Space–wavenumber and time–frequency analysis for damage inspection of thin-walled structures

Abstract

This article presents a dynamics-based methodology for accurate damage inspection of thin-walled structures by combining a boundary effect evaluation method (BEEM) for space–wavenumber analysis of measured operational deflection shapes (ODSs) and a conjugate-pair decomposition (CPD) method for time–frequency analysis of time traces of measured points. BEEM is for locating and estimating small structural damages by processing ODSs measured by a full-field measurement system (e.g. a scanning laser vibrometer or a camera-based motion measurement system). BEEM is a nondestructive spatial domain method based on sliding-window processing of ODSs, and it works without using any structural model or historical data for comparison. Similar to the short-time Fourier transform and wavelet transform, CPD uses adaptive windowed regular harmonics and function orthogonality to perform time–frequency analysis of time traces by extracting time-localized regular and/or distorted harmonics. Both BEEM and CPD are local spectral analyses based on local, adaptive curve fitting. The first estimation of the wavenumber for BEEM and the frequency for CPD is obtained using a four-point Teager–Kaiser algorithm based on the use of finite difference. Numerical simulations and experimental results show that the combination of BEEM and CPD for space–wavenumber and time–frequency analyses provide an accurate tool for damage inspection of thin-walled structures.