Interior noise problems become more important due to the tendency to construct lighter vehicles. An important source for interior noise in a vehicle is the engine. The structural vibrations induced by the engine will transmit through the vehicle and will finally result in interior noise elsewhere in the vehicle, so-called structure-borne sound. To reduce the interior noise a solution is sought in a combination of passive and active isolation (hybrid isolation) of the engine. A project has been started to investigate this type of isolation and to develop experimentally validated numerical simulations for the design of hybrid isolation system. \ud
This paper focuses on the numerical modelling approach for this type of problems. The model consists of a structural and a bounded acoustic part that are representative for a vehicle. The responses of both parts are determined efficiently with modal superposition. The controller design, necessary for the active part of the isolation, is performed with the optimal control theory that is based on minimization of a cost function. Different cost functions will be compared with each other with emphasis on the performance of the structural related cost functions (e.g. minimization of structural velocities) in comparison with the acoustical cost functions (e.g. minimization of sound pressures)
