STRUCTURE OPTIMIZATION TO ENHANCE ITS NATURAL FREQUENCIES BASED ON MEASURED FREQUENCY RESPONSE FUNCTIONS

Abstract

A measured frequency response function (FRF) based structural modification method is presented to obtain optimal structural changes to enhance its natural frequencies. Structural dynamics modification (SDM) has been widely used for improvements of built-in structures. However, the optimum design obtained by SDM differs from the true optimal solution when large modal changes happen. In this paper, a substructure-coupling concept is used to get system equations in order to extend its use to large modal changes. FRF matrix of baseline structure and those of modification structures are coupled at the connection points under the condition of force equilibrium and geometric compatibility constraints. Thus, exact modified modal properties can be calculated even for the case of large modal changes. The optimal structural modification is calculated by combining eigenvalue sensitivities and eigenvalue reanalysis technique iteratively. Special attention is given to the case where baseline structure has some unidentified structural parameters to enlighten the advantage of this proposed method. An application to the case of beam stiffener optimization indicates that the proposed method can provide an accurate optimal structural change just based on measured FRFs without any kind of numerical models.