Resumen de Vibration transmission between double walls in cars with damping and sound bridges
Takao Yamagychi, Ikuo Shirota, Kurosawa Yoshio, Hideki Enemoto
To analyze sound bridge phenomena for the double walls in cars in the low frequency region, we applied a numerical method previously proposed by the authors. Vibration transmission properties are analyzed for mixed structures composed of a porous material sandwiched between a damped steel beam and a resin sheet. As a model for floors in cars, the damped steel beam is fixed at both ends, and the edges of the resin sheet are free. An elastic or viscoelastic spacer is installed between the steel beam and the resin sheet, to analyze the deterioration of vibration by the sound bridge. Effects of the spacer on eigenmodes, strain energy, dissipated energy and loss factors are computed. The numerical method includes a finite element method for the damping properties for the structures involving elastic materials, viscoelastic materials, air and porous materials. In the method, complex effective density and complex modulus of the volume elasticity are used for the sound field in porous materials. Elements of the porous materials are formulated using particle displacements as unknown variables. The coupled vibro-acoustical problem is solved numerically within the consideration of damping using displacement as a common unknown parameter for the mixed structure. Expressions of modal loss factors for the structures are derived by applying an asymptotic method to the complex eigenvalue problem. This method can reduce computational time for large-scaled models. An expression to calculate dissipated energy in an each element is also derived. This yields the contribution to the damping by an each element. Using these proposed methods, damping couplings of the double walls by an elastic spacer or viscoelastic spacer are investigated.
