Hybrid approaches for vibroacoustical problems based on the finite element method and statistical energy analysis

The prediction of structure borne sound in vehicles or buildings and the induced sound fields in acoustic volumes is typically carried out either with a finite element (FEM) fluid-structure interaction (FSI) approach or with the help of energy methods like the statistical energy analysis (SEA). In the first part of the paper a coupled FEM/FSI approach for the calculation of vibrations and the radiated sound in adjacent cavities according to Buchschmid (2011) is presented. For the description of the sound field in the cavity model reduction techniques are applied, superposing modes for reflective boundary conditions and form functions, which provide displacements at the FSI-interface. Wavenumber dependent impedances for complex boundaries like porous absorbers, which can be derived analytically, are introduced in the calculation scheme. In the second part of the paper an inverse SEA-like approach, which can be applied in the postprocessing of an FEM computation, is presented. For the description of the structural and acoustical response in the mid-frequency range time- and space-averaged subsystem energies are discussed as state variables. Consequently the excitation is described by means of the input power into the subsystems, which, in contrast to the SEA, do not have to be weakly coupled. The resulting kinetic and potential energies can be visualized for all substructures. The ratio between these energies provides an insight into the coupling-characteristics of adjacent structures.