Research On Modal Parameters Identification Of Time-varying Structures Under Complex Ambient Excitation

It is difficult to measure the inputs with complex nature when the time-varying structures are in natural working conditions,such as the dynamical feature extraction of large spacecraft flexible structure,varying mass problems of rocket, bridge vibration caused by high-speed train, etc. The modal analysis on the measured responses-only under complex ambient excitation is of major importance.The modal parameter identification techniques of the time-varying structures under the complex excitation composed of white-noise, harmonic and transient components are proposed in this paper. The singular-value decomposition (SVD) is proposed to denoise, the band-pass filtering is used to select the interested frequencies, and then the values of the correlation coefficients between the IMFs and the inspected raw signal is used to select the vital IMFs. The method based on Hilbert-Huang transformation and that based on combining EMD with Neural Network are proposed to identify the modal parameters of the structures under complex ambient excitations.The applications of the outlined methods are illustrated using three degree of freedom systems with changing stiffness characteristics using MATLAB software. Numerical simulation results demonstrate that the method based on Hilbert-Huang transformation and the method based on combining EMD with Neural Network yield good results.A simple-supported beam system with moving mass is built with ADAMS software. The results show that the method based on Hilbert-Huang transformation and that based on combining EMD with Neural Network are effective in estimating the modal parameters of time-varying structures.However, both of them are affected by the end effects, the method based on Hilbert-Huang transformation has more seriously influence.