A study on Normalization of Complex Eigenmodes by Mass Change Method

Abstract

This study examines the mass change method, which can obtain normalized eigenmodes under unknown excitation input conditions. The mass change method is a method to obtain scaling factors using only the vibration response of a mechanical structure, utilizing the vibration characteristics before and after the addition of an additional mass. As constraint conditions, the conditions that the eigenmodes do not change before and after the added mass is added and that M-orthogonality is satisfied are used, but in general, a formulation that does not consider damping is used. However, in experimental modal property identification, damping is assumed first and then vibration characteristics are extracted. In this study, we analyze the system with damping taken into account and propose a formulation of the mass change method for the system assuming general viscous damping system. Numerical calculations are performed to derive the normalized eigenmodes, and the effectiveness of the damping-aware mass change method is examined.