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Powertrain units such as engine and gearbox are important components affecting the noise and vibration performance of a vehicle. This paper presents a unique technique that uses structural shape optimization together with an acoustic transfer vector (ATV) technique to minimize the noise radiated from a gearbox casing. The ATVs relate the normal velocities of the gear case surface to the sound pressure at points in the acoustic field around the structure. The ATVs are calculated once only in an initial step using a boundary element method (BEM). By integrating the pre-calculated ATVs into the structural model as a frequency-dependent constraint relationship, the sound pressure at any position in the acoustic domain can be obtained as a response quantity in the FEM calculation. This makes it possible to use the standard structural optimization tools available in advanced FEM software to minimize the radiated noise.

Car floor structures typically contain a number of smaller-scale features which make them challenging for vibro-acoustic modelling beyond the low frequency regime. The floor structure considered here consists of a thin shell floor panel connected to a number of rails through spot welds leading to an interesting multi-scale modelling problem. Structures of this type are arguably best modelled using hybrid methods, where a Statistical Energy Analysis (SEA) description of the larger thin shell regions is combined with a finite element model (FEM) for the stiffer rails. In this way the modal peaks from the stiff regions are included in the overall prediction, which a pure SEA treatment would not capture. However, in the SEA regions, spot welds, geometrically dependent features and directivity of the wave field are all omitted. In this work we present an SEA/FEM hybrid model of a car floor and discuss an alternative model for the SEA subsystem using Discrete Flow Mapping (DFM).