Vehicle validation of the structure-borne noise of a lightweight body and trim design solution obtained with new integrated FE optimization

In the context of the development of lightweight and vehicle-NVH-refined sound package solutions, car manufacturers have identified that it is essential to promote new dedicated CAE design methods which can be applied at a very early stage, before body and trim designs are frozen.In the case of body NVH design, simulation methods based on FE modelling are increasingly used in order to influence the weight reduction of damping products by finding their optimal layout on the body structure, while meeting panel vibration targets. Due to the availability of validated FE models even before the shape and stiffness of the different panels of the vehicle body are fixed, it is also becoming practically possible to perform optimizations of the damping pads simultaneously with smart panel local stiffening, thus offering further weight savings in the low and medium frequency range [1]. Some efforts are also spent in this context, to quantify the design performance with respect to panel radiated noise [2].On the other hand in the case of trim NVH design, the parts are traditionally optimized with respect to airborne noise transmission in the medium and high frequency range, without systematically considering their side influence on the panel vibration. However, with the growing importance of rolling noise contribution to vehicle NVH, and with the introduction of light weight trim parts on body structures, it is shown that the vibroacoustic interaction of body structure and soft poro-elastic trim has increasing importance at medium frequencies, where structure borne noise propagation is dominant in vehicles. In this case, it becomes even more important to assess the design of the body NVH not only at the panel vibration level, but more at the panel radiated noise level.This paper is bringing one major advancement in this CAE problematic, with the release and application at vehicle level of a methodology based on FE optimization for the design of the body NVH including damping and local stiffeners, while taking into account the influence of the trim, to be assessed on the SPL performance improvement, thus offering additionally the integration of the trim in a fully integrated optimization.First of all, the FE representation of the trim can be included into the vehicle FE models that are traditionally used for structural optimization, so that the body vibration target can be substituted by a more realistic interior SPL target. Then the concept is extended to the inclusion of the trim variables (like poro-elastic materials) into the optimization variables, so that the body and trim designs can be accomplished simultaneously, taking into account the mutual influences. The technical aspects of this “integrated” simulation-based optimization have already been presented for a simple validation case [3]. In the present paper, the method is applied on an existing vehicle body in white, demonstrating the interactive influence of damping, stiffening and trim on the structure borne noise of a vehicle. The demonstration is completed by the execution of a simultaneous optimization, leading to an increased weight advantage, and by an interesting outlook towards future design strategies. Finally, the different intermediate optimization results, including the effect of both body and trim design changes, have been validated against test results on two different BIW and trim variants of the vehicle under consideration, using an experimental SPL contribution analysis based on the utilization of PU probes.