Method for determining minimum-order mass and stiffness matrices from modal test data

Abstract

A new method for determining mass and stiffness matrices from modal test data is presented. The method builds on the identified modes and the mass-normalized mode shapes at the sensor locations and is not limited by either the number of driving points or measurement points, and so it is applicable to most general test settings. A mixed coordinate basis is defined for the mass and stiffness matrices which is analogous to the Craig-Bampton component mode synthesis method for finite element models. The resultant mass and stiffness are of minimal order necessary to span the measured modes, and the resulting generalized coordinates provide an objective basis for the test-derived matrices to be used as if they are component mode-synthesized finite element matrices. Inclusion of rigid-body modes and the relationship of the new method to traditional physical parameter computations based on mobility curves is considered. Examples of the method as applied to numerical and experimental data are provided.