System identification from stationary ambient response using wavelet analysis with variable modal scales

This study used a wavelet-based technique with variable modal scales to achieve the identification of modal parameters. Combined with the correlation technique or random decrement algorithm, the stationary response can be transformed into a quasi-free response, which can be employed to estimate the number of excited modes of structures and determine the modal scale corresponding to the major modes solely through the wavelet analysis. An improvement method is also proposed for the amplitude maximum method (AM) in the determination of modal scale obtained from the ridges in the time–frequency wavelet spectrum. The amplitude accumulation method can be employed to more accurately estimate the corresponding scale of each mode and avoid the disadvantage of low robustness of the conventional AM method for measurements contaminated with noise. Numerical simulations and an experimental validation of a realistic 6061-T6 aluminum alloy beam are used to demonstrate the effectiveness and robustness of the proposed method to identify modal parameters from the response of structures subjected to stationary ambient excitation under noisy conditions.