Research On Some Key Problem Of Experimental Modal Analysis

Through the research on the sophisticated physical and mathematical separation technique of modes in experimental modal analysis, this thesis intends to improve the estimated accuracy and efficiency of modal parameters of highly damped structure or structure with close frequency modes and the automatization of the technique in the process of analysis.The thesis starts with theoretic principles of structural and modal parameters. The key of multiple sine excitation normal mode testing technique in physical separation technique of modes is to seek the optimal shaker force vector. Conditions of normal mode realization are deduced and optimized model with the multivariate mode indicator function as the target function is built. Through solving the maximal eigenvalue problem, the original shaker force vector of appropriation is reached. Then the realization approach of the optimal shaker force vector based on single shape principle is proposed and at the same time the automatization of normal mode appropriation is realized. As to the polyreference implemention of the least-squares complex frequency-domain estimator in mathematical separation technique of modes, this thesis builds a right matrix-fraction description model to estimate the system poles. Then frequency point stabilization diagram is set up and analyzed to automatically determine natural frequencies, modal damping ratios and modal participation factors. Finally mode shapes are identified based on the least squares theory. The research realizes the modes determination of highly damped or close frequency modes structure and the accurate and efficient estimation of modal parameters.