Modal Parameters Identification Based On Wavelet Analyses Under Ambient Excitation

The paper discusses the application of wavelet analysis theory in the modal identification underambient excitation. First, we extract the equivalent impulse response signal from the random responseby the natural excitation technology (NExT) or random decrement technology (RDT). Second, weobtain the modal wavelet ridges through wavelet transform analysis and relevant optimization method.Finally, we fit the wavelet coefficients corresponding to the scales that wavelet ridges contain andthen identifying the modal parameters that include natural frequencies, damping ratios and modeshapes. In this paper, the Crazy climber algorithm is proposed to extract the wavelet ridge，it is a kindof mathematical statistics method which can be used to extract multi-ridges, so it provides the basisfor identifying the multi-freedom system. In addition, we generally assume the environment incentiveto be white noise incentive when doing operational modal analysis. While the actual engineering testoften mixed with some non-stationary, impulse, periodic components, which would affect theaccuracy of the modal identification. Thus, the paper introduces some methods for signal stationeriesand proposes an amplitude curve diagram to identify the periodic signal. Then take measures to getrid of the periodic components. Due to edge effect problem, the paper adopts the SVM technologywhich can do small sample prediction and continuation processing for the original signal.Finally, in order to verify and analyze the feasibility of the proposed theory, the paper simulate acantilever beam structure which is set in two conditions and analyzed by ERA and wavelet analysisalgorithms respectively. The results show that the method can decouple dense modes and identifyaccuracy results. It has a good reference value for the engineering and technical personnel.