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Summary: Comparison of FRF and Modal Methods for Combining
Experimental and Analytical Substructures
Matthew S. Allen1
and Randall L. Mayes2
1
University of Wisconsin-Madison, Corresponding Author: msallen@cae.wisc.edu
2
Sandia National Laboratories*
, rlmayes@sandia.gov
Abstract:
This paper investigates methods for coupling analytical dynamic models of
subcomponents with experimentally derived models in order to predict the response of the
combined system, focusing on modal substructuring or Component Mode Synthesis (CMS), the
experimental analog to the ubiquitous Craig-Bampton method. While the basic methods for
combining experimental and analytical models have been around for many years, it appears that
these are not often applied successfully. The CMS theory is presented along with a new strategy,
dubbed the Maximum Rank Coordinate Choice (MRCC), that ensures that the constrained
degrees of freedom can be found from the unconstrained without encountering numerical ill
conditioning. The experimental modal substructuring approach is also compared with frequency
response function coupling, sometimes called admittance or impedance coupling. These
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