Propriétés de moyennage d'ensemble des signaux acoustiques en milieu réverbérant et applications potentielles au contrôle et à la caractérisation des structures.

摘要

The propagation of acoustic and elastic waves in a finite media with low attenuation leads to measured signals of long durations (reverberation). In conventional techniques for non-destructive testing and imaging, only the first wave packets are usually exploited, and the information potentially contained in reverberation codas is lost. The work presented in this thesis aims to exploit the overall behavior of codas recorded in plate-like structures, in order to extract the maximum information from a limited number of sensors and simple processing. We have developed statistical models to predict the behavior of reverberant acoustic waves in a plate (in the form of ensemble-averages), from a limited set of experimentally accessible parameters. Thus, it is shown that theoretical expressions for the mathematical expectations of the envelopes, the correlation functions or the so-called Schroeder’s integral of reverberant signals received at some points contain potentially useful information about the structural properties of the medium, the sources or the defects. After numerical and experimental validation, potential applications are presented, such as the estimate of structural properties of a plate or source location. In addition, these techniques do not require any time measurement or even trigger synchronization between the input channels of instrumentation, thus implying low hardware constraints. Such methods could also be used to characterize a defect in a reverberant structure and can be considered as complementary to conventional NDT techniques and structural health monitoring.