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Advanced Processing of Collocated Acceleration Signals in Symmetric Beam-Like Structures With Applications to Damage Detection in a Propeller

It is found that ensembles of collocated experimental acceleration signals induced by impulses applied sequentially over the surface of beam-like structures are characterized by fast-decaying POD-modal energy spectra. Governed by a power law, this type of quite fast decay directly reflects high level of spatio-temporal coherence. Collocated ensembles of acceleration signals at various locations are governed by identical POD modes representing normal modes of vibration. Thus, collocated measurements of impulse-induced acceleration signals furnish a physics-carrying spatially distributed sensing of free dynamics. In view of this fact, three accelerometers were placed on strategic locations on an aircraft propeller to acquire collocated databases and thus we obtained an optimal reduced modal characterization of impulse-induced free dynamics. Quite interesting from the standpoint of size of damage detection, it is found that the first POD mode is quite sensitive to a small defect located at one of the propeller tips. Damage size sensitivity is distributed and depends on the sensor-defect relative distance. It is enhanced considerably in regimes of initial wave-vibration transients. Using the POD modal structure, damage indices are introduced and computed at the first-POD energy level. Accurate estimates for dissipation factor are obtained via the non-linear dynamics return map notion.