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Micro model for calculating flow resistivity for anisotropic open cell materials with high aspect ratio of struts
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. (MWL)ORCID iD: 0000-0001-9948-249X
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. (MWL)ORCID iD: 0000-0003-1855-5437
2016 (English)Report (Other academic)
Abstract [en]

Micro-structure models for calculating flow resistivity for open cell materials with high aspect ratio of struts are presented.  Two micro-geometries are analyzed and compared: the hexahedral model, with the solid frame in shape of a cube for the isotropic case, 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. In order to evaluate how the redistribution of material affects the flow resistivity, the porosity of the material is kept constant. Since the porosity is defined as unity minus the ratio of strut volume of the cell to the total volume of the cell, there are different ways of linking the micro level properties to the macro level. The first approach presented here 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 be constant, i.e. if a strut is elongated, it is also thinner. In this case the cell volume must equal the isotropic volume. For uniform strut thickness the flow resistivity increases substantially with increasing height to width ratio for the hexahedral model, and decreases for the Kelvin cell. For constant strut volume the flow resistivity perpendicular to the flow direction increases, and the other direction (where the strut thickness increases) will be reduced. The average flow resistivity will in this case be almost constant. The method of scaling the micro-cell properties has a high influence on the resulting average flow resistivity, as does the cell volume in relation to the isotropic volume. For open porous materials which are approximately isotropic, the choice of micro geometry is not so critical and can be determined by other considerations, such as elasticity.

Place, publisher, year, edition, pages
2016. , 19 p.
Keyword [en]
acoustics, foam, micro-structure, flow resistivity, strut, anisotropy
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187321OAI: oai:DiVA.org:kth-187321DiVA: diva2:929826
Note

QC 20160524

Available from: 2016-05-20 Created: 2016-05-20 Last updated: 2016-05-24Bibliographically 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.
Series
TRITA-AVE, ISSN 1651-7660 ; 2016:24
Keyword
acoustics, porous material, flow resistivity, micro-structure, anisotropic, foam, strut
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-187322 (URN)978-91-7729-040-7 (ISBN)
Presentation
2016-06-15, Munin, KTH Royal Institute of Technology, Teknikringen 8, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

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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