Jean-Daniel Chazot

Prediction of transmission loss of double panels with a patch-mobility method

Sound transmission loss through double panels is studied with a patch-mobility approach. An overview of the method is given with details on acoustic and structural patch mobilities. Plate excitation is characterized by blocked patch pressures that take into account room geometry and source location. Hence, panel patch velocities before coupling can be determined and used as excitation in the mobility model. Then a convergence criterion of the model is given. Finally, transmission loss predicted with a patch-mobility method is compared with measurements.

Acoustical and mechanical characterization of poroelastic materials using a Bayesian approach

A characterization method of poroelastic materials saturated by air is described. This inverse method enables the evaluation of all the parameters with a simple measurement in a standing wave tube. Moreover, a Bayesian approach is used to return probabilistic data such as the maximum a posteriori and the confidence interval of each parameter. To get these data, it is necessary to define prior probability distributions on the parameters characterizing the studied material. This last point is very important to regularize the inverse problem of identification. In a first step, the direct problem formulation is presented. Then, the inverse characterization is developed and applied to simulated and experimental data.

A Plane and Thin Panel with Representative Simply Supported Boundary Conditions for Laboratory Vibroacoustic Tests

A technique to setup a simply supported rectangular plane panel for laboratory vibroacoustic tests is described and validated. For a given panel fixed to thin vertical supports, a dimensionless parameter is proposed to size these supports following a desired frequency precision compared to theoretical eigenfrequencies of a panel with such boundary conditions. A numerical study confirms the potential of this design parameter. Detailed instructions for assembling a panel with adequate thin vertical supports on a rigid frame are then given. Finally, three laboratory cases are described which illustrate possible experimental vibroacoustic applications using a panel assembled following previous guidelines. The design parameter viability is experimentally confirmed, and all obtained results depicted good agreement with analytical solutions and numerical predictions.

The Partition of Unity Finite Element Method for the simulation of waves in air and poroelastic media

Recently Chazot et al. [J. Sound Vib. 332, 1918-1929 (2013)] applied the Partition of Unity Finite Element Method for the analysis of interior sound fields with absorbing materials. The method was shown to allow a substantial reduction of the number of degrees of freedom compared to the standard Finite Element Method. The work is however restricted to a certain class of absorbing materials that react like an equivalent fluid. This paper presents an extension of the method to the numerical simulation of Biots waves in poroelastic materials. The technique relies mainly on expanding the elastic displacement as well as the fluid phase pressure using sets of plane waves which are solutions to the governing partial differential equations. To show the interest of the method for tackling problems of practical interests, poroelastic-acoustic coupling conditions as well as fixed or sliding edge conditions are presented and numerically tested. It is shown that the technique is a good candidate for solving noise control problems at medium and high frequency.

Transmission loss of double panels filled with porogranular materials

Sound transmission through hollow structures found its interest in several industrial domains such as building acoustics, automotive industry, and aeronautics. However, in practice, hollow structures are often filled with porous materials to improve acoustic properties without adding an excessive mass. Recently a lot of interest arises for granular materials of low density that can be an alternative to standard absorbing materials. This paper aims to predict vibro-acoustic behavior of double panels filled with porogranular materials by using the patch-mobility method recently published. Biots theory is a basic tool for the description of porous material but is quite difficult to use in practice, mostly because of the solid phase characterization. The original simplified Biots model (fluid-fluid model) for porogranular material permitting a considerable reduction in data necessary for calculation has been recently published. The aim of the present paper is to propose a model to predict sound transmission through a double panel filled with a porogranular material. The method is an extension of a previous paper to take into account the porogranular material through fluid-fluid Biots model. After a global overview of the method, the case of a double panel filled with expanded polystyrene beads is studied and a comparison with measurements is realized.

Influence of solid phase elasticity in poroelastic liners submitted to grazing flows

In the present work, we study the sound propagation in a duct treated with a poroelastic liner exposed to a grazing flow. Acoustic propagation in the liner and in the fluid domain is respectively governed by Biots model and Galbruns equation. Here, the coupling between Galbruns and Biots equation is carried out with a mixed pressure‐displacement FE. On one hand, a mixed formulation is used in Galbruns equation to avoid numerical locking. And on the other hand, in poroelastic media, the description of both phases involves the displacement of the solid phase and the pressure in the fluid phase. In addition of using the complete Biots model, simplified models are also tested. A fluid equivalent model that does not take into account solid phase elasticity and a model that neglects only the shear stress are hence used. These two simplified models enable to evaluate the contributions of the compressional and shear waves in the solid phase. Finally, validity of each simplified model in the specific case of...

Bayesian identification of acoustic impedance in treated ducts

The noise reduction of a liner placed in the nacelle of a turbofan engine is still difficult to predict due to the lack of knowledge of its acoustic impedance that depends on grazing flow profile, mode order, and sound pressure level. An eduction method, based on a Bayesian approach, is presented here to adjust an impedance model of the liner from sound pressures measured in a rectangular treated duct under multimodal propagation and flow. The cost function is regularized with prior information provided by Guesss [J. Sound Vib. 40, 119-137 (1975)] impedance of a perforated plate. The multi-parameter optimization is achieved with an Evolutionary-Markov-Chain-Monte-Carlo algorithm.

Sound Source Localization from Uncertain Information Using the Evidential EM Algorithm

We consider the problem of sound sources localization from acoustical measurements obtained from a set of microphones. We formalize the problem within a statistical framework: the pressure measured by a microphone is interpreted as a mixture of the signals emitted by the sources, pervaded by a Gaussian noise. Maximum-likelihood estimates of the parameters of the model (locations and strengths of the sources) may then be computed via the EM algorithm. In this work, we introduce two sources of uncertainties: the location of the microphones and the wavenumber. First, we show how these uncertainties may be transposed to the data using belief functions. Then, we detail how the localization problem may be studied using a variant of the EM algorithm, known as Evidential EM algorithm. Eventually, we present simulation experiments which illustrate the advantage of using the Evidential EM algorithm when uncertain data are available.

Parametric identification of elastic modulus of polymeric material in laminated glasses

Abstract This paper addresses an inverse approach to characterize the frequency-dependent elastic modulus of the polymer layer in laminated structures. Represented by fractional derivative models, the modulus is identified based on a finite element model of the laminated structure from the experimental frequency response functions. An efficient Markov Chain Monte Carlo method is implemented to learn the identification parameters from a Bayesian perspective. A surrogate model is applied to alleviate Bayesian computation through the use of artificial neutral network. The proposed approach is experimentally validated on a laminated glass.

On the efficiency of the method of fundamental solutions for acoustic scattering by a poroelastic material

The Method of Fundamental Solutions is now a well established technique that has proved to be reliable for a specific range of wave problems such as the scattering of acoustic and elastic waves by obstacles and inclusions of regular shapes. The goal of this paper is to show that the technique can be extended in order to solve transmission problems whereby an incident acoustic pressure wave impinges on a poroelastic material of finite dimension. For homogeneous and isotropic materials, the wave equation for the fluid phase and solid phase displacements are found to be decoupled thanks to the Helmholtz decomposition. This allows a systematic way for obtaining an analytic expression for the fundamental solution describing the wave displacement field in the material. The efficiency of the technique relies on choosing an appropriate set of fundamental solutions as well as properly imposing the transmission conditions at the air-porous interface. In this paper, we address this issue showing results involving bidimensional scatterers of various shapes. In particular, it is shown that reliable error indicators can be used to assess the quality of the results. Comparisons with results computed using a mixed pressure-displacement finite element formulation illustrate the great advantage of this new technique both in terms of computational resources and mesh preparation.