EXTRACTION OF NORMAL-MODES FROM CONTAMINATED MEASUREMENT WITH NOISE FOR HIGHLY COUPLED STRUCTURES

A frequency-domain technique to extract the normal mode shapes from th e contaminated FRF measurements for highly coupled structures is devel oped. The relation between the complex FRFs and the normal mode shapes is derived. It is found that the normal mode shape cannot be extracte d exactly from the complex mode shape. However, an exact relation betw een the normal mode shape and the complex FRF does exist. In the prese nt method, only the magnitude and phase data at the undamped natural f requencies are utilized to extract the normal mode shapes. Hence, the effects of measurement noise can be reduced. A numerical example is em ployed to illustrate the applicability of the technique. The results i ndicate that this technique can successfully extract the normal modes from the noisy frequency response functions of a highly coupled struct ure.