This study is focused on the superelastic Ni-based shape memory alloy (SMA) for finite-element applications. SMA has presented excellent characterisations in biomedical application, mechanical application, aerospace application, seismic prevention, disaster reduction and so on. In this study, a SMA constitutive model is proposed that is capable of describing SMA superelastic features and its plasticity effects. Finally, the analysed results show good ability to predict the experimental data.
Vehicle aerodynamic shape optimisation is a typical non-linear and computationally expensive black box problem, which is severely limited by time and cost of the objective function evaluations during the global optimisation process. To solve the shortcomings of low efficiency and high cost of the existing vehicle drag reduction method, an improved efficient global optimisation (EGO) algorithm is used to optimise a four-dimensional aerodynamic drag reduction design of a vehicle combined with computational fluid dynamics numerical simulation technology. Moreover, data mining technologies are used to reveal the influence mechanisms of design variables on aerodynamic drag and to analyse the relationship between the variables. It is demonstrated that the improved EGO algorithm, based on the kriging response surface and expected improvement function, can achieve the global optimum with minimum function evaluations. The aerodynamic drag of the optimal design is 1.56% lower than that of the original vehicle. The data mining results showed that the engine hood inclination and the tail upturn angle play a leading role in the vehicle&apos;s aerodynamic drag, and the hood inclination has the greatest impact.
With the use of large eddy simulation (LES), the initial structure and mixing characteristics of both the subsonic and supersonic circular jets are studied, respectively. The stretched-vortex model combined with the high-order hybrid scheme is employed to solve the LES equations. The typical structures of the initial jet at different conditions have been presented and discussed. The formation and evolution process of the vortex ring has been displayed in detail, and the unique characteristics of a compressible vortex ring generated by the unsteady jet have been identified. Furthermore, the engulfment and mixture of ambient gas with the jet gases have been discussed, the different mixing processes of both subsonic and supersonic jets, especially the shock wave effect in a supersonic jet on mixing process, have been illustrated.
Piezopositioning stage is widely used in the field of precision positioning. However, the positioning accuracy of the stage is primarily affected by the hysteresis property and dynamic property. In order to obtain high positioning precision, a mathematical model of the micro-displacement stage needs to be accurately modelled. They take a comprehensive consideration of the hysteresis property and dynamic property of stage and then build a mathematical model by combining these two properties, which can reflect both of the two properties. PI model is adopted to model the hysteresis property, the threshold r is determined by the non-uniform threshold method, and weight coefficient w is firstly identified by fitting the initial curve under the condition of off-line, and then on-line modified when the stage works. Dynamic modelling adopts a second-order system whose parameters of transfer function model are determined by the frequency analysis method. Comparing with the experiment results and the simulation, the maximum error and the mean error of this model are, respectively, 0.124 and 0.061 µm when the positioning range is 10 V. It indicates that this mathematical model of piezopositioning stage can meet the needs of the precision positioning of the micro-displacement stage.
The pivotal steering ability of vehicles is important in the case of narrow steering space. In this study, a pivot steering system for the rescue vehicle is designed, and the 1D + 3D co-simulation model is established based on automatic dynamic analysis of mechanical systems (Adams) and advanced modelling environment for performing simulation of engineering systems (AMESim). The dynamic analysis of the pivot steering system has been compared with the theoretical calculations, which proved the correction of the model. In addition, through the simulation, the authors can hold the conclusion that the tyre cornering stiffness has a great influence on the pivot steering system.
The aero-engine to be cleaned online can significantly improve compressor performance and increase maintenance intervals, but the cleaning online cannot achieve the anticipated effects due to the lack of cognisance of the internal multiphase flow field. In order to explore the characteristics of the compressor&apos;s internal flow field, a compressor and nozzle&apos;s flow channel model was established based on the data of the Rotor36 compressor blades published by NASA. The fluid simulation software was used to analyse the effects of circumferential vortex and axial vortex on the wall surface at different jet parameters and characteristics of the gas–liquid flow field formed by the compressor blades at different rotation speeds. It is concluded that the flow field formed at a jet pressure of 5 atm and a rotational speed of 2880 rpm is more favourable to the removal of fouling.
Time-varying contact line and mesh stiffness are important parameters for dynamic investigation of helical gear pair with profile modification; however, the calculation methods of the time-varying mesh with high accuracy and high efficiency are also very limited currently. A new mesh stiffness calculation method for helical gear pairs with profile modification is proposed. The new method is conducted by cutting the helical gear tooth into slices to obtain the change of the contact line and the time-varying mesh stiffness with considering the change of each slice&apos;s engagement performance introduced by the profile modification. Then, the mesh stiffness of the assumed three different modification cases is calculated by using the proposed method. The calculated results indicate that the proposed method can be used to calculate the mesh stiffness of helical gear pairs, especially of those with tooth profile modification.
To handle the increasingly serious air pollution issue, the concept of atmospheric air purification tower already has been proposed. The first prototype of such a novel system had been built in Xi&apos;an, China. The aim of this study is to numerically study how the crosswind affects the dust removal performance of the atmospheric air purification tower and which counter-wind strategy is optimal choice. To achieve that, a three-dimensional model considering the external environment was developed in ANSYS Fluent. With the help of the proposed model, the benefits of three wind breaking designs were quantified and compared. The results showed that the design with inner union-jack shaped wind break walls is the optimal for the atmospheric air purification tower. It can maintain the dust removal rate of the system at relatively high level (3.5 kg/h) no matter what crosswind intensity is.
Pneumatic actuators (referred to as pneu-nets) are drawing increasing attention due to their high customisability, ease of fabrication and innate softness. The actuator&apos;s ability to bend is one of the important parameters characterising its performance and related to its structure. Some structures are developed. In this work, a new structure (NS) pneu-nets is developed, and its bending ability is compared with the currently common Mosadegh pneu-nets structure (developed by Mosadegh). These two are analysed in two aspects: the trajectories of the pneu-nets actuator&apos;s tip, and the defined angle of bending. The results indicate that the NS pneu-nets actuators are able to achieve greater bending at higher pressures and can be lightweight. These pneumatic actuators provide improved structure for soft robotics.