Optimization of multilayered porous acoustic absorbers

A new method for the optimal material and layer design of acoustic trims without the usage of prototypes is presented. As an example the acoustic behaviour of a two-layered ceiling panel is optimized without increasing its weight or its thickness. The optimization method consists of two steps: (1) The possible varieties of porous materials are analysed by computer simulation on the microscale, i.e. a certain set of boundary value problems is solved on the fully resolved microstructure. In a subsequent homogenization procedure a characteristic set of effective acoustic material parameters is computed together with their dependency on microstructural parameters like porosity. (2) A data base of these pre-computed characteristic material parameters is used in the proper?? optimization algorithm, which determines both the optimal thickness of the layers and their optimal microstructure with respect to a desired acoustic absorption behaviour. A wide variety of materials can be taken into consideration: fibrous absorbers, open and closed cell foams, viscoelastic solids, porous or viscoelastic composites. Since the main difficulty in this procedure is the computation of the characteristic acoustic parameters, we present the verification of the numerical scheme used for the computation of these parameters for the case of cylindrical pores.