THE MULTIVARIATE MODE INDICATOR FUNCTION IN MODAL ANALYSIS

In the sine dwell school of modal testing, a frequency domain function, most often called the Mode Indicator Function (MIF), has been employed for several years to detect the presence of real normal modes. This function is calculated from Frequency Response Functions from a single exciter location to highlight those frequencies where the global response phase lags the sinusoidal excitation by 90 degrees. Recently, a multivariate mode indicator procedure was presented, that, using FRF's from several exciter locations, can detect repeated roots, as well as providing initial force patterns for the sine dwell tuning of the associated modes. This paper presents a brief outline of the theory of this multivariate mode indicator and then shows how the information generated by this procedure may be used for the extraction of selected modal parameters through function enhancement and frequency domain SDOF techniques. The use of the multivariate mode indicator in the traditional MDOF procedures will also be discussed. Examples will be presented from several tests.