New method for accurate and consistent identification of modal parameters

Abstract

A new method for the estimation of modal parameters is presented. Unlike the majority of existing methods, which involve complicated curvefitting and interpolative procedures, the proposed method calculates the modal parameters by solving the eigenvalue problem of an equivalent eigensystem derived from measured frequency response function (FRF) data. It is developed based on the practical assumption that only one incomplete column of the FRF matrix of the test structure has been measured in a frequency range of interest. All measured FRFs are used simultaneously to construct the equivalent eigensystem matrices from which natural frequencies, damping loss factors, and mode shape vectors of interest are solved. Because the identification problem is reduced to an eigenvalue problem of an equivalent system, natural frequencies and damping loss factors identified are consistent. Further procedures for normalizing the identified eigenvectors so that they become mass normalized are developed. Applications of the method to both numerically simulated and practically measured FRF data are given to demonstrate the practicality of the proposed method, and the results obtained are indeed very promising.