Experience with a test-based hybrid component mode synthesis approach

Experience gained in the application of a new approach of component mode synthesis (CMS) in which the characteristics of individual components are determined experimentally through modal and static tests is described. The new technique is referred to as the experimental hybrid CMS approach. The component characteristics used in the technique are the mass matrix, rigid-support normal modes and frequencies, residual flexibility attachment modes, and static constraint modes. All component characteristics, except the mass matrix, are obtained through tests. A novelty of the approach is that it allows determination of the test-based characteristics by testing the components attached to supports of arbitrary stiffness. This procedure obviates the need for providing fully rigid or highly flexible supports, as is normally done. In addition, reaction forces at the supports need not be measured during modal testing. The theoretical formulation is summarized. The use of CMS approach and its associated test procedures for experimental verification of the modal parameters of a free-free grid system is described. For the purpose of testing, the two grid components are supported on four flexible supports. For this type of structure, the system parameters obtained from the experimental hybrid CMS approach exhibit significant improvement in the accuracy when a certain minimum number of residual flexibility terms is included in parameter estimation, in comparison to the case when such terms are completely ignored.