A comparison among modal parameter extraction methods

An effective comparison among several methods for extraction of the modal parameters from the frequency response functions measurements is presented in this research. In particular, several curve fitting methods, which are the peak amplitude method, the circle fit method, the least square complex exponential method, the eigensystem realization algorithm method and the rational fraction polynomial method were implemented in Matlab environment and compared in terms of natural frequencies, modal damping and mode shapes. Measurements were performed on a carcass of the gearbox in free–free condition. A hammer has been used with a periodic impulsive excitation signal. The natural frequencies values obtained by all methods were very similar and the differences between the results were insignificant. The peak amplitude and the circle fit gave good results for the damping ratios. The rational fraction polynomial method did the best job in detecting the damping and frequency values. The results obtained by the least square complex exponential method and the eigensystem realization algorithm method were reasonable for both frequency and damping.