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In this paper a low noise flow duct facility that performs a multimodal characterization of the passive and active acoustic properties of obstacles in the aero-acoustic conditions of an automotive air conditioning system is presented. The experimental procedure is made of two steps. In the first one the passive data, i.e. the multimodal scattering matrix, is measured with a multi-sources method. In the second step the outgoing modal pressure spectra radiated upstream and downstream by the flow obstacle interaction source is achieved. A numerical simulation of the experiment based on a 3D-Finite Element Method is developed. A very good agreement between the theoretical and experimental results of the no flow scattering matrix of a diaphragm is found. The effect of the flow on the scattering matrix is shown before performing the measurement of the aero-acoustic source characteristics of the diaphragm.

After a quick review of the domain decomposition methods, and, more particularly on their application to large size problems relative to radiation and scattering of time-harmonic waves, we describe two contributions of the authors in this context. The two contributions are related to the scattering of a time-harmonic electromagnetic wave by a large perfectly conducting structure including a deep cavity. The first contribution is a substructuring technique. It is used to increase the speed of the convergence of the iterative algorithm in a Multi-Level Fast Multipol Method (MLFMM) solution. Numerical experiments illustrate the effectiveness of the approach since the number of iterations of the underlying Krylov iterative method remains almost constant while increasing a characteristic length in the problem. The second contribution proposes an adaptation of the overlapping domain decomposition techniques for a boundary integral formulation. It is used here to perform a hybridization of an exact formulation, used at the opening of the cavity, with an asymptotic high-frequency method employed for the rest of the exterior boundary of the structure. Numerical results demonstrate the reliability and the efficiency of the method. To cite this article: N. Balin et al., C. R. Physique 7 (2006).

The problem of the radiation pattern from sources in the presence of perfectly conducting objects is of great interest in the design of transmitting or receiving antennas on structures. The optimal antenna location is particularly hard to find because of the many costly tests which must be managed. A reliable and fast electromagnetic code, able to model antenna/structure couplings, can allow engineers to reduce this cost considerably. In this article, we present two different numerical approaches to solve this problem, according to the kind of antenna, and its location. In the first case, the antenna is in the vicinity of the structure and is only known by its radiation pattern in free-space. A new far to near field transformation is used to compute the incident field induced by the antenna on the structure. In the second case, the antenna is integrated into the structure. The technique consists in a physical and geometrical modeling of the antenna, using a Finite Element Method. In both cases, a Boundary Element Method coupled with a Fast Multipole Method, is used because of its suitability to cope with propagation outside the obstacle. Some numerical examples are given to illustrate the accuracy and efficiency of these two approaches. To cite this article: N. Zerbib et al., C. R. Physique 6 (2005).

first published online October 3, 2013 doi:10.1093/imanum/drt038; International audience; The wave propagation problems addressed in this paper involve a relatively large and impenetrable surface on which is posed a comparatively small penetrable heterogeneous material. Typically the numerical solution of such kinds of problems is solved by coupling boundary and finite element methods. However, a straightforward application of this technique gives rise to some difficulties which mainly are related to the solution of a large linear system whose matrix consists of sparse and dense blocks. To face such difficulties, the adaptive radiation condition technique is modified by localizing the truncation interface only around the heterogeneous material. Stability and error estimates are established for the underlying approximation scheme. Some alternative methods are recalled or designed making it possible to compare the numerical efficiency of the proposed approach.