Research On Identification Of Time-Varying Modal Parameters By Time-Frequency Technology

It is difficult to identify modal parameter of time-varying structures, but there are many problems in engineering to solve urgently, such as the dynamical feature extraction of large spacecraft flexible structure, varying mass problems of rocket, bridge vibration causing high-speed train, etc.This paper aims at modal parameter identification of time-varying structures. The main work is as follow:(1),A new correlation coefficient method based on singular-value decomposition (SVD) is proposed to denoise and analysize frequency bands. Firstly, decompose the response signal by SVD, and then select a reasonable order for noise reduction according to the correlation coefficient between each reconstructed signal and original signal ;Another processing technique based on wavelet-SVD is introduced in this paper .(2),The analytical vibration equation schemes on empirical mode decomposition(EMD) and on wavelet packet transform(WPT) are proposed to identify modal parameter of time-varying structures.(3),The analytical response signal schemes on EMD and on WPT are studied to identify modal parameter of time-varying structures.(4),The technique of wavelet transform(WT) based on EMD is applied to extract time-varying modal parameters. The applications of the proposed method are illustrated using three degree of freedom systems with changing stiffness characteristics. Numerical simulation results demonstrate that that the methods based on EMD yield accurate results, but the methods based on WPT yield poor results.A simple-supported beam system with moving mass is built with ADAMS software .Simulation results show that the methods based on EMD yield good results.