on the Ulysses spacecraft have shown the presence of high-velocity [open quotes]tails[close quotes] on the velocity distribution of protons. Similar features have also been observed on the velocity distributions of helium and oxygen ions. Of the order of 1% of the solar wind density is involved in these tails, which are approximately exponential in shape and persist to V = V[sub B] + 10V[sub th] or beyond, where V[sub B] is the bulk velocity and V[sub th] the thermal velocity of the solar wind. This paper contains a preliminary description of the phenomenon. It is clear that it is ultimately connected with the passage of interplanetary shocks past the spacecraft and that particle acceleration at oblique shocks is involved. 21 refs., 6 figs., 2 tabs.
Comparison of VLF Wave Activity in the Solar Wind During Solar Maximum and Minimum
California at Berkeley, University of
Comparison of VLF Wave Activity in the Solar Wind During Solar Maximum and Minimum: Ulysses and intermediate speed solar wind. The maximum intensity of the electromagnetic waves for the two solar cycle are similar for the slow and intermediate solar wind in both solar maximum and minimum phases. It is also
Mixture Models for Estimating Maximum Blood Flow Velocity
Marzban, Caren
. Here, two generalizations are examined: 1) skewed gaussian and 2) non- gaussian mixture models. Both ultrasound data. The method was based on a gaussian mixture model for the distribution of blood flow. Mixture" blood flow velocity. But gaussian mixture models are restric- tive in that the distribution of blood
A proposed method for wind velocity measurement from space
NASA Technical Reports Server (NTRS)
Censor, D.; Levine, D. M.
An investigation was made of the feasibility of making wind velocity measurements from space by monitoring the apparent change in the refractive index of the atmosphere induced by motion of the air. The physical principle is the same as that resulting in the phase changes measured in the Fizeau experiment. It is proposed that this phase change could be measured using a three cornered arrangement of satellite borne source and reflectors, around which two laser beams propagate in opposite directions. It is shown that even though the velocity of the satellites is much larger than the wind velocity, factors such as change in satellite position and Doppler shifts can be taken into account in a reasonable manner and the Fizeau phase measured. This phase measurement yields an average wind velocity along the ray path through the atmosphere. The method requires neither high accuracy for satellite position or velocity, nor precise knowledge of the refractive index or its gradient in the atmosphere. However, the method intrinsically yields wind velocity integrated along the ray path; hence to obtain higher spatial resolution, inversion techniques are required.
On the long-tail solar wind electron velocity distribution
NASA Technical Reports Server (NTRS)
Shlesinger, Michael F.; Coplan, Michael A.
The role of the log-normal distribution in the description of the high-energy tail of the electron velocity distribution in the solar wind plasma is examined. Specifically, it is shown that the core-halo solar wind distribution function can be understood in terms of a simple phenomenological model of general applicability in which the core has a Maxwellian or normal distribution and the halo a log-normal distribution. In the presence of structures in the interplanetary medium capable of interacting with the electrons, the model predicts a transition at the highest velocities to a secondary halo distribution.
The turbulence structure of katabatic flows below and above wind-speed maximum
NASA Astrophysics Data System (ADS)
Grachev, Andrey; Leo, Laura; Di Sabatino, Silvana; Fernando, Harindra; Pardyjak, Eric; Fairall, Christopher
Measurements of atmospheric small-scale turbulence made over the complex-terrain at the US Army Dugway Proving Grounds in Utah during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program are used to describe the turbulence structure of katabatic flows. Turbulent and mean meteorological data were continuously measured at multiple levels (up to seven) on four towers deployed along East lower slope (2-4 degrees) of Granite Mountain. The multi-level, multi-tower observations obtained during a 30-day long MATERHORN-Fall field campaign in September-October 2102 allow studying temporal and spatial structure of nocturnal slope flows in detail. In this study, we focus on the various statistics (fluxes, variances, spectra, cospectra, etc.) of the small-scale turbulence of katabatic winds. Observed vertical profiles of velocity, turbulent fluxes, and other quantities show steep gradients near the surface but in the layer above the slope jet these variables vary with height more slowly than near the surface. It is found that vertical momentum flux and horizontal heat (buoyancy) flux in a slope-following coordinate system change their sign below and above the wind maximum of a katabatic flow. The vertical momentum flux is directed downward (upward) whereas the horizontal heat flux is downslope (upslope) below (above) the wind maximum. Our study, therefore, suggests that a position of the jet speed maximum can be derived from linear interpolation between positive and negative values of the momentum flux (or the horizontal heat flux) and determination of a height where a flux becomes zero. It is shown that the standard deviations of all wind speed components (and therefore the turbulent kinetic energy) and the dissipation rate of turbulent kinetic energy have a local minimum, whereas the standard deviation of air temperature has an absolute maximum at the height of wind speed maximum. We report several cases when the destructive effect of vertical heat (buoyancy) flux is completely cancelled by the generation of turbulence due to the horizontal heat (buoyancy) flux. Turbulence in the layer above the wind-speed maximum is decoupled from the surface and it is consistent with the classical local z-less predictions for stably stratified boundary layer.
Terminal velocities of the winds from rapidly rotating OB stars
NASA Technical Reports Server (NTRS)
Friend, David B.
This paper presents measurements of terminal velocities of OB stars which are rapid rotators, based on archival high-dispersion IUE spectra of the C IV resonance doublet. The terminal velocities of the most rapidly rotating stars appear to be systematically lower than those of the less rapidly rotating stars (at least for the cooler stars), although the number of very rapid rotators is only three. The modified line-radiation driven wind model of Friend and Abbott, which takes into account the finite size of the star as well as its rotation, predicts that the terminal velocity should drop with increasing rotational velocity. However, when a smaller but very homogeneous subset of the data is used (BO giants only), the correlation between terminal velocity and rotational velocity disappears.
Long-tail solar wind electron velocity distribution
Shlesinger, M.F.; Coplan, M.A.
We show that the core-halo solar wind velocity distribution function can be understood in terms of a simple phenomenological model of general applicability in which the core has a Maxwellian or normal distribution and the halo a log-normal distribution. Furthermore, in the presence of structures in the interplanetary medium capable of interacting with the electrons, the model predicts a transition at the highest velocities to a secondary halo distribution.
Helium and hydrogen velocity differences in the solar wind
J. R. Asbridge; S. J. Bame; W. C. Feldman; M. D. Montgomery
Scalar and vector velocity differences between helium and hydrogen ions in the solar wind measured with the Los Alamos plasma analyzers on Imp 6 and 7 are presented and interpreted. From the bulk speeds and azimuthal components of flow direction for both types of ions the ecliptic projection of the helium to hydrogen velocity difference vector v\\/subo\\/\\/subp\\/ is determined. Short-term
Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions
NASA Astrophysics Data System (ADS)
Fahr, H.-J.; Chashei, I. V.; Siewert, M.
From most in-situ plasma observations made in the outer heliosphere it became evident that above the injection border of pick-up ions (?1 keV), an extended suprathermal ion tail is found which in most cases can be fitted by a power law with velocity power indices of (-6) ? ?v ? (-4). As has been shown by theory such energetic ion tails cannot be explained by Fermi-2 type velocity diffusion, since in the outer heliosphere both Alfvenic and magnetoacoustic turbulences become too weak. Here we come to a new solution of this unsolved problem by studying the action of solar wind bulk velocity fluctuations on ions co-moving with the wind. As we show the passage of such fluctuations results in energization of each individual ion and systematic evolution of the ion distribution function towards suprathermal tails. From the basic knowledge that we can obtain on this process we can calculate the velocity divergence of the ion phasespace flow and thus can derive a velocity diffusion operator. As we can show here this operator leads to a velocity diffusion coefficient proportional to the square of the ion velocity and, when employed in the phasespace transport equation, together with terms for convective changes, cooling processes and pick-up ion injection, interestingly enough, permits to find solutions for suprathermal power law tails with power indices of ?v ? -5 as very often observed.
Analysis of the velocity law in the wind of the Be star Lambda Pavonis
NASA Technical Reports Server (NTRS)
Chen, Haiqi; Ringuelet, Adela; Sahade, Jorge; Kondo, Yoji
This paper reanalyzes the IUE spectra of Lambda Pavonis secured in 1982 (Sahade et al.). It is found that the profiles of the broad UV lines are either rotationally broadened or nonrotationally broadened and that the rotationally broadened profiles can be sorted out in two groups characterized by rotational velocity values of 170 km/s and of 210 km/s, respectively. From the analysis of the rotational and of the radial velocities it is possible to distinguish two regions in the extended atmosphere of the star, namely, a region which is rotating and a region which is expanding. In the rotating region, the radial velocities are about zero, and the rotational velocity increases from 170 km/s to 250 km/s. In the expanding region, the rotational energy dissipates, the wind is accelerated to a maximum of -155 km/s, and farther out it decelerates.
Electronic frequency modulation for the increase of maximum measurable velocity in a heterodyne laser interferometer
Choi, Hyunseung; La, Jongpil; Park, Kyihwan [Intelligent Manufacturing Group, LG Production Engineering Research Institute, 19-1 Cheongho-Ri, Jinwuy-myun, Pyungtaik, Kyunggi-Do 451-713 (Korea, Republic of); Compressor Development Group, Samsung Gwangju Electronic Company, 1119 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Department of Mechatronics, Gwangju Institute of Science and Technology, 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of)
A Zeeman-type He-Ne laser is frequently used as a heterodyne laser due to the simple construction and the small loss of a light. However, the low beat frequency of the Zeeman-type laser limits the maximum measurable velocity. In this article, an electronic frequency modulation algorithm is proposed to overcome the drawback of the low velocity measurement capability by increasing the beat frequency electronically. The brief analysis, the measurement scheme of the proposed algorithm, and the experimental results are presented. It is demonstrated that the proposed algorithm is proven to enhance the maximum measurable velocity.
Maximum power tracking control scheme for wind generator systems
Mena, Hugo Eduardo
solution to the complicated aerodynamic system. This control scheme provides a response to the wind changes without the knowledge of wind speed and turbine parameters. The system consists of a permanent magnet synchronous machine (PMSM), a passive rectifier...
Maximum power tracking control scheme for wind generator systems
Mena Lopez, Hugo Eduardo
solution to the complicated aerodynamic system. This control scheme provides a response to the wind changes without the knowledge of wind speed and turbine parameters. The system consists of a permanent magnet synchronous machine (PMSM), a passive rectifier...
Polar low-speed solar wind at the solar activity maximum
NASA Astrophysics Data System (ADS)
Ohmi, T.; Kojima, M.; Yokobe, A.; Tokumaru, M.; Fujiki, K.; Hakamada, K.
The tomographic analysis of interplanetary scintillation (IPS) showed that low-speed winds (<= 370 kms-1) emanated out from the polar region at the last solar activity maximum. In order to investigate the origin of those low-speed winds, we compared the velocity distribution derived from the IPS tomographic analysis to the magnetic field structure derived from the potential field analysis. We found that the polar low-speed winds appeared for a short period just before and after the disappearance of polar open fields. When the polar coronal hole shrank very small before its disappearance, the coronal polar open field was encircled by large-scale closed loops and became super radially diverging field into the interplanetary space. A low-speed region appeared in this diverging polar magnetic field region. This situation is a condition very similar to the compact low-speed streams associated with equatorial active regions, which were found by Kojima et al. [1999]. After the open field regions had disappeared from the pole, the polar regions were occupied with closed loops. These closed loops were overlapped by the magnetic field which fanned out from the midlatitudes. A low-speed streamer located above these closed loops even after the polar open field had disappeared. The velocities of polar low-speed streams before polar hole disappearance were much lower than those after disappearance. This result suggests that the physical conditions to generate much lower speed streams are closely associated with large expansion from small open field regions encircled by large-scale closed loops. Finally, a reliability of the IPS measurement of polar low-speed wind was examined by simulating synthetic IPS observations in hypothetical model polar streams.
The stellar wind velocity field of HD 77581
Manousakis, A
The early acceleration of stellar winds in massive stars is poorly constrained. The scattering of hard X-ray photons emitted by the pulsar in the high-mass X-ray binary Vela X-1 can be used to probe the stellar wind velocity and density profile close to the surface of its supergiant companion HD 77581. We built a high signal-to-noise and high resolution hard X-ray lightcurve of Vela X-1 measured by Swift/BAT over 300 orbital periods of the system and compared it with the predictions of a grid of hydrodynamic simulations. We obtain a very good agreement between observations and simulations for a narrow set of parameters, implying that the wind velocity close to the stellar surface is twice larger than usually assumed with the standard beta law. Locally a velocity gradient of $\\beta\\sim0.5$ is favoured. Even if still incomplete, hydrodynamic simulations are successfully reproducing several observational properties of Vela X-1.
Estimation of power in low velocity vertical axis wind turbine
NASA Astrophysics Data System (ADS)
Sampath, S. S.; Shetty, Sawan; Chithirai Pon Selvan, M.
The present work involves in the construction of a vertical axis wind turbine and the determination of power. Various different types of turbine blades are considered and the optimum blade is selected. Mechanical components of the entire setup are built to obtain maximum rotation per minute. The mechanical energy is converted into the electrical energy by coupling coaxially between the shaft and the generator. This setup produces sufficient power for consumption of household purposes which is economic and easily available.
The role of maximum wind speed in sand-transporting events
NASA Astrophysics Data System (ADS)
Liu, LianYou; Yang, YanYan; Shi, PeiJun; Zhang, GuoMing; Qu, ZhiQiang
A sand-transporting event is the minimum unit of aeolian sand transport process. To understand the role of maximum wind speed in such sand-transporting events, wind speeds were measured at a height of 2 m above the ground in the arid (Menggen) and semi-arid (Taibus Banner) regions in north China during 2009 and 2011. The sand transport flux of each sand-transporting event was calculated based on theoretical equations. Then, the relationships between the maximum wind speed and the average wind speed, the duration and sand transport flux of sand-transporting events were analyzed. It was found that the maximum wind speed was proportional to the average wind speed of sand-transporting events, with a linear model fit, and was also significantly correlated with the duration of sand-transporting events with a power model fit. The maximum wind speed was also positively correlated with sand transport flux of sand-transporting events according to a power model. The maximum wind speed could therefore represent both wind speed and the duration of sand-transporting events, and play a decisive role in the sand transport process of these events. The sand transport flux of sand-transporting events can be predicted rapidly and conveniently by monitoring maximum wind speed.
The Enhanced-model Ladar Wind Sensor and Its Application in Planetary Wind Velocity Measurements
NASA Technical Reports Server (NTRS)
Soreide, D. C.; Mcgann, R. L.; Erwin, L. L.; Morris, D. J.
For several years we have been developing an optical air-speed sensor that has a clear application as a meteorological wind-speed sensor for the Mars landers. This sensor has been developed for aircraft use to replace the familiar, pressure-based Pitot probe. Our approach utilizes a new concept in the laser-based optical measurement of air velocity (the Enhanced-Mode Ladar), which allows us to make velocity measurements with significantly lower laser power than conventional methods. The application of the Enhanced-Mode Ladar to measuring wind speeds in the martian atmosphere is discussed.
Characteristics of Wind Velocity and Temperature Change Near an Escarpment-Shaped Road Embankment
Kim, Young-Moon; You, Ki-Pyo; You, Jang-Youl
Artificial structures such as embankments built during the construction of highways influence the surrounding airflow. Various types of damage can occur due to changes in the wind velocity and temperature around highway embankments. However, no study has accurately measured micrometeorological changes (wind velocity and temperature) due to embankments. This study conducted a wind tunnel test and field measurement to identify changes in wind velocity and temperature before and after the construction of embankments around roads. Changes in wind velocity around an embankment after its construction were found to be influenced by the surrounding wind velocity, wind angle, and the level difference and distance from the embankment. When the level difference from the embankment was large and the distance was up to 3H, the degree of wind velocity declines was found to be large. In changes in reference wind velocities around the embankment, wind velocity increases were not proportional to the rate at which wind velocities declined. The construction of the embankment influenced surrounding temperatures. The degree of temperature change was large in locations with large level differences from the embankment at daybreak and during evening hours when wind velocity changes were small. PMID:25136681
Characteristics of wind velocity and temperature change near an escarpment-shaped road embankment.
Kim, Young-Moon; You, Ki-Pyo; You, Jang-Youl
Artificial structures such as embankments built during the construction of highways influence the surrounding airflow. Various types of damage can occur due to changes in the wind velocity and temperature around highway embankments. However, no study has accurately measured micrometeorological changes (wind velocity and temperature) due to embankments. This study conducted a wind tunnel test and field measurement to identify changes in wind velocity and temperature before and after the construction of embankments around roads. Changes in wind velocity around an embankment after its construction were found to be influenced by the surrounding wind velocity, wind angle, and the level difference and distance from the embankment. When the level difference from the embankment was large and the distance was up to 3H, the degree of wind velocity declines was found to be large. In changes in reference wind velocities around the embankment, wind velocity increases were not proportional to the rate at which wind velocities declined. The construction of the embankment influenced surrounding temperatures. The degree of temperature change was large in locations with large level differences from the embankment at daybreak and during evening hours when wind velocity changes were small. PMID:25136681
Low-level nocturnal wind maximum over the Central Amazon Basin
NASA Technical Reports Server (NTRS)
Greco, Steven; Ulanski, Stanley; Garstang, Michael; Houston, Samuel
A low-level nocturnal wind maximum is shown to exist over extensive and nearly undisturbed rainforest near the central Amazon city of Manaus. Meteorological data indicate the presence of this nocturnal wind maximum during both the wet and dry seasons of the Central Amazon Basin. Daytime wind speeds which are characteristically 3-7 m/s between 300 and 1000 m increase to 10-15 m/s shortly after sunset. The wind-speed maximum is reached in the early evening, with wind speeds remaining high until several hours after sunrise. The nocturnal wind maximum is closely linked to a strong low-level inversion formed by radiational cooling of the rainforest canopy. Surface and low-level pressure gradients between the undisturbed forest and the large Amazon river system and the city of Manaus are shown to be responsible for much of the nocturnal wind increase. The pressure gradients are interpreted as a function of the thermal differences between undisturbed forest and the river/city. The importance of both the frictional decoupling and the horizontal pressure gradient suggest that the nocturnal wind maximum does not occur uniformly over all Amazonia. Low-level winds are thought to be pervasive under clear skies and strong surface cooling and that, in many places (i.e., near rivers), local pressure gradients enhance the low-level nocturnal winds.
Effect of operating methods of wind turbine generator system on net power extraction under wind velocity fluctuations in fields
Tetsuya Wakui; Kazuya Yamaguchi; Takumi Hashizume; Eisuke Outa; Yoshiaki Tanzawa
The effect of how a wind turbine generator system is operated is discussed from the viewpoint of net power extraction with wind velocity fluctuations in relation to the scale and the dynamic behavior of the system. On a wind turbine generator system consisting of a Darrieus-Savonius hybrid wind turbine, a load generator and a battery, we took up two operating
Observations of the velocity distribution of solar wind ions
NASA Technical Reports Server (NTRS)
Ogilvie, K. W.; Bochsler, P.; Geiss, J.; Coplan, M. A.
Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of 3He(++), 4He(++), 16O(6+), and 16O(7+) in the solar wind. It is found that these temperatures generally obey the relation that T(i)/m(i) equals const, but fluctuations, some of which are caused by dynamical effects in the flow, are observed. The temperature of oxygen sometimes rises above 10 K, which is very strong evidence for heating outside the collisional region of the corona. The tendency toward equal temperatures per nucleon occurs everywhere where collisions are unimportant, suggesting that the temperatures are set up close to the sun rather than elsewhere in the interplanetary medium. The velocity distribution function of helium is observed to be non-Maxwellian, with a pronounced high velocity tail.
Potential for coherent Doppler wind velocity lidar using neodymium lasers
NASA Technical Reports Server (NTRS)
Kane, T. J.; Byer, R. L.; Zhou, B.
Existing techniques for the frequency stabilization of Nd:YAG lasers operating at 1.06 micron, and the high-gain amplification of radiation at that wavelength, make possible the construction of a coherent Doppler wind velocity lidar using Nd:YAG. Velocity accuracy and range resolution are better at 1.06 micron than at 10.6 microns at the same level of the SNR. Backscatter from the atmosphere at 1.06 micron is greater than that at 10.6 microns by about 2 orders of magnitude, but the quantum-limited noise is higher by 100 also. Near-field attenuation and turbulent effects are more severe at 1.06 micron. In some configurations and environments, the 1.06-micron wavelength may be the better choice, and there may be technological advantages favoring the use of solid-state lasers in satellite systems.
Inverting ion images without Abel inversion: maximum entropy reconstruction of velocity maps.
Dick, Bernhard
A new method for the reconstruction of velocity maps from ion images is presented, which is based on the maximum entropy concept. In contrast to other methods used for Abel inversion the new method never applies an inversion or smoothing to the data. Instead, it iteratively finds the map which is the most likely cause for the observed data, using the correct likelihood criterion for data sampled from a Poissonian distribution. The entropy criterion minimizes the information content in this map, which hence contains no information for which there is no evidence in the data. Two implementations are proposed, and their performance is demonstrated with simulated and experimental data: Maximum Entropy Velocity Image Reconstruction (MEVIR) obtains a two-dimensional slice through the velocity distribution and can be compared directly to Abel inversion. Maximum Entropy Velocity Legendre Reconstruction (MEVELER) finds one-dimensional distribution functions Q(l)(v) in an expansion of the velocity distribution in Legendre polynomials P((cos ?) for the angular dependence. Both MEVIR and MEVELER can be used for the analysis of ion images with intensities as low as 0.01 counts per pixel, with MEVELER performing significantly better than MEVIR for images with low intensity. Both methods perform better than pBASEX, in particular for images with less than one average count per pixel. PMID:24172596
Design of wind farm layout for maximum wind energy capture Andrew Kusiak*, Zhe Song
Kusiak, Andrew
turbine placement based on the wind distribution. The model considers wake loss, which can be calculated the offshore wind turbine layout. Details of how to solve the optimization problem are neither discussed in ref Accepted 24 August 2009 Available online 22 September 2009 Keywords: Wind farm Wind turbine Layout design
Maximum group velocity in a one-dimensional model with a sinusoidally varying staggered potential
NASA Astrophysics Data System (ADS)
Nag, Tanay; Sen, Diptiman; Dutta, Amit
We use Floquet theory to study the maximum value of the stroboscopic group velocity in a one-dimensional tight-binding model subjected to an on-site staggered potential varying sinusoidally in time. The results obtained by numerically diagonalizing the Floquet operator are analyzed using a variety of analytical schemes. In the low-frequency limit we use adiabatic theory, while in the high-frequency limit the Magnus expansion of the Floquet Hamiltonian turns out to be appropriate. When the magnitude of the staggered potential is much greater or much less than the hopping, we use degenerate Floquet perturbation theory; we find that dynamical localization occurs in the former case when the maximum group velocity vanishes. Finally, starting from an "engineered" initial state where the particles (taken to be hard-core bosons) are localized in one part of the chain, we demonstrate that the existence of a maximum stroboscopic group velocity manifests in a light-cone-like spreading of the particles in real space.
Southern Hemisphere Westerly Wind Changes during the Last Glacial Maximum: Model-Data Comparison
De Boer, Agatha M.
Glacial Maximum (LGM). Using LGM boundary conditions,9 the maximum in SH westerlies is strengthened by +1 over equatorward extended LGM sea-ice can lead to a small appar-12 ent equatorward shift in the wind against the newly synthesised17 database of moisture observations for the LGM. Although the moisture data
Observations of the velocity distribution of solar wind ions
Ogilvie, K.W.; Bochsler, P.; Geiss, J.; Coplan, M.A.
Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of /sup 3/He/sup + +/, /sup 4/He/sup + +/, /sup 16/O/sup 6 +/, and /sup 16/O/sup 7 +/ in the solar wind. It is found that these temperatures generally obey the relation that T/sub i//m/sub i/=const, but fluctuations, some of which are caused by dynamical effects in the flow, are observed. Whether this relation applies to ions with masses greater than 16 requires more analysis to determine. The temperature of oxygen sometimes rises above 10/sup 6/ /sup 0/K, which is very strong evidence for heating outside the collisional region of the corona. The tendency toward equal temperatures per nucleon occurs everywhere where collisions are unimportant, suggesting that the temperatures are set up close to the sun rather than elsewhere in the interplanetary medium. The velocity distribution function of helium is observed to be non-Maxwellian, with a pronounced high velocity tail. As this is one condition for heating by wave dissipation, this mechanism must still be considered as a heating mechanism.
Loop Current variability due to wind stress and reduced sea level during the Last Glacial Maximum
NASA Astrophysics Data System (ADS)
Mildner, T. C.; Eden, C.; Nuernberg, D.; Schoenfeld, J.
One of the most prominent features of the circulation in the Gulf of Mexico is the Loop Current (LC). It is of special interest as it influences not only the climate in the Gulf of Mexico. Although causation is not well understood yet, dynamical relationships between LC retraction and extension, seasonal migrations of the Intertropical Convergence Zone (ITCZ) and the related wind stress curl over the subtropical North Atlantic, and changes in the thermohaline circulation are indicated by model simulations. A characteristic feature of the LC is the shedding of anticyclonic eddies. These eddies can have depth signatures of up to 1000 m and are of special interest as they supply heat and moisture into the western and northern Gulf. The eddies are generated aperiodically every 3 to 21 months, with an average shedding time of 9.5 months. Eddy shedding appears to be related to a suite of oceanographic forcing fields such as the Yucatan Channel throughflow, the Florida Current and North Brazil Current variability, as well as synoptic meteorological forcing variability. By combining state-of-the-art paleoceanographic and meso-scale eddy-resolving numerical modeling techniques, we examined the Loop Current dynamics and hydrographic changes in the Gulf going back in time up to ~21,000 years. To assess the impact of Last Glacial Maximum (LGM) wind stress and reduced sea level we have re-configured an existing hierarchy of models of the North Atlantic Ocean (FLAME) with a horizontal grid resolution of ca. 30 km (wind stress was taken from the PMIP-II database). The sea level was lowered compared to the CONTROL run by 110 m and 67 m. These sea level changes have been chosen according to the cold-deglacial periods Heinrich I and Younger Dryas. The result of our model simulations is a continuous increase in eddy shedding from the LGM to the Holocene. This increase is predominantly controlled by the continuous deglacial sea level rise. Changes in wind stress curl related to the southward displacement of the ITCZ tend to produce larger Yucatan and Florida Strait throughflow but do not play a dominant role in controlling the eddy shedding, and appear thus of minor importance for the regional climate in the Gulf of Mexico. Comparing our results to observations we found that mean sortable silt values from Florida Strait depict an increase in bottom current velocities during cold climatic periods and times of lowered sea level, too. This is in contrast to recent hydrographic estimates pointing to reduced transports through the Florida Straits.
Effect of wind tunnel air velocity on VOC flux rates from CAFO manure and wastewater
Technology Transfer Automated Retrieval System (TEKTRAN)
Wind tunnels and flux chambers are often used to estimate volatile organic compound (VOC) emissions from animal feeding operations (AFOs) without regard to air velocity or sweep air flow rates. Laboratory experiments were conducted to evaluate the effect of wind tunnel air velocity on VOC emission ...
Sensitivity of estuarine turbidity maximum to settling velocity, tidal mixing, and sediment supply
Warner, J.C.; Sherwood, C.R.; Geyer, W.R.
Estuarine turbidity maximum, numerical modeling, settling velocity, stratification The spatial and temporal distribution of suspended material in an Estuarine Turbidity Maxima (ETM) is primarily controlled by particle settling velocity, tidal mixing, shear-stress thresholds for resuspension, and sediment supply. We vary these parameters in numerical experiments of an idealized two-dimensional (x-z) estuary to demonstrate their affects on the development and retention of particles in an ETM. Parameters varied are the settling velocity (0.01, 0.1, and 0.5 mm/s), tidal amplitude (0.4 m 12 hour tide and 0.3 to 0.6 m 14 day spring neap cycle), and sediment availability (spatial supply limited or unlimited; and temporal supply as a riverine pulse during spring vs. neap tide). Results identify that particles with a low settling velocity are advected out of the estuary and particles with a high settling velocity provide little material transport to an ETM. Particles with an intermediate settling velocity develop an ETM with the greatest amount of material retained. For an unlimited supply of sediment the ETM and limit of salt intrusion co-vary during the spring neap cycle. The ETM migrates landward of the salt intrusion during spring tides and seaward during neap tides. For limited sediment supply the ETM does not respond as an erodible pool of sediment that advects landward and seaward with the salt front. The ETM is maintained seaward of the salt intrusion and controlled by the locus of sediment convergence in the bed. For temporal variability of sediment supplied from a riverine pulse, the ETM traps more sediment if the pulse encounters the salt intrusion at neap tides than during spring tides. ?? 2007 Elsevier B.V. All rights reserved.
The epoch state navigation filter. [for maximum likelihood estimates of position and velocity vectors
NASA Technical Reports Server (NTRS)
Battin, R. H.; Croopnick, S. R.; Edwards, J. A.
The formulation of a recursive maximum likelihood navigation system employing reference position and velocity vectors as state variables is presented. Convenient forms of the required variational equations of motion are developed together with an explicit form of the associated state transition matrix needed to refer measurement data from the measurement time to the epoch time. Computational advantages accrue from this design in that the usual forward extrapolation of the covariance matrix of estimation errors can be avoided without incurring unacceptable system errors. Simulation data for earth orbiting satellites are provided to substantiate this assertion.
Probabilistic estimates of maximum acceleration and velocity in rock in the contiguous United States
Algermissen, Sylvester Theodore; Perkins, D.M.; Thenhaus, P.C.; Hanson, S.L.; Bender, B.L.
Maximum horizontal accelerations and velocities caused by earthquakes are mapped for exposure times of 10, 50 and 250 years at the 90-percent probability level of nonexceedance for the contiguous United States. In many areas these new maps differ significantly from the 1976 probabilistic acceleration map by Algermlssen and Perkins because of the increase in detail, resulting from greater emphasis on the geologic basis for seismic source zones. This new emphasis is possible because of extensive data recently acquired on Holocene and Quaternary faulting in the western United States and new interpretations of geologic structures controlling the seismicity pattern in the central and eastern United States.
Three dimensional structure of correlations between intensity variation of cosmic rays and solar wind velocity
H. Kojima; T. Fujii; Y. Hayashi; S. Kawakami; M. Minamino; H. Miyauchi; T. Nonaka; S. Ogio; H. Tanaka; E. Usui; Y. Yamashita; A. Oshima; H. M. Antia; S. R. Dugad; U. D. Goswami; S. K. Gupta; P. K. Mohanty; P. K. Nayak; P. Subramanian; S. C. Tonwar; S. Shibata; I. Morishita
A three dimensional structure of a solar wind effect on the intensity variation of cosmic rays has been investigated by using the regression analysis method in this paper. The solar wind effect discussed here is represented by the regression coefficients between the intensity variation of cosmic rays and the solar wind velocity. The data of cosmic ray intensity used in
Nearfield acoustic holography in wind tunnel by means of velocity LDV measurements
Boyer, Edmond
Nearfield acoustic holography in wind tunnel by means of velocity LDV measurements H. Parisot in wind tunnel are required to charac- terize the main sources during airplanes conception. For a long disturbances. That is why it is interesting to develop another method allowing wind tunnel aeroacoustic sources
Wind Velocities at the Chajnantor and Mauna Kea Sites and the Effect on MMA Pointing
Groppi, Christopher
Wind Velocities at the Chajnantor and Mauna Kea Sites and the Effect on MMA Pointing M.A. Holdaway email: (mholdawa, sfoster, demerson, jcheng, fschwab)@nrao.edu August 9, 1996 Abstract We analyze wind April 1996 for the purposes of understanding the effects of the winds on pointing errors. Both
Effects of forward velocity on noise for a J85 turbojet engine with multitube suppressor from wind tunnel and flight tests
NASA Technical Reports Server (NTRS)
Stone, J. R.; Miles, J. H.; Sargent, N. B.
Flight and wind tunnel noise tests were conducted using a J85 turbojet engine as a part of comprehensive programs to obtain an understanding of forward velocity effects on jet exhaust noise. Nozzle configurations of primary interest were a 104-tube suppressor with and without an acoustically-treated shroud. The installed configuration of the engine was as similar as possible in the flight and wind tunnel tests. Exact simultaneous matching of engine speed, exhaust velocity, and exhaust temperature was not possible, and the wind tunnel maximum Mach number was approximately 0.27, while the flight Mach number was approximately 0.37. The nominal jet velocity range was 450 to 640 m/sec. For both experiments, background noise limited the jet velocity range for which significant data could be obtained. In the present tests the observed directivity and forward velocity effects for the suppressor are more similar to predicted trends for internally-generated noise than unsuppressed jet noise.
Gas transfer velocities measured at low wind speed over a lake
Crusius, J.; Wanninkhof, R.
The relationship between gas transfer velocity and wind speed was evaluated at low wind speeds by quantifying the rate of evasion of the deliberate tracer, SF6, from a small oligotrophic lake. Several possible relationships between gas transfer velocity and low wind speed were evaluated by using 1-min-averaged wind speeds as a measure of the instantaneous wind speed values. Gas transfer velocities in this data set can be estimated virtually equally well by assuming any of three widely used relationships between k600 and winds referenced to 10-m height, U10: (1) a bilinear dependence with a break in the slope at ???3.7 m s-1, which resulted in the best fit; (2) a power dependence; and (3) a constant transfer velocity for U10 3.7 m s-1 which, coupled with the typical variability in instantaneous wind speeds observed in the field, leads to average transfer velocity estimates that are higher than those predicted for steady wind trends. The transfer velocities predicted by the bilinear steady wind relationship for U10 < ???3.7 m s-1 are virtually identical to the theoretical predictions for transfer across a smooth surface.
Phase diagrams on an unsignalized intersection for the cases of different maximum velocities of vehicles
NASA Astrophysics Data System (ADS)
Li, Qi-Lang; Wang, Bing-Hong; Liu, Mu-Ren
Using the cellular automaton traffic flow model, we investigate an unsignalized intersection which consists of two perpendicular one-lane roads. Both the roads cross at a point and the intersecting roads are cyclic. Each vehicle may pass or occupy the intersection where all the vehicles on both roads are not allowed to turn. Different from Ishibashi and Fukui's studies in which the update is carried out for both roads in turn, the parallel update is proposed and its detailed rules are presented in our model. In this work, the cases of different maximum vehicle velocities on both roads are considered. Based on simulation results and the principle for constructing phase diagrams, phase diagrams are mapped out and their specific flow formulas for all the regions in the phase diagrams are obtained for various vehicle densities, which are seldom done in previous studies. One also finds that the topology of phase diagrams depends on the update rules of eastbound and northbound roads and their maximum velocities of vehicles.
Wind Observations of Anomalous Cosmic Rays from Solar Minimum to Maximum
NASA Technical Reports Server (NTRS)
Reames, D. V.; McDonald, F. B.
We report the first observation near Earth of the time behavior of anomalous cosmic-ray N, O, and Ne ions through the period surrounding the maximum of the solar cycle. These observations were made by the Wind spacecraft during the 1995-2002 period spanning times from solar minimum through solar maximum. Comparison of anomalous and galactic cosmic rays provides a powerful tool for the study of the physics of solar modulation throughout the solar cycle.
Acoustic sounding of wind velocity profiles in a stratified moving atmosphere.
Ostashev, V E; Georges, T M; Clifford, S F; Goedecke, G H
The paper deals with analytical and numerical studies of the effects of atmospheric stratification on acoustic remote sensing of wind velocity profiles by sodars. Both bistatic and monostatic schemes are considered. Formulas for the Doppler shift of an acoustic echo signal scattered by atmospheric turbulence advected with the mean wind in a stratified moving atmosphere are derived. Numerical studies of these formulas show that errors in retrieving wind velocity can be of the order of 1 m/s if atmospheric stratification is ignored. Formulas for the height at which wind velocity is retrieved are also derived. Approaches are proposed which allow one to take into account the effects of atmospheric stratification when restoring the wind velocity profile from measured values of the Doppler shift and the time interval of acoustic impulse propagation from a sodar to the scattering volume and back to the ground. PMID:11425111
Sensorless maximum power point tracking control in wind energy generation using permanent magnet synchronous generator
N. Srighakollapu; P. S. Sensarma
This paper proposes a control strategy for variable speed wind energy conversion system (WECS), incorporating maximum power point tracking (MPPT) algorithm, using direct driven permanent magnet synchronous generator (PMSG). The generator is operated in the speed control mode below the base speed by controlling the terminal voltage using three phase front-end active-rectifier feeding power to the DC bus. The voltage
Remote Sensing of Solar Wind Velocity Applying IPS Technique using MEXART
NASA Astrophysics Data System (ADS)
Mejia-Ambriz, J. C.; Gonzalez-Esparza, A.; Romero Hernandez, E.
Radio waves coming from compact cosmic radio sources are scattered by electron density fluctuations in the solar wind plasma, producing a diffraction pattern at Earth which moves along with the solar wind. This phenomenon results into flux density fluctuations observed by a radio telescope and it is known as Interplanetary Scintillation (IPS). By employing IPS observations, it is possible to track solar wind velocities in the inner heliosphere. The Mexican Array Radio Telescope (MEXART) is an new instrument devoted to IPS observations at 140 MHz. We present preliminar estimates of solar wind velocities by using IPS observations of the MEXART.
Absolute wind velocities in the lower thermosphere of Venus using infrared heterodyne spectroscopy
NASA Technical Reports Server (NTRS)
Goldstein, Jeffrey J.; Mumma, Michael J.; Kostiuk, Theodor; Deming, Drake; Espenak, Fred; Zipoy, David
NASA's IR Telescope Facility and the McMath Solar Telescope have yielded absolute wind velocities in the Venus thermosphere for December 1985 to March 1987 with sufficient spatial resolution for circulation model discrimination. A qualitative analysis of beam-integrated winds indicates subsolar-to-antisolar circulation in the lower thermosphere; horizontal wind velocity was derived from a two-parameter model wind field of subsolar-antisolar and zonal components. A unique model fit common to all observing periods possessed 120 m/sec subsolar-antisolar and 25 m/sec zonal retrograde components, consistent with the Bougher et al. (1986, 1988) hydrodynamical models for 110 km.
Factors Affecting Young's Modulus of Torch Plasma with Low Velocity Cross Wind
NASA Astrophysics Data System (ADS)
Liu, Bin; Miyashita, Yoshio; Inaba, Tsuginori
Figure modes of Ar torch plasmas with an air cross wind were investigated. In fact, torch plasmas resemble ōbambooö with a low velocity cross wind; they revert to their original position when the low cross wind is removed. Torch plasmas have abundant elasticity; their Young's modulus has been calculated using measured deflection figures on the anode. Adopting the influence factors as the plasma current, the velocity of cross wind and the outside electrode interval, those influence on the figure modes and its Young's modulus was investigated. The Young's modulus increases to the 0.67th power of the plasma current.
Effect of Ambient Wind Velocity on the Shaping of Planetary Nebulae
NASA Astrophysics Data System (ADS)
Dwarkadas, V. V.; Chevalier, R. A.; Blondin, J.
We have modelled planetary nebulae (PNe) using a 2-wind interacting-stellar-winds (ISW) model. If the two interacting winds have constant properties, the velocity of the PN shell tends towards a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. We have computed the shapes of PNe in the self-similar stage with both semi-analytic methods and numerical hydrodynamic simulations. An asymmetric density profile was assumed for the slow wind. We include the effects of the ambient wind velocity. Though the ambient velocity is often comparable to the expansion velocity of the PN, it has not received much attention since the work of Kahn & West (1985). The morphological appearance depends on the density contrast, steepness of the density profile with polar angle and velocity of the ambient medium; classification of PNe purely on the basis of the first two factors may be misleading. In particular the ambient wind velocity determines whether the PN will show a bulge or a cusp at the equator. Moderate values of the density contrast result in a cusp at the equator. Higher density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximicrons of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. Our work shows that bipolar nebulae result when the expansion velocity of the PN is much larger than that of the external wind. An asymmetry in the external wind velocity can also lead to a bipolar shape if the equatorial velocity is sufficiently low. Our simulations indicate that all PNe may not reach the isobaric, self-similar shape. A ratio of interior sound speed to shell velocity ga 10 is found to yield nebulae whose shapes match those given by the isobaric approximation. Furthermore, asymmetric PNe shells are corrugated by the presence of Kelvin-Helmholtz instabilities.
Determination of maximum leaf velocity and acceleration of a dynamic multileaf collimator: Implications for 4D radiotherapy
Wijesooriya, K.; Bartee, C.; Siebers, J.V.; Vedam, S.S.; Keall, P.J. [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States)
The dynamic multileaf collimator (MLC) can be used for four-dimensional (4D), or tumor tracking radiotherapy. However, the leaf velocity and acceleration limitations become a crucial factor as the MLC leaves need to respond in near real time to the incoming respiration signal. The aims of this paper are to measure maximum leaf velocity, acceleration, and deceleration to obtain the mechanical response times for the MLC, and determine whether the MLC is suitable for 4D radiotherapy. MLC leaf sequence files, requiring the leaves to reach maximum acceleration and velocity during motion, were written. The leaf positions were recorded every 50 ms, from which the maximum leaf velocity, acceleration, and deceleration were derived. The dependence on the velocity and acceleration of the following variables were studied: leaf banks, inner and outer leaves, MLC-MLC variations, gravity, friction, and the stability of measurements over time. Measurement results show that the two leaf banks of a MLC behave similarly, while the inner and outer leaves have significantly different maximum leaf velocities. The MLC-MLC variations and the dependence of gravity on maximum leaf velocity are statistically significant. The average maximum leaf velocity at the isocenter plane of the MLC ranged from 3.3 to 3.9 cm/s. The acceleration and deceleration at the isocenter plane of the MLC ranged from 50 to 69 cm/s{sup 2} and 46 to 52 cm/s{sup 2}, respectively. Interleaf friction had a negligible effect on the results, and the MLC parameters remained stable with time. Equations of motion were derived to determine the ability of the MLC response to fluoroscopy-measured diaphragm motion. Given the present MLC mechanical characteristics, 4D radiotherapy is feasible for up to 97% of respiratory motion. For the largest respiratory motion velocities observed, beam delivery should be temporarily stopped (beam hold)
Dependence of velocity fluctuations on solar wind speeds: A simple analysis with IPS method
NASA Technical Reports Server (NTRS)
Misawa, H.; Kojima, M.
A number of theoretical works have suggested that MHD plasma fluctuations in solar winds should play an important role particularly in the acceleration of high speed winds inside or near 0.1 AU from the sun. Since velocity fluctuations in solar winds are expected to be caused by the MHD plasma fluctuations, measurements of the velocity fluctuations give clues to reveal the acceleration process of solar winds. We made interplanetary scintillation (IPS) observations at the region out of 0.1 AU to investigate dependence of velocity fluctuations on flow speeds. For evaluating the velocity fluctuation of a flow, we selected the IPS data-set acquired at 2 separate antennas which located in the projected flow direction onto the baseline plane, and tried to compare skewness of the observed cross correlation function(CCF) with skewness of modeled CCFs in which velocity fluctuations were parametrized. The integration effect of IPS along a ray path was also taken into account in the estimation of modeled CCFs. Although this analysis method is significant to derive only parallel fluctuation components to the flow directions, preliminary analyses show following results: (1) High speed winds (Vsw greater than or equal to 500 km/s out of 0.3 AU) indicate enhancement of velocity fluctuations near 0.1 AU; and (2) Low speed winds (Vsw less than or equal to 400 Km/s out of 0.3 AU) indicate small velocity fluctuations at any distances.
AMSU-A Tropical Cyclone Maximum Sustained Winds and Web Site
NASA Technical Reports Server (NTRS)
Spencer, Roy; Goodman, H. Michael (Technical Monitor)
The Advanced Microwave Sounding Unit (AMSU)-A instruments on the NOAA-15 and NOAA-16 satellites provide information on the warm cores of tropical cyclones from oxygen channel brightness temperature (Tb) measurements near 55 GHz. With appropriate assumptions, cyclone-scale Tb gradients can be directly related to middle-to-lower tropospheric height gradients. We have developed a method for diagnosis of maximum sustained winds (Vmax) from radially averaged Tb gradients in several of the AMSU channels. Calibration of the method with recon-based (or other in situ) winds results in better agreement than with Dvorak wind estimates. Gradient wind theory shows that the warm core Tb gradient signal increases non-linearly with wind speed, making microwave temperature sounders useful for diagnosing high wind speeds, but at the expense of a minimum useful detection limit of about 40 knots. It is found that accurate wind diagnoses depend upon (1) accounting for hydrometeor effects in the AMSU channels, and (2) maximizing signal-to-noise, since the 50 km resolution data cannot fully resolve the temperature gradients in the Vmax region, typically 10-20 km in scale. AMSU imagery and max diagnoses from specific hurricanes will be shown, including independent tests from the 2000 hurricane season.
The Determination of the `Diffusion Coefficients' and the Stellar Wind Velocities for X-Ray Binaries
V. M. Lipunov; S. B. Popov
The distribution of neutron stars (NS's) is determined by stationary solution of the Fokker-Planck equation. In this work using the observed period changes for four systems: Vela X-1, GX 301-2, Her X-1 and Cen X-3 we determined D, the 'diffusion coefficient',-parameter from the Fokker-Planck equation. Using strong dependence of D on the velocity for Vela X-1 and GX 301-2, systems accreting from a stellar wind, we determined the stellar wind velocity. For different assumptions for a turbulent velocity we obtained $V=(660-1440) km s ^{-1}$. It is in good agreement with the stellar wind velocity determined by other methods. We also determined the specific characteristic time scales for the 'diffusion processes' in X-ray pulsars. It is of order of 200 sec for wind-fed pulsars and 1000-10000 sec for the disk accreting systems.
The stellar wind velocity function for red supergiants determined in eclipsing binaries
NASA Technical Reports Server (NTRS)
Ahmad, Imad A.; Stencel, Robert E.
The potential for direct measurement of the acceleration of stellar winds from the supergiant component of Zeta Aurigae-type binary stars is discussed. The aberration angle of the interaction shock cone centered on the hot star provides a measure of the velocity of the cool star wind at the orbit of the secondary. This is confirmed by direct observations of stellar wind (P Cygni) line profile variations. This velocity is generally smaller than the final (terminal) velocity of the wind, deduced from the P Cygni line profiles. The contrast between these results and previously published supergiant wind models is discussed. The implication on the physics of energy source dissipation predicted in the theoretical models is considered.
A large enhancement of the maximum drift velocity of electrons in the channel of a field-effect heterotransistor
Pozela, J. K. [Semiconductor Physics Institute (Lithuania)], E-mail: firstname.lastname@example.com; Mokerov, V. G. [Russian Academy of Sciences, Institute of the Microwave Semiconductor Electronics (Russian Federation)
It is shown that the optical-phonon momentum quantization in a GaAs quantum well resulting from the introduction of an InAs quantum-dot barrier layer provides for the elimination of inelastic scattering of electrons by optical phonons and, thus, makes the acceleration of electrons above the saturation drift velocity possible. It is shown experimentally that the maximum drift velocity of electrons in high electric fields in AlGaAs/GaAs heterostructure with InAs quantum-dot barriers introduced into the GaAs quantum well exceeds the saturation drift velocity in bulk GaAs by as much as a factor of 10. Such a rise in the maximum drift velocity of electrons ensures increased maximum current density, transconductance, and cutoff frequency of the heterostructure field-effect transistor with quantum dots.
Velocity and energy conversion efficiency characteristics of ionic wind generator in a multistage configuration
C. Kim; K. C. Noh; J. Hwang
This paper reports the experimental and theoretical analysis of the ionic wind velocity and electrical-to-kinetic energy conversion efficiency in an ionic wind generator with six stages in series. Each stage contained a pair of cylindrical multipin-to-ring electrodes. The experiments were carried out in a negative dc corona discharge and the experimental results showed that both the velocity and efficiency are
Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus
NASA Technical Reports Server (NTRS)
Betz, A. L.; Johnson, M. A.; Mclaren, R. A.; Sutton, E. C.
Strong 10 micrometer line emission from (c-12)(o-16)2 in the upper atmosphere of Venus was detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicate mean zonal wind velocities less than 10 m/sec in the upper atmosphere near the equator. No evidence was found of the 100 m/sec wind velocity implied by the apparent 4-day rotation period of ultraviolet cloud features.
RW Sextantis, a disk with a hot, high-velocity wind
NASA Technical Reports Server (NTRS)
Greenstein, J. L.; Oke, J. B.
The continuum spectrum of the flickering blue variable RW Sex was observed from 10,000 to 1150 A. The star is a cataclysmic variable currently stabilized at maximum, and the spectrum is dominated by an accretion disk, with flat spectrum in the ultraviolet, except at more than 5000 A, where a blackbody near 7000 K is seen. A distance of 400 pc is derived, if the latter arises from an F type main sequence star. The accretion rate required is near 10 to the -8th solar masses per year. Only weak emission is seen, except for Lyman alpha; strong, broad UV absorption lines are seen with centers displaced up to -3000 km/s, with terminal velocities up to -4500 km/s, the velocity of escape from a white dwarf. The low X-ray flux may arise from absorption within an unusually dense, hot wind from the innermost portions of the disk. The estimated mass loss rate is nearly 10 to the -12th solar masses per year.
A Summary of Convective-Core Vertical Velocity Properties Using ARM UHF Wind Profilers in Oklahoma
Ohta, Shigemi
A Summary of Convective-Core Vertical Velocity Properties Using ARM UHF Wind Profilers in Oklahoma cores over the central plains of the United States, accomplished using a novel and now-standard Atmospheric Radiation Measurement Program (ARM) scanning mode for a commercial wind-profiler system. A unique
An aerostat-lofted, sonic anemometer was used to determine instantaneous 3 dimensional wind velocities at altitudes relevant to fire plume dispersion modeling. An integrated GPS, inertial measurement unit, and attitude heading and reference system corrected the wind data for th...
Solar wind velocity and temperature in the outer heliosphere
NASA Technical Reports Server (NTRS)
Gazis, P. R.; Barnes, A.; Mihalov, J. D.; Lazarus, A. J.
At the end of 1992, the Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were at heliocentric distances of 56.0, 37.3, and 39.0 AU and heliographic latitudes of 3.3 deg N, 17.4 deg N, and 8.6 deg S, respectively. Pioneer 11 and Voyager 2 are at similar celestial longitudes, while Pioneer 10 is on the opposite side of the Sun. All three spacecraft have working plasma analyzers, so intercomparison of data from these spacecraft provides important information about the global character of the solar wind in the outer heliosphere. The averaged solar wind speed continued to exhibit its well-known variation with solar cycle: Even at heliocentric distances greater than 50 AU, the average speed is highest during the declining phase of the solar cycle and lowest near solar minimum. There was a strong latitudinal gradient in solar wind speed between 3 deg and 17 deg N during the last solar minimum, but this gradient has since disappeared. The solar wind temperature declined with increasing heliocentric distance out to a heliocentric distance of at least 20 AU; this decline appeared to continue at larger heliocentric distances, but temperatures in the outer heliosphere were suprisingly high. While Pioneer 10 and Voyager 2 observed comparable solar wind temperatures, the temperature at Pioneer 11 was significantly higher, which suggests the existence of a large-scale variation of temperature with heliographic longitude. There was also some suggestion that solar wind temperatures were higher near solar minimum.
Altitude profile of the polar wind velocity and its relationship to ionospheric conditions
Abe, T. (Aoyama Gakuin Univ., Tokyo (Japan)); Whalen, B.A.; Yau, A.W. (National Research Council Canada, Ottawa (Canada)); Watanabe, S. (Hokkado Institute of Information Technology, Hokkaido (Japan)); Sagawa, E. (Communications Research Lab., Tokyo (Japan)); Oyama, K.I. (Institute of Space and Astronautical Science, Kanagawa (Japan))
The authors report recent results from the Akebono satellite. They present data on polar wind velocities, examined in conjunction with electron properties, as a function of altitude in the ionosphere. This data came from the Suprathermal ion Mass Spectrometer and the Thermal Electron energy Distribution instruments. The measurements show a vertical component to the polar wind, consistent with model results, when measured in terms of H[sup +] ions. There was a definite altitude dependence of the velocity of the hydrogen ions, and there was also a positive correlation of this velocity with the measured electron temperature.
Density, Velocity and Ionization Structure in Accretion-Disc Winds
NASA Technical Reports Server (NTRS)
Sonneborn, George (Technical Monitor); Long, Knox
This was a project to exploit the unique capabilities of FUSE to monitor variations in the wind- formed spectral lines of the luminous, low-inclination, cataclysmic variables(CV) -- RW Sex. (The original proposal contained two additional objects but these were not approved.) These observations were intended to allow us to determine the relative roles of density and ionization state changes in the outflow and to search for spectroscopic signatures of stochastic small-scale structure and shocked gas. By monitoring the temporal behavior of blue-ward extended absorption lines with a wide range of ionization potentials and excitation energies, we proposed to track the changing physical conditions in the outflow. We planned to use a new Monte Carlo code to calculate the ionization structure of and radiative transfer through the CV wind. The analysis therefore was intended to establish the wind geometry, kinematics and ionization state, both in a time-averaged sense and as a function of time.
Wind power conversion and control system
A combination wind rotor and output energy transducer to provide output energy from the system and to automatically regulate the wind rotor at all wind velocities to thereby allow the wind rotor to operate at a constant tip speed\\/wind velocity ratio and at its maximum efficiency. The energy transducer is a combination of positive displacement hydraulic pump and an orifice
Observations of the velocity distribution of solar wind ions
K. W. Ogilvie; P. Bochsler; J. Geiss; M. A. Coplan
Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of ┬│He\\/sup + +\\/, Ōü┤He\\/sup + +\\/, ┬╣ŌüČO\\/sup 6 +\\/, and ┬╣ŌüČO\\/sup 7 +\\/ in the solar wind. It is found that these temperatures generally obey the relation that T\\/sub i\\/\\/m\\/sub i\\/=const, but fluctuations, some of which are caused by dynamical effects in
Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: II.
Kaganovich, Igor
compression is a standard technique used to increase the beam intensity in various accelerators [1]. PreviousEffects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: II. Analysis of experimental data of the Neutralized Drift Compression e
Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses
Kaganovich, Igor
intensity in various accelerators [1]. Long- itudinal compression during neutralized drift is achievedEffects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: I. general description Igor D. Kaganovich a,n , Scott Massidda a , Edward
Sensory and motor maximum nerve conduction velocity in the peripheral and central nervous system of the beagle dog
U. Schaeppi; M. Teste; U. Siegenthaler
Sensory maximum nerve conduction velocity (MNCV) and motor MNCV were monitored in altogether 14 beagle dogs anaesthetized with pentobarbital. Sensory MNCV was determined by averaging cortically evoked potentials from somatosensory area I (SS I) in response to repeated electrical stimulation of digital paw pads, tibial nerve at calcaneus or sciatic nerve at trochanter.
Occurrence of high-speed solar wind streams over the Grand Modern Maximum
NASA Astrophysics Data System (ADS)
Mursula, Kalevi; Lukianova, Renata; Holappa, Lauri
In the declining phase of the solar cycle, when the new-polarity fields of the solar poles are strengthened by the transport of same-signed magnetic flux from lower latitudes, the polar coronal holes expand and form non-axisymmetric extensions toward the solar equator. These extensions enhance the occurrence of high-speed solar wind streams (HSS) and related co-rotating interaction regions in the low-latitude heliosphere, and cause moderate, recurrent geomagnetic activity in the near-Earth space. Here, using a novel definition of geomagnetic activity at high (polar cap) latitudes and the longest record of magnetic observations at a polar cap station, we calculate the annually averaged solar wind speeds as proxies for the effective annual occurrence of HSS over the whole Grand Modern Maximum (GMM) from 1920s onwards. We find that a period of high annual speeds (frequent occurrence of HSS) occurs in the declining phase of each solar cycle 16-23. For most cycles the HSS activity clearly maximizes during one year, suggesting that typically only one strong activation leading to a coronal hole extension is responsible for the HSS maximum. We find that the most persistent HSS activity occurred in the declining phase of solar cycle 18. This suggests that cycle 19, which marks the sunspot maximum period of the GMM, was preceded by exceptionally strong polar fields during the previous sunspot minimum. This gives interesting support for the validity of solar dynamo theory during this dramatic period of solar magnetism.
FIS/ANFIS Based Optimal Control for Maximum Power Extraction in Variable-speed Wind Energy Conversion System
NASA Astrophysics Data System (ADS)
Nadhir, Ahmad; Naba, Agus; Hiyama, Takashi
An optimal control for maximizing extraction of power in variable-speed wind energy conversion system is presented. Intelligent gradient detection by fuzzy inference system (FIS) in maximum power point tracking control is proposed to achieve power curve operating near optimal point. Speed rotor reference can be adjusted by maximum power point tracking fuzzy controller (MPPTFC) such that the turbine operates around maximum power. Power curve model can be modelled by using adaptive neuro fuzzy inference system (ANFIS). It is required to simply well estimate just a few number of maximum power points corresponding to optimum generator rotor speed under varying wind speed, implying its training can be done with less effort. Using the trained fuzzy model, some estimated maximum power points as well as their corresponding generator rotor speed and wind speed are determined, from which a linear wind speed feedback controller (LWSFC) capable of producing optimum generator speed can be obtained. Applied to a squirrel-cage induction generator based wind energy conversion system, MPPTFC and LWSFC could maximize extraction of the wind energy, verified by a power coefficient stay at its maximum almost all the time and an actual power line close to a maximum power efficiency line reference.
A wind tunnel study of air flow in waving wheat: Two-point velocity statistics
NASA Astrophysics Data System (ADS)
Shaw, R. H.; Brunet, Y.; Finnigan, J. J.; Raupach, M. R.
Two-point, space-time correlations of streamwise and vertical velocity were obtained from a wind tunnel simulation of an atmospheric surface layer with an underlying model wheat canopy constructed of flexible nylon stalks. Velocity data extend from 1/6 canopy height to several canopy heights, with in excess of 2000 three-dimensional vector separations of the two x-wire probes. Isocorrelation contours over an x, z slice show the streamwise velocity autocorrelation to be roughly circular, such that vertical velocities at the same horizontal position but different heights are closely in phase. Cross-correlations between the two velocity components reflect this difference to some extent. Lateral displacements of the probes revealed side lobes with correlations of reversed sign but we cannot positively link this pattern to particular vorticular structures. Integral length scales obtained directly from the spatial correlations match similar scales deduced from single-point time series with Taylor's hypothesis at 2 to 3 times the canopy height but greatly exceed such scales at lower levels, particularly within the wheat. We conclude that the reversed sign lateral lobes are important components of the correlation field and that an integral length scale for the lateral direction must be defined such that they are included. Convective velocities obtained from the time lag to optimally restore correlation lost by physical separation of the probes change only slowly with height and greatly exceed the mean wind velocity within and immediately above the canopy. Thus, mean wind velocity is not a suitable proxy for convective velocity in the application of Taylor's hypothesis in this situation. The ratio of vertical to longitudinal convective velocity for the streawise velocity signal yields a downwind tilt angle of about 39░ which is probably a better estimate of the slope of the dominant fluid motions than the tilt of the major axis of the isocorrellation contours mentioned previously.
A wind tunnel study of air flow in waving wheat: Single-point velocity statistics
Y. Brunet; J. J. Finnigan; M. R. Raupach
We analyse single-point velocity statistics obtained in a wind tunnel within and above a model of a waving wheat crop, consisting of nylon stalks 47 mm high and 0.25 mm wide in a square array with frontal area index 0.47. The variability of turbulence measurements in the wind tunnel is illustrated by using a set of 71 vertical traverses made
IPS observations of the solar wind velocity and the acceleration mechanism
NASA Technical Reports Server (NTRS)
Ofman, L.; Davila, J. M.; Coles, W. A.; Grall, R. R.; Klinglesmith, M. T.
Coronal holes are well know sources of high speed solar wind, however, the exact acceleration mechanism of the wind is still unknown. Interplanetary scintillation (IPS) observations indicate that the fast solar wind reaches an average velocity of 800 km s(exp -1) within several solar radii with large velocity fluctuations. However, the origin of the IPS velocity spread below 10 solar radii is unclear. A previously developed coronal home model with a more realistic initial state is applied, and time-dependent, nonlinear, resistive 2.5-DMHD equations are numerically solved. It is found that nonlinear solitary-like waves with a supersonic phase speed are generated in coronal holes by torisonal Alfven waves in the radial flow velocity. The outward propagating nonlinear waves are similar in properties to sound solitons. When these waves are present, the solar wind speed and density fluctuate considerably on a time scale of an hour and on spatial scales of several solar radii in addition to the Alfvenic fluctuations. This is in qualitative agreement with the IPS velocity observations beyond 10 solar radii.
Observations of the cross-wind velocity variance in the stable boundary layer
Dean Vickers; L. Mahrt
Nine tower datasets over grassland, brush rangeland, snow covered plain, the ocean, three different pine forests, an aspen\\u000a forest and an urban site, are used to document the scale-dependence of the cross-wind velocity variance in the stable boundary\\u000a layer. The turbulence velocity variance scales with the surface momentum flux, as reported in previous studies. Such scaling\\u000a removes the stability dependence
A wind tunnel study of air flow in waving wheat: Two-point velocity statistics
R. H. Shaw; Y. Brunet; J. J. Finnigan; M. R. Raupach
Two-point, space-time correlations of streamwise and vertical velocity were obtained from a wind tunnel simulation of an atmospheric surface layer with an underlying model wheat canopy constructed of flexible nylon stalks. Velocity data extend from 1\\/6 canopy height to several canopy heights, with in excess of 2000 three-dimensional vector separations of the two x-wire probes. Isocorrelation contours over anx, z
Comparison of Solar Source Regions of LASCO Coronal Streamers and Solar Wind Sampled by ACE and Ulysses near Solar Maximum
P. C. Liewer; M. Neugebauer; D. Biesecker; D. Socker
The highly inclined and distorted current sheet seen during the current solar maximum leaves a strong imprint on the solar corona as seen by SOHO LASCO and the solar wind sector structure as seen by Ulysses and ACE. Here we present results of studies to determine the solar source regions of (1) solar wind streams sampled in situ by Ulysses
Solar Wind Driving of Magnetospheric ULF Waves: Pulsations Driven by Velocity Shear at the Magnetopause
Claudepierre, S G; Wiltberger, M; 10.1029/2007JA012890
We present results from global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind/magnetosphere interaction. These MHD simulations are used to study ultra low frequency (ULF) pulsations in the Earth's magnetosphere driven by shear instabilities at the flanks of the magnetopause. We drive the simulations with idealized, constant solar wind input parameters, ensuring that any discrete ULF pulsations generated in the simulation magnetosphere are not due to fluctuations in the solar wind. The simulations presented in this study are driven by purely southward interplanetary magnetic field (IMF) conditions, changing only the solar wind driving velocity while holding all of the other solar wind input parameters constant. We find surface waves near the dawn and dusk flank magnetopause and show that these waves are generated by the Kelvin-Helmholtz (KH) instability. We also find that two KH modes are generated near the magnetopause boundary. One mode, the magnetopause KH mode, propagates tailwa...
Latitude dependence of solar wind velocity observed > or approx. =1 AU
Mitchell, D.G.; Roelof, E.C.; Wolfe, J.H.
The large-scale solar wind velocity structure in the outer heliosphere has been systematically analyzed for Carrington rotations 1587-1541 (March 1972 to April 1976). Spacecraft data were taken from Imp 7/8 at earth, Pioneer 6, 8, and 9 near 1AU, and Pioneer 10 and 11 between 1.6 and 5 AU. Using the constant radial velocity solar wind approximation to map all of the velocity data to its high coronal emission heliolongitude, we examined the velocity structure observed at different spacecraft for latitudinal dependence and compared it with coronal structure in soft X rays and Ha absorption features. The constant radial velocity approximation usually remains self-consistent in decreasing or constant velocity solar wind out to 5 AU, enabling us to separate radial from latitudinal propagation effects. We found several examples of sharp nonmeridional stream boundaries in interplanetary space (approx.5/sup 0/ latitude in width), often directly associated with features in coronal X rays and Ha. In one structure there is evidence for significant (up to 40/sup 0/) nonradial flow of the plasma in the corona below the altitude of transition to super-Alfvenic flow.
Effect of Wind Velocity on Flame Spread in Microgravity
NASA Technical Reports Server (NTRS)
Prasad, Kuldeep; Olson, Sandra L.; Nakamura, Yuji; Fujita, Osamu; Nishizawa, Katsuhiro; Ito, Kenichi; Kashiwagi, Takashi; Simons, Stephen N. (Technical Monitor)
A three-dimensional, time-dependent model is developed describing ignition and subsequent transition to flame spread over a thermally thin cellulosic sheet heated by external radiation in a microgravity environment. A low Mach number approximation to the Navier Stokes equations with global reaction rate equations describing combustion in the gas phase and the condensed phase is numerically solved. The effects of a slow external wind (1-20 cm/s) on flame transition are studied in an atmosphere of 35% oxygen concentration. The ignition is initiated at the center part of the sample by generating a line-shape flame along the width of the sample. The calculated results are compared with data obtained in the 10s drop tower. Numerical results exhibit flame quenching at a wind speed of 1.0 cm/s, two localized flames propagating upstream along the sample edges at 1.5 cm/s, a single line-shape flame front at 5.0 cm/s, three flames structure observed at 10.0 cm/s (consisting of a single line-shape flame propagating upstream and two localized flames propagating downstream along sample edges) and followed by two line-shape flames (one propagating upstream and another propagating downstream) at 20.0 cm/s. These observations qualitatively compare with experimental data. Three-dimensional visualization of the observed flame complex, fuel concentration contours, oxygen and reaction rate isosurfaces, convective and diffusive mass flux are used to obtain a detailed understanding of the controlling mechanism, Physical arguments based on lateral diffusive flux of oxygen, fuel depletion, oxygen shadow of the flame and heat release rate are constructed to explain the various observed flame shapes.
The winds of O-stars. II - The terminal velocities of stellar winds of O-type stars
NASA Technical Reports Server (NTRS)
Groenewegen, M. A. T.; Lamers, H. J. G. L. M.; Pauldrach, A. W. A.
The SEI method (Lamers et al., 1987) is used to obtain P Cygni profiles of the UV resonance lines of C IV, N V, and S IV and of the subordinate UV lines of N IV and C III observed in the spectra of 27 O-type stars. Theoretical profiles which include the turbulence effects agree well with the observations, and they can account for the deep absorption troughs, the shape of the violet absorption wings, and the wavelength of the emission peak. The resulting terminal velocities of the stellar winds are found to be systematically lower by about 400 km/s than previous estimates obtained using the Sobolev approximation (Castor and Lamers, 1979), suggesting that the narrow absorption components, observed in the UV resonance lines of O and B stars, reach the terminal velocity of the winds.
Pheromone-modulated optomotor response in male gypsy moths, Lymantria dispar L.: Upwind flight in a pheromone plume in different wind velocities
Mark A. Willis; Ring T. Cardķ
1.Lymantria dispar males flying in a wind tunnel, up a plume of female sex pheromone, respond to increasing wind velocity by steering a course more precisely upwind. Even though the course angles steered are distributed unimodally about zero degrees (0░), the resulting track angles maintain a remarkably consistent bimodal distribution across all wind velocities tested (Fig. 4).2.As the wind velocity
Estimating attitude and wind velocity using biomimetic sensors on a microrobotic bee
Fuller, Sawyer Buckminster
Estimating attitude and wind velocity using biomimetic sensors on a microrobotic bee Sawyer B discusses recent developments in sen- sors for the Harvard RoboBee. The RoboBee is a sub-100 mg flapping the ocelli on a wire-mounted RoboBee that is free to rotate about its pitch axis. These flight-weight sensors
Remote Sensing of Solar Wind Velocities using Interplanetary Scintillation with MEXART and STELab Stations
NASA Astrophysics Data System (ADS)
Mejia-Ambriz, J. C.; Jackson, B. V.; Gonzalez-Esparza, A.; Tokumaru, M.; Yu, H.; Buffington, A.; Hick, P.
Radio signals from compact radio sources are scattered by electron density irregularities in the solar wind. This effect is registered by radio telescopes as intensity fluctuations of the observed radio source amplitude and known as Interplanetary Scintillation (IPS). The Mexican Array Radio Telescope (MEXART) and the antennas of Solar Terrestrial Environment Laboratory (STELab) are instruments dedicated to studies of IPS signals. In this work we present a technique (Manoharan and Ananthakrishnan, 1990) used to estimate solar wind velocities applied to observations of MEXART and STELab using single station spectra. Currently STELab uses a multi-station IPS technique to determinate solar wind speeds. Here we compare velocities obtained with a single station to those obtained using the multi-station technique for a few strong radio sources using both techniques and with both instruments. At the Center for Astrophysics and Space Sciences - University of California, San Diego (CASS-UCSD), a tomography program is able to reconstruct the dynamics of the inner heliosphere globally using IPS measurements to give solar wind densities and velocities. We show the incorporation of velocities provided by MEXART into this program that has been used successfully for over a decade with STELab IPS measurements.
Nanogenerator as an active sensor for vortex capture and ambient wind-velocity detection
Wang, Zhong L.
as active sensors for heart-pulse,10 tire pressure12 and cantilever vibration13 measurements have beenNanogenerator as an active sensor for vortex capture and ambient wind-velocity detection Rui Zhang sensitivity and good environment-friendly properties, the NG as an active sensor should play an important role
Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds
NASA Technical Reports Server (NTRS)
Spencer, Roy W.; Braswell, William D.
The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle- and upper-tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. The gradient wind equation is recast to include AMSU-A-derived variables, Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V(sub max)). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1-10 T(sub b) data (delta(sub r)T(sub B)), the squares of these gradients, a channel-15-based scattering index (SI(sub 89)), and area-averaged T(sub B). Calculations of T(sub B) and delta(sub r)T(sub B) from mesoscale model simulations of Andrew reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center V(sub max) estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V(sub max), the average error standard deviation was 4.7 m/s. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m/s Operational considerations, including the detection of weak cyclones and false alarm reduction, are also discussed.
Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds
NASA Technical Reports Server (NTRS)
Spencer, Roy; Braswell, William D.; Goodman, H. Michael (Technical Monitor)
The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle and upper tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. We recast the gradient wind equation to include AMSU-A derived variables. Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V(sub max)). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1 through 10 T(sub b) data (delta(sub r)T(sub b)), the squares of these gradients, a channel 15 based scattering index (SI-89), and area averaged T(sub b). Calculations of Tb and delta(sub r)T(sub b) from mesoscale model simulations of Andrew reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center (NHC) V(sub max) estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V(sub max), the average error standard deviation was 4.7 m/s. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m/s. Operational considerations, including the detection of weak cyclones and false alarm reduction are also discussed.
Technology Transfer Automated Retrieval System (TEKTRAN)
Accurately describing the probability density function (PDF) of lift-off or initial velocities of wind-blown sand ejecting from a sand bed is fundamental to understanding the mechanisms of wind-blown sand movement. Our objective was to investigate the efficacy of developing the PDF of lift-off veloc...
An evaluation of errors observed in the measurement of low wind velocities
NASA Technical Reports Server (NTRS)
Williams, S. R.; Thomson, D. W.
Measurements of low wind velocities (the absolute value of V sub H is approx. equal to 6 m/s) with a VHF wind profiler can be difficult if ground clutter or other biases in the system dominate in altering the position of the perceived peak in the calculated power spectrum. A variety of methods for ground clutter suppression are used in profiler systems today (Cornish, 1983). An editing method called zero suppression takes the spectral value of selectable number of points (N) on each side of 0 velocity (one point on either side, in this study) and sets them equal to the mean value of the points exterior to the specified N points on either side of 0. Analysis done with the PSU VHF(1) radar, shows that this zero-suppression method can systematically bias horizontal wings V sub H below 6 m/s. With the zero suppression, an artificial increase in absolute wind velocities occurs when the spectral peaks fall within the plus or minus N points of the FFT (personal communication, Strauch, 1985). It was also established that the method artificially decreases the absolute wind velocities inferred from spectral peaks that are outside but near the suppressed region. Comparisons of wind profiles observed with and without zero suppression are given. The range of the biased velocities extends to about plus or minus 6 m/s. Biases have been deduced to be as much as 2 m/s, but more commonly they are on the order of 1.0 m/s.
Can different elements move with different velocities in a radiatively driven stellar wind?
NASA Astrophysics Data System (ADS)
Oskinova, Lidia
B-type stars of lower luminosity classes have relatively weak stellar winds. In this respect they resemble presumably the more massive, but metal-poor stars in the early Universe. Theory predicts that very thin stellar winds are multi-component fluids. The ions of iron group metals are accelerated by radiation pressure, but do not transfer their momentum to the bulk of material. This dynamical decoupling is not yet observationally confirmed. LETG HRC-S spectra of the X-ray brightest non-degenerate massive star alpha Cru will allow to detect different velocities of particle species in stellar wind. These observations will empirically confirm or disprove the effect of dynamical decoupling in a thin stellar wind.
Study Effects of Maximum Velocity and Delay Probability on Mixed Traffic Flow
Jiaxiu Pan; Sanjuan Kang; Yujuan Liang; Yu Xue
An improved mixed cellular automaton traffic flow model is proposed via considering the effects of the gap between the successive cars and the velocity on the stochastic delay probability on single lane, in which the stochastic delay probability can be classified into three ones: acceleration, follow and deceleration delay probability. By numerical simulation for the mixed traffic flow with different
Numerical Assessment of the Influence of a Flow Wire on its Measured Maximum Velocity
Wim Hillewaert; Piet Claus; Guy Mareels; Pascal Verdonck; Paul Devos; Patrick Segers
? Abstract Ultra-thin Doppler wires (DW) are used to measure blood flow velocity in vessels using ultrasound. However, the presence of a DW will disturb the flow and thus its own measurements. To study the impact of this inherent limitation, we simulated pulsatile flow through a straight artery with a DW situated: (i) perfectly centered and aligned (DWc); and (ii)
On the stability of the moments of the maximum entropy wind wave spectrum
Pena, H.G.
The stability of some current wind wave parameters as a function of high-frequency cut-off and degrees of freedom of the spectrum has been numerically investigated when computed in terms of the moments of the wave energy spectrum. From the Pierson-Moskovitz wave spectrum type, a sea surface profile is simulated and its wave energy spectrum is estimated by the Maximum Entropy Method (MEM). As the degrees of freedom of the MEM spectral estimation are varied, the results show a much better stability of the wave parameters as compared to the classical periodogram and correlogram spectral approaches. The stability of wave parameters as a function of high-frequency cut-off has the same result as obtained by the classical techniques.
The Evolution of the Spectrum of Velocity Fluctuations in the Solar Wind
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron
Recent work has shown that at 1AU from the Sun the power spectrum of the solar wind magnetic field has the -5/3 spectral slope expected for Kolmogorov turbulence, but that the velocity has closer to a -3/2 spectrum. This paper traces the changes in solar wind velocity spectra from 0.3 to 5 AU using data from the Helios and Ulysses spacecraft to show that this is a transient stage in the evolution. The spectrum of the velocity is found to be flatter than that of the magnetic field for the higher frequencies examined for all cases until the slopes become equal (at -5/3) well past 1 AU when the wind is relatively nonAlfvenic. In some respects, in particular in the evolution of the frequency at which the spectrum changes from flatter at larger scales to a traditionally turbulent spectrum at smaller scales, the velocity field evolves more rapidly that the magnetic, and this is associated with the dominance of the magnetic energy over the kinetic at "inertial range" scales. The Alfvenicity of the fluctuations, not the speed of the flow, is shown to control the rate of the spectral evolution. This study shows that, for the solar wind ., the idea of a simple "inertial range" with uniform spectral properties is not realistic, and new phenomenologies will be needed to capture the true situation. In addition a flattening of the velocity spectrum persists at times for small scales, which may provide a clue to the nature of the small-scale interactions.
Predicting solar and wind energy trends using cloud cover and wind velocity
Developments include: (1) a mode to predict potential and clear sky solar radiation on a horizontal surface and clear sky solar radiation on a tilted panel for any latitude, POTSOL; (2) a model to predict solar radiation on a horizontal surface for any latitude as a function of total opaque cloud cover, ESR; and (3) a program to estimate wind
One year variations in the near earth solar wind ion density and bulk flow velocity
NASA Technical Reports Server (NTRS)
Bolton, Scott J.
One-year periodic variations in the near earth solar wind ion density and bulk flow velocity are reported. The variations show an inverse relationship between the ion velocity and density. The peak strength of the observed density variation ranges from 50-100 percent over the background. These variations imply either large scale mass loading inside the earth's orbit or intrinsic solar modulations. Analyses of both near earth and Pioneer Venus Orbiter spacecraft data provide a comparison at two different heliocentric distances. Several explanations for these variations are discussed.
High altitude wind velocity at Sierra Negra and San Pedro Mßrtir
Esperanza Carrasco; Remy Avila; Alberto Carrami±ana
It has been proposed that the global circulation of the atmosphere winds at 200 mb can be used as a criteria to establish the suitability of a site for the development of adaptive optics techniques such as slow wavefront corrugation correction. By using the NOAA NCEP/NCAR Reanalysis data base we analyze the monthly average wind velocity at 200 mb for a 16 year period, for two sites in Mexico: Sierra Negra and San Pedro M\\'artir. We compare the results with those obtained for Mauna Kea, Paranal and La Silla, with Maidanak in Uzbekistan, and with Gamsberg in Namibia. We show that for all the sites under study there is a yearly wind speed modulation and we model that modulation. Our results show that Sierra Negra and San Pedro M\\'artir are comparable with the best observatory sites as Mauna Kea and are amongst the most advantageous sites to apply adaptive optics techniques.
High-Altitude Wind Velocity at Sierra Negra and San Pedro Mßrtir
NASA Astrophysics Data System (ADS)
Carrasco, Esperanza; Avila, Remy; Carrami±ana, Alberto
It has been proposed that the global circulation of atmospheric winds at 200 mbar can be used as a criterion to establish the suitability of a site for the development of adaptive optics techniques such as slow wave front corrugation correction. By using the NOAA NCEP/NCAR reanalysis database, we analyze the monthly average wind velocity at 200 mbar for a 16 yr period for two sites in Mexico: Sierra Negra and San Pedro Mßrtir. We compare the results with those obtained for Mauna Kea, Paranal, and La Silla, and with Maidanak in Uzbekistan and Gamsberg in Namibia. We show that for all the sites studied, there is a yearly wind speed modulation, and we model that modulation. Our results show that Sierra Negra and San Pedro Mßrtir are comparable to the best observatory sites, such as Mauna Kea, and are among the best sites to apply adaptive optics techniques.
A radionuclide counting technique for measuring wind velocity. [drag force anemometers
NASA Technical Reports Server (NTRS)
Singh, J. J.; Khandelwal, G. S.; Mall, G. H.
A technique for measuring wind velocities of meteorological interest is described. It is based on inverse-square-law variation of the counting rates as the radioactive source-to-counter distance is changed by wind drag on the source ball. Results of a feasibility study using a weak bismuth 207 radiation source and three Geiger-Muller radiation counters are reported. The use of the technique is not restricted to Martian or Mars-like environments. A description of the apparatus, typical results, and frequency response characteristics are included. A discussion of a double-pendulum arrangement is presented. Measurements reported herein indicate that the proposed technique may be suitable for measuring wind speeds up to 100 m/sec, which are either steady or whose rates of fluctuation are less than 1 kHz.
Comparative Flight and Full-Scale Wind-Tunnel Measurements of the Maximum Lift of an Airplane
NASA Technical Reports Server (NTRS)
Silverstein, Abe; Katzoff, S; Hootman, James A
Determinations of the power-off maximum lift of a Fairchild 22 airplane were made in the NACA full-scale wind tunnel and in flight. The results from the two types of test were in satisfactory agreement. It was found that, when the airplane was rotated positively in pitch through the angle of stall at rates of the order of 0.1 degree per second, the maximum lift coefficient was considerably higher than that obtained in the standard tests, in which the forces are measured with the angles of attack fixed. Scale effect on the maximum lift coefficient was also investigated.
On line Web-based Maximum Wind Power Monitoring and Control System
H. C. Lin
The shortage of traditional energy sources like fossil fuels is getting worse on earth today. Therefore, the exploitation in dipping renewable energy such as wind power has become an essential issue in both academia and industry recently. The installed wind power capacity in the world has been increasing rapidly over the past decade. However, wind energy is distributed, and varies
Model Predictive Control for maximum power capture of variable speed wind turbines
D. Q. Dang; S. Wu; Y. Wang; W. Cai
Control algorithms for variable speed wind turbines are now more and more interested by engineers and scientists. The dynamic fluctuations of wind require fast dynamic response of controller in order to capture as much power as possible from power available. This makes control system more challenge. In this paper, we present Model Predictive Controller (MPC) for wind turbine system for
Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state
NASA Astrophysics Data System (ADS)
Fahr, H.-J.; Siewert, M.
Context. Throughout the heliosphere, ion power spectra have been found in observations to exhibit suprathermal tails that follow power laws. Ion power-law spectra, though having a broad range of spectral indices 4.4 ? ?v ? 6.6, perhaps favourably seem to have velocity power indices of ?v ? (-5), a phenomenon that can more or less ubiquitously be found in heliospheric space plasmas. This is probably indicative of an as yet unidentified quasi-equilibrium state of collisionless space plasmas. Aims: We develop the idea that these forms of ion spectra could be produced by a continuous back- and forth- shuffling of wind convected ions in consecutive jumps from fast to slow, and vice-versa, bulk velocity regimes. Methods: The appearance of a quasi-equilibrium state due to this shuffling and re-shuffling, as we show, naturally results in ion distribution functions that are superpositions of a series of weighted Maxwellians resulting into power laws beyond a critical velocity border. Spectral intensities thereby anticorrelate with bulk velocities, but power indices depend only slightly on bulk velocity. Results: The fully developed equilibrium state is shown here, however, to be characterized by a power law with power index ?v = ( - 3), instead of 4.4 ? ?v ? 6.6. These latter states, which generally show up in observations, thus may characterize an off-equilibrium state as we discuss in this paper.
Responses of giant interneurons of the cockroach Periplaneta americana to wind puffs of different directions and velocities
Joanne Westin; Jonathan J. Langberg; Jeffrey M. Camhi
1.Controlled wind puffs of different directions and velocities were delivered to the cerci of cockroaches (Periplaneta americana), while the responses of individually identifiable giant interneurons (GI's) were recorded intracellularly.2.All fourteen histologically identified GI's (seven bilateral pairs) respond with a burst of action potentials to wind from some or all directions. The directional sensitivity of a given GI is consistent from
Dynamics of Line-driven Winds from Disks in Cataclysmic Variables. II. Mass-Loss Rates and Velocity Laws
Achim Feldmeier; Isaac Shlosman; Peter Vitello
We analyze the dynamics of two-dimensional stationary, line-driven winds from accretion disks in cataclysmic variable (CV) stars by generalizing the formalism of Castor, Abbott, and Klein (CAK) for O stars. In Paper I, we solved the wind Euler equation, derived its two eigenvalues, and addressed the solution topology and wind geometry. Here, we focus on mass-loss rates and velocity laws
The de-correlation of westerly winds and westerly-wind stress over the Southern Ocean during the Last Glacial Maximum
NASA Astrophysics Data System (ADS)
Liu, Wei; Lu, Jian; Leung, L. Ruby; Xie, Shang-Ping; Liu, Zhengyu; Zhu, Jiang
Motivated by indications from paleo-evidence, this paper investigates the changes of the Southern Westerly Winds (SWW) and westerly-wind stress between the Last Glacial Maximum (LGM) and pre-industrial in the PMIP3/CMIP5 simulations, highlighting the role of Antarctic sea ice in modulating the wind effect on ocean. Particularly, a de-correlation occurs between the changes in SWW and westerly-wind stress, caused primarily by an equatorward expansion of winter Antarctic sea ice that undermines the efficacy of wind in generating stress over the liquid ocean. Such de-correlation may reflect the LGM condition in reality, in view of the fact that the model which simulates this condition has most fidelity in simulating modern SWW and Antarctic sea ice. Therein two models stand out for their agreements with paleo-evidence regarding the change of SWW and the westerly-wind stress. They simulate strengthened and poleward-migrated LGM SWW in the atmosphere, consistent with the indications from dust records. Whilst in the ocean, they well capture an equatorward-shifted pattern of the observed oceanic front shift, with most pronounced equatorward-shifted westerly wind stress during the LGM.
Cluster/Peace Electrons Velocity Distribution Function: Modeling the Strahl in the Solar Wind
NASA Technical Reports Server (NTRS)
Figueroa-Vinas, Adolfo; Gurgiolo, Chris; Goldstein, Melvyn L.
We present a study of kinetic properties of the strahl electron velocity distribution functions (VDF's) in the solar wind. These are used to investigate the pitch-angle scattering and stability of the population to interactions with electromagnetic (whistler) fluctuations. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focuses on the mechanisms that control and regulate the pitch-angle and stability of strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the electron heat-flux and temperature anisotropy. The goal is to check whether the strahl electrons are constrained by some instability (e.g., the whistler instability), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by fitting the VDF's to a spectral spherical harmonic model from which the moments are derived directly from the model coefficients.
Equilibrium Points and Zero Velocity Surfaces in the Restricted Four Body Problem with Solar Wind Drag
Kumari, Reena
We have analyzed the motion of an infinitesimal mass in the restricted four body problem with solar wind drag. It is assumed that forces which govern the motion are mutual gravitational attractions of the primaries, radiation pressure force and solar wind drag. We have derived the equations of motion and find the Jacobi integral, zero velocity surfaces and particular solutions of the system. It is found that three collinear points are real when radiation factor $0<\\beta<0.1$ whereas only one real point obtained when $0.125<\\beta<0.2$. Again, stability property of the system is examined with the help of Poincar\\'{e} surface of section (PSS) and Lyapunov characteristic exponents (LCEs). It is found that in presence of drag forces LCE is negative for a specific initial condition, hence the corresponding trajectory is regular whereas regular islands in the PSS are expanded.
Retrieval and Evaluation of Wind Vectors and Advective Surface Velocities from Synthetic Aperture Radar and Infrared Radiometer Data
NASA Astrophysics Data System (ADS)
Carvajal, Gisela; Eriksson, Leif E. B.
Analysis of ocean surface dynamics has been proven to be of vital importance in many areas (e.g. shipping, fishing). Two important parameters to describe the ocean dynamics are the wind velocity (speed and direction) and advective surface velocities (ocean current velocity). These parameters are currently provided operationally by forecast models, surface sensors (e.g. buoys, coastal radar) and satellite sensors. However, coverage limitations, low resolution and limited temporal availability impose a need for implementation and evaluation of new data sources and techniques for estimation of these parameters. In this paper we implement and evaluate known techniques for determination of wind and ocean current velocity from satellite data. Wind is determined from Synthetic Aperture Radar (SAR) data by applying two algo-rithms. First, the Local Gradient method is implemented to extract wind direction from the SAR data, and then the CMOD-5 Geophysical Model Function of the backscatter is inverted to obtain the wind speed as a function of the wind direction and the incidence angle. Current propagation is estimated by analyzing the Sea Surface Temperature propagation in two consec-utive infrared images of the same area from the Advanced Very High Resolution Radiometer. The evaluation shows a good agreement between estimated wind vectors from SAR and scat-terometer data. Comparison with merged ocean current estimates is addressed. The methods will be implemented in the maritime security service provided by the SECTRONIC project funded by the EU 7th framework program.
Evolution of longitudinal structure in the solar wind with radial distance: comparisons of interplanetary scintillation measurements and in-situ data taken near solar maximum
A. R. Breen; A. Canals; M. Bisi
The distribution of fast and slow streams of solar wind changes dramatically over the solar cycle, with the large polar fast streams and narrow equatorial belt of slow wind replaced at solar maximum by a heliosphere dominated by slow wind, in which narrower fast streams may appear at any latitude - this dramatically increases the importance of stream-stream interaction in
Estimation of Venus wind velocities from high-resolution infrared spectra. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Smith, M. A. H.
Zonal velocity profiles in the Venus atmosphere above the clouds were estimated from measured asymmetries of HCl and HF infrared absorption lines in high-resolution Fourier interferometer spectra of the planet. These asymmetries are caused by both pressure-induced shifts in the positions of the hydrogen-halide lines perturbed by CO2 and Doppler shifts due to atmospheric motions. Particularly in the case of the HCl 2-0 band, the effects of the two types of line shifts can be easily isolated, making it possible to estimate a profile of average Venus equatorial zonal velocity as a function of pressure in the region roughly 60 to 70 km above the surface of the planet. The mean profiles obtained show strong vertical shear in the Venus zonal winds near the cloud-top level, and both the magnitude and direction of winds at all levels in this region appear to vary greatly with longitude relative to the sub-solar point.
Maximum energy of cosmic-ray particles accelerated by supernova remnant shocks in stellar wind cavities
Heinrich J. Voelk; Peter L. Biermann
Diffusive shock acceleration, balanced by adiabatic losses, leads readily to particle energies of more than 10 to the 15th eV in the case of a supernova shock freely expanding into a stellar wind cavity. This process accelerates particles early on out of stellar wind material which is often enriched in certain elements (isotopes), and may thus contribute to explain elemental
Three-dimensional velocity measurements around a rotating vertical axis wind turbine
NASA Astrophysics Data System (ADS)
Coletti, Filippo; Ryan, Kevin; Dabiri, John; Eaton, John
Vertical axis wind turbines (VAWT) can be more closely spaced than conventional horizontal axis wind turbines (HAWT), which points to a potentially greater power that can be extracted from a given wind farm footprint. In order to optimize the inter-turbine spacing and to investigate the potential for constructive aerodynamic interactions, the complex dynamics of VAWT wakes need to be analyzed. To date, only single-point or at best two-dimensional measurements of such wakes have been documented. We have measured the full three-component mean velocity field around and downstream the scaled-down model of a rotating VAWT by Magnetic Resonance Velocimetry (MRV). The high spatial resolution allows to quantitatively explore the structure of the wake, its interaction with the floor, and its development. The flow is shown to be highly three-dimensional and asymmetric for the whole investigated region (up to 7 diameters downstream of the turbine). These results can inform low-order models to predict the performance of turbine arrays.
Vertical velocity variance in the mixed layer from radar wind profilers.
Eng, K.; Coulter, R. L.; Brutsaert, W.; Environmental Research; Cornell Univ.
Vertical velocity variance data were derived from remotely sensed mixed layer turbulence measurements at the Atmospheric Boundary Layer Experiments (ABLE) facility in Butler County, Kansas. These measurements and associated data were provided by a collection of instruments that included two 915 MHz wind profilers, two radio acoustic sounding systems, and two eddy correlation devices. The data from these devices were available through the Atmospheric Boundary Layer Experiment (ABLE) database operated by Argonne National Laboratory. A signal processing procedure outlined by Angevine et al. was adapted and further built upon to derive vertical velocity variance, {omega}'{sup 2}, from 915 MHz wind profiler measurements in the mixed layer. The proposed procedure consisted of the application of a height-dependent signal-to-noise ratio (SNR) filter, removal of outliers plus and minus two standard deviations about the mean on the spectral width squared, and removal of the effects of beam broadening and vertical shearing of horizontal winds. The scatter associated with {omega}'{sup 2} was mainly affected by the choice of SNR filter cutoff values. Several different sets of cutoff values were considered, and the optimal one was selected which reduced the overall scatter on {omega}'{sup 2} and yet retained a sufficient number of data points to average. A similarity relationship of {omega}'{sup 2} versus height was established for the mixed layer on the basis of the available data. A strong link between the SNR and growth/decay phases of turbulence was identified. Thus, the mid to late afternoon hours, when strong surface heating occurred, were observed to produce the highest quality signals.
Vertical velocity variance in the mixed layer from radar wind profilers
Eng, K.; Coulter, R.L.; Brutsaert, W.
Vertical velocity variance data were derived from remotely sensed mixed layer turbulence measurements at the Atmospheric Boundary Layer Experiments (ABLE) facility in Butler County, Kansas. These measurements and associated data were provided by a collection of instruments that included two 915 MHz wind profilers, two radio acoustic sounding systems, and two eddy correlation devices. The data from these devices were available through the Atmospheric Boundary Layer Experiment (ABLE) database operated by Argonne National Laboratory. A signal processing procedure outlined by Angevine et al. was adapted and further built upon to derive vertical velocity variance, w_pm???2, from 915 MHz wind profiler measurements in the mixed layer. The proposed procedure consisted of the application of a height-dependent signal-to-noise ratio (SNR) filter, removal of outliers plus and minus two standard deviations about the mean on the spectral width squared, and removal of the effects of beam broadening and vertical shearing of horizontal winds. The scatter associated with w_pm???2 was mainly affected by the choice of SNR filter cutoff values. Several different sets of cutoff values were considered, and the optimal one was selected which reduced the overall scatter on w_pm???2 and yet retained a sufficient number of data points to average. A similarity relationship of w_pm???2 versus height was established for the mixed layer on the basis of the available data. A strong link between the SNR and growth/decay phases of turbulence was identified. Thus, the mid to late afternoon hours, when strong surface heating occurred, were observed to produce the highest quality signals.
Assessing Southern Hemisphere Westerly Wind Changes during the Last Glacial Maximum using Paleo-data Synthesis (Invited)
NASA Astrophysics Data System (ADS)
Kohfeld, K. E.; Graham, R. M.; De Boer, A. M.; Wolff, E. W.; Sime, L. C.; Le Quere, C.; Bopp, L.
Changes in the strength and position of Southern Hemisphere westerly winds during the last glacial cycle have been invoked to explain glacial-interglacial climate fluctuations. However, neither paleo models nor paleodata agree on the magnitude, or even the sign, of the change in wind strength and latitude during the Last Glacial Maximum (LGM), compared to the recent past. This study synthesizes paleo-environmental data that have been used to infer changes in winds during the LGM compared with the late Holocene. These compilations include changes in terrestrial moisture, dust deposition, and ocean productivity, along with summaries of previously published information on sea surface temperatures (SSTs) and ocean dynamics in the Southern Hemisphere. Our compilations of terrestrial moisture from 94 sites and dust deposition from 87 sites show generally drier conditions for the LGM between 0 and 40S, with wetter conditions along the west coasts and drying along the east coasts of continents. LGM dust deposition rates ranged from 2 to 4.5 times higher over the Southern Ocean and about 13 times higher over the Antarctic continent. For the oceans, reconstructed changes in SSTs show maximum cooling (>4 ░C) in the modern-day Subantarctic Zone, coincident with a region of enhanced export production during the LGM compared with today. We find that any hypothesis of LGM wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents, cooler temperatures and higher productivity in the Subantarctic Zone, and reductions in Agulhas leakage around southern Africa. Our comparison suggests that an overall strengthening, an equatorward displacement, or no change at all in winds could all be interpreted as consistent with observations. If a single cause related to the southern westerlies is sought for all the evidence presented, then an equatorward displacement or strengthening of the winds would be consistent with the largest proportion of the data evidence. However, other processes, such as weakening or poleward shifts in winds, a weakened hydrological cycle, extended sea-ice cover, and changed buoyancy fluxes, cannot be ruled out as potential explanations of observed changes in moisture, surface temperature, and productivity. We contend that resolving the position and strength of westerly winds during the LGM remains elusive based on data reconstructions alone. However, we believe that these data reconstructions of environmental conditions can be used in conjunction with model simulations to identify which processes best represent westerly wind conditions during the LGM.
Maximum velocity of shortening of three fibre types from horse soleus muscle: implications for scaling with body size.
Rome, L C; Sosnicki, A A; Goble, D O
1. To explore how maximum velocity of shortening (Vmax) of fibres varies within one muscle and how Vmax varies with body size, we measured Vmax of muscle fibres from soleus muscle of a large animal, the horse. 2. Vmax was determined by the slack test on skinned single muscle fibres at 15 degrees C during maximal activation (pCa = 5.2). The fibre type was subsequently determined by a combination of single-cell histochemistry and gel electrophoresis of the myosin light chains. 3. Vmax values for the type I, IIA and IIB muscle fibres were 0.33 +/- 0.04 muscle lengths/s (ML/s) (+/- S.E.M., n = 6), 1.33 +/- 0.08 ML/s (n = 7) and 3.20 +/- 0.26 ML/s (n = 6), respectively. It is likely that the large range in Vmax is due to differences observed in the myosin heavy chains and light chains associated with the three fibre types. 4. Comparison of Vmax over a 1200-fold range (450 kg horse vs. 0.38 kg rat) of body mass (Mb) suggests that slow fibres scale more dramatically (Mb-0.18) than do fast glycolytic fibres (Mb-0.07). This difference may enable the slow fibres to work at high efficiencies in the large animal while the fast fibres can still generate a large mechanical power when necessary. PMID:2100306
The Lick AGN Monitoring Project: Velocity-Delay Maps from the Maximum-Entropy Method for Arp 151
Bentz, Misty C; Barth, Aaron J; Bennert, Vardha Nicola; Canalizo, Gabriela; Filippenko, Alexei V; Gates, Elinor L; Malkan, Matthew A; Minezaki, Takeo; Treu, Tommaso; Woo, Jong-Hak; Walsh, Jonelle L
We present velocity-delay maps for optical H I, He I, and He II recombination lines in Arp 151, recovered by fitting a reverberation model to spectrophotometric monitoring data using the maximum-entropy method. H I response is detected over the range 0-15 days, with the response confined within the virial envelope. The Balmer-line maps have similar morphologies but exhibit radial stratification, with progressively longer delays for Hgamma to Hbeta to Halpha. The He I and He II response is confined within 1-2 days. There is a deficit of prompt response in the Balmer-line cores but strong prompt response in the red wings. Comparison with simple models identifies two classes that reproduce these features: freefalling gas, and a half-illuminated disk with a hotspot at small radius on the receding lune. Symmetrically illuminated models with gas orbiting in an inclined disk or an isotropic distribution of randomly inclined circular orbits can reproduce the virial structure but not the observed asymmetry. Radial out...
Measurement of the horizontal velocity of wind perturbations in the middle atmosphere by spaced MF radar systems
NASA Technical Reports Server (NTRS)
Meek, C. E.; Manson, A. H.; Smith, M. J.
Two remote receiving sites have been set up at a distance of approx 40 km from the main MF radar system. This allows measurement of upper atmosphere winds from 60-120 km (3 km resolution) at the corners of an approximately equilateral triangle of side approx 20 km. Some preliminary data are compared through cross correlation and cross spectral analysis in an attempt to determine the horizontal velocity of wind perturbations and/or the horizontal wavelength and phase velocity of gravity waves.
AXAOTHER XL -- A spreadsheet for determining doses for incidents caused by tornadoes or high-velocity straight winds
Simpkins, A.A.
AXAOTHER XL is an Excel Spreadsheet used to determine dose to the maximally exposed offsite individual during high-velocity straight winds or tornado conditions. Both individual and population doses may be considered. Potential exposure pathways are inhalation and plume shine. For high-velocity straight winds the spreadsheet has the capability to determine the downwind relative air concentration, however for the tornado conditions, the user must enter the relative air concentration. Theoretical models are discussed and hand calculations are performed to ensure proper application of methodologies. A section has also been included that contains user instructions for the spreadsheet.
Two-dimensional Cascade Investigation of the Maximum Exit Tangential Velocity Component and Other Flow Conditions at the Exit of Several Turbine Blade Designs at Supercritical Pressure Ratios
NASA Technical Reports Server (NTRS)
Hauser, Cavour H; Plohr, Henry W
The nature of the flow at the exit of a row of turbine blades for the range of conditions represented by four different blade configurations was evaluated by the conservation-of-momentum principle using static-pressure surveys and by analysis of Schlieren photographs of the flow. It was found that for blades of the type investigated, the maximum exit tangential-velocity component is a function of the blade geometry only and can be accurately predicted by the method of characteristics. A maximum value of exit velocity coefficient is obtained at a pressure ratio immediately below that required for maximum blade loading followed by a sharp drop after maximum blade loading occurs.
Wind velocities and their connection to boundary layer characteristics in turbulent Rayleigh-Bķnard convection
NASA Astrophysics Data System (ADS)
Wagner, Sebastian; Shishkina, Olga; Wagner, Claus
Highly resolved direct numerical simulations have been performed for turbulent Rayleigh-Bķnard convection in a cylindrical container with aspect ratio unity and Prandtl number Pr=0.786. The Rayleigh numbers in the simulations are up to 109. The calculated fields are reduced to the plane of the large scale circulation and analyzed with respect to the viscous and thermal boundary layer thickness and corresponding quantities in a statistical manner, i.e. probability density functions and their characteristics have been calculated a posteriori from instantaneous flow fields. Different methods to determine the boundary layer thickness are suggested and compared. The results are analyzed and compared with the Prandtl-Blasius theory of laminar boundary layers as well as the Grossmann-Lohse theory of states in Rayleigh-Bķnard convection. Thereby fundamental relations between wind velocities and the generated wall shear stress are determined. The authors acknowledge support by the Deutsche Forschungs Gemeinschaft (DFG) under grant SH405/2-1.
Wind tunnel investigation of the effect of high relative velocities on the structural integrity of birds
NASA Technical Reports Server (NTRS)
Bresnahan, D. L.
An experimental investigation was conducted in a supersonic wind tunnel to determine the effect a sudden high velocity headwind had on the physical deformation and structural breakup characteristics of birds. Several sizes of recently killed birds were dropped into the test section at free-stream Mach numbers ranging from 0.2 to 0.8 and photographed with high-speed motion-picture cameras. These conditions simulated flow conditions encountered when birds are ingested into the inlets of high speed aircraft, thereby constituting a safety hazard to the aircraft and its occupants. The investigation shows that, over the range of headwind conditions tested, the birds remained structurally intact and did not suffer any appreciable deformation or structural breakup.
Flying Drosophila stabilize their vision-based velocity controller by sensing wind with their antennae
Fuller, Sawyer Buckminster; Straw, Andrew D.; Peek, Martin Y.; Murray, Richard M.; Dickinson, Michael H.
Flies and other insects use vision to regulate their groundspeed in flight, enabling them to fly in varying wind conditions. Compared with mechanosensory modalities, however, vision requires a long processing delay (~100 ms) that might introduce instability if operated at high gain. Flies also sense air motion with their antennae, but how this is used in flight control is unknown. We manipulated the antennal function of fruit flies by ablating their aristae, forcing them to rely on vision alone to regulate groundspeed. Arista-ablated flies in flight exhibited significantly greater groundspeed variability than intact flies. We then subjected them to a series of controlled impulsive wind gusts delivered by an air piston and experimentally manipulated antennae and visual feedback. The results show that an antenna-mediated response alters wing motion to cause flies to accelerate in the same direction as the gust. This response opposes flying into a headwind, but flies regularly fly upwind. To resolve this discrepancy, we obtained a dynamic model of the flyÆs velocity regulator by fitting parameters of candidate models to our experimental data. The model suggests that the groundspeed variability of arista-ablated flies is the result of unstable feedback oscillations caused by the delay and high gain of visual feedback. The antenna response drives active damping with a shorter delay (~20 ms) to stabilize this regulator, in exchange for increasing the effect of rapid wind disturbances. This provides insight into fliesÆ multimodal sensory feedback architecture and constitutes a previously unknown role for the antennae. PMID:24639532
Investigation on the impact of the environment wind velocity on the indirect air-cooling tower performance
NASA Astrophysics Data System (ADS)
Qin, Yongbo; Gu, Hongfang; Wang, Haijun; Chen, Guoyong
The wind velocity plays a crucial role in the operation characteristic of indirect cooling tower. In this paper a 2ū330MW vertical arrangement indirect air-cooled system was taken as research object, and numerical simulation method was used to analyze the relative influence of the wind speed, ranging from 4m/s to 18m/s, on the outlet water temperature of cooling tower, the outlet air temperature of radiator, the facing wind speed of the fan segment and on the outlet air speed of the cooling tower. The result shows that the impact of the natural wind speed on the cooling tower efficiency varies greatly and this impact increases as the wind speed increases.
The velocity distribution function of the neutral lithium cloud produced by an AMPTE solar wind release
NASA Astrophysics Data System (ADS)
Chapman, S. C.; Johnstone, A. D.; Coates, A. J.
On Sept. 20, 1984 a release of photoionizing lithium neutrals was made in the quiet solar wind by the AMPTE-IRM spacecraft. The MSSL ion instrument on board the UKS spacecraft that was positioned about 30 km from the release center enabled measurement of significant fluxes of lithium ions to be made for about 3 min after the release; that is, long after the initial (about 25-s) local perturbation to the field and flow had died away. Here, the MSSL ion detector response to the release ions is examined in detail, showing that the ion measurements are consistent with injection into a cycloidal orbit. Knowing the ion orbit, it is then possible to trace the expansion of the neutral lithium cloud and obtain its initial velocity distribution. Various preliminary analyses suggested a shell-like expansion of the cloud, but disagreed over its velocity. The more detailed analysis of the UKS data presented here shows that it is not possible to determine from these data whether or not the cloud is shell-like, but reveals that significant local anisotropy is present.
Eddy and deep chlorophyl maximum response to wind-shear in the lee of Gran Canaria
G. Basterretxea; E. D. Barton; P. Tett; P. Sangra; E. Navarroperez; J. Ar??stegui
The physical and biological properties of the warm wake of Gran Canaria were examined during a survey carried out in June 1998. The sampling region was dominated by the presence of a warm triangular region downwind the island and an anticyclonic eddy spun off the island. Convergent and divergent frontal regions were generated by the wind shear zones extending along
Assimilation of moored velocity data in a model of coastal wind-driven circulation off Oregon: Multivariate capabilities
Alexander L. Kurapov; J. S. Allen; G. D. Egbert; R. N. Miller; P. M. Kosro; M. D. Levine; T. Boyd; J. A. Barth
Horizontal current measurements from an array of moored acoustic Doppler profilers are assimilated sequentially into a model of coastal wind-driven circulation off Oregon during the upwelling season of May-August 2001. Model results are compared against independent moored and ship survey data to document a positive effect of velocity data assimilation (DA) on other oceanic variables of interest such as the
Investigation on Performance Influence of Maximum Thickness Position on Vertical Axis Wind Turbine Airfoil
Jianjun Qu; Yi Mei; Mingwei Xu
Airfoil geometric configuration is very important for aerodynamic performance of a straight-bladed vertical axis wind turbine (SB-VAWT). In recent study, Islam et al have pointed out old NACA-4 are not perfectly suited for SB-VAWT operating at low Reynolds number and special purpose airfoils is needed. Islam has singled out four required geometric features which would be suitable for SB-VAWT airfoil.
KITANO M. and EGUCHI H. Dynamics of whole plant water balance and leaf growth in response to evaporative demand. II. Effect of change in wind velocity. BIOTRONICS 21, 51-60, 1992. Dynamics of whole plant water balance and leaf expansive growth were analyzed in cucumber plants (Cucumis sativus L.) exposed to step change in wind velocity (U). The effect of step
The Evolution of the Spectrum of Solar Wind Velocity Fluctuations from 0.3 to 5 AU
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron
Recent work has shown that at 1 AU from the Sun the power spectrum of the solar wind magnetic field has the -5/3 spectral slope expected for Kolmogorov turbulence, but that the velocity has closer to a -3/2 spectrum. This paper traces the changes in solar wind velocity spectra from 0.3 to 5 AU using data from the Helios and Ulysses spacecraft to show that this is a transient stage in solar-wind evolution. The spectrum of the velocity is found to be flatter than that of the magnetic field for the higher frequencies examined for all cases until the slopes become equal (at -5/3) well past 1 AU when the wind is relatively nonAlfvenic. In some respects, in particular in the evolution of the frequency at which the spectrum changes from flatter at larger scales to a "turbulent" spectrum at smaller scales, the velocity field evolves more rapidly than the magnetic, and this is associated with the dominance of the magnetic energy over the kinetic at "inertial range" scales. The speed of the flow is argued to be largely unrelated to the spectral slopes, consistent with previous work, whereas high Alfvenicity appears to slow the spectral evolution, as expected from theory. This study shows that, for the solar wind, the idea of a simple "inertial range" with uniform spectral properties is not realistic, and new phenomenologies will be needed to capture the true situation. It is also noted that a flattening of the velocity spectrum often occurs at small scales.
Design of a control scheme for a maximum power extraction in low power wind turbine-generator system
NASA Astrophysics Data System (ADS)
Henao Bravo, Elkin Edilberto
This document presents the modeling of a wind turbine-generator system and developing a control scheme for maximum power extraction. The system comprises a low-power variable speed wind rotor coupled to a squirrel cage induction generator through gearbox. The generator delivers electrical energy to a DC load through a PWM three phase rectifier which control variables are duty cycle and the fundamental frequency of the modulated signal. The control scheme maintains constant relationship voltage/frequency in the stator of the generator to operate the machine with constant air gap flow at its nominal value, thereby decreasing electrical losses in the circuit of the stator and rotor. The controller is based on MPPT algorithms for determining the operating point the system and achieve the proper mechanical speed shaft. The performance is evaluated through simulations in MatlabRTM/simulink. and presents this type of control as a good alternative for handling low-power wind turbine-generator systems effectively and efficiently
Effect of Solar-Wind Velocity, Magnetic Field and Density on Solar Energetic Particle Transport
NASA Astrophysics Data System (ADS)
Ng, C. K.
In large gradual solar energetic particle (SEP) events, energetic protons greatly amplify ambient upstream Alfvķn waves near coronal-mass-ejection (CME) driven shocks. The waves grow until they are swept downstream of the shock. The amplified waves scatter the particles and ōflattenö the SEP intensity energy spectrum at low energy at 1 AU, causing the streaming limit phenomenon. Both the wave and SEP intensities maximize near the shock and fall steeply with distance upstream. The SEPs are focused by the longitudinal gradient of the magnetic field B. The wave growth rate increases with energetic proton streaming and varies as f/?(np), with f the energetic proton phase-space density and np the plasma proton number density. Thus, in addition to the SEP release rate at the shock, the environmental quantities: np(r), B(r), the solar-wind velocity Vsw(r), and the Alfvķn speed VA(r) also influence SEP transport. At heliocentric distance r? 8r?, np as well as B deviate significantly from ś r-2, Vsw rises slowly from near zero on the photosphere, and VA peaks near 4 r?. We have generalized our SEP transport model to take account of realistic radial dependences of the above solar-wind properties down to ś2 r? in addition to the usual processes of wave and particle transport and Alfvķn wave growth. The model has been applied to STEREO A observation of the 2011 March 21 SEP event with the preliminary conclusion that wave-damping processes rather than the environmental quantities are more likely to raise the predicted proton intensity at < 5 MeV to the higher observed values.
Maximum velocity of shortening in relation to myosin isoform composition in single fibres from human skeletal muscles.
Larsson, L; Moss, R L
1. Maximum velocity of shortening (Vmax) and compositions of myosin heavy chain (MHC) and myosin light chain (MLC) isoforms were determined in single fibres from the soleus or the lateral region of the quadriceps (vastus lateralis) muscles in man. Muscle samples were obtained by percutaneous biopsy, and membranes were permeabilized by glycerol treatment (chemical skinning) or by freeze-drying. 2. Types I, IIA and IIB MHCs were resolved from single fibre segments by 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and five different fibre types were identified: fibres containing type I MHC, types I and IIA MHCs, type IIA MHC, types IIA and IIB MHCs, and type IIB MHC. Only a few fibres co-expressed types I and IIA MHCs but 28% of all quadriceps fibres expressed both IIA and IIB MHCs in variable proportions. Fibres co-expressing types I and IIB MHCs were not found. 3. Alkali (MLC1 and MLC3) and dithio nitrobenzoic acid (DTNB) (MLC2) myosin light chains were observed in all type II fibres in variable proportions. MLC (MLC1s and MLC2s) isoforms from type I fibres had lower migration rates than the corresponding isoforms from type II fibres (MLC1f and MLC2f). More than half of type I fibres in both soleus (65%) and quadriceps (68%) muscles also expressed 'fast' MLC3 and 36% of the type II fibres from quadriceps muscle expressed the slow isoform of MLC2. 4. Differences were observed in some mechanical characteristics of freeze-dried versus chemically skinned fibres. Maximum tension (P0) and specific tension were lower in freeze-dried types I and IIA fibres than in chemically skinned, while no differences were observed in the IIA/B fibres. The numbers of types I/IIA and IIB fibres were too low to allow statistical comparisons. In chemically skinned fibres, mean specific tension (0.20 +/- 0.01 N/mm2) did not vary with fibre type. In freeze-dried fibres, on the other hand, specific tensions varied according to MHC type: higher (P < 0.01) specific tensions were observed in types IIB (0.19 +/- 0.01 N/mm2) and type IIA/B fibres (0.18 +/- 0.04 N/mm2) than in type I fibres (0.12 +/- 0.02 N/mm2). The specific tension of type IIA fibres (0.12 +/- 0.05 N/mm2) did not differ significantly from the other fibre types. Cross-sectional areas and mean Vmax did not differ between freeze-dried and chemically skinned fibres, either when all fibres were pooled or within respective fibre types. Vmax data from all fibres of a given type, irrespective of membrane permeabilization technique, have therefore been pooled.(ABSTRACT TRUNCATED AT 400 WORDS) Images Fig. 1 Fig. 2 Fig. 6 PMID:8145163
Duration and fetch-limited growth functions of wind-generated waves parameterized with three different scaling wind velocities
Paul A. Hwang
Under steady wind forcing, wave development follows the duration- and fetch-limited growth laws. These growth functions are used extensively to obtain the sea state information when only limited observations of the environmental variables are available. Validation and verification of wave models also employ numerical experiments of duration- and fetch-limited wave growth as benchmark tests. The reference wind speed reported in
Diode laser lidar wind velocity sensor using a liquid-crystal retarder for non-mechanical beam-steering.
Rodrigo, Peter John; Iversen, Theis F Q; Hu, Qi; Pedersen, Christian
We extend the functionality of a low-cost CW diode laser coherent lidar from radial wind speed (scalar) sensing to wind velocity (vector) measurements. Both speed and horizontal direction of the wind at ~80 m remote distance are derived from two successive radial speed estimates by alternately steering the lidar probe beam in two different lines-of-sight (LOS) with a 60░ angular separation. Dual-LOS beam-steering is implemented optically with no moving parts by means of a controllable liquid-crystal retarder (LCR). The LCR switches the polarization between two orthogonal linear states of the lidar beam so it either transmits through or reflects off a polarization splitter. The room-temperature switching time between the two LOS is measured to be in the order of 100 ?s in one switch direction but 16 ms in the opposite transition. Radial wind speed measurement (at 33 Hz rate) while the lidar beam is repeatedly steered from one LOS to the other every half a second is experimentally demonstrated - resulting in 1 Hz rate estimates of wind velocity magnitude and direction at better than 0.1 m/s and 1░ resolution, respectively. PMID:25401817
Parks, G. K.; Lin, N. [Space Sciences Laboratory, University of California, Berkeley, CA (United States); Lee, E.; Hong, J. [School of Space Research, Kyung Hee University, Yongin, Gyeonggi (Korea, Republic of); Fu, S. Y. [School of Earth and Space Sciences, Peking University, Beijing (China); McCarthy, M. [Earth and Space Sciences, University of Washington, Seattle, WA (United States); Cao, J. B. [Beijing University of Aeronautics and Astronautics, 100190, Beijing (China); Liu, Y.; Shi, J. K. [Space Weather, National Space Science Center, Beijing (China); Goldstein, M. L. [NASA, Goddard Space Flight Center, Greenbelt, MD (United States); Canu, P. [Laboratory for Plasma Physics, Ecole Polytechnique, Paris (France); Dandouras, I. [CNRS, IRAP, 9 Ave. Colonel Roche, Toulouse (France); Reme, H., E-mail: email@example.com [CNRS, IRAP, University of Toulouse, UPS-OMP, Toulouse (France)
Two of the many features associated with nonlinear upstream structures are (1) the solar wind (SW) mean flow slows down and deviates substantially and (2) the temperature of the plasma increases in the structure. In this Letter, we show that the SW beam can be present throughout the entire upstream event maintaining a nearly constant beam velocity and temperature. The decrease of the velocity is due to the appearance of new particles moving in the opposite direction that act against the SW beam and reduce the mean velocity as computed via moments. The new population, which occupies a larger velocity space, also contributes to the second moment, increasing the temperature. The new particles include the reflected SW beam at the bow shock and another population of lower energies, accelerated nearby at the shock or at the boundary of the nonlinear structures.
Measurements of solar transition zone velocities and line broadening using the ultraviolet spectrometer and polarimeter on the Solar Maximum Mission
NASA Technical Reports Server (NTRS)
Simon, G.; Mein, P.; Vial, J. C.; Shine, R. A.; Woodgate, B. E.
The UVSP instrument on SMM is able to observe solar regions at two wavelengths in the same line with a band-pass of 0.3 A. Intensity and Doppler velocity maps are derived. It is shown that the numerical values are sensitive to the adopted Doppler width and the range of velocities is limited to within 30 km/sec. A method called Double Dopplergram Determination (DDD) is described for deriving both the Doppler width and the velocity (up to 80 km/sec), and the main sources of uncertainties are discussed. To illustrate the method, a set of C IV 1548 A observations is analyzed according to this procedure. The mean C IV Doppler width measured (0.15 A) is comparable to previous determinations. A relation is found between bright regions and down-flows. Large Doppler widths correspond to strong velocity gradients.
A wind tunnel study of turbulent flow around single and multiple windbreaks, part I: Velocity fields
M. J. Judd; M. R. Raupach; J. J. Finnigan
This paper describes wind-tunnel experiments on the flow around single and multiple porous windbreaks (height H), sheltering a model plant canopy (height H\\/3). The mean wind is normal to the windbreaks, which span the width of the wind tunnel. The incident turbulent flow simulates the adiabatic atmospheric surface layer. Five configurations are examined: single breaks of three solidities (low, medium,
Some techniques for reducing the tower shadow of the DOE/NASA mod-0 wind turbine tower. [wind tunnel tests to measure effects of tower structure on wind velocity
NASA Technical Reports Server (NTRS)
Burley, R. R.; Savino, J. M.; Wagner, L. H.; Diedrich, J. H.
Wind speed profile measurements to measure the effect of a wind turbine tower on the wind velocity are presented. Measurements were made in the wake of scale models of the tower and in the wake of certain full scale components to determine the magnitude of the speed reduction (tower shadow). Shadow abatement techniques tested on the towers included the removal of diagonals, replacement of diagonals and horizontals with round cross section members, installation of elliptical shapes on horizontal members, installation of airfoils on vertical members, and application of surface roughness to vertical members.
A Determination of the Terminal Velocity and Drag of Small Water Drops by Means of a Wind Tunnel
K. V. Beard; H. R. Pruppacher
Measurements of the drag on small water drops falling in water-saturated air at terminal velocity were carried out in a wind tunnel for Reynolds numbers R between 0.2 and 200. The fractional deviation (D\\/Ds) 1 of the actual drag D from the Stokes drag Ds was determined as a function of R and empirical formulae for (D\\/Ds) 1 were derived
A Wind Tunnel Investigation of the Rate of Evaporation of Small Water Drops Falling at Terminal Velocity in Air
K. V. Beard; H. R. Pruppacher
An experimental study of the effect of ventilation on the rate of evaporation of small water drops falling at terminal velocity in air has been carried out in a wind tunnel where water drops could he suspended freely in the tunnel airstream. For Reynolds numbers NRe2 it was found that the Sherwood number NSh was linearly related to NRe1\\/2NI, in
Critical wind velocity for arresting upwind gas and smoke dispersion induced by near-wall fire in a road tunnel.
Hu, L H; Peng, W; Huo, R
In case of a tunnel fire, toxic gas and smoke particles released are the most fatal contaminations. It is important to supply fresh air from the upwind side to provide a clean and safe environment upstream from the fire source for people evacuation. Thus, the critical longitudinal wind velocity for arresting fire induced upwind gas and smoke dispersion is a key criteria for tunnel safety design. Former studies and thus, the models built for estimating the critical wind velocity are all arbitrarily assuming that the fire takes place at the centre of the tunnel. However, in many real cases in road tunnels, the fire originates near the sidewall. The critical velocity of a near-wall fire should be different with that of a free-standing central fire due to their different plume entrainment process. Theoretical analysis and CFD simulation were performed in this paper to estimate the critical velocity for the fire near the sidewall. Results showed that when fire originates near the sidewall, it needs larger critical velocity to arrest the upwind gas and smoke dispersion than when fire at the centre. The ratio of critical velocity of a near-wall fire to that of a central fire was ideally estimated to be 1.26 by theoretical analysis. Results by CFD modelling showed that the ratio decreased with the increase of the fire size till near to unity. The ratio by CFD modelling was about 1.18 for a 500kW small fire, being near to and a bit lower than the theoretically estimated value of 1.26. However, the former models, including those of Thomas (1958, 1968), Dangizer and Kenndey (1982), Oka and Atkinson (1995), Wu and Barker (2000) and Kunsch (1999, 2002), underestimated the critical velocity needed for a fire near the tunnel sidewall. PMID:17544576
Towards an expert system for estimating wind loads on building attachments using detailed local velocity data
A. J. Minson; R. I. Harris; C. J. Wood
This paper presents a new working method for predicting design wind loads on attachments projecting from the walls of buildings. In the University of Oxford environmental wind tunnel, a two-component fibre-optic laser-Doppler anemometer has been used in a systematic study of highly turbulent wind flows at various locations close to walls and roofs of buildings. This includes instantaneous vertical and
Maximum drift velocity of electrons in selectively doped InAlAs/InGaAs/InAlAs heterostructures with InAs inserts
Silenas, A.; Pozela, Yu., E-mail: email@example.com; Pozela, K.; Juciene, V. [Center for Physical Sciences and Technology, Semiconductor Physics Institute (Lithuania); Vasil'evskii, I. S.; Galiev, G. B.; Pushkarev, S. S.; Klimov, E. A. [Russian Academy of Sciences, Institute of Microwave Semiconductor Electronics (Russian Federation)
The dependence of the electron mobility and drift velocity on the growth conditions, thickness, and doping of an InAs insert placed at the center of the quantum well in a selectively doped InAlAs/InGaAs/InAlAs heterostructure has been investigated. Record enhancement of the maximum drift velocity to (2-4) Multiplication-Sign 10{sup 7} cm/s in an electric field of 5 Multiplication-Sign 10{sup 3} V/cm has been obtained in a 17-nm-wide quantum well with an undoped 4-nm-thick InAs insert. In the structures with additional doping of the InAs insert, which facilitates an increase in the density of electrons in the quantum well to 4.0 Multiplication-Sign 10{sup 12} cm{sup -2}, the maximum drift velocity is as high as 2 Multiplication-Sign 10{sup 7} cm/s in an electric field of 7 Multiplication-Sign 10{sup 3} V/cm.
Solar wind driving of magnetospheric ULF waves: Pulsations driven by velocity shear at the magnetopause
S. G. Claudepierre; S. R. Elkington; M. Wiltberger
We present results from global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind\\/magnetosphere interaction. These MHD simulations are used to study ultra low frequency (ULF) pulsations in the Earth's magnetosphere driven by shear instabilities at the flanks of the magnetopause. We drive the simulations with idealized, constant solar wind input parameters, ensuring that any discrete ULF pulsations generated in the
Linear dependence of the postsunset equatorial anomaly electron density on solar flux and its relation to the maximum prereversal E ū B drift velocity through its dependence on solar flux
James A. Whalen
The postsunset equatorial ionization anomaly, with maximum F layer electron density, Nemax, occurring near 2100 LT, has been found during solar maximum to be a linear function of the maximum prereversal E ū B drift velocity (E ū B drift). In order to examine this relation at all levels of solar flux, Nemax is measured during 13 years of an
Using pollution to determine the dimension of the atmosphere: "Does the wind have a velocity?" reads a subtitle of an eighty-year old paper by
Lovejoy, Shaun
Using pollution to determine the dimension of the atmosphere: "Does the wind have a velocity of the concentrations of small particles pushed around by the wind Ł in our case pollution - is made possible the small scale supposedly 3-D turbulence which is thus reduced to a kind of background noise. But what
Assessing effect of wind tunnel sizes on air velocity and concentration boundary layers and on ammonia emission estimation using computational fluid dynamics (CFD)
Chayan Kumer Saha; Wentao Wu; Guoqiang Zhang; Bjarne Bjerg
The objective of this study was to investigate the effect of different geometric sizes of wind tunnels on aerial boundary layers above the emission surface and therefore their effect on ammonia emission using CFD tool. Five wind tunnels of different sizes were used for the CFD simulation. Detail experimental measurements on air velocity and concentration profiles above the emission surface
An experimental analysis of ionic wind velocity characteristics in a needle-plate electrode system by means of laser-induced phosphorescence
Y. Kitahara; K. Aoyagi; R. Ohyama
A flow velocity measurement of ionic wind fields under DC corona discharge on a needle-plate electrode system was experimentally investigated. In this work, a vapor-phase biacetyl tracer with laser-induced phosphorescence phenomenon was applied to optically characterize the ionic wind profile. The phosphorescence radiation was used as a molecular tagging of the ionic wind and the lifetime of phosphorescence emission from
Simplified equations for the rotational speed response to inflow velocity variation in fixed-pitch small wind turbines
NASA Astrophysics Data System (ADS)
Suzuki, H.; Hasegawa, Y.
We propose simplified equations for the rotational speed response to inflow velocity variation in fixed-pitch small wind turbines. The present formulation is derived by introducing a series expansion for the torque coefficient at the constant tip-speed ratio. By focusing on the first- and second-order differential coefficients of the torque coefficient, we simplify the original differential equation. The governing equation based only on the first-order differential coefficient is found to be linear, whereas the second-order differential coefficient introduces nonlinearity. We compare the numerical solutions of the three governing equations for rotational speed in response to sinusoidal and normal-random variations of inflow velocity. The linear equation gives accurate solutions of amplitude and phase lag. Nonlinearity occurs in the mean value of rotational speed variation. We also simulate the rotational speed in response to a step input of inflow velocity using the conditions of two previous studies, and note that the form of this rotational speed response is a system of first-order time lag. We formulate the gain and time constant for this rotational speed response. The magnitude of the gain is approximately three when the wind turbine is operated at optimal tip-speed ratio. We discuss the physical meaning of the derived time constant.
Competing Mechanisms of Plasma Transport in Inhomogeneous Configurations with Velocity Shear: The Solar-Wind Interaction with Earth's Magnetosphere
Faganello, M.; Califano, F.; Pegoraro, F. [Physics Department, University of Pisa, Pisa (Italy)
Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma.
Competing mechanisms of plasma transport in inhomogeneous configurations with velocity shear: the solar-wind interaction with earth's magnetosphere.
Faganello, M; Califano, F; Pegoraro, F
Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma. PMID:18232777
Effect of Soil Crusting on the Threshold Friction Wind Velocity of Major Soils Across the Columbia Plateau
NASA Astrophysics Data System (ADS)
Vaddella, V. K.; Sharratt, B. S.
Windblown dust emissions from agricultural soils in Columbia Plateau have resulted in exceedance of air quality standards set by the US Environmental Protection Agency (USEPA) and traffic fatalities caused by poor visibility. In addition to these effects, atmospheric dust contributes to global warming and the loss of topsoil depletes the soil of its fertility. Fine aerosols emitted during wind storms have aerodynamic diameters less than or equal to 2.5 and 10 microns, commonly known as PM2.5 and PM10. These aerosols are regulated as criteria pollutants under EPAs National Ambient Air Quality Standards. Several communities in the Columbia Plateau have been in non-attainment for these air pollutants. The objective of this study was to examine the effect of soil crusting on the threshold friction wind velocity of five major soil types commonly found across the Columbia Plateau. Soil crusts of varying thickness were created by altering rainfall intensity. Soil samples were collected from the top 3 cm of the soil profile from five different locations across the Plateau. The samples were screened through a 2 mm sieve to remove debris and non-erodible aggregates and were air dried at 30C. The samples were placed in shallow trays and were subjected to different intensities of rainfall using the Palouse Rainfall Simulator at typical intensities observed in Columbia Plateau. The trays were air dried to allow soil crust formation. The trays were then subjected to a range of wind velocities in a portable wind tunnel. The onset of saltation and suspension of windblown sediment was observed using a Sensit and aerosol samplers (DustTrak and E-samplers) installed at heights of 0.5 to 10 cm above the soil surface. The crust was observed to be the same thickness for every soil at any one particular rainfall intensity. The crust thickness increased with increase in rainfall intensity; hence, the threshold friction velocity increased with an increase in crust thickness. Variations in the threshold friction velocity were observed among the five different soil types. This information will better enable atmospheric scientists to predict dust storms in the Columbia Plateau.
High-velocity, multistage, nozzled, ion driven wind generator and method of operation of the same adaptable to mesoscale realization
NASA Technical Reports Server (NTRS)
Dunn-Rankin, Derek (Inventor); Rickard, Matthew J. A. (Inventor)
Gas flows of modest velocities are generated when an organized ion flux in an electric field initiates an ion-driven wind of neutral molecules. When a needle in ambient air is electrically charged to a potential sufficient to produce a corona discharge near its tip, such a gas flow can be utilized downstream of a ring-shaped or other permeable earthed electrode. In view of the potential practical applications of such devices, as they represent blowers with no moving parts, a methodology for increasing their flow velocities includes exploitation of the divergence of electric field lines, avoidance of regions of high curvature on the second electrode, control of atmospheric humidity, and the use of linear arrays of stages, terminating in a converging nozzle. The design becomes particularly advantageous when implemented in mesoscale domains.
Survey of the spectral properties of turbulence in the solar wind, the magnetospheres of Venus and Earth, at solar minimum and maximum
NASA Astrophysics Data System (ADS)
Echim, Marius M.
In the framework of the European FP7 project STORM ("Solar system plasma Turbulence: Observations, inteRmittency and Multifractals") we analyze the properties of turbulence in various regions of the solar system, for the minimum and respectively maximum of the solar activity. The main scientific objective of STORM is to advance the understanding of the turbulent energy transfer, intermittency and multifractals in space plasmas. Specific analysis methods are applied on magnetic field and plasma data provided by Ulysses, Venus Express and Cluster, as well as other solar system missions (e.g. Giotto, Cassini). In this paper we provide an overview of the spectral properties of turbulence derived from Power Spectral Densities (PSD) computed in the solar wind (from Ulysses, Cluster, Venus Express) and at the interface of planetary magnetospheres with the solar wind (from Venus Express, Cluster). Ulysses provides data in the solar wind between 1992 and 2008, out of the ecliptic, at radial distances ranging between 1.3 and 5.4 AU. We selected only those Ulysses data that satisfy a consolidated set of selection criteria able to identify "pure" fast and slow wind. We analyzed Venus Express data close to the orbital apogee, in the solar wind, at 0.72 AU, and in the Venus magnetosheath. We investigated Cluster data in the solar wind (for time intervals not affected by planetary ions effects), the magnetosheath and few crossings of other key magnetospheric regions (cusp, plasma sheet). We organize our PSD results in three solar wind data bases (one for the solar maximum, 1999-2001, two for the solar minimum, 1997-1998 and respectively, 2007-2008), and two planetary databases (one for the solar maximum, 2000-2001, that includes PSD obtained in the terrestrial magnetosphere, and one for the solar minimum, 2007-2008, that includes PSD obtained in the terrestrial and Venus magnetospheres and magnetosheaths). In addition to investigating the properties of turbulence for the minimum and maximum of the solar cycle we also analyze the spectral similarities and differences between fast and slow wind turbulence. We emphasize the importance of our data survey and analysis in the context of understanding the solar wind turbulence, the exploitation of data bases and as a first step towards developing a (virtual) laboratory for studying solar system plasma turbulence. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS - UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.
Sympathetic skin response versus maximum motor and sensory conduction velocity to detect subclinical neuropathy in non-insulin-dependent diabetics.
Caccia, M R; Dezuanni, E; Salvaggio, A; Osio, M; Bevilacqua, M; Norbiato, G; Mangoni, A
Conventional motor (MCV) and sensory conduction velocity (SCV) of the ulnar (UN), peroneal (PN) and median nerves (MN) and the areas of sympathetic sudomotor response (SSR) recorded from the middle finger were measured on both sides in 20 normal and 20 non-insulin-dependent diabetic (NIDD) subjects. Conventional statistical tests (t test, linear correlation coefficient r) and discrimination analysis were applied to the above electrophysiological parameters. To evaluate the capability of the tests to separate NIDD diseased from normal nerves, the results were represented as generalized distances, i.e., difference between mean discriminant normalized combinations adjusted for intra-group variability. The r values were 0.92 (P less than 0.01) for the UN, 0.40 (P greater than 0.05) for the PN, and 0.86 (P less than 0.01) for the MN sensory action potential (SAP) amplitudes. No significant differences were found for normalized latencies. The r values of the SSR areas were 0.62 (P less than 0.01) at the right and 0.77 (P less than 0.01) at the left, homolaterally to the side of stimulation. SR and MCV generalized distances were 1.35 and 1.39, respectively. The discriminating power of SSR, MCV and SCV considered together was higher (2.40) than that of MCV and SCV (1.70). Since motor, sensory and autonomic alterations often did not coexist in NIDD, it was possible to find at least one type of involvement in most of the diabetic subjects. PMID:1746243
Stawarz, Joshua E.; Vasquez, Bernard J.; Smith, Charles W. [Physics Department, Space Science Center, University of New Hampshire, Durham, NH 03824 (United States); Forman, Miriam A. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY 11794-3800 (United States); Klewicki, Joseph, E-mail: firstname.lastname@example.com, E-mail: email@example.com, E-mail: firstname.lastname@example.com, E-mail: email@example.com, E-mail: firstname.lastname@example.com [Mechanical Engineering Department, University of New Hampshire, Durham, NH 03824 (United States)
We have extended the recent analyses of magnetohydrodynamic third moments as they relate to the turbulent energy cascade in the solar wind to consider the effects of large-scale shear flows. Moments from a large set of Advanced Composition Explorer data have been taken, and chosen data intervals are characterized by the rate of change in the solar wind speed. Mean dissipation rates are obtained in accordance with the predictions of homogeneous shear-driven turbulence. Agreement with predictions is best made for rarefaction intervals where the solar wind speed is decreasing with time. For decreasing speed intervals, we find that the dissipation rates increase with increasing shear magnitude and that the shear-induced fluctuation anisotropy is consistent with a relatively small amount.
Blowing in the Wind: I. Velocities of Chondrule-sized Particles in a Turbulent Protoplanetary Nebula
NASA Technical Reports Server (NTRS)
Cuzzi, Jeffrey N.; Hogan, Robert C.; Fonda, Mark (Technical Monitor)
Small but macroscopic particles - chondrules, higher temperature mineral inclusions, metal grains, and their like - dominate the fabric of primitive meteorites. The properties of these constituents, and their relationship to the fine dust grains which surround them, suggest that they led an extended existence in a gaseous protoplanetary nebula prior to their incorporation into their parent primitive bodies. In this paper we explore in some detail the velocities acquired by such particles in a turbulent nebula. We treat velocities in inertial space (relevant to diffusion), velocities relative to the gas and entrained microscopic dust (relevant to accretion of dust rims), and velocities relative to each other (relevant to collisions). We extend previous work by presenting explicit, closed-form solutions for the magnitude and size dependence of these velocities in this important particle size regime, and compare these expressions with new numerical calculations. The magnitude and size dependence of these velocities have immediate applications to chondrule and CAI rimming by fine dust, and to their diffusion in the nebula, which we explore separately.
Solar wind proton velocity distributions - Comparison of the bi-Maxwellian based 16-moment expansion with observations
NASA Technical Reports Server (NTRS)
Demars, H. G.; Schunk, R. W.
The purpose of this paper is to study the possible types of velocity distributions that can be obtained from the bi-Maxwellian based 16-moment expansion of the distribution function, assuming macroscopic parameter values characteristic of the range of solar wind conditions. While previous studies also took heat flow into account, the theoretical expansions for f and the definitions of the physical moments adopted in these studies were different from those used in this paper. The choice of the 16-moment expansion and corresponding moment definitions was motivated by the fact that this is the correct generalization of the widely-used Maxwellian-based 13-moment expansion to the case where the zeroth-order distribution is a bi-Maxwellian. It is found that most of the features characteristic of solar wind proton distributions can be reproduced with the 16-moment distribution, including the appearance of secondary peaks. It is also shown how each of the physically significant velocity moments affects the shape of the distribution function.
High velocity wind tunnels : their application to ballistics, aerodynamics, and aeronautics
NASA Technical Reports Server (NTRS)
Huguenard, E
The object of this article is to set forth the particular properties of swiftly-moving air, how these affect the installation of a wind tunnel, the experimental results already obtained, the possible applications of such a tunnel, and what can be easily accomplished at the present time.
The distribution of velocity and energy of saltating sand grains in a wind tunnel
Xue-Yong Zou; Zhou-Long Wang; Qing-Zhen Hao; Chun-Lai Zhang; Yu-Zhang Liu; Guang-Rong Dong
Sand transport by wind is a special case of two-phase flow of gas and solids, with saltating grains accounting for about 75% of the transport rate. This form of flow is not only the main external agent moulding aeolian landforms but also the motive force responsible for transport, sorting and deposition of aeolian sediments. High-speed multiflash photography is an effective
Measuring air-sea gas-exchange velocities in a large-scale annular wind-wave tank
NASA Astrophysics Data System (ADS)
Mesarchaki, E.; Krõuter, C.; Krall, K. E.; Bopp, M.; Helleis, F.; Williams, J.; Jõhne, B.
In this study we present gas-exchange measurements conducted in a large-scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, ? = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.73 to 13.2 m s-1) conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas-exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.
A. Laneville; A. Mazouzi
This article deals with new criteria for the ovalling onset of thin circular cylindrical shells exposed to a cross-flow. The onset flow velocity criterion is based on a balance between the negative aerodynamic damping and the shell structural damping coefficients. The vibration mode occurrence criterion is based on a balance between the input energy from the aerodynamic forces acting on
Lidar measurement of wind velocity turbulence spectra encountered by a rotating turbine blade
Hardesty, R.M.; Korrell, J.A.; Hall, F.F. Jr.
A homodyne CO/sub 2/ lidar system beam was conically scanned around a horizontal axis to measure the wind speed and turbulence characteristics encountered by a rotating turbine blade. Turbulence spectra obtained from the scanning lidar differed considerably from those calculated from fixed-point anemometer measurements, showing a redistribution of energy from lower to higher frequencies. The differences appeared more pronounced during periods when the atmosphere was stable.
Power control of a stand-alone photovoltaic\\/ wind\\/ energy storage hybrid generation system with Maximum Power Point Tracker
Yukihiro Ozaki; Masafumi Miyatake; Daisuke Iwaki
In this paper, a hybrid generation system combining photovoltaic (PV), wind turbine (WT) and Electric Double Layer Capacitor (EDLC) is presented to supply stable power to residential power applications as stand-alone loads. The photovoltaic and wind systems are used as main energy sources while the EDLC is used as storage device. Three individual DC\\/DC converters are used to control the
On the relationship of the 27-day variations of the solar wind velocity and galactic cosmic ray intensity in minimum epoch of solar activity
Alania, M V; Wawrzynczak, A
We study the relationship of the 27-day variation of the galactic cosmic ray intensity with similar changes of the solar wind velocity and the interplanetary magnetic field based on the experimental data for the Bartels rotation period 2379 of 23 November 2007-19 December 2007. We develop a three dimensional (3-D) model of the 27-day variation of galactic cosmic ray intensity based on the heliolongitudinally dependent solar wind velocity. A consistent, divergence-free interplanetary magnetic field is derived by solving Maxwells equations with a heliolongitudinally dependent 27-day variation of the solar wind velocity reproducing in situ observations. We consider two types of 3-D models of the 27-day variation of galactic cosmic ray intensity - (1) with a plane heliospheric neutral sheet, and (2)- with the sector structure of the interplanetary magnetic field. The theoretical calculation shows that the sector structure does not influence significantly on the 27-day variation of galactic cosmic ray intensity as...
Velocity profile similarity for viscous flow development along a longitudinally slotted wind-tunnel wall
NASA Technical Reports Server (NTRS)
Everhart, Joel L.; Goradia, Suresh H.
A discussion of the flow field measurements on the slot centerline of two different longitudinally slotted wind-tunnel walls is presented. The longitudinal and transverse components of these data are then transformed using the concept of flow similarity to demonstrate the applicability of the technique to the development of the viscous shear flow along and through a slotted wall. Results are presented showing the performance of the similarity transformations with variations in tunnel station, Mach number, and airfoil-induced curvature of the tunnel free stream.
An atlas of monthly mean distributions of SSMI surface wind speed, AVHRR/2 sea surface temperature, AMI surface wind velocity, TOPEX/POSEIDON sea surface height, and ECMWF surface wind velocity during 1993
NASA Technical Reports Server (NTRS)
Halpern, D.; Fu, L.; Knauss, W.; Pihos, G.; Brown, O.; Freilich, M.; Wentz, F.
The following monthly mean global distributions for 1993 are presented with a common color scale and geographical map: 10-m height wind speed estimated from the Special Sensor Microwave Imager (SSMI) on a United States (U.S.) Air Force Defense Meteorological Satellite Program (DMSP) spacecraft; sea surface temperature estimated from the Advanced Very High Resolution Radiometer (AVHRR/2) on a U.S. National Oceanic and Atmospheric Administration (NOAA) satellite; 10-m height wind speed and direction estimated from the Active Microwave Instrument (AMI) on the European Space Agency (ESA) European Remote Sensing (ERS-1) satellite; sea surface height estimated from the joint U.S.-France Topography Experiment (TOPEX)/POSEIDON spacecraft; and 10-m height wind speed and direction produced by the European Center for Medium-Range Weather Forecasting (ECMWF). Charts of annual mean, monthly mean, and sampling distributions are displayed.
Traveling solar-wind bulk-velocity fluctuations and their effects on electron heating in the inner heliosphere
Fahr, Hans J; Verscharen, Daniel
Ambient plasma electrons undergo strong heating in regions associated with compressive traveling interplanetary solar-wind bulk-velocity jumps due to their specific interactions with the jump-inherent electric fields. After thermalization of this energy gain per shock passage through the operation of the Buneman instability, strong electron heating occurs that substantially influences the radial electron temperature profile. We describe the reduction of the jump amplitude due to energy expended by the traveling jump structure. We consider three effects; namely energy loss due to heating of electrons, energy loss due to work done against the pick-up-ion pressure gradient, and an energy gain due to nonlinear jump steepening. Taking these effects into account, we show that the decrease in jump amplitude with solar distance is more pronounced when the initial jump amplitude is higher in the inner solar system. Independent of the initial jump amplitude, it eventually decreases with increasing distance to a value o...
Wind-velocity lidar measurements by use of a Mach-Zehnder interferometer, comparison with a Fabry-Perot interferometer
NASA Astrophysics Data System (ADS)
Bruneau, Didier; Garnier, Anne; Hertzog, Albert; Porteneuve, Jacques
We present the first wind-velocity profiles obtained with a direct-detection Doppler lidar that uses a Mach-Zehnder interferometer (MZI) as spectral discriminator. The measurements were performed in the lower stratosphere, between 10 and 40 km in altitude, at the Observatoire de Haute Provence (OHP), France, during nighttime. They are in excellent agreement with those obtained simultaneously and independently with the already validated double Fabry-Perot interferometer (FPI) of the OHP Doppler lidar (mean difference lower than the combined standard deviation). A statistical analysis shows that the random error obtained with this experimental MZI is 1.94 times the Cramer-Rao lower bound and is approximately half of that given by the FPI (both operating in photometric mode). Nevertheless, the present MZI measurements are sensitive to the presence of atmospheric particles and need an additional correction, whereas the OHP FPI is designed to be insensitive to particulate scattering.
Transducer Shadowing Explains Observed Underestimates in Vertical Wind Velocity from Non-orthogonal Sonic Anemometers
NASA Astrophysics Data System (ADS)
Frank, J. M.; Massman, W. J.; Swiatek, E.; Zimmerman, H.; Ewers, B. E.
Sonic anemometry is fundamental to all eddy-covariance studies of surface energy and ecosystem carbon and water balance. While recent studies have shown that some anemometers underestimate vertical wind, we hypothesize that this is caused by the lack of transducer shadowing correction in non-orthogonal models. We tested this in an experiment comparing three sonic anemometer designs: orthogonal (O), non-orthogonal (NO), and quasi-orthogonal (QO); using four models: K-probe (O) and A-probe (NO) (Applied Technologies, Inc.) and CSAT3 (NO) and CSAT3V (QO) (Campbell Scientific, Inc.). For each of a 12-week experiment at the GLEES AmeriFlux site, five instruments from a pool of twelve (three of each model) were randomly selected and located around a control (CSAT3); mid-week all but the control were re-mounted horizontally. We used Bayesian analysis to test differences between models in half-hour standard deviations (?u, ?v, ?w, and ?T), turbulent kinetic energy (TKE), and the ratio between vertical/horizontal TKE (VHTKE). The K-probe experiences horizontal transducer shadowing which is effectively corrected using an established wind-tunnel derived algorithm. We constructed shadow correction algorithms for the NO/QO anemometers by applying the K-probe function to each non-orthogonal transducer pair (SC1) as well as a stronger correction of twice the magnitude (SC2). While the partitioning of VHTKE was higher in O than NO/QO anemometers, the application of SC1 explained 45-60% of this discrepancy while SC2 overcorrected it. During the horizontal manipulation changes in the NO/QO were moderate in ?u (4-8% decrease), very strong in ?v (9-11% decrease), and minimal in ?w (-3 to 4% change) while only ?u measurements changed (3% decrease) with the K-probe. These changes were predicted by both shadow correction algorithms, with SC2 better explaining the data. This confirms our hypothesis while eliminating others that attribute the underestimate to a systematic bias in the w-axis. All flux sites that employ these non-orthogonal sonic anemometers will underestimate vertical fluxes of mass and energy, but since 1) the correction is a function both of sensor geometry and local wind and 2) the true shadow correction function is unknown at this time, the actual underestimate is uncertain and will vary between sites.
Pitch angle and velocity diffusions of newborn ions by turbulence in the solar wind
NASA Astrophysics Data System (ADS)
Ziebell, L. F.; Yoon, Peter H.
The temporal evolution of the distribution function of newborn ions under the influence of intrinsic low-frequency solar wind turbulences is studied. In particular, an initial ring-beam distribution of newborn ions under the influence of hydromagnetic waves is considered. A simplified treatment of the resonance broadening effect is given, and its role in the pickup process is discussed. Two different configurations of wave polarization amd direction of propagation are considered. The conditions that lead either to the formation of anisotropic shells as a long-duration transient state or to rapid isotropization of the ion pitch angle distribution are discussed, as are the conditions which lead to significant acceleration of the ions.
NSDL National Science Digital Library
National Energy Education Development (NEED) Project
This document examine wind power as an energy resource. The reading will define wind and discuss topics such as (1) The history of wind machines, (2) Today's windmills, and (3) Types of wind machines. This resource is structured as an informational handout to supplement your energy activities or to generate discussion questions. Copyright 2005 International Technology Education Association
Crustal seismicity and the earthquake catalog maximum moment magnitudes (Mcmax) in stable continental regions (SCRs): correlation with the seismic velocity of the lithosphere
Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun
A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (?VS) relative to the Preliminary Reference Earth Model (PREM). We compare ?VS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by ?VS?3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with ?VS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.
The effect of wind velocity, air temperature and humidity on NH 3 and SO 2 transfer into bean leaves ( phaseolus vulgaris L.)
NASA Astrophysics Data System (ADS)
van Hove, L. W. A.; Vredenberg, W. J.; Adema, E. H.
The influence of wind velocity, air temperature and vapour pressure deficit of the air (VPD) on NH 3 and SO 2 transfer into bean leaves ( Phaseolus vulgaris L.) was examined using a leaf chamber. The measurements suggested a transition in the properties of the leaf boundary layer at a wind velocity of 0.3-0.4 ms -1 which corresponds to a Recrit value of about 2000. At higher wind velocities the leaf boundary layer resistance ( rb) was 1.5-2 times lower than can be calculated from the theory. Nevertheless, the assessed relationships between rb and wind velocity appeared to be similar to the theoretical derived relationship for rb. The NH 3 flux and in particular the SO 2 flux into the leaf strongly increased at a VPD decline. The increase of the NH 3 flux could be attributed to an increase of the stomatal conductance ( gs). However, the increase of the SO 2 flux could only partly be explained by an increase of gs. An apparent additional uptake was also observed for the NH 3 uptake at a low temperature and VPD. The SO 2 flux was also influenced by air temperature which could be explained by a temperature effect on gs. The results suggest that calculation of the NH 3 and SO 2 flux using data of gs gives a serious understimation of the real flux of these gases into leaves at a low temperature and VPD.
Hollweg, Joseph V.; Chandran, Benjamin D. G. [Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824 (United States); Kaghashvili, Edisher Kh., E-mail: firstname.lastname@example.com, E-mail: email@example.com, E-mail: firstname.lastname@example.com [Atmospheric and Environmental Research, A Verisk Analytics Company, 131 Hartwell Avenue, Lexington, MA 02421 (United States)
We analytically consider how velocity shear in the corona and solar wind can cause an initial Alfven wave to drive up other propagating signals. The process is similar to the familiar coupling into other modes induced by non-WKB refraction in an inhomogeneous plasma, except here the refraction is a consequence of velocity shear. We limit our discussion to a low-beta plasma, and ignore couplings into signals resembling the slow mode. If the initial Alfven wave is propagating nearly parallel to the background magnetic field, then the induced signals are mainly a forward-going (i.e., propagating in the same sense as the original Alfven wave) fast mode, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; both signals are compressive and subject to damping by the Landau resonance. For an initial Alfven wave propagating obliquely with respect to the magnetic field, the induced signals are mainly forward- and backward-going fast modes, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; these signals are all compressive and subject to damping by the Landau resonance. A backward-going Alfven wave, thought to be important in the development of MHD turbulence, is also produced, but it is very weak. However, we suggest that for oblique propagation of the initial Alfven wave the induced fast-polarized signal propagating like a forward-going Alfven wave may interact coherently with the initial Alfven wave and distort it at a strong-turbulence-like rate.
Coronal holes as sources of solar wind
J. T. Nolte; A. S. Krieger; A. F. Timothy; R. E. Gold; E. C. Roelof; G. Vaiana; A. J. Lazarus; J. D. Sullivan; P. S. McIntosh
We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial
Recent near-surface wind changes in the central Mediterranean and Adriatic areas
Paolo Antonio Pirazzoli; Alberto Tomasin
Trends of change in wind direction and velocity during the second part of the last century are examined at 17 coastal Italian stations along a north-south transect over 1000 km long in the central Mediterranean area. Linear regressions and confidence ranges are provided for the frequency and for annual maximum and mean velocities. It appears that wind activity has been
Scatterometer azimuthal response and wind wave directionality
NASA Technical Reports Server (NTRS)
Giovanangeli, J. P.; Le Calve, O.; Bliven, L.
Azimuthal response of a scatterometer to radiation scattered by the sea surface was studied in a wind-wave tank. The variation of the normalized radar cross section with the azimuth angle is fitted by a three-term series. Results show that the upwind-downwind asymmetry decreases as the wind speed increases. The crosswind modulation depends on the wind velocity. The results show that the evolution of the long-wind-crosswind ratio evolves with wind speed in a manner similar to the evolution of the isotropy of short capillary-gravity waves. The maximum of the isotropy of the short wind waves is obtained for wind velocities close to 4 m/s. For the same value of the velocity, the variations of radar response between long-wind and crosswind directions is minimum. For lower or higher values of wind velocities the directional accuracy of the radar increases, since the wind-wave field tends to align in the wind direction.
The Change in Cosmic Ray Intensity Variation with the Solar Wind Velocity (Using GRAPES3 muon narrow angle telescopes and Kiel neutron monitor)
H. Kojima; Y. Hayashi; K. Hayashi
GRAPES-3 experiment is situated at Ooty in South India 76.7 East 11.4 North. Effective observation area of our muon telescopes is 560 m2. They are the largest detector in the world of its kind. There were several reports that increase of the solar wind velocity suppresses the intensity of cosmic rays. But there are few which studied qualitatively. We have
MACS for Global measurement of the Solar wind velocity and the Thermal electron temperature during the Total solar eclipse on 11 August 1999
Nelson L. Reginald; Joseph M. Davila
MACS for Multi-Aperture Coronal Spectrometer is a fiber-optic-based spectrograph designed and used to perform global measurement of the solar wind velocity and the thermal electron temperature of the solar corona during the total solar eclipse on 11 August 1999. The motivation for the construction of MACS was provided by the theory formulated by Cram (1976) for the formation of the
EnKF OSSE Experiments Assessing the Impact of HIRAD Wind Speed and HIWRAP Radial Velocity Data on Analysis of Hurricane Karl (2010)
NASA Technical Reports Server (NTRS)
Albers, Cerese; Sippel, Jason A.; Braun, Scott A.; Miller, Timothy
Previous studies (e.g., Zhang et al. 2009, Weng et al. 2011) have shown that radial velocity data from airborne and ground-based radars can be assimilated into ensemble Kalman filter (EnKF) systems to produce accurate analyses of tropical cyclone vortices, which can reduce forecast intensity error. Recently, wind speed data from SFMR technology has also been assimilated into the same types of systems and has been shown to improve the forecast intensity of mature tropical cyclones. Two instruments that measure these properties were present during the NASA Genesis and Rapid Intensification Processes (GRIP) field experiment in 2010 which sampled Hurricane Karl, and will next be co-located on the same aircraft for the subsequent NASA HS3 experiment. The High Altitude Wind and Rain Profiling Radar (HIWRAP) is a conically scanning Doppler radar mounted upon NASAs Global Hawk unmanned aerial vehicle, and the usefulness of its radial velocity data for assimilation has not been previously examined. Since the radar scans from above with a fairly large fixed elevation angle, it observes a large component of the vertical wind, which could degrade EnKF analyses compared to analyses with data taken from lesser elevation angles. The NASA Hurricane Imaging Radiometer (HIRAD) is a passive microwave radiometer similar to SFMR, and measures emissivity and retrieves hurricane surface wind speeds and rain rates over a much wider swath. Thus, this study examines the impact of assimilating simulated HIWRAP radial velocity data into an EnKF system, simulated HIRAD wind speed, and HIWRAP+HIRAD with the Weather Research and Forecasting (WRF) model and compares the results to no data assimilation and also to the Truth from which the data was simulated for both instruments.
Modeling and experimental study of the 27-day variation of galactic cosmic-ray intensity for a solar-wind velocity depending on heliolongitude
Alania, M V; Wawrzynczak, A
We develop a three dimensional (3-D) model of the 27-day variation of galactic cosmic ray (GCR) intensity with a spatial variation of the solar wind velocity. A consistent, divergence-free interplanetary magnetic field is derived by solving the corresponding Maxwell equations with a variable solar wind speed, which reproduces in situ observed experimental data for the time interval to be analyzed (24 August 2007-28 February 2008). We perform model calculations for the GCR intensity using the variable solar wind and the corresponding magnetic field. Results are compatible with experimental data; the correlation coefficient between our model predictions and observed 27-day GCR variation is 0.80 0.05.
Results from 1984 airborne Doppler lidar wind measurement program. Flight 6: Analysis of line-of-sight elevation angle errors and apparent Doppler velocities
NASA Technical Reports Server (NTRS)
Rothermel, Jeffry
During the summer of 1984 the Marshall Space Flight Center's Airborne Doppler Lidar System (ADLS) made a series of wind measurements in the California Central Valley. This study quantifies the lidar beam angle errors and velocity errors through analysis of ground return signals. Line-of-sight elevation (LOSE) angle errors are under 1 deg. Apparent Doppler ground velocities, as large as 2m/s, are considerably less than in a previous flight experiment in 1981. No evidence was found of a Schuler resonance phenomenon common to inertial navigation systems (INS), however the aperiodic nature of the apparent velocities implies an error in the INS-derived ground speeds. Certain features and subtleties in the ground returns are explained in terms of atmospheric structure and characteristics of the ADLS hardware and software. Finally, least squares and low-pass filtering techniques are suggested for eliminating errors during post-processing.
MACS, An Instrument and a Methodology for Simultaneous and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona
NASA Technical Reports Server (NTRS)
Reginald, Nelson L.
In Cram's theory for the formation of the K-coronal spectrum he observed the existence of temperature sensitive anti-nodes, which were separated by temperature insensitive nodes, at certain wave-lengths in the K-coronal spectrum. Cram also showed these properties were remarkably independent of altitude above the solar limb. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurements of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 August 1999 in Elazig, Turkey. Here twenty fiber optic tips were positioned in the focal plane of the telescope to observe simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends were vertically stacked and placed at the primary focus of the spectrograph. By isolating the K-coronal spectrum from each fiber the temperature and the wind sensitive intensity ratios were calculated.
The neutral lithium velocity distribution of an AMPTE solar wind release as inferred from lithium ion measurements on the UKS spacecraft
NASA Astrophysics Data System (ADS)
Chapman, S. C.; Cowley, S. W. H.; Johnstone, A. D.
As part of the AMPTE mission on September 20, 1984 a neutral lithium release was made in the quiet solar wind. The MSSL ion instrument on board the AMPTE-UKS spacecraft that was positioned about 30 km from the release center enabled measurements of significant fluxes of lithium ions to be made for about 3 min after the release; that is, long after the effects of the initial local perturbation to the field and flow had died away. These lithium test ions move in cycloidal orbits in the steady ambient fields, so that measurements of their fluxes at the UKS can be used to infer the velocity distribution function of the collisionless neutral cloud over a restricted region in velocity space. These restrictions are such that the ion data can show that significant anisotropy is present.
Wind emission of OB supergiants and the influence of clumping
Michaela Kraus; Jiri Kubat; Jiri Krticka
The influence of the wind to the total continuum of OB supergiants is discussed. For wind velocity distributions with \\beta > 1.0, the wind can have strong influence to the total continuum emission, even at optical wavelengths. Comparing the continuum emission of clumped and unclumped winds, especially for stars with high \\beta values, delivers flux differences of up to 30% with maximum in the near-IR. Continuum observations at these wavelengths are therefore an ideal tool to discriminate between clumped and unclumped winds of OB supergiants.
Dave Glidden is a Field Specialist in Wind and Mountain Climatology, and has conducted wind studies for the National Park Service in Rocky Mountain National Park in Colorado. More recently, he has pursued field work on the variability of mountain winds and gust factors in Denali National Park in Alaska. A strong advocate of women in the sciences, he has
Effect of Soil Crusting on the Threshold Friction Wind Velocity of Major Soils Across the Columbia Plateau
V. K. Vaddella; B. S. Sharratt
Windblown dust emissions from agricultural soils in Columbia Plateau have resulted in exceedance of air quality standards set by the US Environmental Protection Agency (USEPA) and traffic fatalities caused by poor visibility. In addition to these effects, atmospheric dust contributes to global warming and the loss of topsoil depletes the soil of its fertility. Fine aerosols emitted during wind storms
An image analysis of positive ionic wind velocity under the DC corona discharge in needle-cylinder electrode system
H. Nakamura; R. Ohyama
In this work, a micro electrohydrodynamical (EHD) gas pump using a needle-cylindrical electrode system was constructed for an application of ionic wind to fluid flow operations without mechanical parts. The experimental EHD pump was consisted of a tapered glass tube (2 to 10 mm in inner diameters, 45 mm in an axial length) attached with the electrode system, where the
Three-dimensional elastic lidar winds
Buttler, W.T.
Maximum cross-correlation techniques have been used with satellite data to estimate winds and sea surface velocities for several years. Los Alamos National Laboratory (LANL) is currently using a variation of the basic maximum cross-correlation technique, coupled with a deterministic application of a vector median filter, to measure transverse winds as a function of range and altitude from incoherent elastic backscatter lidar data taken throughout large volumes within the atmospheric boundary layer. Hourly representations of three- dimensional wind fields, derived from elastic lidar data taken during an air-quality study performed in a region of complex terrain near Sunland Park, New Mexico, are presented and compared with results from an Environmental Protection Agency (EPA) approved laser doppler velocimeter. The wind fields showed persistent large scale eddies as well as general terrain following winds in the Rio Grande valley.
W. E. Currah; G. W. Harper
A system for conversion of wind power to electrical energy is described. The system provides for use during a wide range of wind velocities by use of the following: an external deflection system consisting of baffles and peripheral turbulence creating walls designed to increase the wind velocity and to divert the wind stream to the aperture of the system; a
Full field flow visualization and computer-aided velocity measurements in a bank of cylinders in a wind tunnel
M. J. Braun; V. A. Canacci; L. M. Russell
The full field flow tracking (FFFT) method that is presented in this paper uses a laser-generated, mechanically strobed planar\\u000a sheet of light, a low luminosity TV camera coupled with a long distance microscope, and a computer-controlled videorecorder\\u000a to study non-intrusively and qualitatively the flow structures in a bank of cylinders that are placed in a wind tunnel. This\\u000a setup simulates
VisibleWind: wind profile measurements at low altitude
NASA Astrophysics Data System (ADS)
Wilkerson, Tom; Bradford, Bill; Marchant, Alan; Apedaile, Tom; Wright, Cordell
VisibleWindTM is developing an inexpensive rapid response system, for accurately characterizing wind shear and small scale wind phenomena in the boundary layer and for prospecting suitable locations for wind power turbines. The ValidWind system can also collect reliable "ground truth" for other remote wind sensors. The system employs small (0.25 m dia.) lightweight balloons and a tracker consisting of an Impulse 200 XL laser rangefinder coupled to a PC for automated data recording. Experiments on balloon trajectories demonstrate that the laser detection of range (+/- 0.5 m), together with measured azimuth and altitude, is an inexpensive, convenient, and capable alternative to other wind tracking methods. The maximum detection range has been increased to 2200 meters using micro-corner-cube retroreflector tape on balloons. Low power LEDs enable nighttime tracking. To avoid large balloon gyrations about the mean trajectory, we use balloons having low ascent rates and subcritical Reynolds numbers. Trajectory points are typically recorded every 4 - 7 seconds. Atmospheric features observed under conditions of inversions or "light and variable winds" include abrupt onsets of shear at altitudes of 100-250 m, velocity changes of order 1-3 m/s within layers of 10-20 m thickness, and veering of the wind direction by 180 degrees or more as altitude increases from 300 to 500 m. We have previously reported comparisons of balloon-based wind profiles with the output of a co-located sodar. Even with the Impulse rangefinder, our system still requires a "man in the loop" to track the balloon. A future system enhancement will automate balloon tracking, so that laser returns are obtained automatically at 1 Hz. While balloon measurements of large-scale, high altitude wind profiles are well known, this novel measurement system provides high-resolution, real-time characterization of the fluctuating local wind fields at the bottom of the boundary layer where wind power turbines and other remote wind sensors must operate.
Microburst Wind Structure and Evaluation of Doppler Radar for Airport Wind Shear Detection
James W. Wilson; Rita D. Roberts; Cathy Kessinger; John McCarthy
Doppler weather radar data from the Joint Airport Weather Studies (JAWS) Project are used to determine the horizontal and vertical structure of airflow within microbursts. Typically, the associated downdraft is about 1 km wide and begins to spread horizontally at a height below 1 km. The median time from initial divergence at the surface to maximum differential wind velocity across
An investigation of flap-lag stability of wind turbine rotors in the presence of velocity gradients and helicopter rotors in forward flight
NASA Technical Reports Server (NTRS)
Kaza, K. R. V.; Hammond, C. E.
The flap-lag equations of motion of a torsionally rigid and centrally hinged spring-restrained rigid blade are developed using quasi-steady blade-element aerodynamic theory. These equations have periodic coefficients and are applicable to both wind-turbine rotors with velocity gradients and helicopter rotors in forward flight. By solving these equations both by the Floquet-Liapunov method and by an approximate method, the range of applicability of the latter method is established. Flap-lag and pure flapping stability boundaries illustrating the effects of flow and rotor parameters are presented. Finally, some discussion on the techniques for generating the Floquet transition matrix and on the relative merits of the coordinate axes system is presented.
Source localization corrections for airborne acoustic platforms based on a climatological assessment of temperature and wind velocity profiles
NASA Astrophysics Data System (ADS)
Ostashev, Vladimir E.; Cheinet, Sylvain; Collier, Sandra L.; Reiff, Christian; Ligon, David A.; Wilson, D. Keith; Noble, John M.; Alberts, W. C. Kirkpatrick, II
Acoustic sensors are being employed on airborne platforms, such as Persistent Threat Detection System (PTDS) and Persistent Ground Surveillance System (PGSS), for source localization. Under certain atmospheric conditions, airborne sensors oer a distinct advantage over ground sensors. The performance of both ground and airborne sensors is aected by environmental factors, such as atmospheric turbulence and wind and temperature proles. For airborne sensors, the eects of refraction must be accounted for in order to determine the source coordinates. Such a method for ground-to-air applications has been developed and is further rened here. Ideally, knowledge of the exact atmospheric proles will allow for the most accurate mitigation of refractive eects. However, acoustic sensors deployed in theater are rarely supported by atmospheric sensing systems that retrieve real-time temperature and wind elds. Atmospheric conditions evolve through seasons, time of day, and are strongly location dependent. Therefore, the development of an atmospheric proles database based on a long time series climatological assessment will provide knowledge for use in physics-based bearing estimation algorithms, where otherwise no correction would have been performed. Long term atmospheric data sets from weather modeling systems are used for a climatological assessment of the refraction corrections and localization errors over selected sites.
An Analysis of a Turbo-Fan Used to Improve the Velocity Distribution in a Low Speed Wind-Tunnel
Wells, Otis Dean
. Hence: VF e =~& j g U c Cdrd(&t). 0 -77 The resultant force on the rotor will be purely axial, so the equation can be written: ? =Ap = e bP US 2 US 0 where S is the turbo-fan disc area. Again quoting from reference 4: U c C dr, a "For subsonic... that the turbo-fan The superscript numbers in this thesis refer to the bibliog- raphy. is inherently more efficient than the screen in removing axial velocity disturbances. Collar executed. a first order approximation to the analysis of the turbo-fan...
Statistical characteristics of instantaneous dense gas clouds released in an atmospheric boundary-layer wind tunnel
Robert N. Meroney; Achim Lohmeyer
Wind tunnel experiments were performed to examine the behavior of suddenly released volumes of dense gas in a turbulent shear layer. Instantaneous concentrations were measured with hot-wire katherometers. Multiple replications of each cloud volume, density, and velocity combination produced statistics for plume arrival time, arrival of maximum concentration time, plume departure time, and maximum concentrations. Probability distributions and standard deviations
Forward velocity effects on fan noise and the suppression characteristics of advanced inlets as measured in the NASA-Ames 40 by 80 foot wind tunnel
NASA Technical Reports Server (NTRS)
Moore, M. T.
Forward velocity effects on the forward radiated fan noise and on the suppression characteristics of three advanced inlets relative to a baseline cylindrical inlet were measured in the NASA Ames Research Center 40 x 80 foot Wind Tunnel. A modified JT15D turbofan engine in a quiet nacelle was the source of fan noise; the advanced inlets were a Conventional Takeoff/Landing (CTOL) hybrid inlet, a Short Takeoff/Landing (STOL) hybrid inlet, and a treated deflector inlet. Also measured were the static to flight effects on the fan noise of canting the baseline inlet 4 deg downward to simulate typical wing mounted turbofan engines. The CTOL hybrid inlet suppressed the high tip speed fan noise as much as 18 PNdB on a 61 m (200 ft) sideline scaled to a CF6 size engine while the STOL hybrid inlet suppressed the low tip speed fan noise as much as 13 PNdB on a 61 m (200 ft) sideline scaled to a OCSEE size engine. The deflector inlet suppressed the high tip speed fan noise as much as 13 PNdB at 61 m (200 ft) overhead scaled to a CF6 size engine. No significant changes in fan noise suppression for the CTOL and STOL hybrid inlets occurred for forward velocity changes above 21 m/s (68 ft/s) or for angle of attack changes up to 15 deg. However, changes in both forward velocity and angle of attack changed the deflector inlet noise unpredictably due to the asymmetry of the inlet flow field into the fan.
Observations of mesospheric wind velocities. I. Gravity wave horizontal scales and phase velocities determined from spaced wind observations. II. Cross sections of power spectral density for 48-8 hours, 8-1 hours, and 1 hour to 10 min over 60-110 km for 1981
Meek, C.E.; Reid, I.M.; Manson, A.H.
Dual bistatic radar and the Saskatoon MF radar were used to obtain horizontal scales, phase velocities and power spectral density cross sections of upper middle atmosphere gravity waves as determined from spaced wind velocities. The wave scales averaged 60-110 km and varied from 44-210 km during the 10-100 min observation periods. The horizontal length scales varied directly with the length of the observation interval, while the phase speeds decreased as the observation interval increased. The rms velocity perturbations were about 5 m/sec. The associated vertical wavelengths were 30 and 6 km for the 10-100 min intervals. The power spectra densities obtained, when compared with similar data from previous compaigns, were found to vary on an annual basis. The spectral densities were noted to track the zero line of mean zonal velocity closely in the 10 min to 8 hr period bands. This last phenomena strongly indicates the occurrence of gravity wave mean flow interactions. 80 references.
The Shaping of Planetary Nebulae: Asymmetry in the External Wind
NASA Astrophysics Data System (ADS)
Dwarkadas, Vikram V.; Chevalier, Roger A.; Blondin, John M.
We have modeled planetary nebulae (PNs) in the context of the interacting stellar winds model. If the two interacting winds have constant properties, the velocity of the PN shell tends toward a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. Using semi-analytical methods, complemented by hydrodynamic simulations, we have calculated the shapes of PNs in the self-similar stage. An asymmetric density profile is assumed for the slow outer wind. The asymmetry is modeled using different functions, which depend on the degree of asymmetry and the steepness of the density profile in the angular direction. We include the effects of the ambient wind velocity, which has not received much attention since the work of Kahn & West (1985). The fact that typical PN velocities (10-40 km s-1) are only marginally greater than typical red giant wind velocities (5-20 km s-1) indicates that this is an important parameter. The morphological appearance is a consequence of the density contrast, steepness of the density profile and velocity of the ambient medium; classification of PNs purely on the basis of the first two factors may be misleading. Moderate values of the density contrast result in a cusp at the equator. A higher density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximum of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. If the external wind velocity is small compared to the expansion velocity of the nebula, the PNs tend to be more bipolar, even with a moderate density contrast. If the PN velocity is close to that of the external wind, the shape is relatively spherical. However, a velocity asymmetry in the external wind can lead to a bipolar shape if the equatorial velocity is sufficiently low. Our numerical simulations show that asymmetric PN shells are corrugated because of Kelvin-Helmholtz instabilities. They also indicate that several doubling times are needed to approach the self-similar state. A ratio of interior sound speed to shell velocity ?10 is found to yield nebulae whose shapes match those given by the isobaric approximation.
Saturation wind power potential and its implications for wind energy
Saturation wind power potential and its implications for wind energy Mark Z. Jacobsona,1 to determine the maximum theo- retical wind power potential on Earth, based on the concept of "saturation". The saturation wind power potential (SWPP) is the maximum wind power that can be extracted upon increasing
Analysis of CASES99 Lidar and Turbulence Data in Support of Wind Turbine Effects: April 1, 2001 to Januay 31, 2003
The nocturnal low-level jet (LLJ) of the Great Plains of the central United States has been identified as a promising source of high-momentum wind flow for wind energy. The acceleration of the winds after sunset above the surface produces a jet profile in the wind velocity, with maximum speeds that often exceed 10 m s-1 or more at heights near
Microburst Wind Structure and Evaluation of Doppler Radar for Airport Wind Shear Detection.
NASA Astrophysics Data System (ADS)
Wilson, James W.; Roberts, Rita D.; Kessinger, Cathy; McCarthy, John
Doppler weather radar data from the Joint Airport Weather Studies (JAWS) Project are used to determine the horizontal and vertical structure of airflow within microbursts. Typically, the associated downdraft is about 1 km wide and begins to spread horizontally at a height below 1 km. The median time from initial divergence at the surface to maximum differential wind velocity across the microburst is 5 min. The height of maximum differential velocity is 75 m. The median velocity differential is 22 m s1 over an average distance of 3.1 km. The outflow is asymmetric, averaging twice as strong along the maximum shear axis compared to the minimum axis.Doppler radar could be an effective means for identifying microbursts and warning aircraft of wind shear hazards. For microburst detection such a radar must be able to measure wind velocities in clear air as well as in heavy rain and hail. Scan update rates should be approximately every 2 min and the lowest few hundred meters of the atmosphere must be observed. Ground clutter must be considerably reduced from levels typically obtained with present Doppler radars. New antenna technology and signal processing techniques may solve this problem. Automated range and velocity unfolding is required, as well as automated identification and dissemination techniques.
Wind loads on flat plate photovoltaic array fields. Phase III, final report
Miller, R.D.; Zimmerman, D.K.
The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads.
Sehmel, G.A.
Dry deposition velocities are very difficult to predict accurately. In this article, reported values of dry deposition velocities are summarized. This summary includes values from the literature on field measurements of gas and particle dry deposition velocities, and the uncertainties inherent in extrapolating field results to predict dry deposition velocities are discussed. A new method is described for predicting dry deposition velocity using a least-squares correlation of surface mass transfer resistances evaluated in wind tunnel experiments. 14 references, 4 figures, 1 table.
Calculation of wind speeds required to damage or destroy buildings
NASA Astrophysics Data System (ADS)
Liu, Henry
Determination of wind speeds required to damage or destroy a building is important not only for the improvement of building design and construction but also for the estimation of wind speeds in tornadoes and other damaging storms. For instance, since 1973 the U.S. National Weather Service has been using the well-known Fujita scale (F scale) to estimate the maximum wind speeds of tornadoes [Fujita, 1981]. The F scale classifies tornadoes into 13 numbers, F-0 through F-12. The wind speed (maximum gust speed) associated with each F number is given in Table 1. Note that F-6 through F-12 are for wind speeds between 319 mi/hr (mph) and the sonic velocity (approximately 760 mph; 1 mph = 1.6 km/kr). However, since no tornadoes have been classified to exceed F-5, the F-6 through F-12 categories have no practical meaning [Fujita, 1981].
Wind regime and sand transport in China's Badain Jaran Desert
NASA Astrophysics Data System (ADS)
Zhang, Zhengcai; Dong, Zhibao; Li, Chunxiao
Wind controls the formation and development of aeolian dunes, therefore understanding the wind environment is necessary in aeolian dune research. In recent years, climate has changed in and around the Badain Jaran Desert, and the factors that control aeolian dune development have changed with it. In this paper, we analyzed characteristics of the desert's wind regime based on data from seven weather stations in and around the desert. The temporal and spatial variation in the wind regime's characteristics have different effects on dune formation and development. The annual mean wind velocity, maximum wind velocity, and the proportion of the time the wind exceeded the sand-entrainment threshold are largest at the northern margin of the desert, and these values decrease from north to south and from east to west. The dominant winds are from the northwest, northeast, and southwest. The drift potential (DP) in the desert decreases from north to south, and can be divided into three regions: high in the north, intermediate in the central region, and low in the south. The effects of climate change on the calculated DP will be complex; although DP increased with increasing mean wind velocity and temperature, there was little or no relationship with precipitation and relative humidity.
R. H. Miller; M. Martinez-Sanchez; J. Dugundji; E. E. Larrabee; I. Chopra; T. Humes; S. Y. Chung; J. C. Gohard; J. T. Edwards
Various problems associated with the design of horizontal axis, low solidity, and high performance wind turbines are investigated. Wind turbine performance as determined from various elementary and more refined momentum theories, aerodynamic vortex theories for blade loadings including unsteady effects and wind shear velocity gradients, and nonlinear dynamic response of rotor blades including gravity and wind shear excitation were studied.
Yeoman, D.R.
This patent describes a wind turbine. It comprises: a vertical axis rotor assembly coupled to a rotatable drive shaft for driving electrical power generating means; first wind deflector means for initially reflecting wind current into the rotor assembly; second wind deflector means to redirect the initially deflected wind current into the rotor assembly; and mounting means for mounting the first and second wind deflector means in the normal positions. The mounting means including an outer shaft through which the drive shaft extends and which is normally fixed with respect thereto. The outer shaft having at least one lower groove winding in one of a left-hand or right-hand direction, at least one lower groove constituting a first lower groove set, and at least one upper groove winding in the other of the left-hand or right-hand direction, at least one upper groove constituting a second upper groove set, and first lower and second upper connector rings coupled to the first and second wind deflector means respectively, and mounted on the outer shaft proximate to the first and second groove sets respectively. The first and second connector rings including guide means cooperating with at least one groove of the first and second groove sets respectively. The mounting means allowing at least one of the first and second wind deflector means to automatically move relative to each other and from its respective normal position when the velocity of the wind current exceeds a first predetermined value to increase the inter-deflector spacing and causing at least one of the first and second wind deflector means to automatically return to its respective normal position when the velocity of the wind current diminishes to a value below the first predetermined value.
Full-scale-wind-tunnel Tests of a 35 Degree Sweptback Wing Airplane with High-velocity Blowing over the Training-edge Flaps
NASA Technical Reports Server (NTRS)
Kelley, Mark W; Tolhurst, William H JR
A wind-tunnel investigation was made to determine the effects of ejecting high-velocity air near the leading edge of plain trailing-edge flaps on a 35 degree sweptback wing. The tests were made with flap deflections from 45 degrees to 85 degrees and with pressure ratios across the flap nozzles from sub-critical up to 2.9. A limited study of the effects of nozzle location and configuration on the efficiency of the flap was made. Measurements of the lift, drag, and pitching moment were made for Reynolds numbers from 5.8 to 10.1x10(6). Measurements were also made of the weight rate of flow, pressure, and temperature of the air supplied to the flap nozzles.The results show that blowing on the deflected flap produced large flap lift increments. The amount of air required to prevent flow separation on the flap was significantly less than that estimated from published two-dimensional data. When the amount of air ejected over the flap was just sufficient to prevent flow separation, the lift increment obtained agreed well with linear inviscid fluid theory up to flap deflections of 60 degrees. The flap lift increment at 85 degrees flap deflection was about 80 percent of that predicted theoretically.With larger amounts of air blown over the flap, these lift increments could be significantly increased. It was found that the performance of the flap was relatively insensitive to the location of the flap nozzle, to spacers in the nozzle, and to flow disturbances such as those caused by leading-edge slats or discontinuities on the wing or flap surfaces. Analysis of the results indicated that installation of this system on an F-86 airplane is feasible.
Aspects of the determination of winds by means of scatterometry and of the utilization of vector wind data for meteorological forecasts
NASA Technical Reports Server (NTRS)
Pierson, W. J., Jr.; Sylvester, W. B.; Donelan, M. A.
The present paper provides a description of four aspects of scatterometer winds and their uses. The theory of wave generation by the wind is considered along with an analysis of the properties of superobservations, and studies of intermittent versus continuous data assimilation methods for numerical weather predictions which use remotely sensed data. A comparison of the sum of squares versus the maximum likelihood method for recovering the vector winds is also conducted. Questions regarding wind speed, friction velocity, or normal stress are discussed and synoptic scale fields from Seasat-SASS data are examined.
Wind tunnel investigation on wind turbine wakes and wind farms
NASA Astrophysics Data System (ADS)
Iungo, G. V.; Coļffķ, J.; Portķ-Agel, F.
The interaction between atmospheric boundary layer and wind farms leads to flow modifications, which need to be deeply characterized in order to relate them to wind farm performance. The wake flow produced from a wind farm is the result of a strong interaction between multiple turbine wakes, so that the wind farm configuration turns out to be one of the dominant features to enhance power production. For the present work a wind tunnel investigation was carried out with hot-wire anemometry and velocity measurements performed with multi-hole pressure probes. The tested wind farms consist of miniature three-bladed wind turbine models. Preliminarily, the wake flow generated from a single wind turbine is surveyed, which is characterized by a strong velocity defect lying in proximity of the wind turbine hub height. The wake gradually recovers by moving downstream; the characteristics of the incoming boundary layer and wind turbulence intensity can strongly affect the wake recovery, and thus performance of following wind turbines. An increased turbulence level is typically detected downstream of each wind turbine for heights comparable to the wind turbine blade top-tip. These wake flow fluctuations produce increased fatigue loads on the following wind turbines within a wind farm, which could represent a significant hazard for real wind turbines. Dynamics of vorticity structures present in wind turbine wakes are also investigated; particular attention is paid to the downstream evolution of the tip helicoidal vortices and to oscillations of the hub vortex. The effect of wind farm layout on power production is deeply investigated. Particular emphasis is placed on studying how the flow adjusts as it moves inside the wind farm and can affect the power production. Aligned and staggered wind farm configurations are analysed, also with varying separation distances in the streamwise and spanwise directions. The present experimental results are being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).
Wind loads on flat plate photovoltaic array fields
NASA Technical Reports Server (NTRS)
Miller, R. D.; Zimmerman, D. K.
The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads. The arrays located at the outer boundary of an array field have a protective influence on the interior arrays of the field. A significant decrease of the array wind loads were recorded in the wind tunnel test on array panels located behind a fence and/or interior to the array field compared to the arrays on the boundary and unprotected from the wind. The magnitude of this decrease was the same whether caused by a fence or upwind arrays.
Fuzzy regulator design for wind turbine yaw control.
Theodoropoulos, Stefanos; Kandris, Dionisis; Samarakou, Maria; Koulouras, Grigorios
This paper proposes the development of an advanced fuzzy logic controller which aims to perform intelligent automatic control of the yaw movement of wind turbines. The specific fuzzy controller takes into account both the wind velocity and the acceptable yaw error correlation in order to achieve maximum performance efficacy. In this way, the proposed yaw control system is remarkably adaptive to the existing conditions. In this way, the wind turbine is enabled to retain its power output close to its nominal value and at the same time preserve its yaw system from pointless movement. Thorough simulation tests evaluate the proposed system effectiveness. PMID:24693237
Convenient methods were developed for measuring maximum oxygen consumption(Vo2max ) in untrained small mammals during treadmill exercise and cold exposure. Deer mice (Peromyscus maniculatus) were run once, for 6-rain periods at velocities exceeding maximal aerobic running speed, while instantaneous oxygen consumption was measured. The ~'o2max during cold exposure was deter- mined using high wind speeds to increase heat loss rates.
Wind speeds in two tornadic storms and a tornado, deduced from Doppler Spectra
Zrnic, D.; Istok, M.
Doppler spectra of a tornado were collected with a radar having a large unambiguous velocity range, +- 91 m s/sup -1/. Thus for the first time a presentation of nonaliased spectra was possible, showing direct measurement of radial velocities. By fitting the tornado model spectrum to data, the radius of maximum winds and tornado center location are deduced. Tornado spectral signature is defined as a double peak, symmetric with respect to the mean wind spectrum. Histograms of maximum measured wind speeds (from spectrum skirts) for two tornadic storms are obtained, and the histograms of velocity difference (between the left and right spectrum skirt) suggest that smaller scale turbulence (<500 m) is principally responsible for spectrum broadness.
Effects of atmospheric stability on the evolution of wind turbine wakes: Volumetric LiDAR scans
NASA Astrophysics Data System (ADS)
Valerio Iungo, Giacomo; Portķ-Agel, Fernando
Aerodynamic optimization of wind farm layout is a fundamental task to reduce wake effects on downstream wind turbines, thus to maximize wind power harvesting. However, downstream evolution and recovery of wind turbine wakes are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, like the vertical profiles of the mean wind velocity and the turbulence intensity, which are in turn affected by the ABL stability regime. Therefore, the characterization of the variability of wind turbine wakes under different ABL stability regimes becomes fundamental to better predict wind power harvesting and improve wind farm efficiency. To this aim, wind velocity measurements of the wake produced by a 2 MW Enercon E-70 wind turbine were performed with three scanning Doppler wind Light Detection and Ranging (LiDAR) instruments. One LiDAR was typically devoted to the characterization of the incoming wind, in particular wind velocity, shear and turbulence intensity at the height of the rotor disc. The other two LiDARs performed scans in order to characterize the wake velocity field produced by the tested wind turbine. The main challenge in performing field measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between LiDAR measurement volume and wake location, different LiDAR measurement procedures were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. Furthermore, volumetric scans of the wind turbine wake were performed under different wind conditions via two simultaneous LiDARs. Through the evaluation of the minimum wake velocity deficit as a function of the downstream distance, it is shown that the stability regime of the ABL has a significant effect on the wake evolution; specifically the wake recovers faster under convective conditions. This result suggests that atmospheric inflow conditions, and particularly thermal stability, should be considered for improved wake models and predictions of wind power harvesting.
NSDL National Science Digital Library
Siegrist, Kyle
This material introduces the basic theory of maximum likelihood estimation by discussing the likelihood function, the log likelihood function, and maximizing these functions using calculus. Several exercises ask students to derive certain estimators, while others have students compare the behavior of those estimators with other possibilities through the use of various JAVA applets. The applets use the same control features: the sliders set the parameter values, the ┬?Stop #┬? drop down menu sets the number of samples taken, the ┬?Update #┬? drop down menu sets how often the graph and tables update during the experiment, the single arrow takes one sample, the double arrow runs the full experiment, the square stops the experiment, and the back arrow resets the applet. This page is one lesson from the Virtual Laboratories in Statistics.
Campanelli, Manuela; Lousto, Carlos O; Zlochower, Yosef; Merritt, David
Recent calculations of gravitational radiation recoil generated during black-hole binary mergers have reopened the possibility that a merged binary can be ejected even from the nucleus of a massive host galaxy. Here we report the first systematic study of gravitational recoil of equal-mass binaries with equal, but counteraligned, spins parallel to the orbital plane. Such an orientation of the spins is expected to maximize the recoil. We find that recoil velocity (which is perpendicular to the orbital plane) varies sinusoidally with the angle that the initial spin directions make with the initial linear momenta of each hole and scales up to a maximum of approximately 4000 km s-1 for maximally rotating holes. Our results show that the amplitude of the recoil velocity can depend sensitively on spin orientations of the black holes prior to merger. PMID:17677894
Erwin Sedlmayr; Carsten Dominik
The status of dust driven winds, constituting an important subclass of essentially radiation generated winds, is surveyed. Dust driven winds are conceived as a long lasting phenomenon of heavy mass loss concerning those luminous cool giants and supergiants, where dust condensation in the expanding flow determines both thestellar mass loss rate and thesubsonic-supersonic transition of the velocity field. Our contribution
ERIC Educational Resources Information Center
Pelka, David G.; And Others
The large-scale generation of electrical power by wind turbine fields is discussed. It is shown that the maximum power that can be extracted by a wind turbine is 16/27 of the power available in the wind. (BB)
Technology Transfer Automated Retrieval System (TEKTRAN)
Wind movement and velocities can have profound effect on some aspects of the soil erosion process. In the case of wind-driven rain, differences in raindrop trajectory are expected: wind-driven raindrops achieve some degree of horizontal velocity, which increases their resultant impact velocity and s...
Efficient Low-Speed Flight in a Wind Field
NASA Technical Reports Server (NTRS)
Feldman, Michael A.
A new software tool was needed for flight planning of a high altitude, low speed unmanned aerial vehicle which would be flying in winds close to the actual airspeed of the vehicle. An energy modeled NLP (non-linear programming) formulation was used to obtain results for a variety of missions and wind profiles. The energy constraint derived included terms due to the wind field and the performance index was a weighted combination of the amount of fuel used and the final time. With no emphasis on time and with no winds the vehicle was found to fly at maximum lift to drag velocity, V(sub md). When flying in tail winds the velocity was less than V(sub md), while flying in head winds the velocity was higher than V(sub md). A family of solutions was found with varying times of flight and varying fuel amounts consumed which will aid the operator in choosing a flight plan depending on a desired landing time. At certain parts of the flight, the turning terms in the energy constraint equation were found to be significant. An analysis of a simpler vertical plane cruise optimal control problem was used to explain some of the characteristics of the vertical plane NLP results.
Flow velocity and angularity measurements in the FDL trisonic gasdynamic facility and self-adaptive wall wind tunnels with a laser transit anemometer
W. T. Mayo Jr.; A. E. Smart; R. J. Hermes; J. D. Trolinger
The measurement of a backscatter laser transit anemometer was tested in the FDL Trisonic Gasdynamics Facility (TGF) and the nine-inch Self Adapting Wall (SAW) wind tunnel. The tests included flow analysis in the two foot by two foot subsonic, transonic and supersonic test sections as well as the fifteen-inch transonic test section insert all in the TGF. The magnitude and
MACS, an instrument, and a methodology for simultaneous and global measurements of the coronal electron temperature and the solar wind velocity on the solar corona
Nelson Leslie Reginald
The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of great importance in understanding the coronal heating mechanism and the dynamics of coronal expansion. Cram (1976) presented the theory for the formation of the K- coronal spectrum and identified two important observations. He observed the existence of temperature sensitive anti-nodes at certain wavelengths
MACS, An Instrument, and a Methodology for Simulations and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona
Nelson L. Reginald
The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of great importance in understanding the coronal heating mechanism and the dynamics of coronal expansion. Cram presented the theory for the formation of the K-coronal spectrum and identified two important observations. He observed the existence of temperature sensitive anti-nodes at certain wavelengths in the
Velocity and rolling-moment measurements in the wake of a swept-wing model in the 40 by 80 foot wind tunnel
NASA Technical Reports Server (NTRS)
Rossow, V. J.; Corsiglia, V. R.; Schwind, R. G.; Frick, J. K. D.; Lemmer, O. J.
Measurements were made in the wake of a swept wing model to study the structure of lift generated vortex wakes shed by conventional span loadings and by several span loadings designed to reduce wake velocities. Variations in the span loading on the swept wing generator were obtained by deflecting seven flap segments on each side by amounts determined by vortex lattice theory to approximate the desired span loadings. The resulting wakes were probed with a three component, hot wire probe to measure velocity, and with a wing to measure the rolling moment that would be induced on a following aircraft. The experimental techniques are described herein, and the measured velocity and rolling moments are presented, along with some comparisons with the applicable theories.
Field measurements of horizontal forward motion velocities of terrestrial dust devils: Towards a proxy for ambient winds on Mars and Earth
Spiga, Aymeric
Field measurements of horizontal forward motion velocities of terrestrial dust devils: Towards Mars a b s t r a c t Dust devils Ł convective vortices made visible by the dust and debris they entrain Ł are common in arid environments and have been observed on Earth and Mars. Martian dust devils have been
The existence of long-lived rays of the coronal streamer belt ¢ Radial density and velocity distributions of the solar wind flowing in them
V. G. Eselevich; V. G. Fainshtein; M. V. Eselevich
A technique is proposed for separating the rays of the streamer belt with quasi-stationary and non-stationary solar wind (SW) flows. It is shown that the lifetime of rays with a quasi-stationary SW can exceed 20 days. A new method has been developed for measuring the relative density distribution of a quasi-stationary slow SW flowing along the streamer belt's ray of
The wind instability and the resonant interaction of the elastic vibration of a thin plate with a supersonic gas stream
NASA Astrophysics Data System (ADS)
Gestrin, S. G.; Sergeeva, E. K.
In a supersonic flow, the longwave perturbations running along the stream are stable, whereas the most rapidly growing waves propagate at an angle to the flow velocity. It has been shown that the wind instability of a nonuniform compressible gas flow having a velocity profile can give rise to elastic vibrations of a thin plate at a characteristic wavelength. The dispersion equation and the instability increment showing a maximum in the longwave band have been obtained.
Dust-driven winds. I - A two-fluid model and its numerical solution
NASA Astrophysics Data System (ADS)
Berruyer, N.; Frisch, H.
A model of dust-driven wind relevant to red giant stars is investigated, in which the usual hypothesis of 'momentum coupling' (amounting to neglect of grain particle mass) is relaxed. When the momentum coupling approximation is abandoned, the sonic point is shifted outwards, and the gas and grain expansion velocities are reduced. In the supersonic part of the wind the diminution is of the order of 30 percent, but it may reach several orders of magnitude below the sonic point. An asymptotic analysis of the flow at the base of the wind shows the existence of a boundary layer where the grains suffer a very strong acceleration, the gas velocity staying almost constant. The coupling between the grains and the gas is maximum just outside the boundary layer, and decreases gradually outwards. Beyond a thousand inner envelope radii the grains and the gas are fully uncoupled. The coupling is still very strong when the velocities have saturated the almost constant values.
Cheney, Jr., Marvin C. (Glastonbury, CT)
A wind turbine of the type having an airfoil blade (15) mounted on a flexible beam (20) and a pitch governor (55) which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter (85) which restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing overspeed operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum (65,70) which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member (90) which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment.
Analysis of change in the wind speed ratio according to apartment layout and solutions.
Hyung, Won-gil; Kim, Young-Moon; You, Ki-Pyo
Apartment complexes in various forms are built in downtown areas. The arrangement of an apartment complex has great influence on the wind flow inside it. There are issues of residents' walking due to gust occurrence within apartment complexes, problems with pollutant emission due to airflow congestion, and heat island and cool island phenomena in apartment complexes. Currently, the forms of internal arrangements of apartment complexes are divided into the flat type and the tower type. In the present study, a wind tunnel experiment and computational fluid dynamics (CFD) simulation were performed with respect to internal wind flows in different apartment arrangement forms. Findings of the wind tunnel experiment showed that the internal form and arrangement of an apartment complex had significant influence on its internal airflow. The wind velocity of the buildings increased by 80% at maximum due to the proximity effects between the buildings. The CFD simulation for relaxing such wind flows indicated that the wind velocity reduced by 40% or more at maximum when the paths between the lateral sides of the buildings were extended. PMID:24688430
Wind-Turbine Wakes in a Convective Boundary Layer: A Wind-Tunnel Study
NASA Astrophysics Data System (ADS)
Zhang, Wei; Markfort, Corey D.; Portķ-Agel, Fernando
Thermal stability changes the properties of the turbulent atmospheric boundary layer, and in turn affects the behaviour of wind-turbine wakes. To better understand the effects of thermal stability on the wind-turbine wake structure, wind-tunnel experiments were carried out with a simulated convective boundary layer (CBL) and a neutral boundary layer. The CBL was generated by cooling the airflow to 12-15 ░C and heating up the test section floor to 73-75 ░C. The freestream wind speed was set at about 2.5 m s-1, resulting in a bulk Richardson number of -0.13. The wake of a horizontal-axis 3-blade wind-turbine model, whose height was within the lowest one third of the boundary layer, was studied using stereoscopic particle image velocimetry (S-PIV) and triple-wire (x-wire/cold-wire) anemometry. Data acquired with the S-PIV were analyzed to characterize the highly three-dimensional turbulent flow in the near wake (0.2-3.2 rotor diameters) as well as to visualize the shedding of tip vortices. Profiles of the mean flow, turbulence intensity, and turbulent momentum and heat fluxes were measured with the triple-wire anemometer at downwind locations from 2-20 rotor diameters in the centre plane of the wake. In comparison with the wake of the same wind turbine in a neutral boundary layer, a smaller velocity deficit (about 15 % at the wake centre) is observed in the CBL, where an enhanced radial momentum transport leads to a more rapid momentum recovery, particularly in the lower part of the wake. The velocity deficit at the wake centre decays following a power law regardless of the thermal stability. While the peak turbulence intensity (and the maximum added turbulence) occurs at the top-tip height at a downwind distance of about three rotor diameters in both cases, the magnitude is about 20 % higher in the CBL than in the neutral boundary layer. Correspondingly, the turbulent heat flux is also enhanced by approximately 25 % in the lower part of the wake, compared to that in the undisturbed CBL inflow. This study represents the first controlled wind-tunnel experiment to study the effects of the CBL on wind-turbine wakes. The results on decreased velocity deficit and increased turbulence in wind-turbine wakes associated with atmospheric thermal stability are important to be taken into account in the design of wind farms, in order to reduce the impact of wakes on power output and fatigue loads on downwind wind turbines.
Solar wind eddies and the heliospheric current sheet
NASA Technical Reports Server (NTRS)
Suess, S. T.; Mccomas, D. J.; Bame, S. J.; Goldstein, B. E.
Ulysses has collected data between 1 and 5 AU during, and just following solar maximum, when the heliospheric current sheet (HCS) can be thought of as reaching its maximum tilt and being subject to the maximum amount of turbulence in the solar wind. The Ulysses solar wind plasma instrument measures the vector velocity and can be used to estimate the flow speed and direction in turbulent 'eddies' in the solar wind that are a fraction of an astronomical unit in size and last (have either a turnover or dynamical interaction time of) several hours to more than a day. Here, in a simple exercise, these solar wind eddies at the HCS are characterized using Ulysses data. This character is then used to define a model flow field with eddies that is imposed on an ideal HCS to estimate how the HCS will be deformed by the flow. This model inherently results in the complexity of the HCS increasing with heliocentric distance, but the result is a measure of the degree to which the observed change in complexity is a measure of the importance of solar wind flows in deforming the HCS. By comparison with randomly selected intervals not located on the HCS, it appears that eddies on the HCS are similar to those elsewhere at this time during the solar cycle, as is the resultant deformation of the interplanetary magnetic field (IMF). The IMF deformation is analogous to what is often termed the 'random walk' of interplanetary magnetic field lines.
High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?
Terlevich, R; Bosch, G; Diaz, A I; Hagele, G; Cardaci, M; Firpo, V
X-shooter and ISIS WHT spectra of the starforming galaxy PHL 293B also known as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000km/s) and very broad (FWZI = 4000km/s) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800km/s, previously undetected FeII multiplet (42) absorptions also blueshifted by 800km/s, IR CaII triplet stellar absorptions consistent with [Fe/H] blue variables or SN IIn as the origin of the blue shifted absorptions of HI and FeII. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster w...
NASA Technical Reports Server (NTRS)
Britt, Charles L.
Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.
The divergent wind component in data sparse tropical wind fieldsĀ
Snyder, Bruce Alan
. Poisson equation solver d. Evaluation of stresmfunction/velocity potential algorithms e. Computing divergent and nondivergent winds. . . . f. Analydcal studies of the divergent wind component g. Aliasing of divergence estimates CHAPTER VI RESULTS... AND DISCUSSION a. Methods of computing stresmfunction and velocity potential 14 30 33 36 36 Table of Contents (Continued) Page b. Analysis of Sangster's method c. Manipulation of divergent wind component fields d. Time continuity e. Vector error...
Impact of wind on the dynamics of explosive volcanic plumes inferred from analog experiments
NASA Astrophysics Data System (ADS)
Carazzo, G.; Girault, F.; Aubry, T. J.; Bouquerel, H.; Kaminski, E. C.
Volcanic plumes produced by explosive eruptions commonly interact with atmospheric wind causing plume bending and a reduction of its maximum height. Strength of the wind field and intensity of the eruption control the behavior of the column in the atmosphere, which may form either a strong plume that is little affected by the presence of wind or a weak plume that is bent-over in the wind field. To better understand the transition between weak and strong plumes, we present a series of new laboratory reproducing a buoyant jet rising in a stratified environment with a uniform cross-flow. The experiments consist in injecting downward fresh water in a tank containing an aqueous NaCl solution with linear density stratification. The jet source is towed at a constant speed through the stationary fluid in order to produce a cross-flow. We show that depending on the environmental and source conditions, the buoyant jet may form either a strong, distorted, or weak plume. The transition from one dynamical regime to another is governed by the strength of the horizontal wind velocity compared to the vertical buoyant rise of the plume. A review of field data on historical eruptions confirms that the experimentally-determined transition curves capture the behavior of volcanic columns. We quantify the impact of wind on the maximum height reached by the column, and we propose a universal scaling relationship to link the mass discharge rate feeding an eruption to its observed maximum height in the presence of wind.
Discontinuities in the solar wind
D. S. Colburn; C. P. Sonett
The nonuniform emission of the solar wind from the sun means that conditions are established which favor the development of discontinuities in the plasma parameters. Since the solar wind is in rapid proper motion with respect to the sun and the earth, examination of these discontinuities requires that the wind velocity be transformed away. Then it is found that they
Technology Transfer Automated Retrieval System (TEKTRAN)
In wind-driven rains, variations in raindrop trajectory and frequency are highly expected due to the changes in the angle of raindrop incidence. This paper presents experimental data obtained on the effects of horizontal wind velocity on physical raindrop impact and rainsplash detachment. In a wind ...
Estimation of mesoscale thermospheric wind structure using a network of interferometers
NASA Astrophysics Data System (ADS)
Harding, Brian J.; Makela, Jonathan J.; Meriwether, John W.
We introduce a technique for estimating the regional thermospheric wind field from measurements made by a network of interferometers. Unlike previous work, this technique does not make assumptions about the functional form of the wind field and instead uses inverse theory to find the smoothest wind field that agrees with the measurements. This technique is general and applies to any network making radial velocity measurements. We show reconstructions of the thermospheric wind field over the eastern United States and over eastern Brazil, using data from two distinct networks of Fabry-Perot interferometers measuring the Doppler shift of the 630.0 nm airglow emission. In Brazil, we find direct evidence of a convergent wind field during the period of rapid thermospheric temperature increase associated with the equatorial midnight temperature maximum.
Comparison of wind-stress algorithms and their influence on wind-stress curl using buoy measurements over the shelf off Bodega Bay, California
NASA Astrophysics Data System (ADS)
Kochanski, Adam; Kora?in, Darko; Dorman, Clive E.
The main objectives of this study were to compare three wind-stress algorithms of varying intricacy and estimate the extent to which each method altered computed wind-stress curl. The algorithms included (1) a simple bulk formula for neutral conditions that is dependent only on wind velocity components; (2) a formula that in addition to dependence on wind components includes a simplified effect of thermal stability through differences in air and sea temperatures; and (3) an algorithm that includes full treatment of dynamics and atmospheric stability. Data for the analysis were from a field program that used a special buoy network off Bodega Bay during 28 June-4 August 2001. A diamond-shaped setup of five closely separated buoys in Bodega Bay allowed for one of the first attempts to compute wind-stress curl over the ocean using buoy measurements. Based on an analysis of the available dataset, the marine layer over Bodega Bay is characterized by positive wind-stress curl with a median value around 0.2 Pa (100 km) -1 and maximum values reaching 2.5 Pa (100 km) -1. Positive wind-stress curl was observed for all wind speed conditions, whereas negative wind-stress curl episodes were associated mostly with low-wind conditions. Comparison of wind-stress curl computed using the three algorithms showed that differences among them can be significant. The first and third algorithms indicated similar stress curl (difference around 10%), but the differences between these two and the second algorithm were much higher (approximately 40%). The reason for the difference is the stability correction, which in the third algorithm strongly decreases with an increase in wind speeds, but stays at a similar level for all wind speeds in the second algorithm. Consequently, for higher wind speeds the variability of wind stress calculated using the second algorithm is greater than for the other two algorithms, causing significant differences in computed wind-stress curl (root mean-square error equal to 0.19 Pa (100 km) -1). Despite the apparent biases in computed wind stress and wind-stress curl among the algorithms, all of them show a significant trend of decreasing sea-surface temperature (SST) with increasing wind-stress curl. The bootstrapping analysis has revealed that both the along-shore wind stress and wind-stress curl have noticeable correlation with the changes in the sea-surface temperature as an indirect indication of the upwelling. An additional analysis, based on the low-pass filtered data, showed also significant agreement between the measured divergence in the cross-shore surface transport and the wind-stress curl computed for all three algorithms.
Sensitivities of eyewall replacement cycle to model physics, vortex structure, and background winds in numerical simulations of tropical cyclones
NASA Astrophysics Data System (ADS)
Zhu, Zhenduo; Zhu, Ping
series of sensitivity experiments by the Weather Research and Forecasting (WRF) model is used to investigate the impact of model physics, vortex axisymmetric radial structure, and background wind on secondary eyewall formation (SEF) and eyewall replacement cycle (ERC) in three-dimensional full physics numerical simulations. It is found that the vertical turbulent mixing parameterization can substantially affect the concentric ring structure of tangential wind associated with SEF through a complicated interaction among eyewall and outer rainband heating, radial inflow in the boundary layer, surface layer processes, and shallow convection in the moat. Large snow terminal velocity can substantially change the vertical distribution of eyewall diabatic heating to result in a strong radial inflow in the boundary layer, and thus, favors the development of shallow convection in the moat allowing the outer rainband convection to move closer to the inner eyewall, which may leave little room both temporally and spatially for a full development of a secondary maximum of tangential wind. Small radius of maximum wind (RMW) of a vortex and small potential vorticity (PV) skirt outside the RMW tend to generate double-eyewall replacement and may lead to an ERC without a clean secondary concentric maximum of tangential wind. A sufficiently large background wind can smooth out an ERC that would otherwise occur without background wind for a vortex with a small or moderate PV skirt. However, background wind does not appear to have an impact on an ERC if the vortex has a sufficiently large PV skirt.
Magnetic shaping of planetary nebulae and other stellar wind bubbles
NASA Technical Reports Server (NTRS)
Chevalier, Roger A.; Luo, Ding
As in the case of the solar wind, the magnetic field in the wind from a magnetized, rotating star becomes increasingly toroidal with distance from the star. The strength of the magnetic field can be characterized by sigma, the ratio of toroidal magnetic energy density to kinetic energy density in the equatorial plane of the wind. A fast wind shocks against the external medium and creates a bubble whose volume is dominated by shocked gas. The toroidal magnetic field increases in the shocked bubble and can dominate the thermal pressure. Because of the low velocities in the bubble, hydrostatic equilibrium is a good approximation and allows the calculation of the thermal and magnetic pressure in the bubble, as in the model of Begelman and Li (1992) for the Crab Nebula. The structure, which is axisymmetric and extended in the polar direction, depends on two parameters: sigma nu(sub w)/w(sub 0), where nu(sub w) is the wind velocity and w(sub 0) is the shell velocity in the polar direction, and lambda = nu(sub a)/w(sub 0), where nu(sub a) is the velocity of the slow wind. For small values of lambda, there is a cusp in the shell in the equatorial plane, i.e., there is an equatorial ring. For larger values of lambda, the maximum of the surface density moves away from the equator i.e., a double ring structure. Our models should apply to planetary nebulae, if their central stars are sufficiently magnetized; the calculated shapes do resemble the observed shapes of planetaries. In all cases, our model predicts that X-ray emission from the bubble is concentrated toward the polar axis. Finally, we briefly discuss the asymmetry of the Crab Nebula and 3C 58.
The sun and heliosphere at solar maximum.
Smith, E J; Marsden, R G; Balogh, A; Gloeckler, G; Geiss, J; McComas, D J; McKibben, R B; MacDowall, R J; Lanzerotti, L J; Krupp, N; Krueger, H; Landgraf, M
Recent Ulysses observations from the Sun's equator to the poles reveal fundamental properties of the three-dimensional heliosphere at the maximum in solar activity. The heliospheric magnetic field originates from a magnetic dipole oriented nearly perpendicular to, instead of nearly parallel to, the Sun's rotation axis. Magnetic fields, solar wind, and energetic charged particles from low-latitude sources reach all latitudes, including the polar caps. The very fast high-latitude wind and polar coronal holes disappear and reappear together. Solar wind speed continues to be inversely correlated with coronal temperature. The cosmic ray flux is reduced symmetrically at all latitudes. PMID:14615526
Magnetospheric feedback in solar wind energy transfer
M. Palmroth; H. E. J. Koskinen; T. I. Pulkkinen; P. K. Toivanen; P. Janhunen; S. E. Milan; M. Lester
The solar wind kinetic energy fueling all dynamical processes within the near-Earth space is extracted in a dynamo process at the magnetopause. This direct energy transfer from the solar wind into the magnetosphere depends on the orientation of the interplanetary magnetic field (IMF) as well as other solar wind parameters, such as the IMF magnitude and solar wind velocity. Using
Performance test of a low cost roof-mounted wind turbine
NASA Astrophysics Data System (ADS)
Figueroa-Espinoza, Bernardo; Quintal, Roberto; Gou, Clķment; Aguilar, Alicia
A low cost wind turbine was implemented based on the ideas put forward by Hugh Piggot in his book ``A wind turbine recipe book,'' where such device is developed using materials and manufacturing processes available (as much as possible) in developing countries or isolated communities. The wind turbine is to be mounted on a two stories building roof in a coastal zone of Mexico. The velocity profiles and turbulence intensities for typical wind conditions on top of the building roof were analyzed using numerical simulations (RANS) in order to locate the turbine hub above any recirculation and near the maximum average speed. The coefficient of performance is going to be evaluated experimentally by measuring the electrical power generation and wind characteristics that drive the wind turbine on the field. These experimental results will be applied on the improvement of the wind turbine design, as well as the validation of a numerical simulation model that couples the wind characteristics obtained through CFD with the Blade Element Method (BEM) and an electro-mechanical model of the turbine-shaft-generator ensemble. A low cost wind turbine was implemented based on the ideas put forward by Hugh Piggot in his book ``A wind turbine recipe book,'' where such device is developed using materials and manufacturing processes available (as much as possible) in developing countries or isolated communities. The wind turbine is to be mounted on a two stories building roof in a coastal zone of Mexico. The velocity profiles and turbulence intensities for typical wind conditions on top of the building roof were analyzed using numerical simulations (RANS) in order to locate the turbine hub above any recirculation and near the maximum average speed. The coefficient of performance is going to be evaluated experimentally by measuring the electrical power generation and wind characteristics that drive the wind turbine on the field. These experimental results will be applied on the improvement of the wind turbine design, as well as the validation of a numerical simulation model that couples the wind characteristics obtained through CFD with the Blade Element Method (BEM) and an electro-mechanical model of the turbine-shaft-generator ensemble. Special thanks to the Coordinaci¾n de Investigaci¾n CientĒfica of the Universidad Michoacana de San Nicolßs de Hidalgo for their support.
Velocity determination from velocity spectra
Yang, Sung Jin
. correction values, ms Sp no. correction values, ms 1 2 3 4 5 6 7 8 9 10 ll 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 source 30 30 32 27 27 27 33 33 32 29 25 25 29 27 25 25 25 26 31 40 23 23... Figure 14. CDP gathers at some shot points. . . Figure 15. Velocity spectra at SP 12. 5 and 20. 5. . 30 Figure 16. Velocity spectra at SP 28. 5 and 39. . 31 Figure 17. Velocity spectra at SP 43 and 52. . Figure 18. Stacked section. 37 Figure 19...
Velocity determination from velocity spectraĀ
Yang, Sung Jin
. on from Velocity Spectra (December 1973) Sung Jin Yang, B. S. Seoul National University; Korea Directed by: Dr. Anthony F. Gangi The reflected signals on the traces of a common-depth-point (CDP) gather appear along a hyperbolic curve which is a...VELOCITY DETERMINATION FRON VELOCITY SPECTRA A Thesis by SUNG JIN YANG Submutted to the Graduate C:lleEe of Texas ASM University in partial fulfill sent of requirement for the degree of EASTER GF SCIENCE December 1973 Naj or Subject...
Wind Tunnel Analysis of the Detachment Bubble on Bolund Island
NASA Astrophysics Data System (ADS)
Yeow, T. S.; Cuerva, A.; Conan, B.; J, Pķrez-┴lvarez
The flow topology on two scaled models (1:230 and 1:115) of the Bolund Island is analysed in two wind tunnels, focusing on the characteristics of the detachment pattern when the wind blows from 270░ wind direction and the atmospheric condition is neutral. Since the experiments are designed as the simplest possible reference cases, no additional roughness is added neither to the models surface nor to the wind tunnel floor. Pressure measurements on the surface of the 1:230 scale model are used to estimate the horizontal extension of the intermittent recirculation region, by applying the diagnostic means based in exploring the pressure statistics, proposed in the literature for characterising bubbles on canonical obstacles. The analysis is done for a range of Reynolds numbers based on the mean undisturbed wind speed, U? and the maximum height of the island, h[5.1ū104,8.5ū104]. An isoheight mapping of the velocity field is obtained using 3D hotwire (3D HW). The velocity field in a vertical plane is determined using 3D HW and 2D particle image velocimetry (PIV) on the 1:115 scale model in order to reproduce and complete already existing results in the literature.
Does the Milky Way Produce a Nuclear Galactic Wind?
NASA Astrophysics Data System (ADS)
Keeney, Brian A.; Danforth, Charles W.; Stocke, John T.; Penton, Steven V.; Shull, J. Michael; Sembach, Kenneth R.
We detect high-velocity absorbing gas using Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer medium-resolution spectroscopy along two high-latitude active galactic nucleus (AGN) sight lines (Mrk 1383 and PKS 2005-489) above and below the Galactic center (GC). These absorptions are most straightforwardly interpreted as a wind emanating from the GC that does not escape from the Galaxy's gravitational potential. Spectra of four comparison B stars are used to identify and remove foreground velocity components from the absorption-line profiles of O VI, N V, C II, C III, C IV, Si II, Si III, and Si IV. Two high-velocity (HV) absorption components are detected along each AGN sight line, three redshifted and one blueshifted. Assuming that the four HV features trace a large-scale Galactic wind emanating from the GC, the blueshifted absorber is falling toward the GC at a velocity of 250+/-20 km s-1, which can be explained by ``Galactic fountain'' material that originated in a bound Galactic wind. The other three absorbers represent outflowing material; the largest derived outflow velocity is +250+/-20 km s-1, which is only 45% of the velocity necessary for the absorber to escape from its current position in the Galactic gravitational potential. All four HV absorbers are found to reach the same maximum height above the Galactic plane (zmax=12+/-1 kpc), implying that they were all ejected from the GC with the same initial velocity. The derived metallicity limits of >~10%-20% solar are lower than expected for material recently ejected from the GC unless these absorbers also contain significant amounts of hotter gas in unseen ionization stages.
Performance of a 2-micrometer coherent Doppler lidar for wind measurements
NASA Technical Reports Server (NTRS)
Frehlich, Rod; Hannon, Stephen M.; Henderson, Sammy W.
Measurements of boundary layer winds are presented using a 2-micrometer coherent Doppler lidar and the optimal performance of the maximum likelihood estimator. The systematic error for single-shot estimates was estimated as 3.6 cm/s using measurements from a stationary hard target. The estimation error for measurements of the radial component of the wind field was determined, as well as the fraction of the estimates that are randomly distributed over the velocity search space, when the signal power is low and speckle fading is important. The results from actual data are compared with the results from ideal simulations. The first direct estimation of the spatial structure function of the radial wind field and of the energy dissipation rate is presented for both horizontal and vertical directions of propagation. The rms estimation error of the velocity estimates is found to be within 30% of ideal performance based on simulation.
Vidotto, A. A.; Jatenco-Pereira, V. [University of Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090 (Brazil); Opher, M. [George Mason University, 4400 University Drive, Fairfax, VA 22030-4444 (United States); Gombosi, T. I. [University of Michigan, 1517 Space Research Building, Ann Arbor, MI 48109-2143 (United States)], E-mail: email@example.com
By means of self-consistent three-dimensional magnetohydrodynamics (MHD) numerical simulations, we analyze magnetized solar-like stellar winds and their dependence on the plasma-{beta} parameter (the ratio between thermal and magnetic energy densities). This is the first study to perform such analysis solving the fully ideal three-dimensional MHD equations. We adopt in our simulations a heating parameter described by {gamma}, which is responsible for the thermal acceleration of the wind. We analyze winds with polar magnetic field intensities ranging from 1 to 20 G. We show that the wind structure presents characteristics that are similar to the solar coronal wind. The steady-state magnetic field topology for all cases is similar, presenting a configuration of helmet streamer-type, with zones of closed field lines and open field lines coexisting. Higher magnetic field intensities lead to faster and hotter winds. For the maximum magnetic intensity simulated of 20 G and solar coronal base density, the wind velocity reaches values of {approx}1000 km s{sup -1} at r {approx} 20r {sub 0} and a maximum temperature of {approx}6 x 10{sup 6} K at r {approx} 6r {sub 0}. The increase of the field intensity generates a larger 'dead zone' in the wind, i.e., the closed loops that inhibit matter to escape from latitudes lower than {approx}45 deg. extend farther away from the star. The Lorentz force leads naturally to a latitude-dependent wind. We show that by increasing the density and maintaining B {sub 0} = 20 G the system recover back to slower and cooler winds. For a fixed {gamma}, we show that the key parameter in determining the wind velocity profile is the {beta}-parameter at the coronal base. Therefore, there is a group of magnetized flows that would present the same terminal velocity despite its thermal and magnetic energy densities, as long as the plasma-{beta} parameter is the same. This degeneracy, however, can be removed if we compare other physical parameters of the wind, such as the mass-loss rate. We analyze the influence of {gamma} in our results and we show that it is also important in determining the wind structure.
Spatial distribution of threshold wind speeds for dust outbreaks in northeast Asia
NASA Astrophysics Data System (ADS)
Kimura, Reiji; Shinoda, Masato
Asian windblown dust events cause human and animal health effects and agricultural damage in dust source areas such as China and Mongolia and cause "yellow sand" events in Japan and Korea. It is desirable to develop an early warning system to help prevent such damage. We used our observations at a Mongolian station together with data from previous studies to model the spatial distribution of threshold wind speeds for dust events in northeast Asia (35░-45░N and 100░-115░E). Using a map of Normalized Difference Vegetation Index (NDVI), we estimated spatial distributions of vegetation cover, roughness length, threshold friction velocity, and threshold wind speed. We also recognized a relationship between NDVI in the dust season and maximum NDVI in the previous year. Thus, it may be possible to predict the threshold wind speed in the next dust season using the maximum NDVI in the previous year.
Darrieus wind-turbine performance and weight-scaling calculations. Final report
Lapin, E.E.
The distribution of weight by component in three existing vertical axis wind turbines is briefly tabulated. An approach is given for studying Darrieus machine element weights, accounting for the several possible operating regimes and the maximum forces generated in these regimes which produce loads imposed on the blades and the reactions on the interfacing elements. The approach taken is to develop a means for analysis of the dominating load creating member, the blades, and a means for analysis of aerodynamic performance under a typical distribution of wind velocity. Then the blade structural loading is determined for appropriate designs for the conditions of use including the blades at rest in maximum winds. Computational results of the investigation are graphed. (LEW)
Helium, hydrogen, and oxygen velocities observed on isee-3
Ogilvie, K.W. (Maryland Univ., College Park); Coplan, M.A. (LASL)
The velocities of hydrogen, helium, and oxygen ions over a full range of solar wind conditions were recorded by the ion composition instrument and Los Alamos National Laboratory plasma instrument aboard the International Sun Earth Explorer. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s(-1) the helium velocity exceeded the hydrogen velocity by 5 km s(-1) the average difference was 14 km s(-1), however no evidence was found for a nonzero average velocity difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Generally helium hydrogen velocity differences are bounded by the Alfven speed. Velocity differences show abrupt changes across interplanetary discontinuities, presumably tangential. The electrostatic potential change across a shock produces differences between the velocities of ions having different charges.
NSDL National Science Digital Library
Michael Horton
This lab is an inquiry activity in that students have not been exposed to the idea of terminal velocity, though they are using skills that they already have to analyze the balloon's motion. The lab is both a review of graphing and translating distance ver
Maximum Power Training and Plyometrics for Cross-Country Running.
ERIC Educational Resources Information Center
Ebben, William P.
Provides a rationale for maximum power training and plyometrics as conditioning strategies for cross-country runners, examining: an evaluation of training methods (strength training and maximum power training and plyometrics); biomechanic and velocity specificity (role in preventing injury); and practical application of maximum power training andģ
Variable Winds and Dust Formation in R Coronae Borealis Stars
Clayton, Geoffrey C; Zhang, Wanshu
We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I 10830 lines of twelve R Coronae Borealis (RCB) stars over short (1 month) and long (3 year) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities ~400 km/s appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.
Clayton, Geoffrey C.; Zhang Wanshu [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Geballe, T. R., E-mail: firstname.lastname@example.com, E-mail: email@example.com, E-mail: email@example.com [Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States)
We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I {lambda}10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities {approx}400 km s{sup -1} appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.
Response of a Vertical Axis Wind Turbine to Time Varying Wind Conditions found within the Urban
Tullis, Stephen
Response of a Vertical Axis Wind Turbine to Time Varying Wind Conditions found within the Urban, 2010 PP 389Ł401 389 ABSTRACT Experimental testing of a vertical axis wind turbine within the urban of the turbine. Temporal variation of the wind with respect to the direction and velocity fluctuations
A wind tunnel investigation of wind turbine wakes: Boundary-layer turbulence and surface roughness effects
L. Chamorro; F. Porte-Agel
Wind turbine wakes are known to have an important effect on power generation and fatigue loads in wind energy parks. Wake characteristics are expected to depend on the incoming atmospheric boundary layer flow statistics (mean velocity and turbulence levels). Here, results are presented from a wind tunnel experiment carried out at the St. Anthony Falls Laboratory atmospheric boundary layer wind
Van Hylckama, T. E. A.
An analysis of hourly wind speeds above and within a stand of saltcedar near Buckeye, Arizona, reveals that in 90% of all observed cases, the wind profiles above the stand can be represented by the simple logarithmic equation: uz = u* k 1n ( z z0) where uz is the velocity at height z. The roughness length (z0), (disregarding zero displacement), varies with a stability ratio similar to Richardson's number. The friction velocity, u*, depends on the wind speeds above the vegetation. Von Karman's constant, k, equals 0.41. Within the thickets there is considerable turbulence, and irregular wind inversions occur during daylight hours. The results are important for estimating water losses by evapotranspiration by either the energy-budget or the mass-transfer formulae. ?? 1970.
Large-scale structure of solar wind as observed on the Prognoz 7 satellite
NASA Technical Reports Server (NTRS)
Yermolaev, Yu. I.
Properties of different solar wind streams depend on the large scale structure of coronal magnetic field and dynamical phenomena in the solar atmosphere. We present average values and distributions of MHD parameters (density, velocity, temperature, fluxes of mass, momentum and energy, ratio of thermal and magnetic pressures, as well as helium abundance) as observed on board the Prognoz 7 satellite in the different types of the solar wind streams connected with solar corona structure and phenomena: (1) heliospheric current sheet, (2) streams from coronal holes, (3) streams from coronal streamers, (4) plasma disturbed by interplanetary shocks, and (5) coronal mass ejections. As for quasistationary streams of solar wind, maximum mass flux is recorded in the streams emanating from the coronal streamers while maximum thermal and kinetic energy fluxes are observed in the streams from the coronal holes. The momentum fluxes are equal in both types of streams. Maximum ratio of thermal and magnetic pressures is observed in heliospheric current sheet. The maximum helium abundance is observed in coronal mass ejection, it is higher in streams from coronal holes than in streams from streamers, and its dependences on density and mass flux are different in different types of the streams. Dynamics of alpha-particle velocity and temperature relative to protons in different streams is discussed.
Wind turbine wake characterization using long-range Doppler lidar
NASA Astrophysics Data System (ADS)
Aitken, M.; Lundquist, J. K.; Hestmark, K.; Banta, R. M.; Pichugina, Y.; Brewer, A.
Wind turbines extract energy from the freestream flow, resulting in a waked region behind the rotor which is characterized by reduced wind speed and increased turbulence. The velocity deficit in the wake diminishes with distance, as faster-moving air outside is gradually entrained. In a concentrated group of turbines, then, downwind machines experience very different inflow conditions compared to those in the front row. As utility-scale turbines rarely exist in isolation, detailed knowledge of the mean flow and turbulence structure inside wakes is needed to correctly model both power production and turbine loading at modern wind farms. To this end, the Turbine Wake and Inflow Characterization Study (TWICS) was conducted in the spring of 2011 to determine the reduction in wind speeds downstream from a multi-MW turbine located at the National Renewable Energy Laboratory's National Wind Technology Center (NWTC) near Boulder, Colorado. Full-scale measurements of wake dynamics are hardly practical or even possible with conventional sensors, such as cup anemometers mounted on meteorological (met) masts. Accordingly, the High Resolution Doppler Lidar (HRDL) developed by the National Oceanic and Atmospheric Administration's Earth System Research Laboratory was employed to investigate the formation and propagation of wakes under varying levels of ambient wind speed, shear, atmospheric stability, and turbulence. HRDL remotely senses line-of-sight wind velocities and has been used in several previous studies of boundary layer aerodynamics. With a fully steerable beam and a maximum range up to about 5 km, depending on atmospheric conditions, HRDL performed a comprehensive survey of the wind flow in front of and behind the turbine to study the shape, meandering, and attenuation of wakes. Due in large part to limited experimental data availability, wind farm wake modeling is still subject to an unacceptable amount of uncertainty, particularly in complex terrain. Here, analytical techniques are developed to distinguish wakes from the background variability, and moreover, wakes are then classified by width, height, length, and velocity deficit based on atmospheric stability and inflow conditions. By integrating these advanced observational capabilities with innovative approaches to atmospheric modeling, this work will help to improve simulation tools used to quantify power loss and fatigue loading due to wake effects, thereby aiding the optimization of wind farm layouts.
On the Effect of Offshore Wind Parks on Ocean Dynamics
NASA Astrophysics Data System (ADS)
Ludewig, E.; Pohlmann, T.
Nowadays renewable energy resources play a key role in the energy supply discussion and especially an increasingly interest in wind energy induces intensified installations of wind parks. At this offshore wind energy gains in popularity in the course of higher and more consistent energy availability than over land. For example Germany's government adopted a national interurban offshore wind energy program comprising the construction of hundreds of wind turbines within Germany's Exclusive Economic Zone to ensure up to 50% of Germany's renewable energy supply. The large number of installation in coastal regions asks for analyzing the impact of offshore wind parks (OWPs) on the atmosphere and the ocean. As known from literature such wind parks excite also-called wake-effect and such an influence on the wind field in turn affects ocean circulation. To cover OWP's impact on ocean dynamics we evaluate model simulations using the Hamburg Shelf-Ocean-Model (HAMSOM). All simulations were driven with a wind forcing produced by the Mesoscale Atmosphere Model of the Hamburg University (METRAS) which has implemented wind turbines. Wind forcing data were generated in collaboration with and by courtesy of the Meteorological Institute of the University of Hamburg, Department Technical Meteorology, Numeric Modeling-METRAS. To evaluate dynamical changes forced by the OWP's wind wake-effect we did a sensitivity study with a theoretical setup of a virtual ocean of 60m depth with a flat bottom and a temperature and salinity stratification according to common North Sea's conditions. Here our results show that already a small OWP of 12 wind turbines, placed in an area of 4 km^2, lead to a complex change in ocean dynamics. Due to the wake-effect zones of upwelling and downwelling are formed within a minute after turning-on wind turbines. The evolving vertical cells have a size of around 15x15 kilometers with a vertical velocity in order of 10^-2 mm/sec influencing the dynamic of an area being hundred times bigger than the wind park itself. The emerged vertical structure is generated due to a newly created geostrophic balance resulting in a redistribution of the ocean mass field. A number of additional upwelling and downwelling cells around the wind park support an intensified vertical dispersion through all layers and incline the thermocline which also influences the lower levels. The disturbances of mass show a dipole structure across the main wind direction with a maximum change in thermocline depth of some meters close to the OWP. Diffusion, mostly driven by direct wind induced surface shear is also modified by the wind turbines and supports a further modification of the vertical patterns. Considering that wind turbines operate only in a special window of wind speed, i.e. wind turbines will stop in case of too weak or too strong wind speeds as well as in case of technical issues, the averaged dimension and intensity of occurring vertical cells depend on the number of rotors and expected wind speeds. Finally we will focus on scenario runs for the North Sea under fully realistic conditions to estimate possible changes in ocean dynamics due to OWPs in future and these results will be further used for process analyzes of the ecosystem. If we assume a continuous operation of North Sea's OWPs in future we expect a fundamental constant change in ocean dynamics and moreover in the ecosystem in its vicinity.
Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet
NASA Technical Reports Server (NTRS)
Simon-Miller, Amy A.; Choi, David; Rogers, John H.; Gierasch, Peter J.; Allison, Michael D.; Adamoli, Gianluigi; Mettig, Hans-Joerg
A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and accelerations over distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of approx 140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75 to 100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 +/- 0.7-day period. This oscillating motion has a wavelength of approx 20 and a speed of 101 +/- 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of mUltiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.
Selected wind tunnel test results for the Darrieus wind turbine
B. F. Blackwell; R. E. Sheldahl
Five blade configurations of a 2-m-diam Darrieus wind turbine have been tested in the Vought Corporation 4.6- x 6.1-m (15- x 20-ft) Low-Speed Wind Tunnel. Rotor solidity, Reynolds number, and freestream velocities tested were in the following ranges: solidity, 13 to 30%; Reynolds number, 1 to 3 x 10ŌüĄ; freestream velocity, 7 to 11 m\\/s. The airfoil selection for all
Selected wind tunnel test results for the Darrieus wind turbine
B. F. Blackwell; R. E. Sheldahl
Five blade configurations of a 2-m-diam Darrieus wind turbine have been tested in a low-speed wind tunnel. Rotor solidity, Reynolds number, and free-stream velocities tested were in the following ranges: solidity, 13-30%; Reynolds number, 100,000-300,000; free-stream velocity, 7-11 m\\/s. The airfoil selection for all configurations was NACA 0012. The parameters measured were rotor torque, rotor rotational speed, and tunnel conditions.
What is a Hurricane? Tropical system with maximum sustained
Meyers, Steven D.
Andrew-Category 4Ę Category 4 Hurricane - Winds 131-155 mph. Wall failures in homes and complete roofHurricane 101 #12;What is a Hurricane? Ę Tropical system with maximum sustained surface wind of 74 mph or greater. A hurricane is the worst and the strongest of all tropical systems. Ę Also known
Coupling a Neural Network-Based forward Model and a Bayesian Inversion Approach to Retrieve Wind Field from Spaceborne Polarimetric Radiometers
Pulvirenti, Luca; Pierdicca, Nazzareno; Marzano, Frank S.
A simulation study to assess the potentiality of sea surface wind vector estimation based on the approximation of the forward model through Neural Networks and on the Bayesian theory of parameter estimation is presented. A polarimetric microwave radiometer has been considered and its observations have been simulated by means of the two scale model. To perform the simulations, the atmospheric and surface parameters have been derived from ECMWF analysis fields. To retrieve wind speed, Minimum Variance (MV) and Maximum Posterior Probability (MAP) criteria have been used while, for wind direction, a Maximum Likelihood (ML) criterion has been exploited. To minimize the cost function of MAP and ML, conventional Gradient Descent method, as well as Simulated Annealing optimization technique, have been employed. Results have shown that the standard deviation of the wind speed retrieval error is approximately 1.1 m/s for the best estimator. As for the wind direction, the standard deviation of the estimation error is less than 13░ for wind speeds larger than 6 m/s. For lower wind velocities, the wind direction signal is too weak to ensure reliable retrievals. A method to deal with the non-uniqueness of the wind direction solution has been also developed. A test on a case study has yielded encouraging results.
Application of a method for the automatic detection and Ground-Based Velocity Track Display (GBVTD) analysis of a tornado crossing the Hong Kong International Airport
NASA Astrophysics Data System (ADS)
Chan, P. W.; Wurman, J.; Shun, C. M.; Robinson, P.; Kosiba, K.
A weak tornado with a maximum Doppler velocity shear of about 40 m s - 1 moved across the Hong Kong International Airport (HKIA) during the evening of 20 May 2002. The tornado caused damage equivalent to F0 on the Fujita Scale, based on a damage survey. The Doppler velocity data from the Hong Kong Terminal Doppler Weather Radar (TDWR) are studied using the Ground-Based Velocity Track Display (GBVTD) method of single Doppler analysis. The GBVTD analysis is able to clearly depict the development and decay of the tornado though it appears to underestimate its magnitude. In the pre-tornadic state, the wind field is characterized by inflow toward the center near the ground and upward motion near the center. When the tornado attains its maximum strength, an eye-like structure with a downdraft appears to form in the center. Several minutes later the tornado begins to decay and outflow dominates at low levels. Assuming cyclostrophic balance, the pressure drop 200 m from the center of the tornado at its maximum strength is calculated to be about 6 hPa. To estimate the maximum ground-relative wind speed of the tornado, the TDWR's Doppler velocities are adjusted for the ratio of the sample-volume size of the radar and the radius of the tornado, resulting in a peak wind speed of 28 m s - 1 , consistent with the readings from a nearby ground-based anemometers and the F0 damage observed. An automatic tornado detection algorithm based on Doppler velocity difference (delta-V) and temporal and spatial continuity is applied to this event. The locations and the core flow radii of the tornado as determined by the automatic method and by subjective analysis agree closely.
Maximum a Posteriori Maximum Entropy Signal Denoising
NASA Astrophysics Data System (ADS)
Seghouane, Abd-Krim; Knockaert, Luc
When fitting wavelet based models, shrinkage of the empirical wavelet coefficients is an effective tool for signal denoising. Based on different approaches, different shrinkage functions have been proposed in the literature. The shrinkage functions derived using Bayesian estimation theory depend on the prior used on the wavelet coefficients. However, no simple and direct method exists for the choice of the prior. In this paper a new method based on maximum entropy considerations is proposed for the construction of the prior on the wavelet coefficients. The new shrinkage function is obtained by coupling this prior to maximum a posteriori arguments. A comparison with classical shrinkage functions is given in a simulation example of image denoising in order to illustrate the effectiveness of the proposed thresholding method.
Hanford Site peak gust wind speeds
Ramsdell, J.V.
Peak gust wind data collected at the Hanford Site since 1945 are analyzed to estimate maximum wind speeds for use in structural design. The results are compared with design wind speeds proposed for the Hanford Site. These comparisons indicate that design wind speeds contained in a January 1998 advisory changing DOE-STD-1020-94 are excessive for the Hanford Site and that the design wind speeds in effect prior to the changes are still appropriate for the Hanford Site.
Exploration of Solar Wind Acceleration Region Using Interplanetary Scintillation of Water Vapor Maser Source and Quasars
NASA Technical Reports Server (NTRS)
Tokumaru, Munetoshi; Yamauchi, Yohei; Kondo, Tetsuro
Single-station observations of interplanetary scintillation (IPS) at three microwave frequencies; 2 GHz, 8 GHz and 22 GHz have been carried out between 1989 and 1998 using a large (34 m farad) radio telescope at the Kashima Space Research Center of the Communications Research Laboratory. The aim of these observations is to explore the near-sun solar wind, which is the key region for the study of the solar wind acceleration mechanism. Strong quasars; 3C279 and 3C273B were used for Kashima IPS observations at 2 GHz and 8 GHz, and a water vapor maser source, IRC20431 was used for the IPS observations at 22 GHz. Solar wind velocities derived from Kashima IPS data suggest that the solar wind acceleration takes place at radial distances between 10 and 30 solar radii (R(sub s)) from the sun. Properties of the turbulence spectrum (e.g. anisotropy, spectral index, inner scale) inferred from Kashima data are found to change systematically in the solar wind acceleration region. While the solar wind in the maximum phase appears to be dominated by the slow wind, fast and rarefied winds associated with coronal holes are found to develop significantly at high latitudes as the solar activity declines. Nevertheless, Kashima data suggests that the location of the acceleration region is stable throughout the solar cycle.
Wind-speed measurements with a scanning elastic-backscatter lidar
Buttler, W.T.; Eichinger, W.E.
During the 1992 Summer Olympics, the Los Alamos National Laboratory (LANL) lidar team participated in the Barcelona Air Quality Initiative (BAQI). One of the main objectives of this experiment was the remote measurement of wind speeds around the city to verify wind speeds and directions predicted by the Nonhydrostatic Mesoscale Model (MEMO). Remote determination of wind velocities in the mixing layer is important for the verification and determination of critical input parameters of urban-pollution transport models. Most present elastic-backscatter-lidar wind-speed-measurement methods rely on data acquired over time periods between 5 to 10 minutes (Matsui, 1990) and 30 minutes to 1 hour (Schols, et al. 1992). Lidar can measure the spatial properties of the wind field over large volumes of space. This capability is an improvement over present methods, which rely on instruments attached to balloons that measure only those winds along the path the balloon travels. The material that follows describes the principles implicit in the measurement of winds with an elastic-backscatter lidar, as well as the maximum cross-correlation algorithm used to extract wind speeds from lidar data acquired during the Summer Olympics at Barcelona, Spain, in July 1992.
Experimental studies of wind effects on runup and overtopping of revetmentsĀ
Wibner, Christopher Gerard
spectrums for cases 7a-d, 37 37 38 38 39 39 40 Figure 5. 8 Wind wave energy spectrum growth for a wind velocity of 6. 5 m/s. . . . . 42 Figure 5. 9 Wind wave energy spectrum growth for a wind velocity of 12 m/s . . . . . . 43 Figure 5. 10 Wind wave... in overtopping due to wind effects. The wind correction factor is given by k = 1. 0 +W[ '+0. 1 sin0 I' ll ? d, t R (2, 12) where values of Wr are given as follows: Wr = 2. 0 for onshore wind velocities of 60 mph, W, = 0. 5 for onshore wind speed of 30 mph...
Extremal Trajectories for Bounded Velocity Differential Drive Robots
and its angular velocity is #. The robot's width is 2b. The wheel angular velocities are # l and # rExtremal Trajectories for Bounded Velocity Differential Drive Robots Devin J. Balkcom Matthew T drive mobile robots with velocity bounds. The Maximum Principle gives necessary conditions for time
Understanding extreme winds in Iceland
NASA Astrophysics Data System (ADS)
Petersen, Gudrun Nina
Iceland is a fairly windy country, due to it's location adjacent the North Atlantic storm track. The orography of the island is rugged, mountains are steep and fjords and valleys narrow, and this impacts local winds. Thus, mountain wind phenomena such as low level jets, gap winds, down-slope wind storms, mountain waves and wind wakes are common. To increase our knowledge of the behaviour of wind in Iceland an extreme value analysis was conducted based on observations from 61 automatic weather stations, applying the Peak Over Threshold technique on maximum daily wind speed and maximum daily wind gust at each site. The time series included at least 10 years of data and the threshold was chosen as the 0.9 quantile of maximum mean wind speed/maximum wind gust at each location. Among the results is the larger impact the local orography has on the extreme wind gusts compared to the mean wind. With extreme value models in place, a few significant weather events were selected from recent years and the observed wind speeds compared to the models in order to evaluate how extreme the events were and how large area they impacted. Actually, in most of these events the observed wind speed only turned out to be extreme at a few stations, emphasising the local effects. However, in an event from December 2007, when the observed maximum wind speed exceeded 23 m/s in most of western Iceland, the event was estimated as rare at a number of weather stations. Clearly this gives indication for further studying this particular weather event. An automatic system has been set up, running once an hour, comparing observed wind measurements to the extreme value models and producing maps of the return periods for all sites. This system gives us the possibility to, on a daily basis, evaluate the extremeness of each situation and simultaneously increase our knowledge of extreme wind behaviour in Iceland. This work is a foundation for studying changes in extreme winds in Iceland.
Preliminary Velocity Measurements in the Wake of a Submarine Model
NASA Astrophysics Data System (ADS)
Jimenez, J. M.; Reynolds, R.; Smits, A. J.
Preliminary Particle Image Velocimetry (PIV) over a submarine shape has been conducted in a low speed wind tunnel at Princeton University. The model is a 1/67 replica of the USS Albacore, an experimental submarine designed to achieve maximum underwater performance, and based on "bodies of revolution." The model is tested with a sail, and different tail appendages. Velocity vector fields and flow visualizations in the wake region are presented for Reynolds numbers based on model length up to 10^5. The experiments establish the groundwork for future investigations of submarine models in the new High Reynolds Number Test Facility (http://www.princeton.edu/ gasdyn/HRTF.html). Supported by ONR Grants N00014-97-1-0325, N00014-97-1-0340 and N00014-97-1-0618.
Solar wind proton deposition into the Martian atmosphere
Stephen H. Brecht
The direct impact of solar wind H + with the planet Mars is calculated using a three- dimensional hybrid particle code. The simulation results show a strong dependence on solar wind velocity and interplanetary magnetic field angle with the solar wind velocity vector. The energy fluxes calculated approach the solar EUV heating rates fxom photoelectrons and are found to be
Stability Simulation of Wind Turbine Systems
P. M. Anderson; Anjan Bose
A simulation and digital computer modeling effort is described in which a wind turbine-generator system is adapted for stability evaluation using a large scale transient stability computer program. Component models of the MOD-2 wind generator system are described and their digital model equations are provided. A versatile wind velocity model is described, which provides the capability of simulating a wide
Fast solar wind monitoring available: BMSW in operation
NASA Astrophysics Data System (ADS)
Ŗafrßnkovß, J.; N?me?ek, Z.; P?ech, L.; Zastenker, G.
The Spektr-R spacecraft was launched on a Zenit-3F rocket into an orbit with a perigee of 10.000 kilometers and apogee of 390.000 km on July 18, 2011. The spacecraft operational lifetime would exceed five years. The main task of the mission is investigations of distant sources of electromagnetic emissions but, as a supporting measurement, the spacecraft carries a complex of instruments for solar wind monitoring because it will spend there ~ 8 days out of the 9-day orbit. The main task of the solar wind monitor (BMSW) is to provide fast measurements of the solar wind density, velocity, and temperature with a maximum time resolution of 31 ms. Such time resolution was obtained using simultaneous measurements of several Faraday cups oriented permanently nearly in the solar wind direction. In this paper, we describe briefly basic principles of the BMSWoperation, and show a few examples its observations. We present frequency spectra of the solar wind turbulence at the kinetic scale and an example of high-frequency waves associated with an IP shock.
Solar Wind ~20-300 keV Superhalo Electrons
NASA Astrophysics Data System (ADS)
Wang, L.; Yang, L.; He, J.; Tu, C. Y.; Pei, Z.
High-energy superhalo electrons are present in the interplanetary medium even in absence of any solar activity, carrying important information on the electron acceleration in the solar wind. We present a statistical survey of ~20-300 keV superhalo electrons measured at 1 AU by the WIND 3DP instrument during quiet-time periods from 1995 January through 2013 December. The velocity distribution function of the observed quiet-time superhalo electrons generally fits to a power-law spectrum, f ~ v-?, with ? ranging from ~4 to ~10. The integrated density of these superhalo electrons at 20-300 keV, nsup, ranges from 10?9 cm?3 to 10?5 cm?3. Both log(nsup) and ? show a good correlation with the sunspot number, with larger density and softer spectrum (?~ 6-8) at solar maximum, and smaller density and harder spectrum (?~ 4-5) at solar minimum. The observed power-law spectrum also has no clear association with flares, CMEs, active regions and solar wind core populations, while it shows a weak (~0.3) correlation with in situ solar wind turbulence spectrum. These results suggest that the seed particles of quiet-time superhalo electrons could originate from the Sun, and their acceleration could mainly occur in the interplanetary medium, probably by the electron interaction with solar wind turbulence, or by acceleration at the CIRs.
High-resolution IUE spectroscopy of fast winds from cataclysmic variables
NASA Astrophysics Data System (ADS)
Prinja, Raman K.; Rosen, R.
The winds from six dwarf novae and four nova-like cataclysmic variables are studied using 31 high-resolution IUE spectra. The data provide details on athe time- and phase-averaged nature of disc-driven outflows, which are diagnosed via the presence of P Cygni-like and extended absorption profiles due to the C IV, N V and Si IV resonance line doublets, and He II lambda 1640. The profiles are parametrized using measures of the absorption and emission velocities, widths and strengths. The maximum wind velocity can exceed -4000 km s^-1, although the absorption maximum (minimum flux) typically occurs at ~20 per cent of the shortward profile edge. Optical depth and velocity structure is identified in the absorption troughs which may indicate inhomogeneities in the outflows. The relative ion behaviour and the respective contributions to the emission profiles of the inner disc and wind are discussed. Synthesized model profiles are used to estimate the products of mass-loss rate and C^3+ ion fractions.
Wind turbine control using a gearless epicyclic transmission
Xiao Qing Ma; Vikram Chopra; S. H. H. Zargarbashi; Jorge Angeles
A recurrent problem in energy production by means of wind turbines is how to keep a constant angular velocity at the shaft driving the alternator in the presence of a randomly varying turbine angular velocity. The latter is caused by the random nature of the wind velocity. Proposed in this paper is an innovative two-degree-of-freedom mechanism, with the morphology of
Long term variability of B supergiant winds
NASA Technical Reports Server (NTRS)
Massa, Derck L.
The object of this observing proposal was to sample wind variability in B supergiants on a daily basis over a period of several days in order to determine the time scale with which density variability occurs in their winds. Three stars were selected for this project: 69 Cyg (B0 Ib), HD 164402 (B0 Ib), and HD 47240 (B1 Ib). Three grey scale representations of the Si IV lambda lambda 1400 doublet in each star are attached. In these figures, time (in days) increases upward, and the wavelength (in terms of velocity relative to the rest wavelength of the violet component of the doublet) is the abscissa. The spectra are normalized by a minimum absorption (maximum flux) template, so that all changes appear as absorptions. As a result of these observations, we can now state with some certainty that typical B supergiants develop significant wind inhomogeneities with recurrence times of a few days, and that some of these events show signs of strong temporal coherence.
Detection of Solar Wind Disturbances: Mexican Array Radio Telescope IPS Observations at 140 MHz
NASA Astrophysics Data System (ADS)
Romero-Hernandez, E.; Gonzalez-Esparza, J. A.; Aguilar-Rodriguez, E.; Ontiveros-Hernandez, V.; Villanueva-Hernandez, P.
The interplanetary scintillation (IPS) technique is a remote-sensing method for monitoring solar-wind perturbations. The Mexican Array Radio Telescope (MEXART) is a single-station instrument operating at 140 MHz, fully dedicated to performing solar-wind studies employing the IPS technique. We report MEXART solar-wind measurements (scintillation indices and solar-wind velocities) using data obtained during the 2013 and 2014 campaigns. These solar-wind measurements were calculated employing a new methodology based on the wavelet transform (WT) function. We report the variation of the scintillation indices versus the heliocentric distance for two IPS sources (3C48 and 3C147). We found different average conditions of the solar-wind density fluctuations in 2013 and 2014. We used the fittings of the radial dependence of the scintillation index to calculate g-indices. Based on the g-index value, we identified 17 events that could be associated with strong compression regions in the solar wind. We present the first ICME identifications in our data. We associated 14 IPS events with preceding CME counterparts by employing white-light observations from the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) spacecraft. We found that most of the IPS events, detected during the solar maximum of Cycle 24 were associated with complex CME events. For the IPS events associated with single CME counterparts, we found a deceleration tendency of the CMEs as they propagate in the interplanetary medium. These results show that the instrument detects solar-wind disturbances, and the WT methodology provides solar-wind information with good accuracy. The MEXART observations will complement solar-wind IPS studies using other frequencies, and the tracking of solar-wind disturbances by other stations located at different longitudes.
Screening length and the direction of plasma winds
Makoto Natsuume; Takashi Okamura
We study the screening length of a heavy quark-antiquark pair in strongly coupled gauge theory plasmas flowing at velocity v following a proposal by Liu, Rajagopal, and Wiedemann. We analyze the screening length as the direction of the plasma winds vary. To leading order in v, this angle-dependence can be studied analytically for many theories by extending our previous formalism. We show that the screening length is locally a minimum (maximum) when the pair is perpendicular (parallel) to the plasma winds, which has been observed for the N=4 plasma. Also, we compare AdS/CFT results with weak coupling ones, and we discuss the subleading dependence on v for the Dp-brane.
Optimum windings for linear induction machines.
NASA Technical Reports Server (NTRS)
Elliott, D. G.
The matrix method of calculating linear induction machine performance as a function of winding current distribution was extended to determine the winding current distribution for maximum efficiency. Application of the method to typical magnetohydrodynamic generator geometries showed that electrical efficiencies of 0.5 to 0.6 are possible with fractional wavelength windings and without insulating vanes in the flow.
High-resolution optical spectroscopy of the R Coronae Borealis star V532 Ophiuchi at maximum light
Rao, N Kameswara; Woolf, Vincent M; Hema, B P
High-resolution optical spectra of the R Coronae Borealis (RCB) star V532 Oph at light maximum are discussed. The absolute visual magnitude M_V of the star is found to be -4.9 \\pm 0.5. The elemental abundances suggest the star belongs to the majority class of RCB stars but is among the most O-poor of this class with mild enhancements of heavy elements Y, Zr, Ba and La. The C_2 Swan bands are weak in V532 Oph relative to R CrB. Other aspects of the high-resolution spectrum confirm that V532 Oph is representative of majority RCBs, i.e., the radial velocity is variable, circumstellar material is present and the photosphere feeds a high-velocity stellar wind.
Condition monitoring and fault detection of wind turbines and related algorithms: A review
Z. Hameed; Y. S. Hong; Y. M. Cho; S. H. Ahn; C. K. Song
Renewable energy sources like wind energy are copiously available without any limitation. Wind turbines are used to tap the potential of wind energy, which is available in millions of MW. Reliability of wind turbine is critical to extract this maximum amount of energy from the wind. We reviewed different techniques, methodologies and algorithms developed to monitor the performance of wind
A modification of the method of Carey and Sparks (1986) to estimate eruption column height from maximum clast dispersal
NASA Astrophysics Data System (ADS)
Espindola, J.
The method of Carey and Sparks (1986) has been widely applied to estimate the hight of eruptive columns from the dispersal of the maximum clast size. These authors presented curves of maximum downwind range versus crosswind range for different clast diameters and wind speeds obtained from the numerical solution of a column model developed by Sparks(1986). An improved model of eruptive column was later developed by Woods (1988). In this work we present the results of the simulation of clast dispersal following the procedure of Carey and Sparks (1986) and the eruption column of Woods (1988). The numerical calculations were carried out with a code that computes the height of the column and the vertical velocity, the density and the radius along the column. The code determines then the support envelopes for a given clast size and their fall, after leaving the column, are computed from the equations of motion with viscous friction. For the same downwind and crosswind ranges, this method yields column heights about 10% smaller than the method of Carey and Sparks and about 20% higher wind velocities. The height of the crater above sea level plays also a small role in the results. We present comparisons for the 1982 eruption columns from El Chichon volcano. References Carey S and RSJ Sparks (1986) Bull. Volcanol. 48: 109-125 Sparks RSJ (1986) Bull. Volcanol. 48: 3-15 Woods AW (1988) Bull. Volcanol. 50: 169-193
Daytime lidar measurements of tidal winds in the mesospheric sodium layer at Urbana, Illinois
Kwon, K.H.; Gardner, C.S.; Senft, D.C. (Univ. of Illinois, Urbana-Champaign (United States)); Roesler, F.L.; Harlander, J. (Univ. of Wisconsin, Madison (United States))
The first daytime lidar observations of the mesospheric Na layer at Urbana, Illinois (40{degrees}N, 88{degrees}W), were made in January and March 1986. The data show strong 12-hour oscillations of the Na density and layer centroid height which appear to be caused by the semidiurnal tide. The peak-to-peak variations in column abundance and centroid height were of the order of 100% and 3 km, respectively. The vertical wind velocities were inferred from the temporal variations of the density gradients on the layer topside. The inferred wind amplitudes and vertical wavelengths for the semidiurnal tide were {approximately}30 cm s{sup {minus}1} and {approximately}50 km, respectively. The maximum upward vertical velocity occurs at about 1,100 LST and 2,300 LST.
Multicomponent radiatively driven stellar winds. IV. On the helium decoupling in the wind of sigma Orionis E
J. Krticka; J. Kubßt; D. Groote
We study the possibility of the helium decoupling in the stellar wind of sigma Ori E. To obtain reliable wind parameters for this star we first calculate NLTE wind model and derive wind mass-loss rate and terminal velocity. Using corresponding force multipliers we study the possibility of helium decoupling. We find that helium decoupling is not possible for realistic values
Vertical wind estimation from horizontal wind measurements
NASA Technical Reports Server (NTRS)
Vicroy, Dan D.
The objective of this study was to assess the ability of simple vertical wind models to improve the hazard prediction capability of an airborne Doppler sensor in a realistic microburst environment. The results indicate that in the altitude region of interest (at or below 300 meters), both the linear and empirical vertical wind models improved the hazard estimate. The radar simulation study showed that the magnitude of the performance improvement was altitude dependent. The altitude of maximum performance improvement occurred at about 300 meters. At the lower altitudes the percent improvement was minimized by the diminished contribution of the vertical wind. The vertical hazard estimate errors from flight tests were less than those of the radar simulation study.
Wind noise under a pine tree canopy.
Raspet, Richard; Webster, Jeremy
It is well known that infrasonic wind noise levels are lower for arrays placed in forests and under vegetation than for those in open areas. In this research, the wind noise levels, turbulence spectra, and wind velocity profiles are measured in a pine forest. A prediction of the wind noise spectra from the measured meteorological parameters is developed based on recent research on wind noise above a flat plane. The resulting wind noise spectrum is the sum of the low frequency wind noise generated by the turbulence-shear interaction near and above the tops of the trees and higher frequency wind noise generated by the turbulence-turbulence interaction near the ground within the tree layer. The convection velocity of the low frequency wind noise corresponds to the wind speed above the trees while the measurements showed that the wind noise generated by the turbulence-turbulence interaction is near stationary and is generated by the slow moving turbulence adjacent to the ground. Comparison of the predicted wind noise spectrum with the measured wind noise spectrum shows good agreement for four measurement sets. The prediction can be applied to meteorological estimates to predict the wind noise under other pine forests. PMID:25698000
Fuzzy logic based intelligent control of a variable speed cage machine wind generation system
Simoes, M.G. [Univ. of Sao Paulo (Brazil)] [Univ. of Sao Paulo (Brazil); Bose, B.K. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Electrical Engineering] [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Electrical Engineering; Spiegel, R.J. [Environmental Protection Agency, Research Triangle Park, NC (United States), Air and Energy Engineering Research Lab.] [Environmental Protection Agency, Research Triangle Park, NC (United States), Air and Energy Engineering Research Lab.
The paper describes a variable speed wind generation system where fuzzy logic principles are used for efficiency optimization and performance enhancement control. A squirrel cage induction generator feeds the power to a double-sided pulse width modulated converter system which pumps power to a utility grid or can supply to an autonomous system. The generation system has fuzzy logic control with vector control in the inner loops. A fuzzy controller tracks the generator speed with the wind velocity to extract the maximum power. A second fuzzy controller programs the machine flux for light load efficiency improvement, and a third fuzzy controller gives robust speed control against wind gust and turbine oscillatory torque. The complete control system has been developed, analyzed, and validated by simulation study. Performances have then been evaluated in detail.
On the theory of the horizontal-axis wind turbine
NASA Astrophysics Data System (ADS)
de Vries, O.
The fluid mechanical theory of horizontal axis wind turbines (HAWT) in homogeneous, steady flows is presented. HAWT aerodynamic performance is governed by rotor torque and drag, the angular velocity, and power output, with governing equations for momentum, mass, and energy. The lift force and profile drag acting on the airfoil blades depend on the flow velocity, the chord length, the angle of attack, and the lift and drag coefficients. Single streamtube and multiple-stream tube and angular momentum analyses are employed to quantify the maximum wind turbine performance. Optimization studies for HAWT blades have indicated that a considerable amount of blade twist and taper enhances HAWT performance. Blade-element and vortex theory combined with panel methods are used to study optimum blade shapes. Techniques for assuring that wind tunnel studies of scale models are valid for full scale machines are defined. Sample runs have shown the accuracy of the blade element theory and the inaccuracies of two-dimensional analyses when stall is reached. The acquisition of more aerodynamic data on HAWT performance is indicated.
Benchmarking for maximum value.
Baldwin, Ed
Speaking at the most recent Healthcare Estates conference, Ed Baldwin, of international built asset consultancy EC Harris LLP, examined the role of benchmarking and market-testing--two of the key methods used to evaluate the quality and cost-effectiveness of hard and soft FM services provided under PFI healthcare schemes to ensure they are offering maximum value for money. PMID:19344004
NSDL National Science Digital Library
Kristine DeLong
In this activity for undergraduates, students explore the CLIMAP (Climate: Long-Range Investigation, Mapping and Prediction) model results for differences between the modern and the Last Glacial Maximum (LGM) and discover the how climate and vegetation may have changed in different regions of the Earth based on scientific data.
Honeycutt, R. K. [Astronomy Department, Indiana University, Swain Hall West, Bloomington, IN 47405 (United States); Kafka, S. [Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Broad Branch Road NW, Washington, DC 2001 (United States); Robertson, J. W., E-mail: firstname.lastname@example.com, E-mail: email@example.com, E-mail: firstname.lastname@example.com [Department of Physical Sciences, Arkansas Tech University, 1701 North Boulder Avenue, Russellville, AR 72801-2222 (United States)
Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur frequently in this star. We confirm the results of Ringwald and Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We also commonly find blueshifted emission components in the H{alpha} line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald and Naylor reported common occurrences of redshifted H{alpha} emission components in their BZ Cam spectra. We have attributed these emission components in H{alpha} to occasions when gas concentrations in the bipolar wind (both front side and back side) become manifested as emission lines as they move beyond the disk's outer edge. We also suggest, based on changes in the P-Cygni profiles during an episode, that the progression from larger to smaller expansion velocities is due to the higher velocity portions of a wind concentration moving beyond the edge of the continuum light of the disk first, leaving a net redward shift of the remaining absorption profile. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the He I {lambda}5876 line, finding P = 0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We argue that the radiation-driven wind in BZ Cam receives an initial boost by acting on gas that has been lifted above the disk by the interaction of the accretion stream with the disk, thereby imposing flickering timescales onto the wind events, as well as leading to an orbital modulation of the wind due to the non-axisymmetric nature of the stream/disk interaction. Simultaneous photometry and spectroscopy were acquired on three nights in order to test the possible connection between flickering continuum light and the strength of the front-side wind. We found strong agreement on one night, some agreement on another, and no agreement on the third. We suggest that some flickering events lead to only back-side winds which will not have associated P-Cygni profiles.
Technology Transfer Automated Retrieval System (TEKTRAN)
Wind erosion refers to the detachment, transport and deposition of sediment by wind. It is a dynamic, physical process where loose, dry, bare soils are transported by strong winds. Wind erosion is a soil degrading process that affects over 500 million ha of land worldwide and creates between 500 an...
Tomographic inversion of R sub g wave group velocities for regional near-surface velocity structure
Argun H. Kocaoglu; Leland T. Long
Mapping lateral variations in the lithology of sedimentary basins may be done using the technique of tomographic inversion of the group velocities of R sub g waves. The velocity structure is determined by first using the moving-window maximum entropy spectral analysis to measure the average R sub g wave group travel times. Tomographic inversion is then used to determine the
Question of the Day: Flow of Winds and Moisture
NSDL National Science Digital Library
This activity addresses the flow of surface winds and moisture. On the figure below, draw a)direction of air flow (winds), b) locations with highest evaporation from the sea surface, and zone(s) of maximum ...
A correlative study of simultaneously measured He(++) fluxes in the solar wind and in the magnetosphere utilizing Imp-1 and 1971-089A satellite data
NASA Technical Reports Server (NTRS)
Shelley, E. G.
Simultaneously measured He(++) fluxes in the solar wind and in the magnetosphere were studied using data from the plasma spectrometer on the Imp I satellite and the energetic ion mass spectrometer on the low altitude polar orbiting satellite 1971-89A. A detailed comparison of the He(++) energy spectra measured simultaneously in the solar wind and in the low altitude dayside polar cusp on March 7, 1972 was made. The energy-per-unit-charge range of the energetic ion mass spectrometer on board the polar orbiting satellite was 700 eV to 12 keV. Within this range there was a clear maximum in the He(++) energy spectrum at approximately 1.5 keV/nucleon. There was not a clearly defined maximum in the H(+) spectrum, but the data were consistent with a peak between 0.7 and 1.0 keV/nucleon. Both spectra could be reasonably well fit with a convecting Maxwellian plus a high energy tail; however, the mean velocity for He(++) distribution was significantly greater than that for the H(+) distribution. The simultaneous solar wind measurements showed the mean velocities for both ion species to be approximately 600 km/sec. The discrepancies between the relative velocity distributions in the low altitude cusp and those in the solar wind are consistent with a potential difference of approximately 1.4 kV along their flow direction between the two points of observation.
Maximum windmill efficiency in finite time
NASA Astrophysics Data System (ADS)
Huleihil, Mahmoud
The fraction of the kinetic energy of the wind impinging on the rotor-swept area that a wind turbine can convert to useful power has been shown by Betz in an idealized laminar-flow model to have an upper limit of 16/27 or 59% approximately [I. H. Shames, Mechanics of Fluids, 2nd ed. (McGraw-Hill, New York, 1982), pp. A26-A31]. This figure is known as Betz number. Other studies [A. Rauh and W. Seelret, Appl. Energy 17, 15 (1984)] suggested that this figure should be considered as a guideline. In this paper, a new model is introduced and its efficiency at maximum power output is derived. The derived value is shown to be a function of the Betz number B and given by the formula ?mp=1-?1-B . This value is 36.2%, which agrees well with those of actually operating wind turbines. As a guideline, the wind turbine efficiency can be considered to be within the range of the two numbers of merit, the Betz number and ?mp.
Wind height distribution influence on offshore wind farm feasibility study
NASA Astrophysics Data System (ADS)
Benassai, Guido; Della Morte, Renata; Matarazzo, Antonio; Cozzolino, Luca
The economic feasibility of offshore wind power utilization depends on the favourable wind conditions offshore as compared to sites on land. The higher wind speeds have to compensate the additional cost of offshore developments. However, not only the mean wind speed is different, but the whole flow regime, as can be seen in the vertical wind speed profile. The commonly used models to describe this profile have been developed mainly for land sites, so they have to be verified on the basis of field data. Monin-Obukhov theory is often used for the description of the wind speed profile at a different height with respect to a measurement height. Starting from the former, , the profile is predicted using two parameters, Obukhov length and sea surface roughness. For situations with near-neutral and stable atmospheric stratification and long (>30km) fetch, the wind speed increase with height is larger than what is predicted from Monin-Obukhov theory. It is also found that this deviation occurs at wind speeds important for wind power utilization, mainly at 5-9 ms-1. In the present study the influence of these aspects on the potential site productivity of an offshore wind farm were investigated, namely the deviation from the theory of Monin-Obukhov due to atmospheric stability and the influence of the fetch length on the Charnock model. Both these physical effects were discussed and examined in view of a feasibility study of a site for offshore wind farm in Southern Italy. Available data consisted of time histories of wind speeds and directions collected by National Tidegauge Network (Rete Mareografica Nazionale) at the height of 10m a.s.l. in ports. The theory of Monin-Obukhov was used to extrapolate the data to the height of the wind blades, while the Charnock model was used to extend the wind speed on the sea surface from the friction velocity on the ground. The models described were used to perform calculations for a feasibility study of an offshore wind farm in Southern Italy. The potential site productivity was established on the basis of the wind speed distribution function for different heights (site specific) and the power law of the wind turbine considered, as a function of the wind speed at the nacelle height (machine specific). The results of the optimization study for different sites and different wind turbines were compared with the power estimates of Italian Wind Atlas, which provided useful insights for further study.
NASA Technical Reports Server (NTRS)
Ogilvie, K. W.; Coplan, M. A.
Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.
NASA Astrophysics Data System (ADS)
Sedlmayr, Erwin; Dominik, Carsten
The status of dust driven winds, constituting an important subclass of essentially radiation generated winds, is surveyed. Dust driven winds are conceived as a long lasting phenomenon of heavy mass loss concerning those luminous cool giants and supergiants, where dust condensation in the expanding flow determines both thestellar mass loss rate and thesubsonic-supersonic transition of the velocity field. Our contribution aims at a self-consistent description of the dynamical shell structure with particular emphasis to the theoretical aspects of this important phenomenon. Thus, not only the complex coupling of the various ingredients (hydrodynamics, chemistry, radiative transfer, dust nucleation, and growth) is outlined in detail, but also general arguments regarding the overall structure of such winds and the expected position of their central objects in the Hertzsprung-Russel diagram are conducted. A selected typical self-consistent model for a stationary C-star shell demonstrates the characteristic wind structure and gives insight into the close nonlinear interplay between dust formation and wind generation. During the late evolutionary stages of a star along the AGB dust driven mass loss provides a natural self-accelerating mechanism which easily can produce very high mass loss rates, an effect which possibly might play an important role for the Tip-AGB objects and the AGB-PN-transition.
Winds from T Tauri stars. II - Balmer line profiles for inner disk winds
NASA Technical Reports Server (NTRS)
Calvet, Nuria; Hartmann, Lee; Hewett, Robert
Results are presented of calculations of Balmer emission line profiles using escape probability methods for T Tauri wind models with nonspherically symmetric geometry. The wind is assumed to originate in the inner regions of an accretion disk surrounding the T Tauri star, and flows outward in a 'cone' geometry. Two types of wind models are considered, both with monotonically increasing expansion velocities as a function of radial distance. For flows with large turbulent velocities, such as the HF Alfven wave-driven wind models, the effect of cone geometry is to increase the blue wing emission, and to move the absorption reversal close to line center. Line profiles for a wind model rotating with the same angular velocity as the inner disk are also calculated. The Balmer lines of this model are significantly broader than observed in most objects, suggesting that the observed emission lines do not arise in a region rotating at Keplerian velocity.
W. C. Feldman; J. R. Asbridge; S. J. Bame; M. D. Montgomery; S. P. Gary
Average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented. The measured distributions are generally symmetric about the heat flux direction and are adequately parameterized by the superposition of a nearly bi-Maxwellian function which characterizes the low-energy electrons and a bi-Maxwellian function which characterizes a distinct, ubiquitous component of higher-energy
Maximum range three-dimensional lifting planetary entry
NASA Technical Reports Server (NTRS)
Dickmanns, E. D.
Variational equations for maximum range three-dimensional quasisteady glide are given. Nonlinear oscillatory maximum range trajectories obtained with a refined gradient program are approximated by a superposition of quasisteady glide and linearized perturbation equation results. A basic control law is found which is closely followed for maximum cross-range trajectories. The effect of a reradiative heating constraint involving velocity, altitude and angle of attack on a maximum cross-range trajectory for a space shuttle orbiter-type vehicle reentering the earth's atmosphere is investigated numerically.
RAWS: The spaceborne radar wind sounder
NASA Astrophysics Data System (ADS)
Moore, Richard K.
The concept of the Radar Wind Sounder (RAWS) is discussed. The goals of the RAWS is to estimate the following three qualities: the echo power, to determine rain rate and surface wind velocity; the mean Doppler frequency, to determine the wind velocity in hydrometers; and the spread of the Doppler frequency, to determine the turbulent spread of the wind velocity. Researchers made significant progress during the first year. The feasibility of the concept seems certain. Studies indicate that a reasonably sized system can measure in the presence of ice clouds and dense water clouds. No sensitivity problems exist in rainy environments. More research is needed on the application of the radar to the measurement of rain rates and winds at the sea surface.
RAWS: The spaceborne radar wind sounder
NASA Technical Reports Server (NTRS)
Moore, Richard K.
The concept of the Radar Wind Sounder (RAWS) is discussed. The goals of the RAWS is to estimate the following three qualities: the echo power, to determine rain rate and surface wind velocity; the mean Doppler frequency, to determine the wind velocity in hydrometers; and the spread of the Doppler frequency, to determine the turbulent spread of the wind velocity. Researchers made significant progress during the first year. The feasibility of the concept seems certain. Studies indicate that a reasonably sized system can measure in the presence of ice clouds and dense water clouds. No sensitivity problems exist in rainy environments. More research is needed on the application of the radar to the measurement of rain rates and winds at the sea surface.
Helium, hydrogen, and oxygen velocities observed in ISEE 3
Ogilvie, K.W.; Coplan, M.A.; Zwickl, R.D.
The velocities of helium, oxygen, and hydrogen ions have been recorded over a full range of solar wind conditions by the ion composition instrument (ICI) and Los Alamos National Laboratory plasma instrument (LANLPI), respectively, aboard the ISEE 3 spacecraft between August 1978 and December 1979. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s/sup -1/ the velocity exceeded the hydrogen velocity by 5 km s/sup -1/ on the average. For solar wind velocities between 400 and 500 km s/sup -1/ the average difference was 14 km s/sup -1/; however, no evidence was found for a systematic nonzero average difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Helium-hydrogen velocity differences are generally bounded by the Alfven speed. Velocity differences show abrupt changes across interplanetary discontinuities, persumably tangential. Differences between the speeds of differently charged minor ions appear also to result from the electrostatic potential differences across the interplanetary shocks. The potential difference, calculated from the energy jump condition for a perpendicular hydromagnetic shock, is of the correct magnitude to produce the observed effects.
Using a new characterization of turbulent wind for accurate correlation of wind turbine response with wind speed
Connell, J.R.; George, R.L.
The turbulence encountered by a point on a rotating wind turbine blade has characteristics that in some important respects are different from those measured by a stationary anemometer. The conventional one-peaked continuous spectrum becomes, broadly, a two-peaked spectrum that in addition contains a set of narrow-band spikes of turbulence energy, one centered on the frequency of rotor rotation and the others centered on multiples of that frequency. The rotational sampling effect on wind spectra is quantified using measurements of wind velocity by anemometers on stationary crosswind circular arrays. Characteristics of fluctuating wind are compared to measured fluctuations of bending moments of the rotor blades and power output fluctuations of a horizontal-axis wind turbine at the same site. The wind characteristics and the correlations between wind fluctuations and wind turbine fluctuations provide a basis for improving turbine design, siting, and control. 6 refs., 11 figs., 1 tab.
Wind profiles for Space Shuttle loads analysis
NASA Technical Reports Server (NTRS)
Adelfang, S. I.
The small scale wind velocity perturbations in vertical wind profiles at Cape Kennedy, Florida were analyzed in order to derive information for simulations of space shuttle ascent through the perturbed atmosphere. The available statistical data does not permit specification of various aspects of idealized singularities and wavelike perturbations with a reasonable degree of confidence. The information developed as a result of the analysis described in Section 3 of this report is suitable for the further development of idealized models. The term perturbation is used instead of the more common term, gust. According to the conventional approach, a gust profile is calculated by applying a high pass digital filter to a Jimsphere profile; all the speeds in the filtered profile are defined as gusts. The high pass filtered profile is defined as a residual profile and the maximum residual in the vicinity of a specified reference height is defined as the gust. Gusts defined in this manner represent the perturbation peaks. A detailed discussion of the calculation of residual profiles and gusts is given. The meteorological coordinate system, the data sample, and Jimsphere profiles are also described. Recommendations and conclusions are presented.
NSDL National Science Digital Library
Integrated Teaching and Learning Program,
Students learn about wind energy by making a pinwheel to model a wind turbine. Just like engineers, they decide where and how their turbine works best by testing it in different areas of the playground.
Optimal Velocity Model with Relative Velocity
NASA Astrophysics Data System (ADS)
Sawada, Shiro
The optimal velocity model which depends not only on the headway but also on the relative velocity is analyzed in detail. We investigate the effect of considering the relative velocity based on the linear and nonlinear analysis of the model. The linear stability analysis shows that the improvement in the stability of the traffic flow is obtained by taking into account the relative velocity. From the nonlinear analysis, the relative velocity dependence of the propagating kink solution for traffic jam is obtained. The relation between the headway and the velocity and the fundamental diagram are examined by numerical simulation. We find that the results by the linear and nonlinear analysis of the model are in good agreement with the numerical results.
Sea surface velocities from visible and infrared multispectral atmospheric mapping sensor imagery
NASA Technical Reports Server (NTRS)
Pope, P. A.; Emery, W. J.; Radebaugh, M.
High resolution (100 m), sequential Multispectral Atmospheric Mapping Sensor (MAMS) images were used in a study to calculate advective surface velocities using the Maximum Cross Correlation (MCC) technique. Radiance and brightness temperature gradient magnitude images were formed from visible (0.48 microns) and infrared (11.12 microns) image pairs, respectively, of Chandeleur Sound, which is a shallow body of water northeast of the Mississippi delta, at 145546 GMT and 170701 GMT on 30 Mar. 1989. The gradient magnitude images enhanced the surface water feature boundaries, and a lower cutoff on the gradient magnitudes calculated allowed the undesirable sunglare and backscatter gradients in the visible images, and the water vapor absorption gradients in the infrared images, to be reduced in strength. Requiring high (greater than 0.4) maximum cross correlation coefficients and spatial coherence of the vector field aided in the selection of an optimal template size of 10 x 10 pixels (first image) and search limit of 20 pixels (second image) to use in the MCC technique. Use of these optimum input parameters to the MCC algorithm, and high correlation and spatial coherence filtering of the resulting velocity field from the MCC calculation yielded a clustered velocity distribution over the visible and infrared gradient images. The velocity field calculated from the visible gradient image pair agreed well with a subjective analysis of the motion, but the velocity field from the infrared gradient image pair did not. This was attributed to the changing shapes of the gradient features, their nonuniqueness, and large displacements relative to the mean distance between them. These problems implied a lower repeat time for the imagery was needed in order to improve the velocity field derived from gradient imagery. Suggestions are given for optimizing the repeat time of sequential imagery when using the MCC method for motion studies. Applying the MCC method to the infrared brightness temperature imagery yielded a velocity field which did agree with the subjective analysis of the motion and that derived from the visible gradient imagery. Differences between the visible and infrared derived velocities were 14.9 cm/s in speed and 56.7 degrees in direction. Both of these velocity fields also agreed well with the motion expected from considerations of the ocean bottom topography and wind and tidal forcing in the study area during the 2.175 hour time interval.
The Average Velocity in a Queue
ERIC Educational Resources Information Center
Frette, Vidar
A number of cars drive along a narrow road that does not allow overtaking. Each driver has a certain maximum speed at which he or she will drive if alone on the road. As a result of slower cars ahead, many cars are forced to drive at speeds lower than their maximum ones. The average velocity in the queue offers a non-trivial example of a meanģ
The critical ionization velocity
M. A. Raadu
The critical ionization velocity effect is discussed in the context of space plasmas. This effect occurs for a neutral gas moving through a magnetized plasma and leads to rapid ionization and braking of the relative motion when a certain marginal velocity, the critical velocity, is exceeded. Laboratory experiments clearly establish the significance of the critical velocity and provide evidence for
Introduction to maximum entropy
Sivia, D.S.
The maximum entropy (MaxEnt) principle has been successfully used in image reconstruction in a wide variety of fields. We review the need for such methods in data analysis and show, by use of a very simple example, why MaxEnt is to be preferred over other regularizing functions. This leads to a more general interpretation of the MaxEnt method, and its use is illustrated with several different examples. Practical difficulties with non-linear problems still remain, this being highlighted by the notorious phase problem in crystallography. We conclude with an example from neutron scattering, using data from a filter difference spectrometer to contrast MaxEnt with a conventional deconvolution. 12 refs., 8 figs., 1 tab.
Tangler, James L. (Boulder, CO); Somers, Dan M. (State College, PA)
Airfoils for the blade of a wind turbine wherein each airfoil is characterized by a thickness in a range from 16%-24% and a maximum lift coefficient designed to be largely insensitive to roughness effects. The airfoils include a family of airfoils for a blade 15 to 25 meters in length, a family of airfoils for a blade 1 to 5 meters in length, and a family of airfoils for a blade 5 to 10 meters in length.
NSDL National Science Digital Library
The Advanced Technology Environmental and Energy Center (ATEEC) provides this presentation on the career and technical aspects of wind energy. In addition to discussing careers in wind, the presentation covers the siting of wind turbines and some electricity basics. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.
Evidence for mass loss at moderate to high velocity in Be stars
NASA Technical Reports Server (NTRS)
Snow, T. P., Jr.; Marlborough, J. M.
Ultraviolet spectra of intermediate resolution have been obtained with Copernicus for 12 objects classified as Be or shell stars and for 19 additional early B dwarfs. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si IV doublet at 1400 A, indicating the presence in some cases of outflowing material with maximum velocities of nearly 1000 km/s. Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5; the only objects later than B0.5 which show this effect are Be or shell stars. Among the stars considered, there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the ultraviolet flux from B1-B2 dwarfs is sufficient to drive high-velocity stellar winds only if rotational effects reduce the effective gravity near the equator. The mass-loss rate for one of the most active Be stars, 59 Cyg, is crudely estimated to be one billionth or one ten-billionth of a solar mass per year. The data suggest that the extended atmospheres associated with Be-star phenomena may be formed by mass ejection.
Outer electron radiation belt evolution during weak high-speed solar-wind streams (HSSs): Density, temperature, and flux
NASA Astrophysics Data System (ADS)
Denton, M. H.; Borovsky, J. E.
Electrons in the Earth's outer radiation belt are known to correlate strongly with the duration of elevated solar wind velocity. During the recent solar minimum the outer radiation belt was repeatedly enhanced following the arrival of a number of high-speed solar-wind streams (HSSs) at the magnetopause. These events were particularly 'weak' in comparison to HSSs during the earlier declining phase - the streams were of shorter duration, with lower maximum wind speeds. We present a superposed epoch study of 15 weak HSS-driven storms and examine the evolution of the outer radiation belt and the plasma sheet before, during, and after the storm onset. Our results indicate that the flux, density, and temperature of the outer electron radiation belt all increased to levels equal or in excess of those during earlier 'stronger' HSSs. We discuss possible reasons for this in terms of the system-response to HSSs.
Fuzzy logic based intelligent control of a variable speed cage machine wind generation system. Report for January 1994-June 1995
Simoes, M.G.; Bose, B.K.; Spiegel, R.J.
The paper describes a variable speed wind generation system where fuzzy logic principles are used for efficiency optimization and performance enhancement control. A squirrel cage induction generator feeds the power to a double-sided pulse width modulated converter system which pumps power to a utility grid or can supply to an autonomous system. The generation system has fuzzy logic control with vector control in the inner loops. A fuzzy controller tracks the generator speed with the wind velocity to extract the maximum power. A second fuzzy controller programs the machine flux for light load efficiency improvement, and third fuzzy controller gives robust speed control against wind gust and turbine oscillatory torque. The complete control system has been developed, analyzed, validated by simulation study, and then performances have been evaluated in detail.
High-velocity regions in planetary nebulae
Krzysztof Gesicki; Albert A. Zijlstra
The internal velocity fields of planetary nebulae are studied with a resolution of 5 km s$^{-1}$. We analyze deep echelle spectra from three nebulae in the Bulge, the Sagittarius Dwarf and the SMC. No effects of metallicity is seen, except possibly a slower onset of the fast wind from the central star. Robust evidence is found for the existence of a high-velocity shock at the inner edges of the nebulae. Such a shock is predicted in hydrodynamical models but had not previously been observed. The shock gas is accelerated by the fast wind from the central star. A similar shock at the outer edges traces the expansion of the ionized shell into the ambient AGB wind. Evidence for localized regions of high velocity is also found from lines of intermediate excitation, for two of nebulae. We explore several possible interpretations: (1) an embedded shock at intermediate radii, as predicted by hydrodynamic models at the position of the outer edge of the swept-up inner shell; (2) deviations form spherical symmetry, where in some directions the intermediate-excitation lines extend into the region of the outer shock; (3) An intermediate swept-up shell, as seen in some Galactic planetary nebulae. The remaining nebula, with a [WC] star, shows strong turbulence. This may trace a superposition of many embedded shock-lets. We suggest a relation to the time-variable [WC] wind, giving a planetary nebula subjected to a multitude of sound waves.
Wind-Blown Sand: Threshold of MotionĀ
Swann, Christy Michelle
The fluid threshold for wind-blown sand is the minimum shear velocity required to initiate grain movement by the force of the wind alone, and is used to predict dust emission and landform change in sandy environments. R.A. ...
Shipment and storage effects on the terminal velocity of seeds
Katherine M. Marchetto; Eelke Jongejans; Matthew L. Jennis; Emily M. Haner; Caitlin T. Sullivan; Dave Kelly; Katriona Shea
Mechanistic models of seed dispersal by wind include terminal velocity as the main seed characteristic that influences the\\u000a dispersal process and hence the resulting dispersal kernels and spread rates. Accurate measurement of the terminal velocity\\u000a of seeds is therefore pivotal. However, compression during shipment through the post or during storage between collection\\u000a in the field and terminal velocity measurements in
A Windmill's Theoretical Maximum Extraction of Power from the Wind.
ERIC Educational Resources Information Center
Inglis, David Rittenhouse
Explains that the efficiency and the useful power available from a windmill turbine, of a laminar-flow model, will vary due to rotational kinetic energy of the downwind stream and turbulent mixing from outside the boundaries of the idealized stream. (GA)
Aeroacoustic noise measurements in wind tunnel
H. N. Alemdaroglu
The paper describes the general characteristics of the lowspeed Acoustic Research Wind Tunnel constructed in the Aerodynamics Laboratory of E.N.S.M.A (poitiers\\/France) and presents the results of the preliminary experiments conducted in this wind tunnel. The wind tunnel is of open test section, open circuit and blower type. It has a test section of 30x30 sq cm and a mean velocity
Minimum maximum temperature gradient coil design.
While, Peter T; Poole, Michael S; Forbes, Larry K; Crozier, Stuart
Ohmic heating is a serious problem in gradient coil operation. A method is presented for redesigning cylindrical gradient coils to operate at minimum peak temperature, while maintaining field homogeneity and coil performance. To generate these minimaxT coil windings, an existing analytic method for simulating the spatial temperature distribution of single layer gradient coils is combined with a minimax optimization routine based on sequential quadratic programming. Simulations are provided for symmetric and asymmetric gradient coils that show considerable improvements in reducing maximum temperature over existing methods. The winding patterns of the minimaxT coils were found to be heavily dependent on the assumed thermal material properties and generally display an interesting "fish-eye" spreading of windings in the dense regions of the coil. Small prototype coils were constructed and tested for experimental validation and these demonstrate that with a reasonable estimate of material properties, thermal performance can be improved considerably with negligible change to the field error or standard figures of merit. PMID:23042696
Modeling and controller design of a wind energy conversion system including a matrix converter
NASA Astrophysics Data System (ADS)
Barakati, S. Masoud
In this thesis, a grid-connected wind-energy converter system including a matrix converter is proposed. The matrix converter, as a power electronic converter, is used to interface the induction generator with the grid and control the wind turbine shaft speed. At a given wind velocity, the mechanical power available from a wind turbine is a function of its shaft speed. Through the matrix converter, the terminal voltage and frequency of the induction generator is controlled, based on a constant V/f strategy, to adjust the turbine shaft speed and accordingly, control the active power injected into the grid to track maximum power for all wind velocities. The power factor at the interface with the grid is also controlled by the matrix converter to either ensure purely active power injection into the grid for optimal utilization of the installed wind turbine capacity or assist in regulation of voltage at the point of connection. Furthermore, the reactive power requirements of the induction generator are satisfied by the matrix converter to avoid use of self-excitation capacitors. The thesis addresses two dynamic models: a comprehensive dynamic model for a matrix converter and an overall dynamical model for the proposed wind turbine system. The developed matrix converter dynamic model is valid for both steady-state and transient analyses, and includes all required functions, i.e., control of the output voltage, output frequency, and input displacement power factor. The model is in the qdo reference frame for the matrix converter input and output voltage and current fundamental components. The validity of this model is confirmed by comparing the results obtained from the developed model and a simplified fundamental-frequency equivalent circuit-based model. In developing the overall dynamic model of the proposed wind turbine system, individual models of the mechanical aerodynamic conversion, drive train, matrix converter, and squirrel-cage induction generator are developed and combined to enable steady-state and transient simulations of the overall system. In addition, the constraint constant V/f strategy is included in the final dynamic model. The model is intended to be useful for controller design purposes. The dynamic behavior of the model is investigated by simulating the response of the overall model to step changes in selected input variables. Moreover, a linearized model of the system is developed at a typical operating point, and stability, controllability, and observability of the system are investigated. Two control design methods are adopted for the design of the closed-loop controller: a state-feedback controller and an output feedback controller. The state-feedback controller is designed based on the Linear Quadratic method. An observer block is used to estimate the states in the state-feedback controller. Two other controllers based on transfer-function techniques and output feedback are developed for the wind turbine system. Finally, a maximum power point tracking method, referred to as mechanical speed-sensorless power signal feedback, is developed for the wind turbine system under study to control the matrix converter control variables in order to capture the maximum wind energy without measuring the wind velocity or the turbine shaft speed.
Erratum: ``An Extensive Collection of Stellar Wind X-Ray Source Region Emission Line Parameters, Temperatures, Velocities, and Their Radial Distributions as Obtained from Chandra Observations of 17 OB Stars'' (ApJ, 668, 456 [2007])
W. L. Waldron; J. P. Cassinelli
The major objective of the paper was to provide a detailed tabulation of the observed HETGS X-ray emission-line flux ratios. We presented the MEG and HEG He-like f\\/i line ratios, the H-like to He-like (H\\/He) line ratios, and the He-like G-ratios. The stellar wind spatial locations of the X-ray sources were derived from the f\\/i ratios, and their associated X-ray
Towers for Offshore Wind Turbines
NASA Astrophysics Data System (ADS)
Kurian, V. J.; Narayanan, S. P.; Ganapathy, C.
Increasing energy demand coupled with pollution free production of energy has found a viable solution in wind energy. Land based windmills have been utilized for power generation for more than two thousand years. In modern times wind generated power has become popular in many countries. Offshore wind turbines are being used in a number of countries to tap the energy from wind over the oceans and convert to electric energy. The advantages of offshore wind turbines as compared to land are that offshore winds flow at higher speed than onshore winds and the more available space. In some land based settings, for better efficiency, turbines are separated as much as 10 rotor diameters from each other. In offshore applications where only two wind directions are likely to predominate, the distances between the turbines arranged in a line can be shortened to as little as two or four rotor diameters. Today, more than a dozen offshore European wind facilities with turbine ratings of 450 kw to 3.6 MW exist offshore in very shallow waters of 5 to 12 m. Compared to onshore wind turbines, offshore wind turbines are bigger and the tower height in offshore are in the range of 60 to 80 m. The water depths in oceans where offshore turbines can be located are within 30 m. However as the distance from land increases, the costs of building and maintaining the turbines and transmitting the power back to shore also increase sharply. The objective of this paper is to review the parameters of design for the maximum efficiency of offshore wind turbines and to develop types offshore towers to support the wind turbines. The methodology of design of offshore towers to support the wind turbine would be given and the environmental loads for the design of the towers would be calculated for specific cases. The marine corrosion on the towers and the methods to control the corrosion also would be briefly presented. As the wind speeds tend to increase with distance from the shore, turbines build father offshore will be able to capture more wind energy. Currently two types of towers are considered. Cylindrical tubular structures and truss type structures. But truss type structures have less weight and flexibility in design. The construction of the offshore towers to harness the wind energy is also presented. The results will include the calculation of wind and wave forces on the tower and the design details for the tower.
Calculations of the cosmic ray modulation in interplanetary space taking into account the possible dependence of the transport travel for the scattering of the particles and of the velocity of the solar winds on the angles they make with the helioequator plane: The case of isotropic diffusion
NASA Technical Reports Server (NTRS)
Dorman, L. I.; Kobilinski, Z.
The modulation of galactic cosmic rays is studied by the magnetic heterogeneities stream on the assumption that the diffusion coefficient is reduced whereas the solar wind velocity is increased with the growth of the angle between the sun's rotation axis and the direction of solar plasma motion. The stationary plane problem of isotropic diffusion is solved as it applies to two cases: (1) with due account of particle retardation by the antiphermium mechanism; and (2) without an account of the above mechanism. This problem is solved by the grid method in the polar coordinate system. The results of the calculations are followed by a discussion of the method of solution and of the errors.
Smoothing effects of distributed wind turbines. Part 1. Coherence and smoothing effects at a wind farm
NASA Astrophysics Data System (ADS)
Nanahara, Toshiya; Asari, Masahiro; Sato, Takamitsu; Yamaguchi, Koji; Shibata, Masaaki; Maejima, Tsutomu
Recently there has been a marked increase in wind power generation. From a power system point of view, because a wind turbine is an intermittent generator with large output fluctuation, any increase in the number of wind turbines gives rise to concerns about the adverse effects of wind turbines on power quality. The smoothing effects of wind turbine output fluctuation are of great importance in assessing the impacts of a large number of wind turbines. This article examines smoothing effects at a wind farm. First it presents a summary of wind measurements taken at two locations with six masts over a period of 1 year on both flat and complex terrain. Then the spatial coherence of wind speed is analysed, paying special attention to its dependence on the distance between observation points, wind direction, wind velocity and fluctuation frequency. Approximation equations for coherence of frequency and distance are obtained by applying Davenport's expression to the observed data. Second, coherence between turbine output at a wind farm is investigated; the results indicate that coherence for wind speed and turbine output shows a considerable resemblance. The article also examines smoothing effects at a wind farm using power spectral density through a theoretical approach. The study proves that smoothing effects can be approximated with a lowpass filter and that the effects at a wind farm should not be taken into account for periods of more than 10 min in case of assessing them on the safe side. Copyright
Design and Power characterization of a novel Vertical Axis Wind Energy Conversion system (VAWECS)
Terrence Sankar; Murat Tiryakiolu
The power output characteristics of a novel vertical axis wind turbine system were investigated via computational fluid dynamics. The system was tested at seven wind velocities. Results showed that the efficiency of the new system increases with increasing wind velocities up to approximately 30 m\\/s, after which the efficiency remains constant at 0.45. Moreover it was found that system reacts
A short physical note on a new wind power formulation
Zekai ?en
Classical wind energy formulation is based on the kinetic energy definition whereby the mass is considered as a constant. Consequently, the wind energy is obtained as directly related to half (1\\/2) of the specific mass multiplied by the cube of wind velocity. The new approach in this note is based first on the basic definition of force and then energy
Theory of Winds from Hot, Luminous Massive Stars
Stan Owocki
The high luminosities of massive stars drive strong stellar winds, through line scattering of the star's continuum radiation. This paper reviews the dynamics of such line driving, building first upon the standard CAK model for steady winds, and deriving the associated analytic scalings for the mass loss rate and wind velocity law. It next summarizes the origin and nature of
Constraints on Deep-seated Zonal Winds Inside Jupiter and Saturn
Junjun Liu; Peter Goldreich; David Stevenson
The atmospheres of Jupiter and Saturn exhibit strong and stable zonal winds. How deep the winds penetrate unabated into each planet is unknown. Our investigation favors shallow winds. It consists of two parts. The first part makes use of an Ohmic constraint; Ohmic dissipation associated with the planet's magnetic field cannot exceed the planet's net luminosity. Application to Jupiter (J) and Saturn (S) shows that the observed zonal winds cannot penetrate below a depth at which the electrical conductivity is about six orders of magnitude smaller than its value at the molecular-metallic transition. Measured values of the electrical conductivity of molecular hydrogen yield radii of maximum penetration of 0.96R_J and 0.86R_S, with uncertainties of a few percent of R. At these radii, the magnetic Reynolds number based on the zonal wind velocity and the scale height of the magnetic diffusivity is of order unity. These limits are insensitive to difficulties in modeling turbulent convection. They permit complete penetration along cylinders of the equatorial jets observed in the atmospheres of Jupiter and Saturn. The second part investigates how deep the observed zonal winds actually do penetrate. Truncation of the winds in the planet's convective envelope would involve breaking the Taylor-Proudman constraint on cylindrical flow. This would require a suitable nonpotential acceleration which none of the obvious candidates appears able to provide. Accelerations arising from entropy gradients, magnetic stresses, and Reynolds stresses appear to be much too weak. These considerations suggest that strong zonal winds are confined to shallow, stably stratified layers, with equatorial jets being the possible exception.
A new analytical model for wind farm power prediction
NASA Astrophysics Data System (ADS)
Niayifar, Amin; Porte-Agel, Fernando
In this study, a new analytical approach is presented and validated to predict wind farm power production. The new model assumes a Gaussian distribution for the velocity deficit in the wake which has been recently proposed by Bastankhah and Portķ-Agel (2014). To estimate the velocity deficit in the wake, this model needs the local wake growth rate parameter which is calculated based on the local turbulence intensity in the wind farm. The interaction of the wakes is modeled by use of the velocity deficit superposition principle. Finally, the power curve is used to estimate the power production from the wind turbines. The wind farm model is compared to large-eddy simulation (LES) data of Horns Rev wind farm for a wide range of wind directions. Reasonable agreement between the proposed analytical model and LES data is obtained. This prediction is substantially better than the one obtained with common wind farm softwares such as WAsP.
Physics-based tests to identify the accuracy of solar wind ion measurements: A case study with the Wind Faraday Cups
Richardson, John
with the Wind Faraday Cups J. C. Kasper,1 A. J. Lazarus,1 J. T. Steinberg,2 K. W. Ogilvie,3 and A. Szabo3 Experiment Faraday Cup instruments on the Wind spacecraft are used as a case study. The accuracy of velocity to identify the accuracy of solar wind ion measurements: A case study with the Wind Faraday Cups, J. Geophys
Wind generator system for microwave radio relay station
Yamamura, H.; Eguchi, N.
NTT has introduced a wind generator system at microwave relay stations. It consists of a wind turbine generator as main power source and three diesel driven generators as back up. The wind turbine generator adopts a Darrieus unit as the wind driven blades and generates 8 kW maximum power with strong winds blowing over 15 m/s. Before this introduction, NTT manufactured two different wind turbine generator prototypes, one using a propeller and the other a Darrieus unit, and field tests have been carried out since 1978. This paper describes the field tests and the wind generator system for microwave relay stations.
Wind Resource Assessment in Complex Terrain with a High-Resolution Numerical Weather Prediction Model
NASA Astrophysics Data System (ADS)
Gruber, Karin; Serafin, Stefano; GrubiÜi?, Vanda; Dorninger, Manfred; Zauner, Rudolf; Fink, Martin
A crucial step in planning new wind farms is the estimation of the amount of wind energy that can be harvested in possible target sites. Wind resource assessment traditionally entails deployment of masts equipped for wind speed measurements at several heights for a reasonably long period of time. Simplified linear models of atmospheric flow are then used for a spatial extrapolation of point measurements to a wide area. While linear models have been successfully applied in the wind resource assessment in plains and offshore, their reliability in complex terrain is generally poor. This represents a major limitation to wind resource assessment in Austria, where high-altitude locations are being considered for new plant sites, given the higher frequency of sustained winds at such sites. The limitations of linear models stem from two key assumptions in their formulation, the neutral stratification and attached boundary-layer flow, both of which often break down in complex terrain. Consequently, an accurate modeling of near-surface flow over mountains requires the adoption of a NWP model with high horizontal and vertical resolution. This study explores the wind potential of a site in Styria in the North-Eastern Alps. The WRF model is used for simulations with a maximum horizontal resolution of 800 m. Three nested computational domains are defined, with the innermost one encompassing a stretch of the relatively broad Enns Valley, flanked by the main crest of the Alps in the south and the N÷rdliche Kalkalpen of similar height in the north. In addition to the simulation results, we use data from fourteen 10-m wind measurement sites (of which 7 are located within valleys and 5 near mountain tops) and from 2 masts with anemometers at several heights (at hillside locations) in an area of 1600 km2 around the target site. The potential for wind energy production is assessed using the mean wind speed and turbulence intensity at hub height. The capacity factor is also evaluated, considering the frequency of wind speed between cut-in and cut-out speed and of winds with a low vertical velocity component only. Wind turbines do not turn on at wind speeds below cut-in speed. Wind turbines are taken off from the generator in the case of wind speeds higher than cut-out speed and inclination angles of the wind vector greater than 8o. All of these parameters were computed at each model grid point in the innermost domain in order to map their spatial variability. The results show that in complex terrain the annual mean wind speed at hub height is not sufficient to predict the capacity factor of a turbine; vertical wind speed and the frequency of horizontal wind speed out of the range of cut-in and cut-out speed contribute substantially to a reduction of the energy harvest and locally high turbulence may considerably raise the building costs.
An Extensive Collection of Stellar Wind X-ray Source Region Emission Line Parameters,Temperatures, Velocities, and Their Radial Distributions as Obtained from Chandra Observations of 17 OB Stars
Wayne L. Waldron; Joseph P. Cassinelli
Chandra high energy resolution observations have now been obtained from numerous non-peculiar O and early B stars. The observed X-ray emission line properties differ from pre-launch predictions, and the interpretations are still problematic. We present a straightforward analysis of a broad collection of OB stellar line profile data to search for morphological trends. X-ray line emission parameters and the spatial distributions of derived quantities are examined with respect to luminosity class. The X-ray source locations and their corresponding temperatures are extracted by using the He-like f/i line ratios and the H-like to He-like line ratios respectively. Our luminosity class study reveals line widths increasing with luminosity. Although the majority of the OB emission lines are found to be symmetric, with little central line displacement, there is evidence for small, but finite, blue-ward line-shifts that also increase with luminosity. The spatial X-ray temperature distributions indicate that the highest temperatures occur near the star and steadily decrease outward. This trend is most pronounced in the OB supergiants. For the lower density wind stars, both high and low X-ray source temperatures exist near the star. However, we find no evidence of any high temperature X-ray emission in the outer wind regions for any OB star. Since the temperature distributions are counter to basic shock model predictions, we call this the "near-star high-ion problem" for OB stars. By invoking the traditional OB stellar mass loss rates, we find a good correlation between the fir-inferred radii and their associated X-ray continuum optical depth unity radii. We conclude by presenting some possible explanations to the X-ray source problems that have been revealed by this study.
Sea surface wind stress in stratified atmospheric flow
Myrhaug, D. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Marine Hydrodynamics; Slaattelid, O.H. [Norwegian Marine Technology Research Inst., Trondheim (Norway)
The paper presents the wind shear stress on the sea surface as well as the velocity profile in stably stratified atmospheric boundary layer flow over wind waves by using similarity theory. For a given geostrophic velocity, Coriolis parameter, spectral peak period and stratification parameter the sea surface shear stress is determined. Further, the direction of the sea surface shear stress and the velocity profile are given. Parameterizations of the results are also presented. Finally, the engineering relevance of the results is discussed.
Shearing wind helicity and thermal wind helicity
NASA Astrophysics Data System (ADS)
Han, Y.; Wu, R. S.; Fang, J.
Helicity is defined as H = V . omega, where V and omega are the velocity and vorticity vectors, respectively. Many works have pointed out that the larger the helicity is, the longer the life cycle of the weather system is. However, the direct relationship of the helicity to the evolution of the weather system is not quite clear. In this paper, the concept of helicity is generalized as shearing wind helicity (SWH). Dynamically, it is found that the average SWH is directly related to the increase of the average cyclonic rotation of the weather system. Physically, it is also pointed out that the SWH, as a matter of fact, is the sum of the torsion terms and the divergence term in the vorticity equation. Thermal wind helicity (TWH), as a derivative of SWH, is also discussed here because it links the temperature field and the vertical wind field. These two quantities may be effective for diagnosing a weather system. This paper applies these two quantities in cylindrical coordinates to study the development of Hurricane Andrew to validate their practical use. Through analyzing the hurricane, it is found that TWH can well describe the characteristics of the hurricane such as the strong convection and release of latent heat. SWH is not only a good quantity for diagnosing the weather system, but also an effective one for diagnosing the development of the hurricane.
Yeoman, D.R.
A wind turbine is described comprising: a vertical axis rotor assembly coupled to a rotatable drive shaft for driving electrical power generating means; first wind deflector means mounted on the wind turbine normally positioned generally upwind and to one side of the rotor assembly for initially deflecting wind current into the rotor assembly and second wind deflector means mounted on the wind turbine normally positioned on another side of the rotor assembly to redirect the initially deflected wind current into the rotor assembly. The first and second wind deflector means are normally spaced from each other by a certain inter-deflector spacing; mounting means for mounting the first and second wind deflector means in the normal positions, the mounting means including an outer shaft through which the drive shaft extends and which is normally fixed with respect thereto. The outer shaft has an upwardly facing circumferentially extending shoulder formed therein including a first shoulder portion extending around a major portion of the circumference of the outer shaft and a pair of upwardly sloping portions which reet at an apex.
Spall velocity measurements from laboratory impact craters
NASA Technical Reports Server (NTRS)
Polanskey, Carol A.; Ahrens, Thomas J.
Spall velocities were measured for a series of impacts into San Marcos gabbro. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles varied in material and size with a maximum mass of 4g for a lead bullet to a minimum of 0.04 g for an aluminum sphere. The spall velocities were calculated both from measurements taken from films of the events and from estimates based on range measurements of the spall fragments. The maximum spall velocity observed was 27 m/sec, or 0.5 percent of the impact velocity. The measured spall velocities were within the range predicted by the Melosh (1984) spallation model for the given experimental parameters. The compatability between the Melosh model for large planetary impacts and the results of these small scale experiments is considered in detail. The targets were also bisected to observe the internal fractures. A series of fractures were observed whose location coincided with the boundary of the theoretical near surface zone predicted by Melosh. Above this boundary the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
Z-source inverter based wind power generation system
U. Supatti; F. Z. Peng
This paper presents a wind turbine generation system based on the Z-source inverter with maximum boost control. The proposed system can boost and generate the desired output voltage efficiently when the low voltage of the generator is introduced according to the low wind speed. Moreover, when the wind speed is high, providing higher voltage, the system can also work like
Estimating Hurricane Wind Structure in the Absence of Aircraft Reconnaissance
James P. Kossin; John A. Knaff; Howard I. Berger; Derrick C. Herndon; Thomas A. Cram; Christopher S. Velden; Richard J. Murnane; Jeffrey D. Hawkins
New objective methods are introduced that use readily available data to estimate various aspects of the two-dimensional surface wind field structure in hurricanes. The methods correlate a variety of wind field metrics to combinations of storm intensity, storm position, storm age, and information derived from geo- stationary satellite infrared (IR) imagery. The first method estimates the radius of maximum wind
Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission
NASA Astrophysics Data System (ADS)
Zoennchen, J. H.; Nass, U.; Fahr, H. J.
Circumterrestrial Lyman-? column brightness observations above 3 Earth radii (Re) have been used to derive separate 3-D neutral hydrogen density models of the Earth's exosphere for solar minimum (2008, 2010) and near-solar-maximum (2012) conditions. The data used were measured by Lyman-? detectors (LAD1/2) onboard each of the TWINS satellites from very different orbital positions with respect to the exosphere. Exospheric H atoms resonantly scatter the near-line-center solar Lyman-? flux at 121.6 nm. Assuming optically thin conditions above 3Re along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H-column density. We found significant differences in the density distribution of the terrestrial exosphere under different solar conditions. Under solar maximum conditions we found higher H densities and a larger spatial extension compared to solar minimum. After a continuous, 2-month decrease in (27 day averaged) solar activity, significantly lower densities were found. Differences in shape and orientation of the exosphere under different solar conditions exist. Above 3 Re, independent of solar activity, increased H densities appear on the Earth's nightside shifted towards dawn. With increasing distance (as measured at 8Re) this feature is shifted westward/duskward by between -4 and -5░ with respect to midnight. Thus, at larger geocentric distance the exosphere seems to be aligned with the aberrated Earth-solar-wind line, defined by the solar wind velocity and the orbital velocity of the Earth. The results presented in this paper are valid for geocentric distances between 3 and 8Re.
Methodology for reconstructing wind direction, wind speed and duration of wind events from aeolian cross-strata
NASA Astrophysics Data System (ADS)
Eastwood, Erin N.; Kocurek, Gary; Mohrig, David; Swanson, Travis
A methodology for reconstructing wind direction, speed, and event duration from aeolian dune cross-strata was developed from analysis of crescentic dunes at White Sands, New Mexico, during wind events. Dune lee faces were surveyed, lee-face deposits mapped, deposition rates measured, grain size sampled by stratification type, and winds characterized from meteorological and field data. The spatial distribution of lee-face stratification styles is a function of the incidence angle formed between the wind and the brinkline, with secondary controls by wind speed and dune sinuosity and height. Sets of wind-ripple strata form at incidence angles of 25░-40░, grainfall/grainflow foresets over wind-ripple bottomsets at 40░-70░, and grainflow/grainfall foresets at 70░-90░. Erosional reactivation surfaces form at incidence angles up to 15░; bypass surfaces up to 25░. The total sediment load is fractionated within lee-face stratification types. Wind speed can be reconstructed from relationships between grain size, transport mode, shear velocity and grain-settling velocity. Where the full range of grain transport modes occurs and grain size is limited by shear stress, the shear velocity and grain-size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep, and the coarse fraction in grainfall traveled in saltation. The minimum duration of a wind event can be estimated using measures of shear velocity, dune height and dune forward migration. Method limitations arise with source-area control on grain size, extremes in wind events, and severe truncation of sets of cross-strata.
Karen L. Masters
We only see a small fraction of the matter in the universe, but the rest gives itself away by the impact of its gravity. The distortions from pure Hubble flow (or peculiar velocities) that this matter creates have the potential to be a powerful cosmological tool, but are also a nuisance for extragalactic astronomers who wish to use redshifts to estimate distances to local galaxies. We provide a quick overview of work on the local peculiar velocity field, discussing both simple spherical infall models, non-parametric modeling using redshifts surveys, and full velocity and density field reconstruction from peculiar velocities. We discuss results from a multiattractor model fit to data from the SFI++ sample of peculiar velocities - the best peculiar velocity data currently available. We also talk about the future of samples for the study of the local velocity field, especially the 2MASS Tully-Fisher (2MTF) survey.
Performance of a low cost cross-wind-axis sail-wind turbine
G. Ahmadi
The performance of a model of a cross-wind axis sail rotor is investigated. Several sail blade types, with high and low chamber, are employed and the effects of wind velocity, blade pitch angles, and external load on the efficiency of the rotor are studied. It is concluded that though the efficiency of the present model is quite low, the rotor
Reexamination of Tropical Cyclone Wind¢Pressure Relationships
John A. Knaff; Raymond M. Zehr
Tropical cyclone wind-pressure relationships are reexamined using 15 yr of minimum sea level pressure estimates, numerical analysis fields, and best-track intensities. Minimum sea level pressure is estimated from aircraft reconnaissance or measured from dropwindsondes, and maximum wind speeds are interpolated from best-track maximum 1-min wind speed estimates. The aircraft data were collected primarily in the Atlantic but also include eastern
Comparison of Multiple Receiver Techniques for Estimating Horizontal Winds.
NASA Astrophysics Data System (ADS)
Chang, John Yun-Ching
The spaced antenna (SA) and the Doppler beam swinging (DBS) techniques for radar horizontal wind measurements are compared by using three different data sets, the first one from February 22 to 26, 1990, the second one from January 30 to 31, 1992, and the third one from April 27 to May 4, 1992, collected with the MU radar in Japan. The results are also compared with the corresponding rawinsonde data which were collected from four nearby stations, Hamamatsu, Shionomisaki, Wajima, and Yonago. Those data have been chosen to investigate the horizontal wind estimates. In addition to covering a long period, the data set has the advantage that it includes a range of meteorological conditions. It includes periods of warm/cold frontal passages and periods with and without precipitation. The wind velocities estimated with the vertical or oblique SA measurement technique include three different analysis techniques, the Briggs, Fooks and Meek methods. The triangle size effect is discussed. It is shown that the meridional and zonal components of the true velocity determined by the full correlation analysis are affected significantly by the triangle size and especially the shape, and by the direction between the wind velocity and the baselines of the triangle. The apparent velocities are not affected. The true wind velocity estimates are always underestimated due to these factors. The possible biases of the DBS horizontal wind estimates, due to horizontal gradients in the vertical velocities, are also discussed. They depend on the zenith angle of the beam position and the gradient of zonal or meridional wind velocities obtained from the zenith, 10 ^circ, and 20^ circ beams, in this case. Generally, the biases are approximately 1 ms^{-1} below 10 km but variable above 10 km. Therefore, the biases do not cause a serious problem in the upper tropospheric and lower stratospheric wind estimates. In general, the SA apparent velocity appears to provide the best estimate of the wind velocities, indicating that the true velocity is overcorrected.
Danson, D.P.
This patent describes a wind driven turbine of the vertical axis type comprising: (a) a support base; (b) a generally vertical column rotatably mounted to the support base; (c) upper and lower support means respectively mounted on the column for rotation therewith; wind driven blades connected between the upper and lower support means for rotation about the column and each blade being individually rotatable about a blade axis extending longitudinally through the blade to vary a blade angle of attach thereof relative to wind velocity during rotation about the column; and (e) control means for variably adjusting angles of attack of each blade to incident wind, the control means including a connecting rod means having drive means for rotating each blade about the associated blade axis in response to radial movement of the connecting rod means and control shaft pivotally mounted within the column and having a first shaft portion connected to the connecting rod means and a second shaft portion radially offset from the first shaft portion and pivotally connected to radially displace the first portion and thereby the connecting rod means to vary the blade angles of attack during rotation about the column.
Wind-driven circulation in Titan's seas
NASA Astrophysics Data System (ADS)
Tokano, Tetsuya; Lorenz, Ralph D.
Circulation in Titan's seas forced by wind is simulated by an ocean circulation model using surface wind data predicted by a global circulation model. Wind-driven circulation is insignificant throughout much of the annual cycle, but becomes significant from late spring to late summer, when the wind stress becomes strong. The large-scale circulation in summer is predominantly southward near the sea surface and northward near the sea bottom. The sea surface current can get as fast as 5 cms-1 in some areas. Titan's rotation affects the vertical structure of sea currents in the form of an Ekman spiral if the wind is strong. The maximum wind set-up at the shores is of the same order of magnitude as the tidal range. Wind stirring may reduce thermal stratification in summer, but may be unable to destroy stratification of methane-rich liquids on top of ethane-rich liquids that can result from imbalances between evaporation and precipitation.
Highly Alfvenic Slow Solar Wind
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron
It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.
Low and high velocity clouds produced by young stellar clusters
RodrĒguez-G¾nzalez, A; Canto, J
Intermediate and high velocity HI clouds rain onto the plane of our Galaxy. They are observed at heights of between 500 and 1500 pc, falling onto the Galactic plane at velocities from 50 to 140 km s$^{-1}$. To explain the origin of these clouds, we present a galactic fountain model, driven by the wind from a super stellar cluster (SSC). We solve the equations for a steady, radiative de Laval nozzle flow. We consider two effects not considered previously in astrophysical nozzle flow models: cooling functions for different metallicities, and the direct action of the galactic gravitational field on the gas flowing along the nozzle. For an adiabatic nozzle flow, the gravity acting directly on the gas within the nozzle "stalls" the nozzle flow for initial wind velocities lower than the escape velocity from the Galaxy. For the same wind velocity, a radiative nozzle flow stalls at lower altitudes above the galactic plane. We find that SSC winds with velocities of $v_w=500 - 800$ km s$^{-1}$ produce nozzles stall at ...
A portable wind and rainfall simulator for in situ soil erosion measurements
NASA Astrophysics Data System (ADS)
Fister, W.; Iserloh, T.; Ries, J. B.; Schmidt, R.-G.
From laboratory investigations in wind tunnels that include rainfall simulators it is known that wind considerably modifies the velocity, angle and drop size of falling rain, leading to a complex interaction and alteration of the soil erosion process. Only few field investigations, mostly with passive sediment samplers, have been made that included both, wind and water erosion rates. The main reason for this lack of studies is the difficulty to compare the results of the different sampling methods. Consequently the key objective of this study is the development of a single device that is able to simulate erosion by wind and water operational in the field under comparable conditions. During the construction of the device the focus was set on the reproducibility of the simulations and the mobility of the tunnel. For this reason some limitations in the simulation of the natural processes had to be taken into account. The working section of the portable wind and rainfall simulator is 4 m long, 0.7 m high, 0.7 m wide and rectangular in shape. A bounded plot of 2.2 m▓ can be irrigated by four pressure nozzles (Lechler type 460.608) with an intensity of about 90 mmh-1. The nozzles are positioned in the roof of the tunnel which causes a maximum fall height of 0.7 m. For sediment collection, a gutter system was combined with two wedge-shaped sediment traps and a beam with four Modified Wilson & Cook Samplers. The calibration results of the rainfall show, that the spatial drop distribution is not at all homogeneous, but very well reproducible. The simulated drop sizes/spectra correspond satisfactorily with calculated Marshal-Palmer Distributions of same rainfall intensities. Maximum drop velocities of 4-5 ms-1 are caused by the low fall height inside the tunnel. In combination with the simulation of wind, all above mentioned parameters definitely improve. Due to the short length of the tunnel, the pre-shaped boundary layer varies from 15-20 cm in height. Further velocity measurements indicate that the airflow within the lower 30 cm of the tunnel is sufficiently homogenous across the tunnel (deviation from mean 0.4-0.55 ms-1) and that the propeller induced rotating swirl is removed by the honeycomb.
Numerical Calculations of Wind Flow in a Full-Scale Wind Test Facility
Oh, Chang H; Lacey, Jerry Mark
Numerical studies on wind flow around the Texas Tech University (TTU) Wind Engineering Research Field Laboratory (WERFL) building were conducted. The main focus of this paper is wind loads on the TTU building in the INEEL proposed Windstorm Simulation Center. The results are presented in the form of distributions of static pressure, dynamic pressure, pressure coefficients, and velocity vectors on the surface and the vicinity of the TTU building.
Numerical calculations of wind flow in a full-scale wind test facility
C.H. Oh; J.M. Lacey
Numerical studies on wind flow around the Texas Tech University (TTU) Wind Engineering Research Field Laboratory (WERFL) building were conducted. The main focus of this paper is wind loads on the TTU building in the INEEL proposed Windstorm Simulation Center. The results are presented in the form of distributions of static pressure, dynamic pressure, pressure coefficients, and velocity vectors on the surface and the vicinity of the TTU building.
MHD Disk Winds in PNe and pPNe
Adam Frank
Winds from accretion disks have been proposed as the driving source for precessing jets and extreme bipolar morphologies in Planetary Nebulae (PNe) and proto-PNe (pPNe). Here we apply MHD disk wind models to PNe and pPNe by estimating separately the asymptotic MHD wind velocities and mass loss rates. We show that the resulting winds can recover the observed momentum and energy input rates for PNe and pPNe.
Tropospheric Wind Measurements from Space: The SPARCLE Mission and Beyond
NASA Technical Reports Server (NTRS)
Kavaya, Michael J.; Emmitt, G. David
For over 20 years researchers have been investigating the feasibility of profiling tropospheric vector wind velocity from space with a pulsed Doppler lidar. Efforts have included theoretical development, system and mission studies, technology development, and ground-based and airborne measurements. Now NASA plans to take the next logical step towards enabling operational global tropospheric wind profiles by demonstrating horizontal wind measurements from the Space Shuttle in early 2001 using a coherent Doppler wind lidar system.
Radial evolution of the solar wind speed as one source of alpha to proton ratio variations
S. L. McGregor; W. Hughes; J. C. Kasper; C. N. Arge
The relative abundance of alphas to protons in the solar wind varies with solar wind speed and on solar cycle time scales. However, the WSA-Enlil model shows significant stream interactions and solar wind velocity evolution within a few tenths of an AU of the sun, resulting in solar wind speeds observed at 1.0 AU and beyond which can be very
WIND TOMOGRAPHY IN BINARY SYSTEMS O.Knill, R.Dgani and M.Vogel
Knill, Oliver
WIND TOMOGRAPHY IN BINARY SYSTEMS O.Knill, R.Dgani and M.Vogel ETH-Zurich, CH-8092, Switzerland method is particularly suitable for determining the velocity laws of stellar winds. 1. WIND TOMOGRAPHY AND ABEL'S INTEGRAL Binary systems in which a compact, point-like radiation source shines through the wind
Leithead, W E
From its rebirth in the early 1980s, the rate of development of wind energy has been dramatic. Today, other than hydropower, it is the most important of the renewable sources of power. The UK Government and the EU Commission have adopted targets for renewable energy generation of 10 and 12% of consumption, respectively. Much of this, by necessity, must be met by wind energy. The US Department of Energy has set a goal of 6% of electricity supply from wind energy by 2020. For this potential to be fully realized, several aspects, related to public acceptance, and technical issues, related to the expected increase in penetration on the electricity network and the current drive towards larger wind turbines, need to be resolved. Nevertheless, these challenges will be met and wind energy will, very likely, become increasingly important over the next two decades. An overview of the technology is presented. PMID:17272245
Penetration by Shaped Charge Jets of Nonuniform Velocity
G. R. Abrahamson; J. N. Goodier
The simple hydrodynamic theory of penetration by shaped charge jets is extended to include nonuniform jet velocity distributions and stand-off distance. The penetration of a jet with an initial linear velocity distribution is compared to an ideal upper limit and is found to be close to the maximum obtainable in practice. The conclusions concern idealized jets, without regard to the
Video Measurement of the Muzzle Velocity of a Potato Gun
ERIC Educational Resources Information Center
Jasperson, Christopher; Pollman, Anthony
Using first principles, a theoretical equation for the maximum and actual muzzle velocities for a pneumatic cannon was recently derived. For a fixed barrel length, this equation suggests that the muzzle velocity can be enhanced by maximizing the product of the initial pressure and the volume of the propellant gas and decreasing the projectileģ
Perri, S.; Balogh, A., E-mail: email@example.com, E-mail: email@example.com [International Space Science Institute, Hallerstrasse 6, Bern CH-3012 (Switzerland)
By using single-point measurements in space physics it is possible to study a phenomenon only as a function of time. This means that we cannot have direct access to information about spatial variations of a measured quantity. However, the investigation of the properties of turbulence and of related phenomena in the solar wind widely makes use of an approximation frequently adopted in hydrodynamics under certain conditions, the so-called Taylor hypothesis; indeed, the solar wind flow has a bulk velocity along the radial direction which is much higher than the velocity of a single turbulent eddy embedded in the main flow. This implies that the time of evolution of the turbulent features is longer than the transit time of the flow through the spacecraft position, so that the turbulent field can be considered frozen into the solar wind flow. This assumption allows one to easily associate time variations with spatial variations and stationarity to homogeneity. We have investigated, applying criteria for weak stationarity to Ulysses magnetic field data in different solar wind regimes, at which timescale and under which conditions the hypothesis of stationarity, and then of homogeneity, of turbulence in the solar wind is well justified. We extend the conclusions of previous studies by Matthaeus and Goldstein to different parameter ranges in the solar wind. We conclude that the stationarity assumption in the inertial range of turbulence on timescales of 10 minutes to 1 day is reasonably satisfied in fast and uniform solar wind flows, but that in mixed, interacting fast, and slow solar wind streams the assumption is frequently only marginally valid.
Performance assessment of a small wind turbine with crossflow runner by numerical simulations
A. Dragomirescu
Most of the classical wind turbines are not able to start at wind speeds as low as 2¢3Ām\\/s. Other turbines, like Savonius, have a low maximum efficiency, which renders them useless in poor wind conditions. Therefore, new turbine designs are required to harvest wind power even when the wind speed is low. AĀwind turbine having a crossflow runner, similar to
Laboratory modeling of air-sea interaction under severe wind conditions
NASA Astrophysics Data System (ADS)
Troitskaya, Yuliya; Vasiliy, Kazakov; Nicolay, Bogatov; Olga, Ermakova; Mikhail, Salin; Daniil, Sergeev; Maxim, Vdovin
Wind-wave interaction at extreme wind speed is of special interest now in connection with the problem of explanation of the sea surface drag saturation at the wind speed exceeding 30 m/s. The idea on saturation (and even reduction) of the coefficient of aerodynamic resistance of the sea surface at hurricane wind speed was first suggested by Emanuel (1995) on the basis of theoretical analysis of sensitivity of maximum wind speed in a hurricane to the ratio of the enthalpy and momentum exchange coefficients. Both field (Powell, Vickery, Reinhold, 2003, French et al, 2007, Black, et al, 2007) and laboratory (Donelan et al, 2004) experiments confirmed that at hurricane wind speed the sea surface drag coefficient is significantly reduced in comparison with the parameterization obtained at moderate to strong wind conditions. Two groups of possible theoretical mechanisms for explanation of the effect of the sea surface drag reduction can be specified. In the first group of models developed by Kudryavtsev & Makin (2007) and Kukulka,Hara Belcher (2007), the sea surface drag reduction is explained by peculiarities of the air flow over breaking waves. Another approach more appropriate for the conditions of developed sea exploits the effect of sea drops and sprays on the wind-wave momentum exchange (Andreas, 2004; Makin, 2005; Kudryavtsev, 2006). The main objective of this work is investigation of factors determining momentum exchange under high wind speeds basing on the laboratory experiment in a well controlled environment. The experiments were carried out in the Thermo-Stratified WInd-WAve Tank (TSWIWAT) of the Institute of Applied Physics. The parameters of the facility are as follows: airflow 0 - 25 m/s (equivalent 10-m neutral wind speed U10 up to 60 m/s), dimensions 10m x 0.4m x 0.7 m, temperature stratification of the water layer. Simultaneous measurements of the airflow velocity profiles and wind waves were carried out in the wide range of wind velocities. Airflow velocity profile was measured by WindSonic ultrasonic wind sensor. The water elevation was measured by the three-channel wave-gauge. Top and side views of the water surface were fixed by CCD-camera. Wind friction velocity and surface drag coefficients were retrieved from the measurements by the profile method. Obtained values are in good agreement with the data of measurements by Donelan et al (2004). The directional frequency-wave-number spectra of surface waves were retrieved by the wavelet directional method (Donelan et al, 1996). The obtained dependencies of parameters of the wind waves indicate existing of two regimes of the waves with the critical wind speed Ucr about 30 m/s. For U10
A matter of measurement: rotation velocities and the velocity function of dwarf galaxies
Brook, Chris
The velocity function derived from large scale surveys can be compared with the predictions of LCDM cosmology, by matching the measured rotation velocities Vrot of galaxies to the maximum circular velocity of dark matter (DM) halos Vmax. For Vrotdwarf galaxies. We instead relate galaxies to DM halos using the empirical baryon- mass to halo-mass relation, and show that different observational measures of Vrot result in very different velocity functions. We show how the W50 velocity function, i.e. using the HI profile line width at 50% of peak HI flux to measure Vrot, can be reconciled with a LCDM cosmology. Our semi-empirical methodology allows us to determine the region of rotation curves that are probed by HI measurements (RHI), and shows that the Vrot of dwarfs are generally measured at a fraction of...
Velocity Profiles in the Solar Corona from Multi-Instrument Observations
E. Quemerais; R. Lallement; D. Koutroumpa; P. Lamy
We present a method to derive outflow velocities in the solar corona using different data sets including solar wind mass flux coming from the SWAN/SOHO instrument, electron density values from LASCO-C2 and interplanetary solar wind velocities derived from ground-based Interplanetary Scintillation Observations (IPS). In a first step, we combine the LASCO electron densities at 6 solar radii and the IPS velocities, and compare the product to the SWAN mass fluxes. It is found that this product represents the actual mass flux at 6 solar radii for the fast wind, but not for the slow wind. In regions dominated by the slow wind, the fluxes derived from SWAN are systematically smaller. This is interpreted as a proof that the fast solar wind has reached its terminal velocity at about 6 solar radii and expands with constant velocity beyond this distance. On the contrary, the slow solar wind has reached only half of its terminal value and is thus accelerated further out. In a second step, we combine the LASCO-C2 density profiles and the SWAN flux data to derive velocity profiles in the corona between 2.5 and 6 solar radii. Such profiles can be used to test models of the acceleration mechanism of the fast solar wind.
Balasundaram, Balabhaskar "Baski"
Wind Energy Leasing Handbook Wind Energy Leasing Handbook E-1033 Oklahoma Cooperative Extension? .................................................................................................................. 24 How has wind been used to generate power in the past?..................................................................................................................... 31 What do wind developers consider in locating wind energy projects
Relativistic Radiation Hydrodynamical Accretion Disk Winds
Jun Fukue; Chizuru Akizuki
Accretion disk winds browing off perpendicular to a luminous disk are examined in the framework of fully special relativistic radiation hydrodynamics. The wind is assumed to be steady, vertical, and isothermal. %and the gravitational fields is approximated by a pseudo-Newtonian potential. Using a velocity-dependent variable Eddington factor, we can solve the rigorous equations of relativistic radiative hydrodynamics, and can obtain radiatively driven winds accelerated up to the {\\it relativistic} speed. For less luminous cases, disk winds are transonic types passing through saddle type critical points, and the final speed of winds increases as the disk flux and/or the isothermal sound speed increase. For luminous cases, on the other hand, disk winds are always supersonic, since critical points disappear due to the characteristic nature of the disk gravitational fields. The boundary between the transonic and supersonic types is located at around $\\hat{F}_{\\rm c} \\sim 0.1 (\\epsilon+p)/(\\rho c^2)/\\gamma_{\\rm c}$, where $\\hat{F}_{\\rm c}$ is the radiative flux at the critical point normalized by the local Eddington luminosity, $(\\epsilon+p)/(\\rho c^2)$ is the enthalpy of the gas divided by the rest mass energy, and $\\gamma_{\\rm c}$ is the Lorentz factor of the wind velocity at the critical point. In the transonic winds, the final speed becomes 0.4--0.8$c$ for typical parameters, while it can reach $\\sim c$ in the supersonic winds.
Variations of Strahl Properties with Fast and Slow Solar Wind
NASA Technical Reports Server (NTRS)
Figueroa-Vinas, Adolfo; Goldstein, Melvyn L.; Gurgiolo, Chris
The interplanetary solar wind electron velocity distribution function generally shows three different populations. Two of the components, the core and halo, have been the most intensively analyzed and modeled populations using different theoretical models. The third component, the strahl, is usually seen at higher energies, is confined in pitch-angle, is highly field-aligned and skew. This population has been more difficult to identify and to model in the solar wind. In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze this component in the ambient solar wind during high and slow speed solar wind. The moment density and fluid velocity have been computed by a semi-numerical integration method. The variations of solar wind density and drift velocity with the general build solar wind speed could provide some insight into the source, origin, and evolution of the strahl.
Laser-Doppler measurement of crosswind velocity.
Durst, F; Howe, B M; Richter, G
There is a need for the remote sensing of local wind velocities over distances of hundreds of meters, and laser-Doppler anemometry (LDA) has been suggested as a suitable measuring technique. In this paper the major features of an LDA system optimized for crosswind velocity measurements are presented. Computer programs based on Mie scattering theory are used to predict the performance of such systems and to extend the experimentally verified information to larger distances. A complete system for the measurement of the crosswind velocity component is described, and measurements up to 106 m verifying its performance and corresponding predictions are presented and discussed. Suggestions for further studies and developments are given. PMID:20396080
Turbulent velocity spectra in superfluid flows
NASA Astrophysics Data System (ADS)
Salort, J.; Baudet, C.; Castaing, B.; Chabaud, B.; Daviaud, F.; Didelot, T.; Diribarne, P.; Dubrulle, B.; Gagne, Y.; Gauthier, F.; Girard, A.; Hķbral, B.; Rousset, B.; Thibault, P.; Roche, P.-E.
We present velocity spectra measured in three cryogenic liquid H4e steady flows: grid and wake flows in a pressurized wind tunnel capable of achieving mean velocities up to 5 m/s at temperatures above and below the superfluid transition, down to 1.7 K, and a "chunk" turbulence flow at 1.55 K, capable of sustaining mean superfluid velocities up to 1.3 m/s. Depending on the flows, the stagnation pressure probes used for anemometry are resolving from one to two decades of the inertial regime of the turbulent cascade. We do not find any evidence that the second-order statistics of turbulence below the superfluid transition differ from the ones of classical turbulence, above the transition.
Observation and analysis of abrupt changes in the interplanetary plasma velocity and magnetic field.
NASA Technical Reports Server (NTRS)
Martin, R. N.; Belcher, J. W.; Lazarus, A. J.
This paper presents a limited study of the physical nature of abrupt changes in the interplanetary plasma velocity and magnetic field based on 19 day's data from the Pioneer 6 spacecraft. The period was chosen to include a high-velocity solar wind stream and low-velocity wind. Abrupt events were accepted for study if the sum of the energy density in the magnetic field and velocity changes was above a specified minimum. A statistical analysis of the events in the high-velocity solar wind stream shows that Alfvenic changes predominate. This conclusion is independent of whether steady state requirements are imposed on conditions before and after the event. Alfvenic changes do not dominate in the lower-speed wind. This study extends the plasma field evidence for outwardly propagating Alfvenic changes to time scales as small as 1 min (scale lengths on the order of 20,000 km).
The Solar Wind in the Outer Heliosphere at Solar John D. Richardson and Chi Wang
Richardson, John
The Solar Wind in the Outer Heliosphere at Solar Maximum John D. Richardson and Chi Wang Center solar wind observations in the outer heliosphere, concentrating on the recent data near solar maximum. The speed and temperature tend to be lower at solar maximum, due to the lack of coronal holes. The near
. . . . . . . . . . . . . . . . . . , . 67 APPENDIX G DISTRIBUTION OE LAKE CHARLES OBSERVED WIND DIPUECT1ON Wl', 'N TUE OUSL'RVL'D UOUSTON WIND DIR). CTION IS 1'ROill 'lklE EAST-NORTH- EAST, EAST, OR EAST- SOU'lklEAS'lL. . . . . . . . . . P aBa 72 APPENDIX II DETAII ED SOLUT10N... levels ro the results obtained b; rcg: i ssinf the Uouston low- levcl !&inde-aloft on the Houston surface wind. Althou?h d Leisure correlation coofficip!its show a definite urmr)er siinisiurs, they indicate that from &iB'/. to 77X (depending on season...
NASA Astrophysics Data System (ADS)
Owocki, Stan
A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ? evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ś ?? 1. 4M ?. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various dynamical driving processes and what they imply for key wind parameters like the wind flow speed and mass loss rate.
Winds and Accretion in Young Stars
Suzan Edwards
Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin-up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stellar spindown. Although spectroscopic indicators of high velocity T Tauri winds have been known for decades, the line of He I 10830 offers a promising new diagnostic to probe the magnetically controlled star-disk interaction and wind-launching region. The high opacity and resonance scattering properties of this line offer a powerful probe of the geometry of both the funnel flow and the inner wind that, together with other atomic and molecular spectral lines covering a wide range of excitation and ionization states, suggests that the magnetic interaction between the star and disk, and the subsequent launching of the inner high velocity wind, is sensitive to the disk accretion rate.
Winds in cataclysmic variable stars
Cordova, F.A.; Ladd, E.F.; Mason, K.O.
Ultraviolet spectrophotometry of two dwarf novae, CN Ori and RX And, at various phases of their outburst cycles confirms that the far uv flux increases dramatically about 1-2 days after the optical outburst begins. At this time the uv spectral line profiles indicate the presence of a high velocity wind. The detectability of the wind depends more on the steepness of the spectrum, and thus on the flux in the extreme ultraviolet, than on the absolute value of the far uv luminosity. The uv continuum during outburst consists of (at least) two co
Impact Wind Farms on the Marine Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Volker, P.; Capps, S. B.; Huang, H. J.; Sun, F.; Badger, J.; Hahmann, A.
We introduce a new, validated wind farm parametrization (Explicit Wake Parametrization, EWP) which is based on the assumption that the downstream propagation of a single turbine wake can be described by a turbulent diffusion process. Thus, the downstream velocity deficit distribution can be described explicitly. Additionally, it allows us to take into account turbine interactions, making it possible to determine the unresolved turbine hub height velocities. Both the EWP wind farm parametrization and the wind farm scheme available in the Weather Research & Forecasting Model (WRF) have been validated against in situ measurements from Horns Rev I (A large offshore wind farm consisting of 80 2MW turbines situated near the west coast of Denmark). The main quantities of interest are the thrust applied to the flow, a consequence of the energy extracted by the wind turbines which determines mainly the wind farm wake extension (around 50 km for Horns Rev I) and the vertical velocity deficit distribution. Results show that the thrust in the WRF-WF scheme is overestimated inside the wind farm. We noticed that the velocity deficit propagates from the first turbine-containing-grid-cell up to the boundary layer top, which is in contrast to the theoretical expected expansion (confirmed by turbulence resolving models and wind tunnel results). The vertical expansion of the velocity deficit is a consequence of the additional turbulence source term in the WRF-WF scheme. The EWP scheme estimates the total amount of thrust correctly and is also able to follow the reduced thrust downstream since it considers the turbine interaction. From the good agreement with the far wake measurement, we can conclude that the formulation of the sub grid scale vertical extension of the velocity deficit must be correct. We will present results from WRF simulations in which we analyze the atmospheric response within the wake of wind farms resulting from the energy extraction of wind turbines. We place hypotetical wind farms in offshore areas with good wind resources near California. The wind farm sizes are choosen to be comparable to present ones errected in the European North Sea. Of particular interest is the influence of wind farms on the persistent stratocumulus clouds of the California coastal region, the thermal stratification of the boundary layer and wind stress changes due to reduced wind speeds near the surface. Although no wind farms are presently constructed along the Californian coast, fast and steady wind speeds makes it an attractive region for future offshore wind farms, especially if the first floating turbines near the coast of Norway are proven to be a success.
Wind mass transfer in S-type symbiotic binaries. I. Focusing by the wind compression model
NASA Astrophysics Data System (ADS)
Skopal, A.; Carikovß, Z.
Context. Luminosities of hot components in symbiotic binaries require accretion rates that are higher than those that can be achieved via a standard Bondi-Hoyle accretion. This implies that the wind mass transfer in symbiotic binaries has to be more efficient. Aims: We suggest that the accretion rate onto the white dwarfs (WDs) in S-type symbiotic binaries can be enhanced sufficiently by focusing the wind from their slowly rotating normal giants towards the binary orbital plane. Methods: We applied the wind compression model to the stellar wind of slowly rotating red giants in S-type symbiotic binaries. Results: Our analysis reveals that for typical terminal velocities of the giant wind, 20 to 50 km s-1, and measured rotational velocities between 6 and 10 km s-1, the densities of the compressed wind at a typical distance of the accretor from its donor correspond to the mass-loss rate, which can be a factor of ~10 higher than for the spherically symmetric wind. This allows the WD to accrete at rates of 10-8-10-7 M? yr-1, and thus to power its luminosity. Conclusions: We show that the high wind-mass-transfer efficiency in S-type symbiotic stars can be caused by compression of the wind from their slowly rotating normal giants, whereas in D-type symbiotic stars, the high mass transfer ratio can be achieved via the gravitational focusing, which has recently been suggested for very slow winds in Mira-type binaries.
Group velocity Roger Grimshaw July 2, 2002 Abstract A short and largely traditional review on the water surface propagates outwards as a wave group; within the group, however, one can see that the wave, called the phase velocity, is dif- ferent from that of the group as a whole, this speed being called
Ground Water and Frost Induced Seismic Velocity Changes in Ketzin (Germany)
NASA Astrophysics Data System (ADS)
Gassenmeier, Martina; Sens-Sch÷nfelder, Christoph; Korn, Michael
The principle of Seismic Interferometry (SI) is that the correlation of a random wave field like seismic noise recorded by distant receivers can be used to infer the Green function (or at least part of it) of the medium between the receivers. Beside tomographic inversion for the subsurface velocity it can also be used to detect small temporal changes in the propagation of the seismic wave field. As these changes can be related to changes of elastic properties in the propagation medium, SI can characterize dynamic processes in the earth's crust. This technique was successfully applied, inter alia, to monitor seasonal variations in response to environmental influences, shaking caused by earthquakes or material changes due to the eruption of volcanoes. We work with data acquired with a seismic network in Ketzin (Brandenburg, Germany), where CO2 is injected into a saline aquifer at a depth of about 650 m. We calculated daily cross-correlation functions (CCFs) of the ambient noise field for a time period of about 4 years from the beginning of the injection. Spectra showed that the frequency band between 1 and 3.5 Hz does neither show an annual periodicity (like for microseism) nor temporal shifts of peak frequencies. For this frequency band we estimated the noise propagation direction over two years and found a predominant direction from north-east. This direction matches with the location of a large wind park a few km away from the array. The direction of the noise wave field shows a good stability, which excludes variations of the noise source distribution as a cause of spurious velocity variations. To analyze possible velocity changes for each day, we computed stretched versions of a reference CCF and calculated correlation values between different time windows in the coda part of the stretched traces and the reference trace. We can observe velocity variations with a period of approx. one year that are not caused by the CO2 injection. Due to the almost continuous injection of CO2 we would expect a monotonic decrease of the seismic velocities if caused by the CO2. Based on an amplitude decrease when using time windows in the later part of the coda, we show that the variations must be generated in the shallow subsurface. A comparison to ground water level data reveals a direct correlation between the depth of the ground water level and the seismic velocity. The influence of ground frost on the seismic velocities is documented in a sharp increase of velocity when the maximum daily temperature does not exceed 0░C.
Effects of incoming wind condition and wind turbine aerodynamics on the hub vortex instability
NASA Astrophysics Data System (ADS)
Ashton, R.; Viola, F.; Gallaire, F.; Iungo, G. V.
Dynamics and instabilities occurring in the near-wake of wind turbines have a crucial role for the wake downstream evolution, and for the onset of far-wake instabilities. Furthermore, wake dynamics significantly affect the intra-wind farm wake flow, wake interactions and potential power losses. Therefore, the physical understanding and predictability of wind turbine wake instabilities become a nodal point for prediction of wind power harvesting and optimization of wind farm layout. This study is focused on the prediction of the hub vortex instability encountered within wind turbine wakes under different operational conditions of the wind turbine. Linear stability analysis of the wake flow is performed by means of a novel approach that enables to take effects of turbulence on wake instabilities into account. Stability analysis is performed by using as base flow the time-averaged wake velocity field at a specific downstream location. The latter is modeled through Carton-McWilliams velocity profiles by mimicking the presence of the hub vortex and helicoidal tip vortices, and matching the wind turbine thrust coefficient predicted through the actuator disc model. The results show that hub vortex instability is promoted by increasing the turbine thrust coefficient. Indeed, a larger aerodynamic load produces an enhanced wake velocity deficit and axial shear, which are considered the main sources for the wake instability. Nonetheless, wake swirl also promotes hub vortex instability, and it can also affect the azimuthal wavenumber of the most unstable mode.
Calibration of 3-D wind measurements on a single engine research aircraft
NASA Astrophysics Data System (ADS)
Mallaun, C.; Giez, A.; Baumann, R.
An innovative calibration method for the wind speed measurement using a boom mounted Rosemount model 858 AJ air velocity probe is introduced. The method is demonstrated for a sensor system installed on a medium size research aircraft which is used for measurements in the atmospheric boundary layer. The method encounters a series of coordinated flight manoeuvres to directly estimate the aerodynamic influences on the probe and to calculate the measurement uncertainties. The introduction of a differential Global Positioning System (DGPS) combined with a high accuracy Inertial Reference System (IRS) has brought major advances to airborne measurement techniques. The exact determination of geometrical height allows the use of the pressure signal as an independent parameter. Furthermore, the exact height information and the stepwise calibration process lead to maximum accuracy. The results show a measurement uncertainty for the aerodynamic influence of the dynamic and static pressures of 0.1 hPa. The applied parametrisation does not require any height dependencies or time shifts. After extensive flight tests a correction for the flow angles (attack and sideslip angles) was found, which is necessary for a successful wind calculation. A new method is demonstrated to correct for the aerodynamic influence on the sideslip angle. For the 3-D wind vector (with 100 Hz resolution) a novel error propagation scheme is tested, which determines the measurement uncertainties to be 0.3 m s-1 for the horizontal and 0.2 m s-1 for the vertical wind components.
Efficiency at maximum power of motor traffic on networks
NASA Astrophysics Data System (ADS)
Golubeva, N.; Imparato, A.
We study motor traffic on Bethe networks subject to hard-core exclusion for both tightly coupled one-state machines and loosely coupled two-state machines that perform work against a constant load. In both cases we find an interaction-induced enhancement of the efficiency at maximum power (EMP) as compared to noninteracting motors. The EMP enhancement occurs for a wide range of network and single-motor parameters and is due to a change in the characteristic load-velocity relation caused by phase transitions in the system. Using a quantitative measure of the trade-off between the EMP enhancement and the corresponding loss in the maximum output power we identify parameter regimes where motor traffic systems operate efficiently at maximum power without a significant decrease in the maximum power output due to jamming effects.
Efficiency at maximum power of motor traffic on networks.
Golubeva, N; Imparato, A
We study motor traffic on Bethe networks subject to hard-core exclusion for both tightly coupled one-state machines and loosely coupled two-state machines that perform work against a constant load. In both cases we find an interaction-induced enhancement of the efficiency at maximum power (EMP) as compared to noninteracting motors. The EMP enhancement occurs for a wide range of network and single-motor parameters and is due to a change in the characteristic load-velocity relation caused by phase transitions in the system. Using a quantitative measure of the trade-off between the EMP enhancement and the corresponding loss in the maximum output power we identify parameter regimes where motor traffic systems operate efficiently at maximum power without a significant decrease in the maximum power output due to jamming effects. PMID:25019736
Summary of forward velocity effects on fan noise
NASA Technical Reports Server (NTRS)
Feiler, C. E.; Groeneweg, J. F.
Available experimental data comparing the in-flight and static behavior of fan noise are reviewed. These results are then compared with recent data obtained for a fan stage tested with forward velocity in a low speed wind tunnel. Tentative conclusions are presented about the significance and nature of the changes in noise observed when a forward velocity is imposed. Finally, the implications of the emerging picture of in-flight fan source noise for suppressor design are discussed.
A complex high velocity outflow in PG1211+143
NASA Astrophysics Data System (ADS)
Pounds, K.; Lobban, A.; Reeves, J.; Vaughan, S.
An extended XMM-Newton observation of the luminous narrow-line Seyfert galaxy PG1211+143 in 2014 has revealed a more complex high velocity outflow, with components distinguished in velocity, ionization and short-term variability.The new results will be presented and briefly discussed - as time allows - in relation to current views on the nature of AGN winds and galaxy feedback.
Tangler, James L. (Boulder, CO); Somers, Dan M. (State College, PA)
Airfoils for the tip and mid-span regions of a wind turbine blade have upper surface and lower surface shapes and contours between a leading edge and a trailing edge that minimize roughness effects of the airfoil and provide maximum lift coefficients that are largely insensitive to roughness effects. The airfoil in one embodiment is shaped and contoured to have a thickness in a range of about fourteen to seventeen percent, a Reynolds number in a range of about 1,500,000 to 2,000,000, and a maximum lift coefficient in a range of about 1.4 to 1.5. In another embodiment, the airfoil is shaped and contoured to have a thickness in a range of about fourteen percent to sixteen percent, a Reynolds number in a range of about 1,500,000 to 3,000,000, and a maximum lift coefficient in a range of about 0.7 to 1.5. Another embodiment of the airfoil is shaped and contoured to have a Reynolds in a range of about 1,500,000 to 4,000,000, and a maximum lift coefficient in a range of about 1.0 to 1.5.
Simulated synchrotron emission from Pulsar Wind Nebulae
Luca Del Zanna; Delia Volpi; Elena Amato; Niccolo' Bucciantini
A complete set of diagnostic tools aimed at producing synthetic synchrotron emissivity, polarization, and spectral index maps from relativistic MHD simulations is presented. As a first application we consider here the case of the emission from Pulsar Wind Nebulae (PWNe). The proposed method is based on the addition, on top of the basic set of MHD equations, of an extra equation describing the evolution of the maximum energy of the emitting particles. This equation takes into account adiabatic and synchrotron losses along streamlines for the distribution of emitting particles and its formulation is such that it is easily implemented in any numerical scheme for relativistic MHD. Application to the axisymmetric simulations of PWNe, analogous to those described by Del Zanna et al. (2004, A&A, 421, 1063), allows direct comparison between the numerical results and observations of the inner structure of the Crab Nebula, and similar objects, in the optical and X-ray bands. We are able to match most of the observed features typical of PWNe, like the equatorial torus and the polar jets, with velocities in the correct range, as well as finer emission details, like arcs, rings and the bright knot, that turn out to arise mainly from Doppler boosting effects. Spectral properties appear to be well reproduced too: detailed spectral index maps are produced for the first time and show softening towards the PWN outer borders, whereas spectral breaks appear in integrated spectra. The emission details are found to strongly depend on both the average wind magnetization (here approximately 2%), and on the magnetic field shape.
Short-Term Wind Power Forecasts using Doppler Lidar
NASA Astrophysics Data System (ADS)
Magerman, Beth
With a ground-based Doppler lidar on the upwind side of a wind farm in the Tehachapi Pass of California, radial wind velocity measurements were collected for repeating sector sweeps, scanning up to 10 kilometers away. This region consisted of complex terrain, with the scans made between mountains. The dataset was utilized for techniques being studied for short-term forecasting of wind power by correlating changes in energy content and of turbulence intensity by tracking spatial variance, in the wind ahead of a wind farm. A ramp event was also captured and its propagation was tracked. Orthogonal horizontal wind vectors were retrieved from the radial velocity using a sector Velocity Azimuth Display method. Streamlines were plotted to determine the potential sites for a correlation of upstream wind speed with wind speed at downstream locations near the wind farm. A "virtual wind turbine" was "placed" in locations along the streamline by using the time-series velocity data at the location as the input to a modeled wind turbine, to determine the extractable energy content at that location. The relationship between this time-dependent energy content upstream and near the wind farm was studied. By correlating the energy content with each upstream location based on a time shift estimated according to advection at the mean wind speed, several fits were evaluated. A prediction of the downstream energy content was produced by shifting the power output in time and applying the best-fit function. This method made predictions of the power near the wind farm several minutes in advance. Predictions were also made up to an hour in advance for a large ramp event. The Magnitude Absolute Error and Standard Deviation are presented for the predictions based on each selected upstream location.
Wind assisted deep-well pumping
Clark, R.N.
A 37-kW, vertical-axis wind turbine was successfully coupled to an existing irrigation pump by installing a combination gear drive between the pump and electric motor. The system operated as a wind-assisted system because the wind turbine reduced the load on the electric motor and saved energy. To synchronize the two power sources, an overrunning clutch was used in the mechanical drive line. This clutch was essential to the power train because it allowed the wind turbine to operate at its maximum efficiency without causing any loading on the electric motor at low windspeeds. The clutch, combination gear drive, and connecting shafting are all commonly available in irrigated areas. Results indicated that as much as 40% of the pesent energy consumed in irrigation pumping can be generated by wind power. Wind energy systems for irrigation appear best suited for limited irrigation of crops like cotton and sorghum, rather than full irrigation of crops like corn and alfalfa.
An experimental investigation on wind turbine aeromechanics and wake interferences among multiple wind turbines
NASA Astrophysics Data System (ADS)
Ozbay, Ahmet
A comprehensive experimental study was conducted to investigate wind turbine aeromechanics and wake interferences among multiple wind turbines sited in onshore and offshore wind farms. The experiments were carried out in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Iowa State University. An array of scaled three-blade Horizontal Axial Wind Turbine (HAWT) models were placed in atmospheric boundary layer winds with different mean and turbulence characteristics to simulate the situations in onshore and offshore wind farms. The effects of the important design parameters for wind farm layout optimization, which include the mean and turbulence characteristics of the oncoming surface winds, the yaw angles of the turbines with respect to the oncoming surface winds, the array spacing and layout pattern, and the terrain topology of wind farms on the turbine performances (i.e., both power output and dynamic wind loadings) and the wake interferences among multiple wind turbines, were assessed in detail. The aeromechanic performance and near wake characteristics of a novel dual-rotor wind turbine (DRWT) design with co-rotating or counter-rotating configuration were also investigated, in comparison to a conventional single rotor wind turbine (SRWT). During the experiments, in addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the scaled turbine models, a high-resolution Particle Image Velocity (PIV) system was used to conduct detailed flow field measurements (i.e., both free-run and phase-locked flow fields measurements) to reveal the transient behavior of the unsteady wake vortices and turbulent flow structures behind wind turbines and to quantify the characteristics of the wake interferences among the wind turbines sited in non-homogenous surface winds. A miniature cobra anemometer was also used to provide high-temporal-resolution data at points of interest to supplement the full field PIV measurement results. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate underlying physics in order to gain further insight into the characteristics of the power generation performance, dynamic wind loads and wake interferences of the wind turbines for higher total power yield and better durability of the wind turbines sited in atmospheric boundary layer (ABL) winds.
A Large Scale Wind Tunnel for the Study of High Reynolds Number Turbulent Boundary Layer Physics
NASA Astrophysics Data System (ADS)
Priyadarshana, Paththage; Klewicki, Joseph; Wosnik, Martin; White, Chris
Progress and the basic features of the University of New Hampshire's very large multi-disciplinary wind tunnel are reported. The refinement of the overall design has been greatly aided through consultations with an external advisory group. The facility test section is 73 m long, 6 m wide, and 2.5 m nominally high, and the maximum free stream velocity is 30 m/s. A very large tunnel with relatively low velocities makes the small scale turbulent motions resolvable by existing measurement systems. The maximum Reynolds number is estimated at &+circ;= ?u?/?ś50000, where ? is the boundary layer thickness and u? is the friction velocity. The effects of scale separation on the generation of the Reynolds stress gradient appearing in the mean momentum equation are briefly discussed to justify the need to attain &+circ; in excess of about 40000. Lastly, plans for future utilization of the facility as a community-wide resource are outlined. This project is supported through the NSF-EPSCoR RII Program, grant number EPS0701730.
Gorsevski, Peter; Afjeh, Abdollah; Jamali, Mohsin; Bingman, Verner
The Coastal Ohio Wind Project intends to address problems that impede deployment of wind turbines in the coastal and offshore regions of Northern Ohio. The project evaluates different wind turbine designs and the potential impact of offshore turbines on migratory and resident birds by developing multidisciplinary research, which involves wildlife biology, electrical and mechanical engineering, and geospatial science. Firstly, the project conducts cost and performance studies of two- and three-blade wind turbines using a turbine design suited for the Great Lakes. The numerical studies comprised an analysis and evaluation of the annual energy production of two- and three-blade wind turbines to determine the levelized cost of energy. This task also involved wind tunnel studies of model wind turbines to quantify the wake flow field of upwind and downwind wind turbine-tower arrangements. The experimental work included a study of a scaled model of an offshore wind turbine platform in a water tunnel. The levelized cost of energy work consisted of the development and application of a cost model to predict the cost of energy produced by a wind turbine system placed offshore. The analysis found that a floating two-blade wind turbine presents the most cost effective alternative for the Great Lakes. The load effects studies showed that the two-blade wind turbine model experiences less torque under all IEC Standard design load cases considered. Other load effects did not show this trend and depending on the design load cases, the two-bladed wind turbine showed higher or lower load effects. The experimental studies of the wake were conducted using smoke flow visualization and hot wire anemometry. Flow visualization studies showed that in the downwind turbine configuration the wake flow was insensitive to the presence of the blade and was very similar to that of the tower alone. On the other hand, in the upwind turbine configuration, increasing the rotor blade angle of attack reduced the wake size and enhanced the vortices in the flow downstream of the turbine-tower compared with the tower alone case. Mean and rms velocity distributions from hot wire anemometer data confirmed that in a downwind configuration, the wake of the tower dominates the flow, thus the flow fields of a tower alone and tower-turbine combinations are nearly the same. For the upwind configuration, the mean velocity shows a narrowing of the wake compared with the tower alone case. The downwind configuration wake persisted longer than that of an upwind configuration; however, it was not possible to quantify this difference because of the size limitation of the wind tunnel downstream of the test section. The water tunnel studies demonstrated that the scale model studies could be used to adequately produce accurate motions to model the motions of a wind turbine platform subject to large waves. It was found that the important factors that affect the platform is whether the platform is submerged or surface piercing. In the former, the loads on the platform will be relatively reduced whereas in the latter case, the structure pierces the wave free surface and gains stiffness and stability. The other important element that affects the movement of the platform is depth of the sea in which the wind turbine will be installed. Furthermore, the wildlife biology component evaluated migratory patterns by different monitoring systems consisting of marine radar, thermal IR camera and acoustic recorders. The types of radar used in the project are weather surveillance radar and marine radar. The weather surveillance radar (1988 Doppler), also known as Next Generation Radar (NEXRAD), provides a network of weather stations in the US. Data generated from this network were used to understand general migratory patterns, migratory stopover habitats, and other patterns caused by the effects of weather conditions. At a local scale our marine radar was used to complement the datasets from NEXRAD and to collect additional monitoring parameters such as passage rates, flight paths, flight directi
Airborne lidar wind detection at 2 ?m
NASA Astrophysics Data System (ADS)
Targ, Russell; Hawley, James G.; Steakley, Bruce C.; Ames, Lawrence L.; Robinson, Paul A.
NASA and the FAA have expressed interest in laser radar's capabilities to detect wind profiles at altitude. A number of programs have been addressing the technical feasibility and utility of laser radar atmospheric backscatter data to determine wind profiles and wind hazards for aircraft guidance and navigation. In addition, the U.S. Air Force is investigating the use of airborne lidar to achieve precision air drop capability, and to increase the accuracy of the AC- 130 gunship and the B-52 bomber by measuring the wind field from the aircraft to the ground. There are emerging capabilities of airborne laser radar to measure wind velocities and detect turbulence and other atmospheric disturbances out in front of an aircraft in real time. The measurement of these parameters can significantly increase fuel efficiency, flight safety, airframe lifetime, and terminal area capacity for new and existing aircraft. This is achieved through wind velocity detection, turbulence avoidance, active control utilization to alleviate gust loading, and detection of wingtip wake vortices produced by landing aircraft. This paper presents the first flight test results of an all solid-state 2-micrometers laser radar system measuring the wind field profile 1 to 2 km in front of an aircraft in real time. We find 0.7-m/s wind measurement accuracy for the system which is configured in a rugged, light weight, high- performance ARINC package.
Radiation-driven winds of hot stars. V - Wind models for central stars of planetary nebulae
NASA Technical Reports Server (NTRS)
Pauldrach, A.; Puls, J.; Kudritzki, R. P.; Mendez, R. H.; Heap, S. R.
Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.
Parameter Trade Studies For Coherent Lidar Wind Measurements of Wind from Space
NASA Technical Reports Server (NTRS)
Kavaya, Michael J.; Frehlich, Rod G.
The design of an orbiting wind profiling lidar requires selection of dozens of lidar, measurement scenario, and mission geometry parameters; in addition to prediction of atmospheric parameters. Typical mission designs do not include a thorough trade optimization of all of these parameters. We report here the integration of a recently published parameterization of coherent lidar wind velocity measurement performance with an orbiting coherent wind lidar computer simulation; and the use of these combined tools to perform some preliminary parameter trades. We use the 2006 NASA Global Wind Observing Sounder mission design as the starting point for the trades.
Alfvķnic fluctuations in ``newborn'' polar solar wind
NASA Astrophysics Data System (ADS)
Bavassano, B.; Pietropaolo, E.; Bruno, R.
The 3-D structure of the solar wind is strongly dependent upon the Sun's activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes, and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-lived feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about polar wind fluctuations. As is well known, the low-solar-activity polar wind is characterized by a strong flow of Alfvķnic fluctuations. Does this hold for the new polar flows too? An answer to this question is given here through a comparative statistical analysis on parameters such as total energy, cross helicity, and residual energy, that are of general use to describe the Alfvķnic character of fluctuations. Our results indicate that the main features of the Alfvķnic fluctuations observed in low-solar-activity polar wind have been quickly recovered in the new polar flows developed shortly after solar maximum. Keywords. Interplanetary physics (MHD waves and turbulence; Sources of the solar wind) Space plasma physics (Turbulence)
NASA Astrophysics Data System (ADS)
Lee, S.; Churchfield, M.; Sirnivas, S.; Moriarty, P.; Nielsen, F. G.; Skaare, B.; Byklum, E.
A team of researchers from the National Renewable Energy Laboratory and Statoil used large-eddy simulations to numerically investigate the merging wakes from upstream offshore wind turbines. Merging wakes are typical phenomena in wind farm flows in which neighboring turbine wakes consolidate to form complex flow patterns that are as yet not well understood. In the present study, three 6-MW turbines in a row were subjected to a neutrally stable atmospheric boundary layer flow. As a result, the wake from the farthest upstream turbine conjoined the downstream wake, which significantly altered the subsequent velocity deficit structures, turbulence intensity, and the global meandering behavior. The complexity increased even more when the combined wakes from the two upstream turbines mixed with the wake generated by the last turbine, thereby forming a ōtripletö structure. Although the influence of the wake generated by the first turbine decayed with downstream distance, the mutated wakes from the second turbine continued to influence the downstream wake. Two mirror-image angles of wind directions that yielded partial wakes impinging on the downstream turbines yielded asymmetric wake profiles that could be attributed to the changing flow directions in the rotor plane induced by the Coriolis force. The turbine wakes persisted for extended distances in the present study, which is a result of low aerodynamic surface roughness typically found in offshore conditions.
Principles of maximum entropy and maximum caliber in statistical physics
NASA Astrophysics Data System (ADS)
Pressķ, Steve; Ghosh, Kingshuk; Lee, Julian; Dill, Ken A.
The variational principles called maximum entropy (MaxEnt) and maximum caliber (MaxCal) are reviewed. MaxEnt originated in the statistical physics of Boltzmann and Gibbs, as a theoretical tool for predicting the equilibrium states of thermal systems. Later, entropy maximization was also applied to matters of information, signal transmission, and image reconstruction. Recently, since the work of Shore and Johnson, MaxEnt has been regarded as a principle that is broader than either physics or information alone. MaxEnt is a procedure that ensures that inferences drawn from stochastic data satisfy basic self-consistency requirements. The different historical justifications for the entropy S=-?ipilog?pi and its corresponding variational principles are reviewed. As an illustration of the broadening purview of maximum entropy principles, maximum caliber, which is path entropy maximization applied to the trajectories of dynamical systems, is also reviewed. Examples are given in which maximum caliber is used to interpret dynamical fluctuations in biology and on the nanoscale, in single-molecule and few-particle systems such as molecular motors, chemical reactions, biological feedback circuits, and diffusion in microfluidics devices.
Viscous Forces in Velocity Boundary Layers around Planetary Ionospheres.
A discussion is presented to examine the role of viscous forces in the transport of solar wind momentum to the ionospheric plasma of weakly magnetized planets (Venus and Mars). Observational data are used to make a comparison of the Reynolds and Maxwell stresses that are operative in the interaction of the solar wind with local plasma (planetary ionospheres). Measurements show the presence of a velocity boundary layer formed around the flanks of the ionosphere where the shocked solar wind has reached super-Alfvķnic speeds. It is found that the Reynolds stresses in the solar wind at that region can be larger than the Maxwell stresses and thus are necessary in the local acceleration of the ionospheric plasma. From an order-of-magnitude calculation of the Reynolds stresses, it is possible to derive values of the kinematic viscosity and the Reynolds number that are suitable to the gyrotropic motion of the solar wind particles across the boundary layer. The value of the kinematic viscosity is comparable to those inferred from studies of the transport of solar wind momentum to the earth's magnetosphere and thus suggest a common property of the solar wind around planetary obstacles. Similar conditions could also be applicable to velocity boundary layers formed in other plasma interaction problems in astrophysics. PMID:10511515
NLTE wind models for SMC stars
Jiri Krticka
We study stellar wind properties of selected late O stars in the Small Magellanic Cloud (SMC). We calculate NLTE line-driven wind models for these stars and compare predicted wind parameters with observed values. We found satisfactory agreement between theoretical and observed terminal velocities. On the other hand, predicted and observed mass-loss rates are in a good agreement only for higher mass-loss rates. For mass-loss rates lower than approximately 10^{-7} M_sun / year we found large discrepancy between theoretical and observed values. We propose a new explanation of this effect based on dynamical decoupling of some atoms. Finally, we study the dependence of wind terminal velocities and mass-loss rates on metallicity.
Solar wind composition. Progress report
Ogilvie, K.W.; Coplan, M.A.
Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.
Integrated roof wind energy system
NASA Astrophysics Data System (ADS)
Suma, A. B.; Ferraro, R. M.; Dano, B.; Moonen, S. P. G.
Wind is an attractive renewable source of energy. Recent innovations in research and design have reduced to a few alternatives with limited impact on residential construction. Cost effective solutions have been found at larger scale, but storage and delivery of energy to the actual location it is used, remain a critical issue. The Integrated Roof Wind Energy System is designed to overcome the current issues of urban and larger scale renewable energy system. The system is built up by an axial array of skewed shaped funnels that make use of the Venturi Effect to accelerate the wind flow. This inventive use of shape and geometry leads to a converging air capturing inlet to create high wind mass flow and velocity toward a vertical-axis wind turbine in the top of the roof for generation of a relatively high amount of energy. The methods used in this overview of studies include an array of tools from analytical modelling, PIV wind tunnel testing, and CFD simulation studies. The results define the main design parameters for an efficient system, and show the potential for the generation of high amounts of renewable energy with a novel and effective system suited for the built environment.
Precision cavity enhanced velocity modulation spectroscopy
Andrew A. Mills; Brian M. Siller; Benjamin J. McCall
The new technique of cavity enhanced velocity modulation spectroscopy has been further developed, incorporating a tighter cavity to laser lock and an optical frequency comb for absolute frequency calibration. Several N2+ transitions have been observed with much higher precision than previously possible, and transitions that were blended in earlier Doppler-limited experiments are now resolved. The full-width at half-maximum of the
Wind tunnel flow generation section
NASA Technical Reports Server (NTRS)
Sorensen, N. E. (inventor)
A flow generation section for a wind tunnel test facility is described which provides a uniform flow for the wind tunnel test section over a range of different flow velocities. The throat of the flow generation section includes a pair of opposed boundary walls which are porous to the flowing medium in order to provide an increase of velocity by expansion. A plenum chamber is associated with the exterior side of each of such porous walls to separate the same from ambient pressure. A suction manifold is connected by suction lines with each one of the chambers. Valves are positioned in each of the lines to enable the suction manifold to be independently varied.
Note: A helical velocity selector for continuous molecular beams
Szewc, Carola; Collier, James D.; Ulbricht, Hendrik [School of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ (United Kingdom)
We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry.
Wind-Flow Dynamics Over a Vineyard
NASA Astrophysics Data System (ADS)
Chahine, Ali; Dupont, Sylvain; Sinfort, Carole; Brunet, Yves
Wind-flow dynamics has been extensively studied over horizontally uniform canopies, but agricultural plantations structured in rows such as vineyards have received less attention. Here, the wind flow over a vineyard is studied in neutral stratification from both large-eddy simulation (LES) and in situ measurements. The impact of row structure on the wind dynamics is investigated over a range of wind directions from cross-row to down-row, and a typical range of row aspect ratio (row separation/height ratio). It is shown that the mean flow over a vineyard is similar to that observed in uniform canopies, especially for wind directions from cross-row to diagonal. For down-row winds, the mean flow exhibits noticeable spatial variability across each elementary row-gap pattern, as the wind is channeled in the inter-row. This spatial variability increases with the aspect ratio. With down-row winds the turbulent structures are also more intermittent and generate larger turbulent kinetic energy and momentum flux. The displacement height and roughness length of the vineyard vary with the aspect ratio in a way similar to their variation with canopy density in uniform canopies. Both parameters take smaller values in down-row wind flow, for which the canopy appears more open. The analysis of velocity spectra and autocorrelation functions shows that vineyard canopies share similar features to uniform canopies in terms of turbulent coherent structures, with only minor changes with wind direction.
Turbulent Velocity-Variance Profiles in the Stable Boundary Layer Generated by a Nocturnal Low-Level Jet
Robert M. Banta; Yelena L. Pichugina; W. Alan Brewer
Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind stable boundary layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component 2 u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to
Fracture ventilation by surface winds
NASA Astrophysics Data System (ADS)
Nachshon, U.; Dragila, M. I.; Weisbrod, N.
Gas exchange between the Earth subsurface and the atmosphere is an important mechanism, affecting hydrological, agricultural and environmental processes. From a hydrological aspect, water vapor transport is the most important process related to Earth-atmosphere gas exchange. In respect to agriculture, gas transport in the upper soil profile is important for soil aeration. From an environmental aspect, emission of volatile radionuclides, such as 3H, 14C and Rd from radioactive waste disposal facilities; volatile organic components from industrial sources and Rn from natural sources, all found in the upper vadose zone, can greatly affect public health when emissions occur in populated areas. Thus, it is vital to better understand gas exchange processes between the Earth's upper crust and atmosphere. Four major mechanisms are known to transfer gases between ground surface and atmosphere: (1) Diffusion; (2) Pressure gradients between ground pores and atmosphere due to changes in barometric pressure; (3) Density-driven gas flow in respond to thermal gradients in the ground; and (4) Winds above the ground surface. Herein, the wind ventilation mechanism is studied. Whereas the wind's impact on ground ventilation was explored in several studies, the physical mechanisms governing this process were hardly quantified or characterized. In this work the physical properties of fracture ventilation due to wind blowing along land surface were explored and quantified. Both field measurements and Hele-Shaw experiments under controlled conditions in the laboratory were used to study this process. It was found that winds in the range of 0.3 m/s result in fracture ventilation down to a depth of 0.2 m. As wind velocity increases, the depth of the ventilation inside the fracture increases respectively, in a linear manner. In addition, the fracture aperture also affects the depth of ventilation, which grows as fracture aperture increases. For the maximal examined aperture of 2 cm and wind velocity of 1.25 m/s, fracture ventilation was deeper than 0.45 m. This study sheds new light on fracture ventilation, showing that moderate winds may increase evaporation and gas exchange between fractured media and the atmosphere. Even though wind impact is limited to the top 0.5 m below the ground surface, it is an important process as most of the biological activities, as well as important hydrological processes occur in this region. Wind effect should be considered when modeling mass and energy balances between the Earth upper crust and atmosphere.
A Double-Gaussian, Percentile-Based Method for Estimating Maximum
Marzban, Caren
, a method for estimating flow velocity and its uncertainty is desirable. Methods--A gaussian mixture model was generally con- sistent with the 90th percentile of the signal distribution derived via the gaussian mixA Double-Gaussian, Percentile-Based Method for Estimating Maximum Blood Flow Velocity Caren Marzban
Flight penetration of wind shear: Control strategies
NASA Technical Reports Server (NTRS)
Joshi, Amit S.
Wind shear is a dangerous condition where there is a sharp change in the direction and magnitude of the wind velocity over a short distance or time. This condition is especially dangerous to aircraft during landing and takeoff and can cause a sudden loss of lift and thereby height at a critical time. A numerical simulation showed the effective performance of the Linear Quadratic Regulator and the Nonlinear Inverse Dynamics controllers. The major conclusions are listed and discussed.
Magnetic energy flow in the solar wind.
NASA Technical Reports Server (NTRS)
Modisette, J. L.
Discussion of the effect of rotation (tangential flow) of the solar wind on the conclusions of Whang (1971) suggesting an increase in the solar wind velocity due to the conversion of magnetic energy to kinetic energy. It is shown that the effect of the rotation of the sun on the magnetic energy flow results in most of the magnetic energy being transported by magnetic shear stress near the sun.
Analysis and Forecasting of Winds and Waves at Floating Type Wind Turbine Demonstration Site
NASA Astrophysics Data System (ADS)
Mase, Hajime; Yasuda, Tomohiro; Mori, Nobuhito; Tom, Tracey; Ikemoto, Ai; Utsunomiya, Tomoaki
1. Introduction The floating type wind turbine demonstration project is being performed in Japan, and a 1:2 scale model was installed off the Kabashima Island in Nagasaki Prefecture on June 11th, 2012. As for the design, external forces such as wind and wave on the floating type wind turbine demonstration site were evaluated using various kinds of re-analysis and prediction data including NCEP wind data, JMA meteorological GPV data and NEDO data. Considerations for the design were given for wave characteristics of maximum and mean wave height, crest height, 2D height-period distribution, and wave energy spectrum. Tides, currents and winds were also evaluated. In addition the extreme wind speed was estimated including typhoon effects considering grid resolution dependence gust factor. A wind and wave prediction system was developed and its validity was examined by statistically comparing predicted values with measured data at the demonstration site. The present information system gives information for various user selected areas and lead times with both visual animations and time series graphs. 2. Design wave and wind The site is located off the Kabashima Island in Nagasaki Prefecture, Japan. Design forces were determined from extreme wind and wave statistics and an empirical method. The results are: 50 years return period wave and wind: Hs = 7.73 m, Ts = 14.0 s, U = 53.1 m/s 100 years return period wave and wind: Hs = 8.20 m, Ts = 14.3 m, U = 57.0 m/s Other characteristics were also determined, such as the maximum wave height, crest height, 2D height-period distribution and wave energy spectrum, tide, current and maximum wind. 3. Wind and wave prediction system The system composed of NCEP GFS (Global Forecasting System) meteorological data, down-scaling wind field by WRF (Weather Research Forecasting), JMA HAGPV (Hourly Analyzed Grid Point Value) 10m wind data, and wind-wave forecast data by SWAN (Simulating Waves Nearshore). The flowchart shown in Fig. 1 displays the information and process flow of wind and wave data, where a new web information site has been developed. 4. Verification of predictions Satisfactorily good agreement between prediction and observation has been found when evaluating the indices of correlation coefficient, root mean square error, and Brier score. The prediction system is shown to be useful for obtaining vital offshore wind and wave information.
ERIC Educational Resources Information Center
Gillespie, A.
Describes a method for the determination of the velocity of sound using a dual oscilloscope on which is displayed the sinusoidal input into a loudspeaker and the signal picked up by a microphone. (GS)
NASA Technical Reports Server (NTRS)
A video tape related to orbital debris research is presented. The video tape covers the process of loading a High Velocity Gas Gun and firing it into a mounted metal plate. The process is then repeated in slow motion.
77 FR 29633 - Alta Wind VII, LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind XII, LLC...
Federal Register 2010, 2011, 2012, 2013, 2014
...EL12-68-000] Alta Wind VII, LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind XII, LLC, Alta Wind XIII...385.207, Alta Wind VII, LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind XII, LLC, Alta Wind...
Radiation driven winds from luminous accretion disks
Daniel Proga; James M. Stone; Janet E. Drew
We study the 2-D, time-dependent hydrodynamics of radiation-driven winds from accretion disks in which the radiation force is mediated by spectral lines. If the dominant contribution to the total radiation field comes from the disk, then we find the outflow is intrinsically unsteady and characterised by large amplitude velocity and density changes. Both infall and outflow can occur in different regions of the wind at the same time. On the other hand, if the total luminosity of the system is dominated by the central star, then the outflow is steady. In either case, we find the 2-D structure of the wind consists of a dense, slow outflow, typically confined to angles within about 45$^o$ of the equatorial plane, that is bounded on the polar side by a high -velocity, lower density stream. The flow geometry is controlled largely by the geometry of the radiation field. Global properties e.g., the total mass loss rate and terminal velocity depend more on the system luminosity and are insensitive to geometry. Matter is fed into the fast wind from within a few stellar radii of the central star. Our solutions agree qualitatively with the kinematics of outflows in CV systems inferred from spectroscopic observations. We predict that low luminosity systems may display unsteady behavior in wind-formed spectral lines. Our study also has application to winds from active galactic nuclei and from high mass YSOs.
Impact and explosion crater ejecta, fragment size, and velocity
NASA Technical Reports Server (NTRS)
Okeefe, J. D.; Ahrens, T. J.
A model was developed for the mass distribution of fragments that are ejected at a given velocity for impact and explosion craters. The model is semi-empirical in nature and is derived from (1) numerical calculations of cratering and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and crater diameter and an assumption on the functional form for the distribution of fragements ejected at a given velocity. This model implies that for planetary impacts into competent rock, the distribution of fragments ejected at a given velocity are nearly monodisperse, e.g., 20% of the mass of the ejecta at a given velocity contain fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. Using this model, the largest fragment that can be ejected from asteroids, the moon, Mars, and Earth is calculated as a function of crater diameter. In addition, the internal energy of ejecta versus ejecta velocity is found. The internal energy of fragments having velocities exceeding the escape velocity of the moon will exceed the energy required for incipient melting for solid silicates and thus, constrains the maximum ejected solid fragment size.
Wind anisotropy and stellar evolution
Cyril Georgy; Georges Meynet; Andrķ Maeder
Mass loss is a determinant factor which strongly affects the evolution and the fate of massive stars. At low metallicity, stars are supposed to rotate faster than at the solar one. This favors the existence of stars near the critical velocity. In this rotation regime, the deformation of the stellar surface becomes important, and wind anisotropy develops. Polar winds are expected to be dominant for fast rotating hot stars. These polar winds allow the star to lose large quantities of mass and still retain a high angular momentum, and they modifie the evolution of the surface velocity and the final angular momentum kept in the star's core. We show here how these winds affect the final stages of massive stars, according to our knowledge about Gamma Ray Bursts. Computation of theoretical Gamma Ray Bursts rate indicates that our models have too fast rotating cores, and that we need to include an additional effect to spin them down. Magnetic fields in stars act in this direction, and we show how they modify the evolution of massive star up to the final stages.
An optimal design of a grid connected hybrid wind\\/photovoltaic\\/fuel cell system for distributed energy production
Debosmita Das; Reza Esmaili; Longya Xu; D. Nichols
This paper proposes a hybrid energy system consisting of wind, photovoltaic and fuel cell designed to supply continuous power to the load. A simple and economic control with DC-DC converter is used for maximum power point tracking and hence maximum power extraction from the wind turbine and photovoltaic array. Due to the intermittent nature of both the wind and photovoltaic
ESL-TR-12-07-01 STATEWIDE AIR EMISSIONS CALCULATIONS FROM WIND AND OTHER RENEWABLES SUMMARY REPORT A Report to the Texas Commission on Environmental Quality For the Period September 2011 ¢ July 2012 Jeff Haberl, Ph.D., P.E... 2003 2004 2005 2006 2007 2008 2009 2010 2011 E l e c t r i c i t y G e n e r a t e d i n M W h Year Annual Electricity Generated in Texas by Renewable Sources Biomass Hydro Landfill gas Solar Wind Figure 1-5: Electricity Generation...
Velocity measurements in rotating Couette flow with axial flow
NASA Astrophysics Data System (ADS)
Stoeckert, Malte; Lueptow, Richard M.
The axial and radial velocity field for rotating Couette flow with an axial flow was measured using PIV for the condition of translating toroidal vortices, spiral vortices, and wavy vortices. In all cases the vortices translate at a velocity greater than the average axial velocity. At high ratios of the rotating Reynolds number to the axial Reynolds number, adjacent vortices exchange little fluid so that most axial fluid transport results from the axial translation of the vortices. At lower Reynolds number ratios, the axial flow winds around the translating vortices, which are somewhat smaller and shifted in an alternating fashion toward the inner and outer cylinder walls. (Partially supported by DARA and NSF)
Wind Resource Evaluation at the Caltech Field Laboratory for Optimized Wind Energy
NASA Astrophysics Data System (ADS)
Mulligan, Quinn; Kinzel, Matthias; Dabiri, John
Wind resources are evaluated at the Caltech Field Laboratory in order to understand how an array of vertical-axis wind turbines extracts energy from the flow. A tower with sonic anemometers placed every meter over the turbine's rotor height is deployed in upwind and downwind positions relative to the array of turbines to obtain the three dimensional wind velocity vectors. Upwind of the array, far enough to be considered free stream, the measured velocity profile represents the turbulent boundary layer flow at the site. Downwind, the measured wind velocities are reduced significantly and display a smaller variance over the rotor height. The topmost sensor, located above the top of the rotor height, reports flow velocities close to the free stream quantities. Sweeps and ejections are both present in the downwind velocity profile. The talk will present the data from these field measurements, discuss the similarities and differences to canopy flows and draw conclusions about the interaction between the wind turbine array and the flow. The financial support of the Moore Foundation is gratefully acknowledged.
Group Velocity Measurement Distance Travelled
Shearer, Peter
on frequency #12;Group Velocity Dispersion Use single, well-dispersed surface wave arrival DispersionWell-dispersed Rayleigh wave #12;Group Velocity Dispersion Use single, well-dispersed surface wave arrival DispersionGroup Velocity Measurement Distance Travelled Time It TookGroup Velocity (8.3) #12;Group Velocity
Satellite Observations of Glacier Surface Velocities in Southeast Alaska
NASA Astrophysics Data System (ADS)
Elliott, J.; Melkonian, A. K.; Pritchard, M. E.
Glaciers in southeast Alaska are undergoing rapid changes and are significant contributors to sea level rise. A key to understanding the ice dynamics is knowledge of the surface velocities, which can be used with ice thickness measurements to derive mass flux rates. For many glaciers in Alaska, surface velocity estimates either do not exist or are based on data that are at least a decade old. Here we present updated maps of glacier surface velocities in southeast Alaska produced through a pixel tracking technique using synthetic aperture radar data and high-resolution optical imagery. For glaciers with previous velocity estimates, we will compare the results and discuss possible implications for ice dynamics. We focus on Glacier Bay and the Stikine Icefield, which contain a number of fast-flowing tidewater glaciers including LeConte, Johns Hopkins, and La Perouse. For the Johns Hopkins, we will also examine the influence a massive landslide in June 2012 had on flow dynamics. Our velocity maps show that within Glacier Bay, the highest surface velocities occur on the tidewater glaciers. La Perouse, the only Glacier Bay glacier to calve directly into the Pacific Ocean, has maximum velocities of 3.5 - 4 m/day. Johns Hopkins Glacier shows 4 m/day velocities at both its terminus and in its upper reaches, with lower velocities of ~1-3 m/day in between those two regions. Further north, the Margerie Glacier has a maximum velocity of ~ 4.5 m/day in its upper reaches and a velocity of ~ 2 m/day at its terminus. Along the Grand Pacific terminus, the western terminus fed by the Ferris Glacier displays velocities of about 1 m/day while the eastern terminus has lower velocities of < 0.5 m/day. The lake terminating glaciers along the Pacific coast have overall lower surface velocities, but they display complex flow patterns. The Alsek Glacier displays maximum velocities of 2.5 m/day above where it divides into two branches. Velocities at the terminus of the northern branch reach 1 m/day while the terminus of the southern branch moves about 2 m/day. Grand Plateau Glacier also divides into two main branches, with a northern branch displaying peak velocities of 1.5 m/day and a southern branch flowing at a rate of 1 m/day. The Stikine Icefield contains a number of large tidewater glaciers showing maximum velocities near their termini. At the terminus of the South Sawyer Glacier, velocities reach a peak of about 2 m/day. Along the terminus of the Dawes Glacier, velocities reach 3.5 m/day. The Baird Glacier displays lower velocities of 1-1.5 m/day. LeConte Glacier has 2-3 m/day velocities in its upper regions with higher velocities near its terminus. In contrast to the pattern shown by the surrounding glaciers, the Great Glacier has a peak velocity of 2 m/day in the upper portion of the glacier and a velocity of only 0.5 m/day near its terminus.
The Eect of the Tilt of the HCS on the Solar Wind Speed in the Outer Heliosphere
Richardson, John
1 The Eect of the Tilt of the HCS on the Solar Wind Speed in the Outer Heliosphere J. D. Richardson: THE HCS TILT AND THE SOLAR WIND SPEED #12;2 Abstract. The ow of solar wind from the Sun is bimodal. High with the HCS tilt controls the solar wind velocities in the outer heliosphere near solar minimum when the Sun
Wind tunnel simulation of wind effects and associated displacement hazards on flat surface construction materials such as plywoodĀ
Madeley, Jack T.
to create such an airborne hazard with flat surface materials such as plywood. This research was developed to show select correlations between the wind velocity, lifting forces and the susceptibility to movement of large surface area flat sheets...
Investigation of gravity waves using horizontally resolved radial velocity measurements
NASA Astrophysics Data System (ADS)
Stober, G.; Sommer, S.; Rapp, M.; Latteck, R.
The Middle Atmosphere Alomar Radar System (MAARSY) on the island of And°ya in Northern Norway (69.3░ N, 16.0░ E) observes polar mesospheric summer echoes (PMSE). These echoes are used as tracers of atmospheric dynamics to investigate the horizontal wind variability at high temporal and spatial resolution. MAARSY has the capability of pulse-to-pulse beam steering allowing for systematic scanning experiments to study the horizontal structure of the backscatterers as well as to measure the radial velocities for each beam direction. Here we present a method to retrieve gravity wave parameters from these horizontally resolved radial wind variations by applying velocity azimuth display and volume velocity processing. Based on the observations a detailed comparison of the two wind analysis techniques is carried out in order to determine the zonal and meridional wind as well as to measure first-order inhomogeneities. Further, we demonstrate the possibility to resolve the horizontal wave properties, e.g., horizontal wavelength, phase velocity and propagation direction. The robustness of the estimated gravity wave parameters is tested by a simple atmospheric model.
Investigation of gravity waves using horizontally resolved radial velocity measurements
NASA Astrophysics Data System (ADS)
Stober, G.; Sommer, S.; Rapp, M.; Latteck, R.
The Middle Atmosphere Alomar Radar System (MAARSY) on the island And°ya in Northern Norway (69.3░ N, 16.0░ E) observes polar mesospheric summer echoes (PMSE). These echoes are used as tracers of atmospheric dynamics to investigate the horizontal wind variability at high temporal and spatial resolution. MAARSY has the capability of a pulse-to-pulse beam steering allowing for systematic scanning experiments to study the horizontal structure of the backscatterers as well as to measure the radial velocities for each beam direction. Here we present a method to retrieve gravity wave parameters from these horizontally resolved radial wind variations by applying velocity azimuth display and volume velocity processing. Based on the observations a detailed comparison of the two wind analysis techniques is carried out in order to determine the zonal and meridional wind as well as to measure first order inhomogeneities. Further, we demonstrate the possibility to resolve the horizontal wave properties, e.g. horizontal wavelength, phase velocity and propagation direction. The robustness of the estimated gravity wave parameters is tested by a simple atmospheric model.
Vertical Velocity Characteristics of Deep Convection over Darwin, Australia
Peter T. May; Deepak K. Rajopadhyaya
Continuous vertical velocity measurements using a 50-MHz wind profiler located at Darwin in northern Australia during periods of active convection have been analyzed. This dataset is dominated by continental-type convection. Numerous examples of shallow, deep, and decaying convection were seen and it is shown that only the deep systems have substantial tilts to the draft structure. The most intense updrafts
Wind tunnel investigation of a 14 foot vertical axis windmill
NASA Technical Reports Server (NTRS)
Muraca, R. J.; Guillotte, R. J.
A full scale wind tunnel investigation was made to determine the performance characteristics of a 14 ft diameter vertical axis windmill. The parameters measured were wind velocity, shaft torque, shaft rotation rate, along with the drag and yawing moment. A velocity survey of the flow field downstream of the windmill was also made. The results of these tests along with some analytically predicted data are presented in the form of generalized data as a function of tip speed ratio.
Interplanetary stream magnetism: Kinematic effects. [solar magnetic fields and wind
NASA Technical Reports Server (NTRS)
Burlaga, L. F.; Barouch, E.
The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.
Wake measurements around operating wind turbines
Baker, R.W.; Katen, P.C.; Walker, S.N.
Researchers at Oregon State University have conducted wind measurement programs to describe the wake behind large horizontal axis turbines at Goodnoe Hills, Washington, (MOD-2), and behind the FloWind vertical axis wind turbine near Ellenburg, Washington. Wake measurements were taken using portable kite anemometers as well as fixed place anemometers under several atmospheric stability conditions and turbine operating conditions. Centerline hub height (midrotor) measurements were taken downwind and crosswind from 3-9 diameters. These wake programs are discussed and the velocity deficits measured are compared to the estimated deficits calculated from wake models.
High Velocity Absorption during Eta Car B's Periastron Passage
NASA Technical Reports Server (NTRS)
Nielsen, Krister E.; Groh, J. H.; Hillier, J.; Gull, Theodore R.; Owocki, S. P.; Okazaki, A. T.; Damineli, A.; Teodoro, M.; Weigelt, G.; Hartman, H.
Eta Car is one of the most luminous massive stars in the Galaxy, with repeated eruptions with a 5.5 year periodicity. These events are caused by the periastron passage of a massive companion in an eccentric orbit. We report the VLT/CRIRES detection of a strong high-velocity, (<1900 km/s) , broad absorption wing in He I at 10833 A during the 2009.0 periastron passage. Previous observations during the 2003.5 event have shown evidence of such high-velocity absorption in the He I 10833 transition, allowing us to conclude that the high-velocity gas is crossing the line-of-sight toward Eta Car over a time period of approximately 2 months. Our analysis of HST/STlS archival data with observations of high velocity absorption in the ultraviolet Si IV and C IV resonance lines, confirm the presence of a high-velocity material during the spectroscopic low state. The observations provide direct detection of high-velocity material flowing from the wind-wind collision zone around the binary system, and we discuss the implications of the presence of high-velocity gas in Eta Car during periastron
Wind field variability in high-resolution simulations for wind energy forecasts and resource assessment
NASA Astrophysics Data System (ADS)
Marjanovic, N.; Chow, F. K.; Wharton, S.; Lundquist, J. K.
Wind farm resource assessment, operational wind power forecasting, and wind turbine micrositing may benefit from high-resolution simulations of atmospheric flow over complex terrain. Domains can be refined from mesoscale to finer scales using grid nesting to adequately resolve turbulence and terrain in the atmospheric boundary layer. In previous work, we showed that nesting down to fine resolutions (~100 m horizontal spacing) using the WRF model does not clearly improve mean wind forecasts for our case study wind farm when modeling either synoptically or locally driven events. Differences due to increased vertical resolution or using one- vs. two-way nesting were also minimal. The LES models we tested gave similar results and were only slightly closer to the observations than the RANS models. For this particular domain, it appears that key topographic features are well resolved even at coarser resolutions, so that there is minimal change in mean winds at finer resolutions. In this work, we investigate temporal and spatial variability of predicted fields to gain further insight into possible differences due to changes in grid configuration. We also perform week-long simulations at fine resolutions of 300 or 100 meters to determine if we can obtain more detailed results for wind energy resource assessment. High-resolution representation of the spatial structure of the wind flow might be able to better capture variations in wind velocity that are relevant to wind resource assessment. Improved turbulence closure schemes will also be tested and should be able to better capture the fluctuations in the wind fields which may contribute to turbine fatigue. Long term, fine resolution runs should provide more insight into wind patterns and yield frequency distributions of wind speed, wind shear, TKE, and other factors that are invaluable to wind farm operators in determining appropriate sites for turbines and times for greatest power output.
Investigation on wind energy-compressed air power system.
Jia, Guang-Zheng; Wang, Xuan-Yin; Wu, Gen-Mao
Wind energy is a pollution free and renewable resource widely distributed over China. Aimed at protecting the environment and enlarging application of wind energy, a new approach to application of wind energy by using compressed air power to some extent instead of electricity put forward. This includes: explaining the working principles and characteristics of the wind energy-compressed air power system; discussing the compatibility of wind energy and compressor capacity; presenting the theoretical model and computational simulation of the system. The obtained compressor capacity vs wind power relationship in certain wind velocity range can be helpful in the designing of the wind power-compressed air system. Results of investigations on the application of high-pressure compressed air for pressure reduction led to conclusion that pressure reduction with expander is better than the throttle regulator in energy saving. PMID:14727304
NSDL National Science Digital Library
K-12 Outreach Office,
Students are challenged to design and build wind chimes using their knowledge of physics and sound waves, and under given constraints such as weight, cost and number of musical notes it must generate. They make mathematical computations to determine the pipe lengths.
NSDL National Science Digital Library
This module provides a basic understanding of why gap winds occur, their typical structures, and how gap wind strength and extent are controlled by larger-scale, or synoptic, conditions. You will learn about a number of important gap flows in coastal regions around the world, with special attention given to comprehensively documented gap wind cases in the Strait of Juan de Fuca and the Columbia River Gorge. Basic techniques for evaluating and predicting gap flows are presented. The module reviews the capabilities and limitations of the current generation of mesoscale models in producing realistic gap winds. By the end of this module, you should have sufficient background to diagnose and forecast gap flows around the world, and to use this knowledge to understand their implications for operational decisions. Other features in this module include a concise summary for quick reference and a final exam to test your knowledge. Like other modules in the Mesoscale Meteorology Primer, this module comes with audio narration, rich graphics, and a companion print version.
Dynamic simulation of dual-speed wind turbine generation
Muljadi, E.; Butterfield, C.P.
Induction generators have been used since the early development of utility-scale wind turbine generation. An induction generator is the generator of choice because of its ruggedness, and low cost. With an induction generator, the operating speed of the wind turbine is limited to a narrow range (almost constant speed). Dual- speed operation can be accomplished by using an induction generator with two different sets of winding configurations or by using two induction generators with two different rated speeds. With single- speed operation, the wind turbine operates at different power coefficients (Cp) as the wind speed varies. The operation at maximum Cp can occur only at a single wind speed. However, if the wind speed varies across a wider range, the operating Cp will vary significantly. Dual-speed operation has the advantage of enabling the wind turbine to operate at near maximum Cp over a wider range of wind-speeds. Thus, annual energy production can be increased. The dual-speed mode may generate less energy than a variable-speed mode; nevertheless, it offers an alternative to capture more energy than single-speed operation. In this paper, dual-speed operation of a wind turbine will be investigated. One type of control algorithm for dual- speed operation is proposed. Results from a dynamic simulation will be presented to show how the control algorithm works and how power, current and torque of the system vary as the wind turbine is exposed to varying wind speeds.
Wind erosion from a sagebrush steppe burned by wildfire: Measurements of PM10 and total horizontal sediment flux
NASA Astrophysics Data System (ADS)
Wagenbrenner, Natalie S.; Germino, Matthew J.; Lamb, Brian K.; Robichaud, Peter R.; Foltz, Randy B.
Wind erosion and aeolian transport processes are under studied compared to rainfall-induced erosion and sediment transport on burned landscapes. Post-fire wind erosion studies have predominantly focused on near-surface sediment transport and associated impacts such as on-site soil loss and site fertility. Downwind impacts, including air quality degradation and deposition of dust or contaminants, are also likely post-fire effects; however, quantitative field measurements of post-fire dust emissions are needed for assessment of these downwind risks. A wind erosion monitoring system was installed immediately following a desert sagebrush and grass wildfire in southeastern Idaho, USA to measure wind erosion from the burned landscape. This paper presents measurements of horizontal sediment flux and PM10 vertical flux from the burned area. We determined threshold wind speeds and corresponding threshold friction velocities to be 6.0 and 0.20 m s-1, respectively, for the 4 months immediately following the fire and 10 and 0.55 m s-1 for the following spring months. Several major wind erosion events were measured in the months following the July 2010 Jefferson Fire. The largest wind erosion event occurred in early September 2010 and produced 1495 kg m-1 of horizontal sediment transport within the first 2 m above the soil surface, had a maximum PM10 vertical flux of 100 mg m-2 s-1, and generated a large dust plume that was visible in satellite imagery. The peak PM10 concentration measured on-site at a height of 2 m in the downwind portion of the burned area was 690 mg m-3. Our results indicate that wildfire can convert a relatively stable landscape into one that is a major dust source.
ERIC Educational Resources Information Center
Greenslade, Thomas B., Jr.
Discusses a series of experiments performed by Thomas Hope in 1805 which show the temperature at which water has its maximum density. Early data cast into a modern form as well as guidelines and recent data collected from the author provide background for duplicating Hope's experiments in the classroom. (JN)
Maximum Chemical and Physical Hardness
Ralph G. Pearson
Density functional theory (DFT) is briefly reviewed, especially concepts such as the electronic chemical potential and the hardness of the electron density function. There is much evidence, and a mathematical proof, that this chemical hardness is a maximum for an equilibrium system. The proof is based on a combination of statistical mechanics, the fluctuation-dissipation theorem, and correlation functions. In MO
Doppler Lidar for Wind Measurements on Venus
NASA Technical Reports Server (NTRS)
Singh, Upendra N.; Emmitt, George D.; Yu, Jirong; Kavaya, Michael J.
NASA Langley Research Center has a long history of developing 2-micron laser transmitter for wind sensing. With support from NASA Laser Risk Reduction Program (LRRP) and Instrument Incubator Program (IIP), NASA Langley Research Center has developed a state-of-the-art compact lidar transceiver for a pulsed coherent Doppler lidar system for wind measurement. The transmitter portion of the transceiver employs the high-pulse-energy, Ho:Tm:LuLiF, partially conductively cooled laser technology developed at NASA Langley. The transceiver is capable of 250 mJ pulses at 10 Hz. It is very similar to the technology envisioned for coherent Doppler lidar wind measurements from Earth and Mars orbit. The transceiver is coupled to the large optics and data acquisition system in the NASA Langley VALIDAR mobile trailer. The large optics consists of a 15-cm off-axis beam expanding telescope, and a full-hemispheric scanner. Vertical and horizontal vector winds are measured, as well as relative backscatter. The data acquisition system employs frequency domain velocity estimation and pulse accumulation. It permits real-time display of the processed winds and archival of all data. This lidar system was recently deployed at Howard University facility in Beltsville, Mary-land, along with other wind lidar systems. Coherent Doppler wind lidar ground-based wind measurements and comparisons with other sensors will be presented. A simulation and data product for wind measurement at Venus will be presented.
Threshold friction velocity of crusted windblown soils in the Columbia Plateau
NASA Astrophysics Data System (ADS)
Sharratt, B. S.; Vaddella, Venkata
Wind erosion processes are governed by soil physical properties and surface characteristics. Erosion is initiated when the friction velocity exceeds the threshold friction velocity (u?t) of soils. Although u?t is influenced by soil physical properties such as wetness and crusting, there is little information available on the effect of soil crusting on u?t. Knowledge of the relationship between soil crusting and u?t is required to improve our ability to predict wind erosion and PM10 (particulates ?10 ?m in aerodynamic diameter) emissions from crusted soils. Threshold friction velocity was assessed on five soil types commonly found across the Columbia Plateau. These soils were obtained from agricultural fields, placed in trays, subject to various rainfall amounts to promote crust formation, and then exposed to winds inside a wind tunnel. Emission of soil particulates and PM10 as a function of wind speed were monitored by saltation and aerosol sensors. Threshold friction velocity was determined by systematically increasing wind speed until we observed an increase in airborne particulate or PM10 concentration. Threshold friction velocity increased with the development of a soil crust; u?t increased exponentially with an increase in crust strength and thickness. The relationship between u?t and crust thickness was influenced by clay content. The relationship between u?t and crust strength and thickness should be considered when simulating wind erosion of agricultural soils.
Velocities of windblown particles in saltation: Venus, Earth, and Mars
NASA Technical Reports Server (NTRS)
Greeley, R.
Particle velocities were determined in environmental wind tunnels capable of simulating aeolian processes on Earth, Mars, and Venus. Comparisons of results for Earth, Mars, and Venus reveal some remarkable differences. Most particles achieve speeds nearly equal to freestream wind speed on Venus, but seldom achieve half the wind speed on Mars; Earth cases are of intermediate values. This is attributed to the differences in atmospheric density and to the threshold wind speeds among the three planetary environments. Particles are more easily moved in the dense venusian atmosphere than on Mars; consequently, threshold speeds are very low, and for the range of wind speeds in which most movement is presumed to occur (just above threshold speeds), the grains need not be moving very fast to achieve 100% of the wind speed. Conversely, particles on Mars must accelerate very rapidly to achieve the speed of the high winds required for threshold, and despite the fact that saltation path lengths are long on Mars, most grains fall to the surface before achieving even 50 to 60% of freestream wind speed.
NASA Astrophysics Data System (ADS)
Tajima, Y.; Madsen, O. S.
The paper will present a theoretical model for the prediction of undertow velocity profiles in the surf zone due to near-normally incident waves. The waves may be periodic or narrow-banded random waves, and the beach may be plane or barred. The theoretical model consists of three components: (i) breaking wave model; (ii) surface roller model; and (iii) undertow velocity profile model. \\textit{The breaking wave model} (Tajima and Madsen, 2002) is based on the concept of an equivalent linear wave and predicts linear wave characteristics for shoaling, breaking and broken waves. Non-linear wave characteristics, e.g., near-bottom orbital velocity, are obtained from equivalent linear wave characteristics and local bottom slope through use of simple transform formulae. \\textit{The surface roller model} is based on the same principle as Dally et al. (1985), but differs from this by transferring only the potential energy lost from the wave motion into the surface roller and calculating the decay of surface roller energy using a decay coefficient equal to that obtained for the breaking wave dissipation model. \\textit{The undertow velocity profile model} assumes a linearly varying shear stress over the water depth combined with an assumed form of the turbulent eddy viscosity. The shear stress at the surface is obtained from the breaking wave and surface roller models, whereas the bottom shear stress is obtained from considerations of mass conservation, i.e., depth-integrated undertow velocity must equal the volume transport of waves and surface roller above trough level. The near-bottom undertow velocity is calculated at the edge of the wave-bottom boundary layer, from knowledge of near-bottom orbital velocity, bottom shear stress and bottom roughness, using the combined wave-current bottom boundary layer theory by Madsen (1994). Comparison of predicted and measured undertow velocity profiles are performed for periodic and random waves normally incident on plane and barred concrete beaches as well as random waves near-normally incident on barred movable bed beach profiles. In general the agreement between predicted and observed undertow velocities is excellent. It is shown that model predictions are fairly insensitive to the choice of turbulent eddy viscosity, which is the only adjustable quantity in the model.
KLUN+ peculiar velocity survey
M O Hanski
The enhanced Kinematics of the Local Universe (KLUN+) galaxy sample is a collection of galaxies suitable for Tully-Fisher (TF) or Faber-Jackson (FJ) distance estimation. Here we extract a subsample of 6229 KLUN+ galaxies closer than 80 Mpc/h, and calculate their distances and peculiar velocities with the Iterative Normalized Distance method. Within this method we can derive an analytical formula, independent from the density inhomogeneities, for correcting the selection biases. The radial peculiar velocities can then be derived from the redshifts and the corrected distances. The velocities are smoothed, and the smoothed velocity field is used as a correction term at the next derivation of normalized distances. This iterative procedure is repeated until converging values are reached. Here we present the resulting map of the radial peculiar velocity field at the < 80 Mpc/h environment. The infall patterns towards the main galaxy clusters are clearly visible. The color version of the map, other figures, and animations are provided on the project web site.
Maximum cooling and maximum efficiency of thermoacoustic refrigerators
NASA Astrophysics Data System (ADS)
Tartibu, L. K.
This work provides valid experimental evidence on the difference between design for maximum cooling and maximum efficiency for thermoacoustic refrigerators. In addition, the influence of the geometry of the honeycomb ceramic stack on the performance of thermoacoustic refrigerators is presented as it affects the cooling power. Sixteen cordierite honeycomb ceramic stacks with square cross sections having four different lengths of 26, 48, 70 and 100 mm are considered. Measurements are taken at six different locations of the stack hot ends from the pressure antinode, namely 100, 200, 300, 400, 500 and 600 mm respectively. Measurement of temperature difference across the stack ends at steady state for different stack geometries are used to compute the cooling load and the coefficient of performance. The results obtained with atmospheric air showed that there is a distinct optimum depending on the design goal.
Effects of Stream-Associated Upon the Radial Variation of Average Solar Wind Parameters
The effects of nonlinear fluctuations due to solar wind streams upon radial gradients of average solar wind parameters are computed by using a numerical MHD model for both spherically symmetric time- dependent and corotating equatorial flow approximations. We find significant effects of correlations between fluctuations upon the gradients of azimuthal magnetic field, radial velocity, density, and azimu- thal velocity. The
On the equation of state of solar wind ions derived from HELIOS measurements
E. Marsch; K. H. Muehlhaeuser; H. Rosenbauer; R. Schwenn
The radial evolution of such adiabatic invariants as the ion magnetic moments are studied on the basis of solar wind ion velocity distribution observations made by the Helios spacecraft between 0.3 and 1 AU. Significant differences between proton and alpha-particle parameters in wind velocity dependence are noted, and adiabaticity is on the average found to be violated. This violation is
Wind induced vibrations of thin-walled cylindrical struc- tures
D. Dooms; G. Degrande; G. De Roeck; E. Reynders
Circular cylindrical shell structures are sensitive to wind induced ovalling oscillations, which is an aeroelastic phenomenon. Coupled numerical models of the structure and the wind o w around the structure aim to predict the onset o w velocity. This paper presents a nite element model of a silo that is validated by means of experimental results that have been measured
Richard A. Elco
Neither Venus nor the moon have a significant dipole magnetic field, and their atmospheres are exposed to the solar wind and the interplanetary magnetic field. As the solar wind ions penetrate the atmosphere, photo and charge-exchange ionization reactions alter the density and velocity of the ion stream. A collisionless reacting hydromagnetic model is used to describe the flow of atmospheric
Robust Multi-loop Airborne SLAM in Unknown Wind Environments
Kim, Jonghyuk "Jon"
platforms which are typically payload limited. Nonlinear filtering, such as the particle filter, can reduceRobust Multi-loop Airborne SLAM in Unknown Wind Environments Jonghyuk Kim Department of Engineering presents a robust multi-loop airborne SLAM structure which also augments wind information. The air velocity
Threshold windspeeds for sand on Mars - Wind tunnel simulations
R. Greeley; R. Leach; B. R. White; J. Iversen; J. B. Pollack
Wind friction threshold speeds for particle movement were determined in a wind tunnel operating at martian surface pressure with a 95 percent CO2 and 5 percent air atmosphere. The relationship between friction speed and free-stream velocity is extended to the critical case for Mars of momentum thickness Reynolds numbers between 425 and 2000. It is determined that the dynamic pressure
Mass spectrometric measurement of thermospheric wind
NASA Technical Reports Server (NTRS)
Knutson, J. R.; Kayser, D. C.; Potter, W. E.
The open source neutral mass spectrometer (OSS) on the Atmosphere Explorer C satellite was periodically operated in an experimental 'fly-through' mode. When the satellite is spinning, the signal from this mode displays a sharp maximum that occurs when the instrument source faces directly into the oncoming gas. Thus the location of this maximum is sensitive to neutral wind components in the spin plane. Twenty-two spinning fly-through orbits were analyzed to determine vertical wind magnitudes in the altitude range 160-250 km. Large (up to 65 m/s) magnitudes were detected in the early morning sector of the auroral zone.
Aerodynamic study of a stall regulated horizontal-axis wind turbine
NASA Astrophysics Data System (ADS)
Constantinescu, S. G.; Crunteanu, D. E.; Niculescu, M. L.
The wind energy is deemed as one of the most durable energetic variants of the future because the wind resources are immense. Furthermore, one predicts that the small wind turbines will play a vital role in the urban environment. Unfortunately, the complexity and the price of pitch regulated small horizontal-axis wind turbines represent ones of the main obstacles to widespread the use in populated zones. Moreover, the energetic efficiency of small stall regulated wind turbines has to be high even at low and medium wind velocities because, usually the cities are not windy places. During the running stall regulated wind turbines, due to the extremely broad range of the wind velocity, the angle of attack can reach high values and some regions of the blade will show stall and post-stall behavior. This paper deals with stall and post-stall regimes because they can induce significant vibrations, fatigue and even the wind turbine failure.
A hybrid cyclogiro-Darrieus-rotor wind turbine
J. A. C. Kentfield
A vertical-axis wind turbine combining features of cyclogiro and Darrieus rotor designs has been developed. The wind turbine has less mechanical complexity than a conventional cyclogiro and shows better performance at low velocity ratios than a Darrieus rotor. Model tests of two- and three-bladed prototypes of the wind turbine prove that both designs are self-starting. Cyclically variable blade angles of
Sea ice motion in response to geostropic winds
A. S. Thorndike; R. Colony
It is an old rule-of-thumb that sea ice moves with a speed of about 2% of the surface wind and about 45░ to the right of the wind. A similar relationship between the ice velocity and the geostrophic wind is examined here. It is found that only about half of the long-term (several month) average ice motion is directly related
Blowdown Wind Tunnels: Latest Citations from the Aerospace Database
NASA Technical Reports Server (NTRS)
The bibliography contains citations concerning the design, construction, operation, and performance of blowdown wind tunnels. The use of compressed gas, mechanical piston, or combustion exhaust to provide continuous or short-duration operation from transonic to hypersonic approach velocities is discussed. Also covered are invasive and non-invasive aerothermodynamic instrumentation, data acquisition and reduction techniques, and test reports on aerospace components. Comprehensive coverage of wind tunnel force balancing systems and supersonic wind tunnels are covered in separate bibliographies.
Lebost wind turbine: laboratory tests and data analysis
M. I. Hoffert; B. A. Rugg
Preliminary aerodynamic torque and power measurements and data analysis are presented for the Lebost Wind Turbine--a recently patented vertical-axis wind energy machine incorporating flow-focusing inlets fixed to a housing shroud surrounding blades rotating normal to the flow. Two laboratory-scale models were constructed, instrumented, and tested in a specially modified section of the NYU 30-m wind tunnel at freestream velocities (U\\/sub
Fluidic angular velocity sensor
NASA Technical Reports Server (NTRS)
Berdahl, C. M. (inventor)
A fluidic sensor providing a differential pressure signal proportional to the angular velocity of a rotary input is described. In one embodiment the sensor includes a fluid pump having an impeller coupled to a rotary input. A housing forming a constricting fluid flow chamber is connected to the fluid input of the pump. The housing is provided with a fluid flow restrictive input to the flow chamber and a port communicating with the interior of the flow chamber. The differential pressure signal measured across the flow restrictive input is relatively noise free and proportional to the square of the angular velocity of the impeller. In an alternative embodiment, the flow chamber has a generally cylindrical configuration and plates having flow restrictive apertures are disposed within the chamber downstream from the housing port. In this embodiment, the differential pressure signal is found to be approximately linear with the angular velocity of the impeller.
Dynamic impact of the vertical shear of gradient wind on the tropical cyclone boundary layer wind field
NASA Astrophysics Data System (ADS)
Cai, Ninghao; Xu, Xin; Song, Lili; Bai, Lina; Ming, Jie; Wang, Yuan
This work studies the impact of the vertical shear of gradient wind (VSGW) in the free atmosphere on the tropical cyclone boundary layer (TCBL). A new TCBL model is established, which relies on fiveforce balance including the pressure gradient force, Coriolis force, centrifugal force, turbulent friction, and inertial deviation force. This model is then employed to idealize tropical cyclones (TCs) produced by DeMaria's model, under different VSGW conditions (non-VSGW, positive VSGW, negative VSGW, and VSGW increase/decrease along the radial direction). The results show that the free-atmosphere VSGW is particularly important to the intensity of TC. For negative VSGW, the total horizontal velocity in the TCBL is somewhat suppressed. However, with the maximum radial inflow displaced upward and outward, the radial velocity notably intensifies. Consequently, the convergence is enhanced throughout the TCBL, giving rise to a stronger vertical pumping at the TCBL top. In contrast, for positive VSGW, the radial inflow is significantly suppressed, even with divergent outflow in the middle-upper TCBL. For varying VSGW along the radial direction, the results indicate that the sign and value of VSGW is more important than its radial distribution, and the negative VSGW induces stronger convergence and Ekman pumping in the TCBL, which favors the formation and intensification of TC.
Measurements of wind friction speeds over lava surfaces and assessment of sediment transport
NASA Technical Reports Server (NTRS)
Greeley, Ronald; Iversen, James D.
Wind velocity profiles were obtained over alluvial plains, lava flows, and a cinder cone in the Mojave Desert to determine the wind shear and the potential for particle transport. It was found that aerodynamic roughness for winds increases nearly a factor of 5 as flow crosses from the alluvium to the lava surface, resulting in wind shear that is 21 percent greater. Thus, wind erosion and sand flux may be substantially enhanced over the lava field. Moreover, wind flow turbulence is enhanced in the wake of the cinder cone, which also increases erosion and sediment transportation by the wind.