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

Use of beamforming for detecting an acoustic source inside a cylindrical shell filled with a heavy fluid

International audienceThe acoustic detection of defects or leaks inside a cylindrical shell containing a fluid is of prime importance in the industry, particularly in the nuclear field. This paper examines the beamforming technique which is used to detect and locate the presence of an acoustic monopole inside a cylindrical elastic shell by measuring the external shell vibrations. In order to study the effect of fluid-structure interactions and the distance of the source from the array of sensors, a vibro-acoustic model of the fluid-loaded shell is first considered for numerical experiments. The beamforming technique is then applied to radial velocities of the shell calculated with the model. Different parameters such as the distance between sensors, the radial position of the source, the damping loss factor of the shell, or of the fluid, and modifications of fluid properties can be considered without difficulty. Analysis of thes

Extension of SmEdA (Statistical model Energy distribution Analysis) to non-resonant transmission

International audienceStatistical modal Energy distribution Analysis (SmEdA) may be used as alternative to Statistical Energy Analysis for describing subsystems with low modal overlap. In its original form, SmEdA predicts the power flow exchanged between the resonant modes of different subsystems. In the case of the sound transmission through a thin light structure, it is well-known than the non-resonant response of the structure may have a significant role on the transmission below the critical frequency. In this paper, one presents an extension of SmEdA taking into account the contributions of the non resonant modes of the thin structure. The dual modal formulation (DMF) is used for describing the behavior of two acoustic cavities separated by a thin structure knowing their subsystem modes. A condensation in the DMF equations is achieved on the amplitudes of the non-resonant modes. Using some simplifications, a new coupling scheme between the resonant modes of the three subsystems is obtained. It shows direct couplings of the cavity modes through stiffness elements characterized by the modes shapes of the cavities and the structure, both. Comparisons with reference results show the ability and the interest of the present approach for representing the nonresonant contributions of the structure

Prédiction de la réponse vibro-acoustique de coques cylindriques revêtues immergées excitées par une onde plane

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A methodology for including the effect of a damping treatment in the mid-frequency domain using SmEdA method

International audienceAn additive damping treatment is an effective tool to control the dynamic response of built-up structures, and it is widely utilized through industrial applications. By applying a viscoelastic layer on a given structure, the vibratory energy is dissipated through shear and in-plane motions at the layer interface. Modeling the effect of such a treatment in a complex mechanical system for the mid frequency domain is of interest. Statistical modal Energy distribution Analysis (SmEdA) has been developed as an alternative approach to Statistical Energy Analysis (SEA) for describing subsystems with low modal overlap. This technique is developed from the knowledge of the uncoupled subsystem modes. In this paper, one proposes to extend SmEdA by including the effect of a damping treatment. A damped subsystem consisting of a composite layer is modeled with the equivalent modulus of a single layer, which gives the same transverse displacement as a multi-layered system. The modal loss factor of a partially damped structure is estimated by the Modal Strain Energy method (MSE), and the results are well agreed with the Complex Eigenvalue Method (CEM). Finally, energy transmission between the damped structure and a coupled cavity can be deduced from SmEdA modeling, knowing the modeshapes and modal loss factors of the equivalent single layer and of the cavity. This method is applied for modeling a rectangular plate partially damped with an unconstrained viscoleastic layer coupled to a small acoustic cavity

Experimental results of passive vibro-acoustic leak detection in SFR steam generator mock-up

International audience# N° 1121 Experimental results of passive vibro-acoustic leak detection in SFR steam generator mock-up 1 Abstract— Regarding to GEN 4 context, it is necessary to fulfil the high safety standards for sodium fast reactors (SFR), particularly against water-sodium reaction which may occur in the steam generator units (SGU) in case of leak. This reaction can cause severe damages in the component in a short time. Detecting such a leak by visual in-sodium inspection is impossible because of sodium opacity. Hydrogen detection is then used but the time response of this method can be high in certain operating conditions. Active and passive acoustic leak detection methods were studied before SUPERPHENIX plant shutdown in 1997 to detect a water-into-sodium leak with a short time response. In the context of the new R&D studies for SFR, an innovative passive vibro-acoustic method is developed in the framework of a Ph.D. thesis to match with GEN 4 safety requirements. The method consists in assuming that a small leak emits spherical acoustic waves in a broadband frequency domain, which propagate in the liquid sodium and excite the SGU cylindrical shell. These spatially coherent waves are supposed to be buried by a spatially incoherent background noise. The radial velocities of the shell is measured by an array of accelerometers positioned on the external envelop of the SGU and a beamforming treatment is applied to increase the signal-to-noise ratio (SNR) and to detect and localize the acoustic source. Previous numerical experiments were achieved and promising results were obtained. In this paper, experimental results of the proposed passive vibro-acoustic leak detection are presented. The experiment consists in a cylindrical water-filled steel pipe representing a model of SGU shell without tube bundle. A hydrophone emitting an acoustic signal is used to simulate an acoustic monopole. Spatially uncorrelated noise or water-flow induced shell vibrations are considered as the background noise. The beamforming method is applied to vibration signals measured by a linear array of accelerometers on the shell. Satisfying results are obtained regarding to detection and localization of the source smothered by the background noise. This research was carried in the framework of the LabEx CeLyA ("Centre Lyonnais d'Acoustique", ANR-10-LABX-60) by the LVA/ INSA de Lyon, in collaboration with AREVA and the CEA (Commissariat à l'Energie Atomique et aux Energies Alternatives) within the framework of a co-financing partnership. The authors are grateful for the interest and financial support received from these two entities. J. Moriot and O. Gastaldi are with DEN/STPA

Modélisation des spectres de pression pariétale en vue de déterminer la réponse vibro-acoustique d'une structure soumise à une couche limite turbulente

Une méthodologie en trois étapes est développée afin de déterminer la réponse vibro-acoustique d’une structure excitée par une couche limite turbulente : Dans un premier temps l’écoulement turbulent est modélisé avec une méthode stationnaire RANS qui permet d’obtenir les paramètres caractéristiques de la couche limite formée sur la structure. L’excitation dynamique générée par cette couche limite est ensuite calculée à partir de modèles semi-empiriques des fluctuations de pression pariétale. Finalement, ces spectres de pression pariétale sont introduits dans un modèle vibro-acoustique de la structure pour en déduire sa réponse. Dans ce papier, on s’intéresse plus particulièrement aux deux premières étapes. On étudie les modèles de fluctuations de pression pariétale qui peuvent traduire au mieux l’excitation induite par la couche limite turbulente, et on cherche à relier les valeurs des différents paramètres de ces modèles à des quantités que l’on peut estimer à partir d’un code RANS. Les cas de validation retenus pour cette phase correspondent à deux séries d’expériences réalisées à l’Ecole Centrale de Lyon dans le cadre du projet européen ENABLE et du projet ANR SONOBL. Ces expériences mettent en jeu un écoulement dans une veine fermée avec un gradient de pression statique nul, favorable ou adverse, induit par une hauteur de conduite variable (paroi supérieure profilée dans le cas du projet ENABLE, et inclinable dans le cas du projet SONOBL). Des calculs RANS k-ϵ et k-ω ont été réalisés et les grandeurs globales comparées aux expériences (épaisseurs caractéristiques de couche limite, pression statique, …), validant les calculs stationnaires. Les paramètres d’écoulement sont ensuite injectés dans différents modèles du spectre de fluctuations de pression pariétale : modèle de Goody [1] en l’absence de gradient de pression moyenne, et modèle récent de Rozenberg [2] en présence d’un gradient de pression défavorable. Les différents spectres pariétaux sont ensuite comparés aux résultats expérimentaux. [1] M. Goody, « Empirical spectral model of surface pressure fluctuations », AIAA journal, 2004, vol. 42, p. 1788-1794. [2] Y. Rozenberg, G. Robert, S. Moreau, « Wall-pressure spectral model including the adverse pressure gradient effects », AIAA Journal, 2012, vol. 50, no 10, p. 2168-2179

Modélisation du comportement vibroacoustique d'une cabine de camion en moyenne fréquence avec prise en compte des habillages

L'objectif principal du projet CLIC (City Lightweight and Innovative Cab) est de proposer une nouvelle cabine de camion allégée, destinée aux transports urbain et péri-urbain. Cet allègement impacte directement le confort vibroacoustique et oblige les concepteurs à prendre en compte des phénomènes non étudiés précédemment, tel le confort vibroacoustique en moyenne fréquence. La méthode SmEdA permet la modélisation d'un tel problème. Il s'agit d'une méthode de sous-structuration par éléments finis, basée sur une formulation énergétique modale. Ce papier s'intéresse à l'interaction plancher-cavité, pour des excitations solidiennes sur les liaisons châssis-cabine, en prenant en compte les matériaux amortissants. Une comparaison numérique expérimentale permet la validation de la méthode

Simulation of the pressure field beneath a turbulent boundary layer using realizations of uncorrelated wall plane waves

International audienceThis paper investigates the modelling of a vibrating structure excited by a turbulent boundary layer (TBL). Although the wall pressure field (WPF) of the TBL constitutes a random excitation, the element-based methods generally used for describing complex mechanical structures consider deterministic loads. The response of such structures to a random excitation like TBL is generally deduced from calculations of numerous Frequency Response Functions. Consequently, the process is computationally expansive. To tackle this issue, an efficient process is proposed for generating realizations of the WPF corresponding to the TBL. This process is based on a formulation of the problem in the wave-number space and the interpretation of the wall pressure field as uncorrelated wall plane waves. Once the WPF has been synthesized, the local vibroacoustic responses are calculated for the different realizations and averaged together in the last step. A numerical application of this process to a plate located beneath a TBL is used to verify its efficiency and ability to reproduce the partial space correlation of the excitation. To further illustrate the proposed method, a stiffened panel modelled using the finite element method is finally examined