Papers by Emmanuel Perrey-debain
Journal of Sound and Vibration, 2014
This paper deals with strategies for computing efficiently the propagation of sound waves in duct... more This paper deals with strategies for computing efficiently the propagation of sound waves in ducts containing passive components. In many cases of practical interest, these components are acoustic cavities which are connected to the duct. Though standard Finite Element software could be used for the numerical prediction of sound transmission through such a system, the method is known to be extremely demanding, both in terms of data preparation and computation, especially in the mid-frequency range. To alleviate this, a numerical technique that exploits the benefit of the FEM and the BEM approach has been devised. First, a set of eigenmodes is computed in the cavity to produce a numerical impedance matrix connecting the pressure and the acoustic velocity on the duct wall interface. Then an integral representation for the acoustic pressure in the main duct is used. By choosing an appropriate Green's function for the duct, the integration procedure is limited to the duct-cavity interface only. This allows an accurate computation of the scattering matrix of such an acoustic system with a numerical complexity that grows very mildly with the frequency. Typical applications involving Helmholtz and Herschel-Quincke resonators are presented.
Les silencieux à baffles parallèles sont largement utilisés dans les systèmes de chauffage, venti... more Les silencieux à baffles parallèles sont largement utilisés dans les systèmes de chauffage, ventilation et climatisation (CVC) pour réduire le bruit généré par les sources aérauliques. Ces silencieux sont composés d'un certain nombre de baffles insérés dans un conduit de section rectangulaire. Chaque baffle est constitué d'un cadre métallique garni de matériaux absorbants. Cette étude vise à déterminer l'influence de la géométrie de ces silencieux afin d'en améliorer les performances. Un modèle bidimensionnel, prenant en compte un nombre arbitraire de baffles de longueur finie, délimités par un cadre métallique ou une impédance de surface, a été développé pour prédire leur perte par transmission (TL). Ce modèle multimodal est facilement implémentable, relativement peu coûteux en temps de calcul, flexible dans la définition des paramètres géométriques du silencieux et permet de modéliser une large variété de configurations. Après une description succincte du modèle, u...
Calcul de la propagation acoustique en milieux non homogènes infinis par la DRBEM
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy, 1998
ABSTRACT We present here an extension of the boundary element method, the DRBEM (Dual Reciprocity... more ABSTRACT We present here an extension of the boundary element method, the DRBEM (Dual Reciprocity Boundary Element Method), in order to solve the Helmholtz equation governing the propagation of linear acoustic waves in an unbounded variable mean temperature medium at rest. The originality of the method is that it allows discretization and integration only on the boundary of the domain, without an inner grid. The method is used here to study the wave propagation inside a non-isothermal flanged cavity, and throughout a thermal flume without mean velocity expending in a medium of constant outer temperature.
A homogenization method used to predict the performance of silencers containing parallel splitters
The Journal of the Acoustical Society of America, 2015
An analytical model based on a homogenization process is used to predict and understand the behav... more An analytical model based on a homogenization process is used to predict and understand the behavior of finite length splitter/baffle-type silencers inserted axially into a rigid rectangular duct. Such silencers consist of a succession of parallel baffles made of porous material and airways inserted axially into a rigid duct. The pore network of the porous material in the baffle and the larger pores due to the airway can be considered as a double porosity (DP) medium with well-separated pore sizes. This scale separation leads by homogenization to the DP model, widely used in the porous material community. This alternative approach based on a homogenization process sheds physical insight into the attenuation mechanisms taking place in the silencer. Numerical comparisons with a reference method are used to show that the theory provides good results as long as the pressure wave in the silencer airways propagates as a plane wave parallel to the duct axis. The explicit expression of the axial wavenumber in the DP medium is used to derive an explicit expression for the optimal resistivity value of the porous material, ensuring the best dissipation for a given silencer geometry.
On the Efficiency of Parallel Baffle-Type Silencers in Rectangular Ducts: Prediction and Measurement
Acta Acustica united with Acustica, 2015
ABSTRACT
On the efficiency of the method of fundamental solutions for acoustic scattering by a poroelastic material
Boundary Elements and Other Mesh Reduction Methods XXXII, 2010
ABSTRACT The Method of Fundamental Solutions is now a well established technique that has proved ... more ABSTRACT 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. Keywords: method of fundamental solutions, Biot’s equations, poroelastic, porous material, scattering.
Boundary Elements and Other Mesh Reduction Methods XXXII, 2010
This paper deals with strategies for computing efficiently the propagation of sound waves in duct... more This paper deals with strategies for computing efficiently the propagation of sound waves in ducts with acoustic lining at its walls. Though efficient these treatments seem to have reach their limit and there is still a need for considering other passive techniques to reduce further the sound radiation at the duct exit. In most cases of practical interest, these added acoustics components can be modelled as acoustic cavities which are connected to the duct and can be either purely reactive or dissipative. The assessment of the efficiency of such a system requires a precise knowledge of the acoustic field in the duct. Though standard Finite Element (FE) software could, in principle, be used for this purpose, a full FE model would be extremely demanding especially in the mid-frequency range and this can have a negative impact when, for instance, some efficient optimizations are needed. In the present work,we present a new numerical procedure that judiciously exploit the benefit of the FEM and the BEM approach. First, a set of FE eigenmode are computed in the cavity to produce a numerical impedance matrix connecting the pressure and the acoustic velocity on the duct wall interface. Then an integral representation for the acoustic pressure in the main duct is used. The presence of acoustic liners on the walls of the duct is taken into account via an appropriate modal decomposition of the Green's function. Typical applications involving Helmholtz resonators and Herschel-Quincke tubes are presented. We show that our algorithm allows a very fast and accurate computation of the scattering matrix of such a system with a numerical complexity that grows very mildly with the frequency.
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, Jan 15, 2004
Classical finite-element and boundary-element formulations for the Helmholtz equation are present... more Classical finite-element and boundary-element formulations for the Helmholtz equation are presented, and their limitations with respect to the number of variables needed to model a wavelength are explained. A new type of approximation for the potential is described in which the usual finite-element and boundary-element shape functions are modified by the inclusion of a set of plane waves, propagating in a range of directions evenly distributed on the unit sphere. Compared with standard piecewise polynomial approximation, the plane-wave basis is shown to give considerable reduction in computational complexity. In practical terms, it is concluded that the frequency for which accurate results can be obtained, using these new techniques, can be up to 60 times higher than that of the conventional finite-element method, and 10 to 15 times higher than that of the conventional boundary-element method.
Modelling of an Acoustic Treatment Based on Porous Materials for Aero-Engine Noise Reduction
Sound Attenuation in Duct Lined with Poroe-Lastic Material Submitted to Grazing Flow: A Mode Matching Approach
Etude d’un traitement acoustique basé sur des matériaux poreux pour la réduction du bruit de soufflante
Application of the dual reciprocity method to acoustic radiation in an inhomogeneous medium
A DRBEM model for sound waves propagation in an inhomogeneous medium
Extension of the DRBEM for acoustic propagation in duct shear flow
Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences: 362 (1816)
Méthode d'ondes planes pour la résolution des problèmes vibroacoustiques en moyennes et hautes fréquences
ABSTRACT La méthode des éléments finis (FEM) est encore aujourd'hui la méthode la plus ut... more ABSTRACT La méthode des éléments finis (FEM) est encore aujourd'hui la méthode la plus utilisée pour résoudre les problèmes vibroacoustiques. Cependant la mise en oeuvre de cette méthode reste difficile et coûteuse dans certain cas, notamment en moyennes et hautes fréquences dues au coût informatique exorbitant que celle-ci occasionne. En effet, une description assez précise du problème nécessite l'utilisation d'environ 10 degrés de liberté par longueur d'onde engendrant des problèmes de très grande taille difficile à résoudre. Pour surmonter ces difficultés des méthodes sont apparues qui consistent à multiplier les fonctions de forme classiques des éléments finis par des fonctions oscillantes pour construire l'espace fonctionnel. Ainsi, les ondes planes progressives sont des fonctions de choix pour l'équation de Helmholtz. La méthode de base d'onde plane a été développée avec succès pour les éléments finis et les éléments finis de frontière pour résoudre l'équation de Helmholtz et elle est étendue pour les problèmes de dispersion des ondes élastiques. Dans ce papier, on s'intéresse à l'extension de la méthode des ondes planes aux problèmes vibroacoustiques. Une formulation couplée est développée basée sur la variable pression pour la cavité fluide et le variable déplacement pour la structure. La cavité fluide est discrétisée par des éléments finis triangulaires linéaires enrichis par base d'ondes planes et la structure est discrétisée par des éléments finis à deux noeuds de type Hermite enrichis par une base déduite de la solution homogène de l'équation dynamique. Des problèmes vibroacoustiques sont traités, les résultats montrent l'efficacité de cette méthode qui peut être étendue pour résoudre une grande classe de problèmes des ondes de grand intérêt pratique.
The Herschel-Quincke (HQ) tubes, consisting in putting tubes in derivation along a main acoustic ... more The Herschel-Quincke (HQ) tubes, consisting in putting tubes in derivation along a main acoustic wave guide, are used as passive devices to control fan noise. In order to assess the efficiency of this system, a new mixed analytical-numerical model is presented. The technique relies on combining Finite Element techniques to accurately describe the HQ tube with an integral representation for the acoustic pressure in the main duct. The presence of acoustic liners on the walls of the duct is taken into account via an appropriate modal decomposition of the Green's function. We show that our algorithm allows a very fast and accurate computation of the scattering matrix of such a system with a numerical complexity that grows very mildly with the frequency. Results show that 'nearly' optimal configurations can be quickly identified with a very small computational expense.
Aeroacoustics Analogies (AA) initiated by Lighthill in the 50's are able to give the acoustic fie... more Aeroacoustics Analogies (AA) initiated by Lighthill in the 50's are able to give the acoustic field radiated by an aero-dynamic flow. In this work, the computation of the Lighthill-Curle's integral formulation for the prediction of the upstream pressure field in a two dimensional duct is presented. We are considering in particular the emitted noise due to low-Mach number flows through geometrical singularities placed in the duct (circular obstacle and diaphragm). The Lighthill stress tensor corresponding to turbulent velocity fluctuations is obtained via a commercial software (ANSYS FLUENT). It is shown that sound levels generated upstream can be particulary sensitive to the wall pressure fluctuations on the obstacle. Mots clefs : 3 maximum : Analogie de Lighthill-Curle, Acoustique en conduit, Bruit de diaphragme
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Papers by Emmanuel Perrey-debain