Acoustic characterization of ducts lined with poroelastic materials based on wave finite element method

Abstract

A wave finite element (FE) approach is presented for investigating acoustic characteristics of an axisymmetric duct lined with poroelastic materials. A short segment of the poroelastic lined duct is modelled using commercial FE software package, and an eigenvalue problem is established by applying periodic conditions, which greatly reduces the complexity associated with the formulation of eigenvalue problem especially when the intricate two-phase interaction within the poroelastic material is of significance. The predicted wavenumbers agree with those by forced response simulation with full FE simulations. The acoustic characteristics of poroelastic lined duct is analyzed based on the numerical model, which is verified by a full FE model, with emphasis on the effect of skeleton elasticity. For the structure-borne modes, a strong coupling between the fluid phase and solid phase is observed; while for the fluid-borne modes, such coupling is found to be negligible. For a poroelastic lined duct silencer, it is found that the structure-borne mode accounts for the spectral peaks in transmission loss spectrum through enhanced absorption and reflection effects. Meanwhile, the boundary condition of poroelastic material has significant effect on the structure-borne mode. In the simulated case, the change of boundary condition from fixed to rolling causes the first structure-borne mode to change from an evanescent higher-order-like mode to a propagating plane-wave-like mode in low frequency range, which affects the acoustic characteristics of the poroelastic lined silencers noticeably.