The Prediction of Substructure and System Modes by the Extended Complex Mode Indication Function

Abstract

Yee and Tsuei (1989) developed the Modal Force Technique (MFT) as a tool for component synthesis. The approach utilizes the frequency response functions at connecting joints to predict the dynamical behavior of a synthesized system. The main difference between the MFT and the traditional impedance modeling approach is that no inversion of the frequency response functions is required for the MFT, which makes the Model Force Technique more efficient. The other major feature is that the Modal Force matrix of the synthesized system equation contains the information of both the substructure and the system modes. To determine the natural frequency and the damping of a complex mode based on the frequency response functions, the Extended Complex Mode Indication Function (Extended CMIF) technique was developed. It performs the singular value decomposition (SVD) of the Modal Force matrix at each spectral line. The peaks of the singular value plot indicate the location of the substructure modes, while the anti-peaks show the location of the system modes. This approach is simple, straightforward and can be efficiently implemented to identify complex modes.