Acoustic impedance of perforations in contact with fibrous material

Lee, Iljae; Selamet, Ahmet; Huff, Norman T.

doi:10.1121/1.2188354

Cited by 42 publications

(37 citation statements)

References 18 publications

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“…A comparison of these results with those of the MPP coupled to an air cavity and a rigid wall leads to the conclusion that the presence of the porous material behind the MPP causes a shift of the limit Reynolds number towards the low ranges regime. This is explained by the fact that the porous material behind the MPP increases the system resistance [2,4] as stipulated earlier. The measurements and prediction are also in good agreement.…”

Section: International Journal Of Engineering and Technologymentioning

confidence: 93%

“…Under low sound pressure levels, such assemblies are known [2][3][4] to result in shifting the resonance frequency, which is mainly induced by the perforated plate, to lowfrequency bands and enhance the acoustic absorption near the resonance frequency. The absorption performance of perforated plates alone is known [5] to be enhanced when the perforation sizes approach the boundary layer thickness sizes (submillimetric sizes very often).…”

Section: Introductionmentioning

confidence: 99%

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Sound absorption of a micro-perforated plate backed by a porous material under high sound excitation: measurement and prediction

Tayong

Dupont²,

Leclaire³

2013

IJET

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The sound absorption coefficient of perforated facings backed by porous materials 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 pressure levels ranging from 90 dB to 150 dB at the surface of the perforated facing. To corroborate the validity of the presented method, two considerations are particularly depicted in the experimental results: first, the case where the perforated facing and the porous material are both directly backed by a rigid wall and the case where there is an air cavity between the porous material and the rigid wall. Good agreement is observed between the simulation and the experimental results.

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Section: International Journal Of Engineering and Technologymentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Sound absorption of a micro-perforated plate backed by a porous material under high sound excitation: measurement and prediction

Tayong

Dupont²,

Leclaire³

2013

IJET

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“…The correction is based on replacing the density of air with the equivalent density ρm. Lee et al [40] also concluded that this procedure captures the effect of the absorbent material on the perforated duct. As shown in reference [34], good agreement between experimental and numerical silencer transmission loss is achieved considering an expression of the form…”

Section: Non-uniform Acoustic Impedance Of the Perforated Surfacementioning

confidence: 99%

“…(47)- (50), however, do not include the effect of the absorbent material on the acoustic impedance of the perforated duct. This influence has received attention in several works [39][40][41]. In reference [39], the effect of a fibrous material on the impedance of the perforated surface was measured and the authors suggested adding a correction to the impedance obtained in the absence of material.…”

Section: Non-uniform Acoustic Impedance Of the Perforated Surfacementioning

confidence: 99%

“…This impedance is defined as the ratio of the pressure difference to the normal acoustic velocity Un [33] a m p n P P Z U − =  (30) and depends, among others, on frequency, hole diameter, thickness, porosity, properties of the absorbent material and mean flow [39][40][41] (see details in section 3.2.). Eq.…”

Section: Acoustic Coupling At the Perforated Surfacementioning

confidence: 99%

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Finite element based acoustic analysis of dissipative silencers with high temperature and thermal-induced heterogeneity

Denia

Sánchez-Orgaz

Martínez‐Casas

et al. 2015

Finite Elements in Analysis and Design

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A mixed finite element model has been derived for the acoustic analysis of perforated dissipative silencers including several effects simultaneously: (1) High temperature and thermal gradients in the central duct and the outer absorbent material; (2) A perforated passage carrying non-uniform axial mean flow. For such a combination, the properties of sound propagation media and flow are inhomogeneous and vary with position. The material of the outer chamber can be modelled by its complex equivalent acoustic properties, which completely determine the propagation of sound waves in the air contained in the absorbent medium. Temperature gradients introduce variations in these properties that can be evaluated through a heterogeneous temperature-dependent resistivity in combination with material models obtained at room temperature. A pressure-based wave equation for stationary medium is then used with the equivalent density and speed of sound of the absorbent material varying as functions of the spatial coordinates. Regarding the central air passage, a wave equation in terms of acoustic velocity potential can be used to model the non-uniform moving medium since the presence of temperature variations introduce not only heterogeneous acoustic properties of the air but also a gradient in the mean flow velocity. The acoustic connection between the central passage and the outer chamber is given by the acoustic impedance of the perforated duct. This impedance depends on the heterogeneous properties of the absorbent material and the non-uniform mean flow, leading to a spatial variation of the acoustic coupling and also to additional convective terms in the governing equations. The results presented show the influence of temperature, thermal gradients and mean flow on the transmission loss of automotive silencers. It has been found that high temperature and thermal-induced heterogeneity can have a significant influence on the acoustic attenuation of an automotive silencer and so should be included in theoretical models. In some particular configurations it may be relatively accurate to approximate the temperature field by using a uniform profile with an average value, specially for low resistivity materials. It has been shown, however, that this is not always possible and attenuation overestimation is likely to be predicted, mainly for high radial thermal gradients and high material flow resistivities, if the temperature distribution is not taken into account.

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Boundary‐Element Analysis

Fahnline

2016

Engineering Vibroacoustic Analysis

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Acoustic impedance of perforations in contact with fibrous material

Cited by 42 publications

References 18 publications

Sound absorption of a micro-perforated plate backed by a porous material under high sound excitation: measurement and prediction

Sound absorption of a micro-perforated plate backed by a porous material under high sound excitation: measurement and prediction

Finite element based acoustic analysis of dissipative silencers with high temperature and thermal-induced heterogeneity

Boundary‐Element Analysis

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