No abstract

In the challenge of reducing the weight of the vehicle structures, a particular focus has to be done on the interior noise. Indeed, the weight reduction of the structure often implies an increase of the noise in the cabin. To maintain a constant acoustic performance, acoustic packages often have to be added, the challenge being that the weight of the acoustic materials added remains lower than the weight saved in the structure. In today's engineering world, numerical simulation is the primary tool to assess the vibro-acoustic behavior of the vehicle during the design phase. To tackle the challenge of weight reduction, it is necessary to simulate accurately the vibro-acoustic response of the structure including the acoustic treatments. This paper presents the validation of a simulation method for the vibro-acoustic response of a truck cabin, taking into account the effect of acoustic treatments, in the frequency range [0-200Hz]. The method combined a modal scheme for the structure and the cavity with a physical scheme for the acoustic treatment (porous materials). The model consists in a truck cabin with its cavity and five acoustic treatments (three floormats, the headliner and the rear trim panel). A measurement campaign is performed to get reference NTFs, VTFs and local inertances. The model without any treatments is first correlated. The noise reduction given by each treatment alone as well as grouped together is simulated. The comparisons between the simulated and measured results show good agreement both in term of spectrum and amplitude. Although some discrepancies in the low frequency range remain unexplained, the method is considered as validated.

Large trimmed models, widely encountered in the automotive industry, generally involve a body-in-white structure coupled to an acoustic cavity and covered by a set of trim components. Due to the large number of degrees of freedom of such models, the direct analysis in physical coordinates, though theoretically correct, is not feasible on current computers. The paper presents an alternative and efficient solution strategy in modal coordinates that relies on an update of the modal parameters of the car body and the acoustic cavity, based on the energetic behaviour of the trim components. The description of the trim component in terms of an energetic database simplifies the data exchange between the automotive manufactor and the trim provider. Furthermore, it enables a fast frequency analysis of various loadcases/trim scenarios and makes optimisation possible. The updated modal approach implemented in Actran/Trim is applied on a simplified car model on which various trim components are applied. The application shows how the stiffening, added mass and damping effects of each trim component can be derived from the energetic database and can guide an optimisation process.