FEA for Effects of Sound Bridge Phenomena on Vibration Transmission with Damping between Automotive Double Walls

摘要

To analyze sound bridge phenomena for the automotive double walls in the low frequency region, we applied numerical method proposed by the authors previously. Vibration transmission properties are analyzed for mixed structures composed of a porous material sandwiched between a damped steel beam and a resin sheet. In consideration of automotive floors, the damped steel beam is fixed at both ends, and the edges of the resin sheet are set as free. An elastic or a viscoelastic spacer is installed between the steel beam and the resin sheet in the structures, to analyze deterioration of vibration by the sound bridge phenomena. Effects of the spacer on eigenmodes, strain energy, dissipated energy and loss factors are computed under the sound bridge phenomena. The numerical method includes finite element method in consideration of damping properties for the mixed soundproof structures involving elastic materials, viscoelastic materials, air and porous materials. In the method, complex effective density and complex volume elasticity are used for internal sound field in porous materials. And, elements of the porous materials are formulated using particle displacements as unknown variables. Coupled vibro-acoustical problem in consideration of damping was solved numerically using displacement as a common unknown parameter for the mixed structure. Expressions of modal loss factor for the structures are derived using applying asymptotic method to complex eigenvalue problem. This method can diminish computational time for large-scaled models. An expression to calculate share of dissipated energy for an each element is also derived. This yields the contribution of damping for an each element. Using these proposed method, damping couplings for automotive double walls with an elastic or a viscoelastic spacer is investigated under sound bridge phenomenon.