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Porous materials are extensively used in the construction of automotive sound package parts, due to their intrinsic capability of dissipating energy through different mechanisms. The issue related to the optimization of sound package parts (in terms of weight, cost, performances) has led to the need of models suitable for the analysis of porous materials' dynamical behavior and for this, along the years, several analytical and numerical models were proposed, all based on the system of equations initially developed by Biot. In particular, since about 10 years, FE implementations of Biot's system of equations have been available in commercial software programs but their application to sound package parts has been limited to a few isolated cases. This is due, partially at least, to the difficulty of smoothly integrating this type of analyses into the virtual NVH vehicle development.

Automotive suppliers provide multi-layer trims mainly made of porous materials. They have a real expertise on the characterization and the modeling of poro-elastic materials. A dozen parameters are used to characterize the acoustical and elastical behavior of such materials. The recent vibro-acoustic simulation tools enable to take into account this type of material but require the Biot parameters as input. Several characterization methods exist and the question of reproducibility and confidence in the parameters arises. A Round Robin test was conducted on three poro-elastic material with four laboratories. Compared to other Round Robin test on the characterization of acoustical and elastical parameters of porous material, this one is more specific since the four laboratories are familiar with automotive applications. Methods and results are compared and discussed in this work.

Generally all OEMs have a distinctive approach in designing their sound packages. Considering the complexity and combination involved in this process, there is no general valid scheme, although there tend to be some common blocks. Also as automotive manufacturers face strong demands to cut CO2 levels there is a trend to reduce prototypes and introduce limitations on weight of sound controlling materials. The supplier of the sound package must therefore be able to support the OEMs in taking design decisions early, quickly and based just on drawings, or even just on sketches in the concept phase. A proposed way forward in designing fast and cost-effective sound packages is by skillfully combining target setting, material characterization measurements, virtual prototyping and optimization tools. The solution should not only be acoustically effective, but also lightweight and cheap.

This work focuses on the modeling of visco-thermal dissipations within porous media used in automotive sound packages. This paper mainly presents a review of works which enable to condense complex physical phenomena in a simple formalism. Rigid porous media are usually modeled as equivalent fluids using two complex and frequency-dependent functions: the dynamic density and the dynamic bulk modulus. Two methods for calculating these equivalent properties from the microstructural are recalled. Then, it is shown how to take into account additional phenomena such as pressure diffusion, tortuous effect at the mesoscopic scale, or inner resonators using simple equivalent fluid representations. This enables to add complex physical phenomena to equivalent fluid models in order to reduce the numerical cost for e.g. finite element models (FEM). The advantage of this formalism is being directly suitable for modeling porous media in complex systems and submitted to various excitations.

The recently updated pass-by noise measurement procedure prescribes a mix of acceleration tests and constant speed tests. This has led to an increased relevance of tire noise relative to the past, when the procedure prescribed only acceleration tests. In addition, the next phase of the roadmap for pass-by noise limits for passenger vehicles is 70 dB(A) by 2020, later followed by 68 dB(A). In this context, exterior tire noise has drawn increasing attention. OEMs, suppliers of passive acoustic treatments, road manufacturers and tire manufacturers are, at the moment, devoting strong efforts to the definition of solutions for the control of exterior noise. This paper is concerned with the potential of existing passive exterior treatments to reduce the exterior noise generated by the tires. Different countermeasures are analyzed, namely wheelhouse liners, under-engine shields, under-body panels and under-trunk panels.