0000000001275175
AUTHOR
Thomas Dupont
Experimental investigation of holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound levels
Abstract This paper experimentally investigates the holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound levels. The theoretical formulations are based on a semi-empirical approach and the use of Fok’s function to model the acoustic surface impedance. For the high sound level regime, an empirical power law involving three coefficients is adapted. It is shown theoretically and experimentally that these coefficients can lead to optimized absorption performance and particularly, a formula relating the critical Reynolds number (Reynolds number value after which the absorption coefficient decreases with the increase of sound level) a…
Recent Highlights on the Parallel Transfer Matrix Method (Ptmm)
International audience; Recently, an extension of the transfer matrix method (TMM) to calculate absorption coefficient and transmission loss of acoustic systems in parallel (one next to each other and not one after the other) has been published [1]. This method (P-TMM) is based on the continuity of flow and pressure on each side of the stack. To comply with these constraints, assumptions must be set: there is only plane waves that propagate, no exchange is allowed between the elements of the stack, the stack is smaller than the wavelength. Further progress has been made. Firstly, a comparison with the method of the sum of admittances (ASM) [2] will be presented. Then, a further extension of…
Holes Interaction and Heterogeinity Distribution Effect for a Multiperforated Plate
International audience; Originally used to protect classical sound absorbing materials from environmental degradation, multi-perforated plates are considered to be one of the next generation soundproof solutions. This paper investigates the effects of holes interaction and heterogeneity distribution on the acoustical properties of a multi-perforated plate. These effects are observable on the specimens with closely separated holes. Multi-perforated plates with different center-to-center holes distances (pitches) are built and tested using an impedance tube. The cases of closely separated holes are analyzed and compared to the cases of widely separated holes. It is observed that in the presen…
Study and Simulation of Helicopter Gearboxes Noise
International audience; Main gearbox is one of the main noise sources in helicopter cabin. In order to improve the comfort of customers and reduce the health impact, acoustic and vibration mechanisms of gearboxes have to be understood and simulated during development phases. Thus, we first present the global methodology chosen to compute main gearboxes noise in helicopter cabins. Secondly, we described the way we compute mechanical excitation sources induced from gear mesh, static transmission error and meshing stiffness. Depending on the type of gear, we compute those using either analytical specially developed code or EC codes. Thirdly, we propose a modeling to compute dynamic loads on be…
Acoustics of porous materials with partially opened porosity
International audience; A theoretical and experimental study of the acoustic properties of porous materials containing dead-end (or partially opened) porosity was recently proposed by Dupont et al. The present article provides a description of partially opened porosity systems and their numerous potential applications in the general context of the study of porous materials, the classical models describing them, and the characterization techniques. It is shown that the dead-end pore effect can be treated independently and that the description of this effect can be associated with any acoustic model of porous media. Different theoretical developments describing the dead-end porosity effect ar…
Propriétés acoustiques de matériaux poreux saturés d'air incluant une porosité partiellement ouverte
International audience; Nous étudions les propriétés d'un matériau à microgéométrie complexe incluant une porosité partiellement ouverte ou de culs-de-sacs. Ce type de matériau peut être obtenu par dissolution de grains de sel (NaCl) noyés dans une matrice de métal solidifié. Cette matrice est obtenue après invasion sous pression négative et à haute température des grains de sels par le métal sous forme liquide, puis refroidissement jusqu'à solidification du métal. La comparaison des résultats expérimentaux et théoriques sur le coefficient d'absorption acoustique d'une couche de ce métal poreux montre que le modèle de Biot-Johnson-Allard ne fournit pas des résultats aussi satisfaisants que …
Sound Propagation in Narrow Tubes with Periodically Spaced Lateral Cavities
International audience
Vibrational damping properties of finite microperforated plates
Microperforated plates (MPP) are traditionally used to advantageously absorb acoustic waves in sound control technologies. However, less is known concerning the additional structural damping they can induce. The latter is activated through exchanges in the viscous and thermal boundary layers near the fluid-structure interface of the microperforations. MPPs therefore offer an alternative to, or can be used together with, viscoelastic materials, commonly implemented to damp vibrations at medium and high frequencies. In this work, the structural damping capabilities of MPP are investigated. To this end, the damping performance of a finite size MPP is explored analytically through an alternativ…
Comportement vibratoire des plaques microperforées finies
Les plaques microperforées sont utilisées dans l’industrie pour leurs propriétés d’absorption acoustique. Ces structures légères, de par des échanges dans les couches limites visqueuses et thermiques près de l’interface fluide-structure, permettent l’absorption des ondes acoustiques. Il est montré dans ce travail que ces structures peuvent également induire un amortissement supplémentaire significatif particulièrement pour les basses fréquences. Ces solutions sans ajout de masse peuvent être un complément ou une alternative aux matériaux viscoélastiques couramment utilisés pour amortir les vibrations en moyennes et hautes fréquences.Ainsi il est proposé dans ce projet d’étudier les effets d…
Acoustical properties of air-saturated porous material with periodically distributed dead-end pores
International audience; A theoretical and numerical study of the sound propagation in air-saturated porous media with straight main pores bearing lateral cavities (dead-ends) is presented. The lateral cavities are located at " nodes " periodically spaced along each main pore. The effect of periodicity in the distribution of the lateral cavities is studied, and the low frequency limit valid for the closely spaced dead-ends is considered separately. It is shown that the absorption coefficient and transmission loss are influenced by the viscous and thermal losses in the main pores as well as their perforation rate. The presence of long or short dead-ends significantly alters the acoustical pro…
Impact Test and Mixture Approach to the Study of the Acoustic Properties of Rigid Frame Porous Materials with Functionally Graded Macroscopic Physical Parameters
International audience
Recent developments in the acoustical properties of perforated and porous materials containing dead-end pores
It was shown recently in Nevers, France, Sherbrooke, Canada and Salford, UK, that porous materials with semi-opened pores or materials with open pores bearing lateral cavities or resonators at the microscopic scale of the pores can result in peculiar sound absorption properties. Various examples of these materials can be found in engineering and in everyday life including bio-based materials. The cavities and resonators can be assimilated to dead-end pores, which are opened at one end and closed at the other. The dead-end pores are known to geophysicists. We studied them more recently in the field of engineering acoustics where the saturating fluid is air. The closed ends prevent the fluid …
High sound pressure model for cellular metallic foam with semi open cells
International audience
Propriétés acoustiques de matériaux perforés comprenant des pores dead-end périodiques pour des applications basses fréquences
International audience; Pour un matériau absorbant tel que la mélamine et pour une épaisseur assez faible (inférieure à 5 cm), l'absorption acoustique devient supérieure à 0.8 à partir d'une fréquence de l'ordre de 1000 Hz. Une étude récente [1] a montré que des matériaux perforés peu épais comportant le long des perforations des pores dead-ends (DE) régulièrement espacés peuvent permettre de produire des pics d'absorption supérieurs à 0.8 en basses fréquences (quelques centaines de Hz). Les dimensions des pores DE ainsi que leur périodicité peuvent être millimétrique ou submillimétrique de sorte que l'épaisseur totale du matériau soit de seulement quelques centimètres. Ces pores DE peuvent…
Transfer matrix modeling and numerical verification of locally reacting acoustic mosaics
International audience; This paper deals with the modeling of the acoustic behavior (absorption and transmission) of an acoustic mosaic having heterogeneous surface properties. On the surface, the material can be viewed as a collection of independent cells reacting locally. Each cell is filled with an absorbent material different from its neighbors. Such a mosaic may be seen as a generalization of the typical case of a honeycomb liner filled with absorbent materials. The originality of the study lies in the modeling of such heterogeneous material by an Admittance Sum Method (ASM) and a Transfer Matrix Method (TMM). The transfer matrix modeling of the heterogeneous material uses the summatio…
On the variations of acoustic absorption peak with particle velocity in micro-perforated panels at high level of excitation.
The acoustic behavior of micro-perforated panels (MPP) is studied theoretically and experimentally at high level of pressure excitation. A model based on Forcheimer's regime of flow velocity in the perforations is proposed. This model is valid at relatively high Reynolds numbers and low Mach numbers. The experimental method consists in measuring the acoustical pressure at three different positions in an impedance tube, the two measurement positions usually considered in an impedance tube and one measurement in the vicinity of the rear surface of the MPP. The impedance tube is equipped with a pressure driver instead of the usual loudspeaker and capable of delivering a high sound pressure lev…
Sound absorption coefficient of a porous material covered with a low open area perforated plate under high sound excitation
International audience; The sound absorption coefficient of porous materials covered with low open area perforated plate is studied under high sound intensities in the absence of mean flow. The theoretical considerations are based on the equivalent fluid following the Johnson-Champoux-Allard approach and the use of the transfer matrix method. To take into account the high sound levels effects, the air flow resistivity of each layer is modified following the Forchheimer law. Two specimens of perforated plate are built and tested when backed by a polymeric foam and a fibrous material. A specific impedance tube setup is developed for the measurement of the surface acoustic impedance for sound …
Acoustic methods for measuring the porosities of porous materials incorporating dead-end pores
International audience; The acoustic properties of porous materials containing dead-end (DE) pores have been proposed by Dupont et al. [J. Appl. Phys. 110, 094903 (2011)]. In the theoretical description, two physical parameters were defined (the dead-end porosity and the average length of the dead-end pores). With the knowledge of the open porosity (measured with non-acoustic methods), and the measurement of kinematic porosity (also called the Biot porosity in this article), it is possible to deduce the dead-end porosity. Two acoustic methods for measuring the Biot porosity for a wide range of porosities are proposed. These methods are based on acoustic transmission and on the low and high …
Added viscous damping in a finite-size microperforated plate within a nonlinear framework
Increasing the damping properties of a structure while limiting the addition of mass is a challenging task. Originally developed for their acoustic absorption capabilities, microperforated plates (MPP) are simple devices that can feature additional viscous damping at low frequencies. Dissipation arises in the boundary layers of the microperforations through viscous friction mechanisms induced by the relative motion between the solid and the fluid in which the MPP is immersed. This leads to sound absorption in an acoustic context and to an added viscous damping in a solid dynamics context. The added viscous damping exhibited by the MPP can be captured by considering adapted fluid-solid inter…
Description of sound absorption by a flat resonator stacking metamaterial with double porosity model
Acoustic metamaterials can be designed by inserting along the path of a sound wave periodically spaced side resonators. An example of efficient design was recently proposed consisting of a perforated stacking of flat annular cavities (the pancake resonator), the perforation allowing the propagation of sound waves. The pancake resonator is used in absorber mode and the theoretical description of sound absorption can be achieved with the help of the theory of sound propagation in fluid saturated porous media in which two porosities are considered: the main porosity associated with the perforation and a porosity associated with the flat cavity volumes. Considering a perforation diameter and fl…
Transfer matrix method applied to the parallel assembly of sound absorbing materials
International audience; The transfer matrix method (TMM) is used conventionally to predict the acoustic properties of laterally infinite homogeneous layers assembled in series to form a multilayer. In this work, a parallel assembly process of transfer matrices is used to model heterogeneous materials such as patchworks, acoustic mosaics, or a collection of acoustic elements in parallel. In this method, it is assumed that each parallel element can be modeled by a 2 × 2 transfer matrix, and no diffusion exists between elements. The resulting transfer matrix of the parallel assembly is also a 2 × 2 matrix that can be assembled in series with the classical TMM. The method is validated by compar…
Damping performance of finite microperforated plates using multi-sized and spacial distributions of perforations
In the context of structural dynamics, recent works by the authors showed that microperforations can be used to mitigate vibration. Microperforated plates (MPPs) have been shown to exhibit substantial added damping stemming from fluid-structure interactions and visco-thermal effect mechanisms in the boundary layers of the perforations during relative motion between the solid and the fluid contained in the perforations. The added damping reaches a maximum for a characteristic frequency, depending only on the perforation diameter. Choosing the perforation diameter so that the characteristic frequency coincides with the natural frequency of the plate reduces the mode contribution of the plate.…
Acoustic properties of perforated plates and screens
International audience; In previous works, an acoustic model for Microperforated Insertion Unit (MIU), was developed to determine the input impedance of a system composed of a thin mesh (or screen) glued onto a perforated plate. An alternative approach is proposed by means of the equivalent fluid model of Johnson-Champoux-Allard involving five physical parameters: the tortuosity, the thermal and viscous characteristic lengths, the porosity and the flow resistivity. The input impedance of a multiple layer system can then be found by use of the transfer matrix method. Since the meshes have fairly simple structures, it was possible to model an elementary representative cell and to use calculat…