Accuracy Improvement to the Identified Modal Parameters of Systems with General Viscous Damping

Abstract

The aim is to model a system by an equivalent one which satisfactorily reproduces the system vibration behaviour over the frequency range of interest. This new system is described by relevant modal parameters which are to be identified from motion measurements when the system is subjected to periodic force excitation at select excitation frequencies. It is assumed that the new system can be represented by symmetric mass, damping and stiffness matrices. General viscous damping is assumed. Earlier work was unable to satisfactorily identify a simple two degree of freedom system when the motion measurement data was accurate to only two digits. Whereas theory requires that the system eigenvalues and eigenvectors be complex conjugates, this did not turn out to be the case. This paper uses two different identification procedures to investigate this anomaly and shows that for this simple system, the upper half plane eigenvalues can be identified far more accurately than their complex conjugates.