AUTOMATED RESPONSE DOF SELECTION FOR MAPPING OF EXPERIMENTAL NORMAL MODES

摘要

A direct method for response "measurement" degree-of-freedom (dof) selection to map experimental normal modes is described and demonstrated. The method utilizes a detailed pre-test finite element model of the subject structure. An initial response "measurement" dof set is first selected for mapping modes in the frequency band of interest. The remaining dofs of the structural model are assumed to respond in a quasi-static manner following a Guyan reduction transformation. Modes formed from the "measurement" partition of the FEM modal vectors and expanded using the Guyan reduction transformation comprise the "approximate" normal mode set. Residual error vectors are formed based on differences between complete FEM normal modes in the frequency band of interest and the set of corresponding "approximate" modes. A residual kinetic energy matrix directly identifies additional dofs (or dof groupings) which must be instrumented in order to experimentally map the normal modes of interest.