Identifying the unmodified structural characteristics using multiple modifications

This paper describes a procedure for estimating the free-free modal characteristics of a system by testing multiple constrained states. The procedure eliminates the influences of the constraints on the modal parameters and provides important information at the connection points. For very stiff or very flexible test articles, it is difficult to support the test article and to measure uncompromised modal parameters. The method described in this paper measures the forces and/or responses at constraint-connection points and uses a direct parameter estimation algorithm to calculate the system's free-free characteristics. These free-free characteristics retain the local information at the connection or boundary points, thereby including the important local high frequency residual effects in the modal model.