In order to meet the customers comfort requirements, reduction of noise in the passenger compartment is one of the primary concerns in the automotive industry. Moreover, for a better reactivity to the market, vehicle development time tends to be shorter and shorter. Instead of constructing many prototypes and running a lot of tests, numerical simulation has to take a bigger part in the design of cars. This would be a cheaper and quicker way of testing many new solutions. We have developed for several years a numerical model, combining by Finite Element Method (FEM) and Boundary Element Method (BEM), for computing the vibro-acoustic behaviour of a fully trimmed car with engine and power train. This model allows prediction of the structure borne sound field due to the engine and wheels excitations at low frequencies (0-200 Hz).
It is shown how such a model can be achieved: for each component of the vehicle, we illustrate how to build up validated structural FE model, i.e. models correlated with experiments. Those local models are assembled to construct a FEM for the whole car. The resultant sound pressure level in the cavity is then computed using FEM or BEM codes coupling acoustics and vibrations.
We also make use of this model for a better understanding of the noise generation mechanisms. It is for instance possible to sort the contribution of each component to the sound pressure level at the passenger's ears.
Rather than to treat the acoustic problem once the car is designed, this kind of model will help to incorporate the acoustic prediction in the early design stage.