Vehicle Exterior Noise Field Analysis Methods & Simulation Models

Nowadays exterior noise emitted by heavy trucks represents a challenge to the builders of these vehicles, test procedure implementation and reduction technologies. Shields applied to vehicle cabs, bulkheads and engine integrated elements and/or engine sound-proofing are used to reduce the exterior noise together with last generation diesel engines. Components size and characteristics, acoustic insulation and absorption properties represent important de-sign variables optimized by structural and vibro-acoustic parametric analysis. Many NVH experimental techniques are well established to check the intervention result effectiveness. As a matter of fact, even though there exist numerical methods that are in principle applicable to the simulation of power-train exterior noise, their use in the industrial design practice was seldom considered as a useful option during the last years. The assessment of a numeri-cal/experimental methodology has been carried out to verify its capability of reproducing ex-terior 'Acoustic Transfer Functions' (ATFs) as well as the computational effort it involves. In particular, the BEM/FEM method has been applied to the simulation of the ATFs of simpli-fied (but not trivial) car engine bay mock-up models and pushed to cover all the frequency range up to 3.5 kHz. The method has been assessed both for what concerns the quality of the correlation with experimental data and its computational efficiency. A special focus has been kept on the possibility that this method offers to analyze in an efficient way the effect of acoustic trim parts and the effect of the positioning of the apertures around the engine bay. This application has to be seen as an assessment of the numerical methods available for the simulation of vehicle exterior noise and the design of acoustic trim parts positioned inside the engine bay and in turn of their capability of tackilng real cases in the automotive industry.