Acquirement and Interpretation of Spatially Distributed Impulsive Acceleration Signals in a Flexible Shaft-Propeller System

This work reports on the spatio-temporal characterization of collocated ensembles of experimental time series of the impulsive dynamics in a complex flexible structural-machinery system composed of a shaft supporting at its free end a three-bladed boat propeller. A few state-of-the-art piezoelectric accelerometers sample simultaneously the impulsive response of the system as a function of the location of a modal hammer force applied sequentially over a global interrogation curve. The typical ensemble of collocated signals is subject to a systematic coherence analysis by advanced tools based on the theory of Proper Orthogonal Decomposition (POD) transforms. It turns out that three different collocated ensembles of acceleration signals, collected at the blades at symmetric locations, are very coherent and robust as distributed information over the space-time domain. The characteristics of coherence of the collocated databases are studied in depth by presenting a detailed POD analysis at the system and subsystems levels. The main result is the fact that the POD modes of collocated acceleration databases that exploit structural symmetries seem to provide reliable means to detect sharply differences-due to damage and perhaps design fault-in the subsystem impulsive response.