The Complex Mode Indicator Function (CMIF) as a parameter estimation method

Abstract

The Complex Mode Indicator Function (CMIF) has evolved from its original usage as simply an indicator of repeated root order to a full fledged parameter estimation algorithm in its own right. When combined with a properly scaled Enhanced Frequency Response Function (eFRF), this spatial domain modal parameter estimation approach provides an effective and efficient technique for the estimation of modal parameters. This paper reviews and presents the development of CMIF and eFRF. The paper presents the basic structure of the modal parameter estimation procedure which first finds the modal vector from the CMIF and then finds the modal frequency, damping and scaling. The paper particularly discusses the issues associated with scaling the eFRF properly and the variations in indicator function that can be used to improve its sensitivity in estimating mode shape information. Results are presented for two example structural systems.