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Characterisation of anisotropic acoustic properties of porous materials - inverse estimation of static flow resistivity
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The production processes of porous materials introduce an inherent geometric anisotropy in the material at micro scale, which influences the material properties at macro scale. In this thesis, the focus is turned to one of these macroscopic properties, the flow resistivity, which is a measure of the resistance felt by the sound pressure waves as they propagate through a porous space. In the current work, two different porous materials have been studied, a fibrous glass wool and a Melamine foam. The two materials are expected to show different degrees of anisotropy with respect to flow resistivity. Glass wool is assumed to be transversely isotropic, as a result of the stacking of layers of fibres. The level of anisotropy in Melamine foam is not as obvious, and might be related to production specific aspects, such as the rise-direction, and the position of the injection nozzles. The thesis begins by giving an introduction to porous materials in general, and to glass wool and Melamine foam in particular, followed by an introduction to flow resistivity, together with two methods to measure the flow resistivity. The full anisotropic flow resistivity of glass wool and Melamine foam samples is determined by means of measurements and inverse estimation. An eigenvalue and eigenvector decomposition of the flow resistivity tensor provides an insight into the connection between the directionality of the flow resistivity in each material, and its production process. A study of the homogeneity in density and flow resistivity for the two materials shows that these properties vary within the block of material. However, for each material, there seems to be no connection between the variation in the two properties, investigated at the macroscopic scale.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 38 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2011:14
National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-31183ISBN: 978-91-7415-894-6OAI: oai:DiVA.org:kth-31183DiVA: diva2:403017
Presentation
2011-03-15, MWL 74, KTH, Teknikringen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20110311Available from: 2011-03-11 Created: 2011-03-10 Last updated: 2012-06-12Bibliographically approved
List of papers
1. Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Melamine Foam
Open this publication in new window or tab >>Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Melamine Foam
2010 (English)Report (Other academic)
Abstract [en]

The flow resistivity tensor, which is the inverse of the viscous per- meability tensor, is one of the most important material properties for the acoustic performance of open cell foams used in acoustic treatments. Due to the manufacturing processes, these foams are most often geomet- rically anisotropic on a microscopic scale. For such a materials there is a need for improved characterisation methods, and this paper discusses the estimation of the flow resistivity tensor of Melamine samples using a methodology which is an improvement of a method previously published by Go ̈ransson et al. The validity of the new method is in addition ver- ified for a wider range of anisotropy. Measurements are performed on cubic Melamine samples, and the resulting 3D flow resistivity tensors are presented. The anisotropic flow resistivity tensors are validated by com- parison to measurements performed on uni-directional cylindrical samples extracted from the previously measured cubic samples. The results sug- gest that there is a relation between the direction of highest flow resistivity, and the rise direction of the material.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2010
Series
Trita-AVE, ISSN 1651-7660
National Category
Vehicle Engineering Fluid Mechanics and Acoustics Aerospace Engineering Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-31153 (URN)
Funder
EU, European Research Council, MRTN-CT-2006-035559
Note

QC 20110311

Available from: 2011-03-10 Created: 2011-03-10 Last updated: 2013-11-28Bibliographically approved
2. Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Glass Wool
Open this publication in new window or tab >>Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Glass Wool
2010 (English)Report (Other academic)
Abstract [en]

The air flow resistivity of nine adjacent glass wool samples is measured and estimated using a previously published method. The samples are extracted from a large slab of glass wool material. Identifying the full flow resistivity tensors for nine adjacent cubic glass wool samples allows for an estimation of the spatial distribution of normal and planar flow resistivity throughout the measured material. The average density of the samples tested is 27.8 kg/m3. The estimated flow resistivity tensors are validated by comparison to uni-directional measurements on cylindrical samples, extracted from the cubic glass wool samples tested. Furthermore, the uni-directional measurement method is studied, providing useful insights on the effect of sample thickness on the measured flow resistivity for an anisotropic material.

Series
TRITA-AVE, ISSN 1651-7660
National Category
Vehicle Engineering Fluid Mechanics and Acoustics Aerospace Engineering Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-31154 (URN)
Funder
EU, European Research Council, MRTN-CT-2006-035559
Note

QC 20110311

Available from: 2011-03-10 Created: 2011-03-10 Last updated: 2016-04-20Bibliographically approved

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