The acoustic trim components play an essential role in NVH behavior by reducing both the structure borne and airborne noise transmission while participating to the absorption inside the car. Over the past years, the interest for numerical solutions to predict the noise transmission through trim packages has grown, leading to the development of dedicated CAE tools. The incrementally restrictive weight and space constraints force today CAE engineers to seek for optimized trim package solution. This paper presents a two-steps process which aims to reduce the structure borne road noise due to floor panel using a coupled simulation with MSC NASTRAN and Actran.
The embossment of the supporting steel structure, the material properties of porous layers and the thickness of visco-elastic patches are the design variables of the optimization process. The optimization of the beads and embossments of the metallic floor structure is first performed using NASTRAN SOL200 topography optimizer while considering a reference acoustic trim configuration. Once the optimum embossment pattern is found, the optimization of the visco-elastic patches properties and the trim package is started as a second step with Actran for Trimmed Body and the embedded optimization library NLOPT.
The case studied consists in a complete car model including the tires, the suspension, the body, the floor trim and the cavity. This model is loaded by realistic excitations representing the road irregularities. The study demonstrates that the trim package cannot be neglected during the structure optimization process. For a given frequency range, the floor beads and embossments have a minor impact on the overall acoustic response in the car cavity, conversely to the properties of the trim package. On the other hand, the optimization of the trim shows very interesting benefits with a limited weight increase. As a consequence, focusing the efforts to improve the acoustic trim is more efficient in the objective to improve road noise comfort of the passengers.