Title: A FE Based Procedure for Optimal Design of Damping Package, with Presence of the Insulation Trim
text: Typically, in the automotive industry, the design of the body damping treatment package with respect to NVH targets is carried out in such a way to achieve panel mobility targets, within given weight and cost constraints. Vibration mobility reduction can be efficiently achieved thanks to dedicated CAE FE tools, which can take into account the properties of damping composites, and also, which can provide their optimal location on the body structure, for a minimal added mass and a maximized efficiency. This need has led to the development of different numerical design and optimization strategies, all based on the modeling of the damping composites by mean of equivalent shell representations, which is a versatile solution for the full vehicle simulation with various damping layouts. However, these approaches, which can estimate correctly the beneficial vibration effect of damping pads application on the vehicle body, address the body NVH target with no consideration of the impact that the presence of the insulation on body panels can have on the final vibration result. On the other hand, the efforts carried out in the last years for FE implementations of Biot's system of equations have led to simulation methods at vehicle level, which can take into consideration the dynamical behaviour of porous materials and which allow including in an efficient and flexible way sound package parts into vehicle FE models used for NVH analyses. This paper presents a FE-based procedure, thanks to which it is possible to design the optimal damping lay-out with respect of panel mobility targets, while taking into account the presence of the insulation part on body panels. In a first section a design methodology for damping layout is presented. This method, that is completely integrated in Nastran, is able to provides the ranking and vibration pattern of the vehicle panels with highest mobility for a given frequency range and set of loads in order to maximize the effect of the damping treatment. Then the problem of the influence of the acoustic treatment on the panel vibrations has been addressed. The proposed solution is represented by an implementation in MSC/Nastran of the Biot-Allard theory for porous media. This procedure allows a smart coupling of structural FE model with a FE boundary representation of the acoustic part. In the last section, the benefits of the joined use of the two techniques are highlighted by mean of their application on a simple test case as well as on a full-vehicle.