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Inverse estimation of static flow resistivity in porous materials: discussion of the method and results for two tested porous materials
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.ORCID iD: 0000-0003-1855-5437
2011 (English)Conference paper, Abstract (Other academic)
Abstract [en]

Porous materials are widely used in applications which focus on noise andvibration control. Their thermal, mechanical and acoustical properties arebenecial for the use of these materials in aeronautical and vehicle industries.Standard measurements for the characterization of porous materials exist andare carried out in many laboratories worldwide. However, these measurementsdo not always consider the possible anisotropy, present in porous materials.The production process of porous materials introduces an inherent geometricanisotropy in the material at micro scale, which in uences the materialproperties at macro scale. It has been shown by Khurana et al. [3] thatthe anisotropy can have a signicant in uence on the acoustical behaviourof the material, especially if the angle of incidence is increased. One ofthe macroscopic parameters, which is important for the performance ofthese material in acoustical applications, is the static ow resistivity. Themethodology to measure the ow resistivity in porous materials is described inISO 9053 [2], giving the ow resistivity of a porous material along one direction.These unidirectional measurements do not allow for a full characterization ofthe ow resistivity tensor, and hence a proper characterization of the porousmaterial. The identication method developed by Goransson et al. [1] providesa non-destructive measurement method to determine the static ow resistivitytensor. The method is based on an inverse estimation of the measured pressure drops over a cubic material sample.The method as described in the work of Goransson et al. [1] has beenimproved in several ways. The Globally Convergent Method of MovingAsymptotes (GCMMA) [5] , which assures convergence, has replaced theMethod of Moving Asymptotes (MMA) [4]. Secondly, the approach of inverseestimation has been veried for a wide range of anisotropy, by setting articialand a priori known anisotropic ow resistivity tensors as a target in theestimation. Furthermore, another approach towards the problem has beentested, in which the focus is on the eigenvalues and eigenvectors of the tensor,in stead of the independent components. In addition, a more precise descriptionof the errors will be presented as well as an error estimation.This method for identication of the anisotropic ow resistivity tensorhas been applied to two dierent porous materials, a brous glass wool anda Melamine foam. The two materials are expected to show dierent degreesof anisotropy with respect to ow resistivity. Glass wool is assumed to betransversely isotropic while the level of anisotropy of Melamine is not asobvious. The full anisotropic ow resistivity tensors of the tested glass wooland Melamine samples are presented, together with their principal valuesand directions. The eigenvalue decomposition provides an insight into theconnection between the directionality of the ow resistivity in each material,and its production process. The overall approach of the method is validated bycomparing the estimated ow resistivity tensors to the ow resistivity measuredin cylindrical samples extracted from the cubic samples tested. Furthermore, astudy of the homogeneity in density and ow resistivity for the two materialsshows that these properties vary within the block of material.References[1] P. Goransson, R. Guastavino, and N. E. Horlin. Measurement and inverseestimation of 3D anisotropic ow resistivity for porous materials.Journalof Sound and Vibration, 327:354{367, 2009.[2] ISO 9053:1991: Acoustics { materials for acoustical applications {determination of air ow resistance, 1991.[3] P. Khurana, L. Boeckx, W. Lauriks, P. Leclaire, O. Dazel, and J.F. Allard.A description of transversely isotropic sound absorbing porous materials bytransfer matrices.Journal of the Acoustical Society of America, 125:915{921,2008.[4] K. Svanberg. The method of moving asymptotes - a new method forstructural optimization.International Journal for Numerical methods inEngineering, 24:359{373, 1987.

Place, publisher, year, edition, pages
National Category
Applied Mechanics Vehicle Engineering Aerospace Engineering Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-82397OAI: diva2:498196
Symposium on Acoustics of Poroelastic Materials. Ferrara – Italy. 14-15-16 December 2011
Smart Structures
TrenOp, Transport Research Environment with Novel PerspectivesEU, European Research Council, MRTN-CT-2006-035559

QC 20120412

Available from: 2012-02-11 Created: 2012-02-11 Last updated: 2016-04-20Bibliographically approved

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