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Numerical simulation techniques are widely used in automotive and aircraft sectors. The optimization of industrial products with respect to acoustic performance requires appropriate modeling strategies in order to handle various noise sources and different propagation paths. The present paper focuses on the application of finite element techniques (FE) to the solution of vibro-acoustic and aero-acoustic problems. State-of-the-art FE techniques are reviewed and illustrated by appropriate examples.

The design of automotive mechanical components requires the consideration of various excitations related to physical tests (involved in the validation process) and/or operational conditions. In such a context, random distributed excitations (like diffuse field and turbulent boundary layer) play a particular role. Modeling and simulation of the vibro-acoustic response of systems subjected to such random excitations is the framework of the present contribution. Based on elasto-acoustic assumptions, on one hand, and the assimilation of the excitation to a weakly stationary random process characterized by a reference power spectrum and a particular spatial correlation function, on the other hand, the authors identify various strategies for evaluating the random response. The analysis is performed in a numerical context. The selected discrete models are based on a finite element formulation and exploit a displacement-pressure formulation.

This paper describes a new approach for modeling a trimmed vehicle body by blending FEA models of the BIW, the passenger compartment and each individual trim component. The approach bases on the update of modal matrices, transforming the untrimmed body-cavity modal representation into an updated modal model including the effect of the trim configuration on the local and global NVH indicators. Results on simple and more realistic models are presented and show that the methodology fulfills the efficiency and accuracy criteria and is thus to guide the NVH development process.

The paper presents an energetic post-processing methodology for large-scale vibro-acoustic finite element models. Starting from a dynamic and an acoustic modal basis produced by a finite element analysis (FEA), the methodology produces: 1 synthetic and pertinent energetic outputs; 2 optimal SEA partitions of the finite element mesh; 3 quality indicators of existing SEA partitions. The methodology involves six different steps, some required, some optional: 1 automatic partitioning of the FEA model in patches; 2 calculation of distribution matrices; 3 definition of mechanical loads; 4 definition of damping characteristics; 5 modal-based vibro-acoustic response calculation; 6 energetic post-processing; 7 automatic partitioning in SEA subsystems; 8 verification of existing SEA partitions. Each step will be presented in turn. The methodology will be illustrated by application of the successive steps to a Renault Laguna body and an Alstom two-storey TGV train section.

The paper focuses on the numerical treatment of transient acoustic problems using finite element (FE) and boundary element (BE) methods. The FE method relies on a pressure formulation and the use of an implicit integration schemes for solving the related second-order differential system. The procedure is shown on cavity (interior) problems but can be extended to exterior problems using the DtN (Dirichlet-to-Neumann) approach. The presented BE method is restricted to 3-D problems and is based on the Kirchhoffs integral representation. The related retarded potential technique presents some interesting features which are stressed: the sparseness of matrices, the particular integration tools required and the time integration procedure for getting boundary variables. An enhanced procedure for reducing the memory requirements is also presented. Numerical applications show the performances of these discrete techniques.

Multi-layer insulation systems are widely used in many industrial sectors (particularly in automotive and aeronautic industries). They have a complex dynamic behavior due to the use of different materials like visco-elastic, poro-elastic and acoustic layers. The interface conditions between these materials play also a significant role in the global behavior. The paper concentrates on modeling poro-elastic layers using a 3-D finite element (FE) approach. A Biot model is selected for that purpose. A mixed displacement formulation is used. This can easily be coupled with other FE sub-models related to elastic thin shell layers or acoustic layers. Applications related to the prediction of the surface impedance of multi-layer configurations are presented.

An indirect variational boundary element formulation and two typical applications are presented in this paper. The significance of this method is that it can include openings in the model, and it considers the acoustic medium on both sides. Computationally it is superior to the direct method because the assembled fully populated boundary element matrices are symmetric. The theoretical background is presented. A typical generic interior cab noise analysis is performed. The excitation is comprised by an exterior impinging acoustic field and loads applied at the mounts. The coupled option was selected to solve this problem. A typical acoustic uncoupled radiation analysis is also performed. The noise radiated from a T-drive is computed and the solution time is compared to the direct method.