Locating Optimal References for Modal Testing - IMAC 20

P.Avitabile, M.Richardson, B.Schwarz

The Complex Mode Indicator Function (CMIF) was originally proposed as a method for improving modal parameter estimation [1], [4]. CMIF utilizes singular value decomposition (SVD) on a set of FRFs as a mechanism for extracting parameters.

The Multivariate Mode Indicator Function (MMIF) was originally proposed as a method for force appropriation to excite normal modes [2]. MMIF utilizes an eigenvalue solution method on a set of FRFs to isolate modes.

Both CMIF & MMIF also have the ability to indicate the presence of closely coupled modes or repeated roots in a structure. Both methods can be used as tools for identifying a minimum set of reference DOFs for performing a modal test.

Using a small set of potential reference FRFs and their cross measurements, either CMIF or MMIF can be used to determine the minimum number of references required to adequately excite all the desired modes in a frequency band.

This technique has previously been demonstrated to provide reasonable results on several test structures [3]. In this paper, the previous work is extended to provide a testing strategy for determining the number and locations of optimum references for modal testing. Examples are provided to demonstrate its use.

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