Modeling of micro-perforated panels in a complex vibro-acoustic environment using patch transfer function approach

International audienceThe micro-perforated panel (MPP) with a backing cavity is a well known efficient device for noise absorption. This device has been thoroughly studied in the experimental conditions of an acoustic tube (Kundt tube), in which the MPP is excited by a normal incident plane wave in one dimension. In an industrial situation, the efficiency of MPP may be influenced by the vibro-acoustic behaviour of the surrounding systems as well as excitation. To deal with this problem, a vibroacoustic formulation based on the Patch Transfer Functions (PTF) approach is proposed to model the behaviour of micro-perforated structure in a complex vibro-acoustic environment. PTF is a substructuring approach which allows assembling different vibro-acoustic subsystems through coupled surfaces. Upon casting micro-perforations and the flexibility of the MPP under transfer function framework, the proposed PTF formulation provides explicit representation of the coupling between subsystems and facilitates explanation of physical phenomenon. As an illustration example, application to a MPP with a backing cavity located in an infinite baffle is demonstrated. The proposed PTF formulation is finally validated through comparison with experimental measurements available in the literature

Modeling of micro-perforated panels in a complex vibro-acoustic environment using patch transfer function approach

2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

SIMULATION OF THE TBL INDUCED VIBRATIONS OF A PLATE USING VIRTUAL SOURCES

International audienceFinding an alternative to common test means (reverberant chamber, wind tunnel facilities, in-situ measurements, etc.) is of particular interest to the transportation industry (automobile, aeronautics , etc.) for the reproduction of the vibroacoustic response of structures under random excitations such as the diffuse acoustic field or the turbulent boundary layer. In this paper a method of achieving this goal using a single acoustic source and the synthetic array principle is proposed. To assess the validity of this method, an academic case study consisting of a simply supported thin aluminum plate under turbulent boundary layer excitation is presented. The vibroacoustic response of the plate is determined with the proposed process and compared to results from random vibration theory and direct measurements in an anechoic wind tunnel facility. This comparison shows good agreement between the proposed approach and both the theoretical and wind tunnel results

Patch transfer function as a tool to couple linear acoustic problems

A method to couple acoustic linear problems is presented in this paper. It allows one to consider several acoustic subsystems, coupled through surfaces divided in elementary areas called patches. These subsystems have to be studied independently with any available method, in order to build a database of transfer functions called patch transfer functions, which are defined using mean values on patches, and rigid boundary conditions on the coupling area. A final assembly, using continuity relations, leads to a very quick resolution of the problem. The basic equations are developed, and the acoustic behavior of a cavity separated in two parts is presented, in order to show the ability of the method to study a strong-coupling case. Optimal meshing size of the coupling area is then discussed, some comparisons with experiments are shown, and finally a complex automotive industrial case is presented

Analyse du bruit rayonné par une structure immergée excitée par une source transitoire

La modernisation des sonars passifs, capables d'analyser les bruits transitoires, rend nécessaire l'optimisation de la discrétion acoustique dans ce domaine. L'industrie doit pouvoir spécifier des exigences sur les matériels, sources de bruit transitoire. L'objectif de cette étude est d'étudier les vibrations et le rayonnement acoustique d'une structure immergée, excitée par une source de bruit transitoire. Les signaux temporels sont évalués à l'aide d'une transformation de Fourier inverse de la réponse en fréquence du système. Afin de valider la méthode, une structure simple est étudiée : une plaque infinie excitée par une force impulsionnelle ponctuelle. La méthode est validée par une comparaison avec une plaque in-vacuo. Lorsque la plaque est immergée, les vibrations et la pression rayonnée sont évaluées par la méthode développée. L'étude des vibrations met en évidence l'effet du fluide, la dispersion des ondes de plaque et les ondes d'interface fluide/solide. L'étude de la pression rayonnée met en évidence une directivité du rayonnement et la propagation des ondes dans la plaque avant d'être rayonnées. Une comparaison entre les modèles de plaque de Love Kirchhoff et Mindlin-Timoshenko est également effectuée et l'effet de l'inertie et du cisaillement sont illustrés

Analysis of the sound radiated by a heavy fluid loaded structure excited by an impulsive force

International audienceThe aim of this work consists in evaluating and analyzing vibrations and radiated pressure from a fluid loaded structure excited by a transient mechanical source. The time signature can be estimated from a discrete inverse Fourier transform of the Frequency Response Functions (FRF) of the considered system. In order to validate the numerical process, a simple structure composed of an infinite flat plate excited by an impulse point force is considered. Results are compared with an analytic result for the in-vacuo plate. When the plate is immerged on one side, the vibrations and radiated pressure from the plate are evaluated with the developed numerical process. Then, one studies the effect of the fluid loading and the dispersive nature of the flexural waves on the vibrations, and radiated pressure time signature in the far field of the plate. A comparison between Khirchoff-Love and Mindlin Timoshenko plate is also made