Identification of Modal Properties Using Linear Fit Method with Polynomial Approximation of Residue Term of Frequency Response Function

Abstract

Experimental modal analyses are widely used to identify modal properties, such as natural frequency, damping characteristics, and residue from vibration tests. When identifying modal properties, it is necessary to determine the analysis frequency range and number of degrees of freedom. The influence of the mode existing outside the analysis frequency range is introduced into the approximate expression as residual mass and residual rigidity in only the real part of the frequency response function (FRF). Those approximate functions may be inappropriate when there are a few modes that lie outside of the analysis frequency range and near the boundary. In this study, an approximate method of the influence of modes that are close to boundaries of the analysis frequency range in the real part and the imaginary part of the FRF is proposed. In this method, mode components that lie outside of the analysis frequency range are modeled with cubic functions, and iterative calculations are conducted using the mode separation method. It is shown that this method improves the identification accuracy of the modal properties.