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Sensitivity of macroscopic properties of a multi-layer panel including porous material on the micro-level parameters of an open cell porous material
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. (Marcus Wallenberg Laboratory for Sound and Vibration Research)ORCID iD: 0000-0001-9948-249X
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. (Marcus Wallenberg Laboratory for Sound and Vibration Research)ORCID iD: 0000-0003-1855-5437
Bombardier Transportation.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Marcus Wallenberg Laboratory for Sound and Vibration Research.
Abstract [en]

The micro-structure of an open cell porous material is modelled as an idealized, periodic structure, allowing anisotropic properties to form on the micro-scale. Using simple analytic descriptions of acoustic and elastic properties calculated from micro-structure geometry, the microstructural properties can be linked to averaged macroscopic elasto-acoustic properties, which can be measured and observed. These macro level properties may be deduced from measurements on a sample of a porous material which is at least a few centimetres across. The most common of the acoustic properties are the flow resistivity or the (dynamic) permeability, the porosity and the viscous and thermal characteristic lengths, together with the tortuosity. For the elasticity, the moduli of the Hooke's law are the most important. The underlying motivation for the current work is that the quantities are interdependent since they all depend on the micro geometry. Thus, to design the macro level acoustic properties for a required performance, physically relevant models linking these to the micro structure would be necessary. In this paper, a set of such models are proposed and utilising these, the influence of the anisotropy on acoustic properties of the foam as well as the transmission loss of a multi-layer plate is investigated. Typical macro level acoustic properties of open cell poro-elastic materials calculated from micro structure parameters are found to give results of the same order of magnitude as measured data found in the literature. Further, the model is applied to evaluate transmission loss of roof constructions with isotropic and anisotropic foam. It is shown that the sound reduction can be improved without changing the overall surface weight of the structure by making use of the anisotropy of the foam. The results Underline the importance of anisotropy and in addition provide guidance for further research.

Place, publisher, year, edition, pages
2014. 2135-2149 p.
National Category
Vehicle Engineering
URN: urn:nbn:se:kth:diva-164938ISI: 000352201002045ScopusID: 2-s2.0-84913591667ISBN: 978-907380291-9OAI: diva2:806522
International Conference on Noise and Vibration Engineering (ISMA), Leuven, BELGIUM, SEP 15-17, 2014

QC 20150512

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2016-05-23Bibliographically approved
In thesis
1. Micro-Structure Modelling of Acoustics of Open Porous Material
Open this publication in new window or tab >>Micro-Structure Modelling of Acoustics of Open Porous Material
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Transportation is a large and growing part of the world’s energy consumption. This drives a need for reduced weight of rail vehicles, just as it does for road vehicles. In spite of weight reductions, the vehicle still has to provide the same level of acoustic comfort for the passengers. Porous materials, with more than 90% air, are often included in multi-layer vehicle panels, contributing to acoustic performance without adding much weight. Here the acoustic performance of open cell porous materials, with focus on flow resistivity, is evaluated based on simplified micro-structure models to investigate the effect of anisotropy on the performance In order to evaluate how the redistribution of material affects the flow resistivity, the porosity of the material is kept constant. Two micro-geometries are analysed and compared: the hexahedral model and the tetrakaidecahedron (Kelvin cell). For flow resistivity calculations the solid frame is assumed to be rigid. The models are elongated in one direction to study the influence of micro-structural anisotropy on the macro level flow resistivity. To keep porosity constant, two different approaches are investigated. The first approach is to let strut thickness be uniform and adjust the volume of the cell to a constant ratio compared to the isotropic case. The second approach is to let the strut volume, and cell volume, be constant. For an anisotropic hexahedral cell with uniform strut thickness, the flow resistivity increases substantially with increasing height to width ratio for the hexahedral model, while the flow resistivity for the tetrakaidecahedron model with uniform strut thickness decreases with increasing height to width ratio. For both geometries and constant strut volume, the average flow resistivity is close to the same constant value. For uniform strut thickness the relative volume of anisotropic to isotropic volume is very important.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 46 p.
TRITA-AVE, ISSN 1651-7660 ; 2016:24
acoustics, porous material, flow resistivity, micro-structure, anisotropic, foam, strut
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
urn:nbn:se:kth:diva-187322 (URN)978-91-7729-040-7 (ISBN)
2016-06-15, Munin, KTH Royal Institute of Technology, Teknikringen 8, Stockholm, 09:00 (English)

The work has been carried out within the Centre for ECO2 Vehicle Design.

QC 20160523

Available from: 2016-05-23 Created: 2016-05-20 Last updated: 2016-05-24Bibliographically approved

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