During the acceleration of a vehicle, the contribution of the exhaust noise to the interior sound pressure level is significant. The acoustic insulation brought by the trim components must be designed with that consideration in mind. As such, there is an increasing need for developing reliable methods for predicting the airborne noise transmission between the exhaust system and the sound pressure level at the passenger's ears, taking into account the positive impact of various trim components.
This paper presents a methodology that has been developed for addressing this need. Based on a finite/infinite element method, the computational procedure is divided in two steps:
- 1
The first step involves the exterior acoustic field all around the vehicle. The acoustic pressure field on the exterior surface of the vehicle is computed by considering the exhaust system as acoustic source;
- 2
The second step consists in computing the interior vibro-acoustic response of the vehicle by using the surface pressure from step one as excitation applied to the trimmed body finite element model.
This second step relies on a FE modal-based approach for the efficient modeling of large trimmed structures coupled to acoustic cavities. In this approach, the trim components are represented by their impedance matrices reduced to the interface degrees of freedom with the body structure and the interior acoustic cavity. These reduced impedance matrices are then projected on the structure/fluid modal bases and injected in the coupled modal system; as such the trim components are accurately taken into account when the vibro-acoustic modal model of the vehicle is solved.
The paper gives the details of the two steps of this approach as well as the key ingredients related to this original technique. Some real life validation cases (including some comparisons with measurements) are presented, proving the reliability of the method and its efficiency in an industrial automotive context.