Abstract
Thin steel panels are widely used for body structure of automotive. They are usually treated with damping sheet and covered with multi-layered sound-proof structure to secure quietness inside passenger compartment. Vibration and noise level induced by external excitation should be predicted to design configuration of damping sheet and multi-layered sound-proof structure. This paper proposes an approximate analytical method that gives a dynamic response for a clamped flat panel covered with multi-layered sound-proof structure and coupled with rectangular parallelepiped acoustic cavity. Equivalent properties of bending stiffness and mass density are applied for a panel treated with unconstrained damping sheet. Transfer matrix formulation is utilized for multi-layered sound-proof structure by assuming that the longitudinal wave propagation is dominant. For transfer matrix in a sound-absorbing layer, analytical solutions for Helmholtz equations of Biot's model are used. Flat panel and acoustic cavity are represented by using modal expansion and coupled equations are solved combined with transfer matrix of multi-layered sound-proof structure. Numerical studies are performed for several multi-layered sound-proof structures by using 2 sound-absorbing materials and 1 sound-insulation material. The results by the proposed method are verified by comparing with numerical solutions by a finite element analysis and are proved to give an valid solution with a much shorter time by a factor of 30.
