Micro-structural based acoustic modelling of anisotropic open cell materials
Time: Fri 2022-09-30 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Subject area: Vehicle and Maritime Engineering
Doctoral student: Eva Lundberg , Teknisk mekanik, VinnExcellence Center for ECO2 Vehicle design, AB Volvo, Volvo Construction Equipment
Opponent: Professor Elke Deckers, KU Leuven, Department of Mechnical Engineering
Supervisor: Peter Göransson, VinnExcellence Center for ECO2 Vehicle design, Strömningsmekanik och Teknisk Akustik
A method for the calculation of the acoustic performance of open-cell foammaterials is discussed. From a known micro-structural geometry and theconstituent material, the relevant acoustic properties are computed using apreviously published analytical method for the calculation of the dynamicdrag impedance and a previously published method for the calculation of theelastic moduli. These have been combined and are here used to generate thenecessary inputs to a fully anisotropic state space formulation of a TransferMatrix Method (TMM) based solution where only geometry and materialproperties need to be known. From the TMM solution, the sound absorptionand sound transmission loss of multilayer panels including anisotropic opencell materials is estimated. It is shown that the proposed method may beused in an optimization of sound absorption in multi-layer porous materials, where the different layers can have different degrees of anisotropy in theiracoustic and elastic properties. In the current work, the micro-geometry is based on the Kelvin cellwhich then is modified to achieve a controlled degree of anisotropy. The method has been validated by comparing the absorption and sound transmission loss for isotropic porous materials have been compared to equivalent structures computed with a commercial TMM mode, including a porous material which has been fully characterized with regard to previously published Johnson-Champoux-Allard parameters. In addition the calculated dynamic drag impedance has been compared to measurements conductedon a series of small samples with a defined 3D printed micro geometry forwhich the static flow resistivity has been measured. The method in general underestimates the dynamic drag impedance compared to the static flowresistivity due to not including the contributions to the losses from the constrictions between the struts close to the cell vertices. All verification showa good degree of agreement, confirming that for open-cell porous materials with reasonably high porosity the method may be used for design of novel acoustic treatments.