Modelling of sound damping multi-layers using a hybrid Finite Element - Wave Based Method S. Jonckheere, D. Vandepitte, W. Desmet KU Leuven, Department of Mechanical Engineering, Celestijnenlaan 300 B, B-3001, Heverlee, Belgium e-mail: Stijn.Jonckheere@mech.kuleuven.be Abstract To assess and optimise the effect of multi-layered trim for the reduction of noise and vibration transmis- sion, design engineers greatly depend on CAE tools. Mostly, these are based on element based simulation techniques such as the Finite Element Method (FEM). In practise, however, these methods are limited to low-frequency simulations due to the strongly increasing computational cost with frequency. They lose even more of their applicable frequency range when used for coupled acoustic-poro-elastic analysis. With the cur- rent simulation technologies, it is very challenging to solve a full FEM-model for the damped vibro-acoustic system into the mid-frequency domain. The Wave Based Method (WBM) is very well suited for this full- system modelling, since it has a very good convergence rate as compared to the FEM. On the other hand, the WBM shows its efficiency best for moderately complex geometries, where the domain can be divided into a (small) number of convex subdomains. To overcome this limitation, hybrid Finite Element - Wave Based approaches have been developed and explored for coupling different physical media; acoustic, structural and structural-acoustic couplings can be tackled. This contribution extends this family of hybrid FE-WBM meth- ods towards the coupling of acoustic WBM models with poro-elastic FEM models. In this way, the method benefits from the computational efficiency of the Wave Based Method for the acoustic calculations without losing the Finite Element Method’s ability to model the often layered and complexly shaped poroelastic materials in great detail. 1 Introduction The quest for quieter, and at the same time lighter materials is ongoing in many product industries. A very important component in the often layered noise reduction treatments are the so-called poro-elastic materials [1]. These materials consist of two phases: a solid, elastic phase and a surrounding acoustic fluid phase in the pores. They operate on both structural, thermal and viscous dissipation effects, all strongly dependent on temperature and frequency. Several methods for modelling poro-elastic materials are available, ranging from highly approximative mod- els, where only a limited number of material parameters are to be known, to approaches which incorporate the full Biot [2] equations, using all material parameters. The focus of this paper will be on this Biot modelling of poro-elastic materials, making use of the Finite Element Method (FEM). Over the past decades, the FEM has become one of the key simulation technologies to predict the behaviour of dynamical systems, such as vibro-acoustics. It has also been applied to the fully coupled Biot equations, based on different formulations, such as the (u s , u f ) formulation [3], the (u s ,p f ) formulation [4] and the (u s ,u t )-formulation [5], where u s , u f and u t represent the solid phase, fluid phase and total displacement and p f represents the pressure in the fluid phase, respectively. The FEM can elegantly tackle the most 4129