Finite-element modelling of compressed fibrous materials: Modelling of the sound absorption and transmission properties of multi-layer assemblies including compressed fibrous materials and comparison to the results obtained from the transfermatrix- method and measurements
Typ
Examensarbete för masterexamen
Program
Sound and vibration (MPSOV), MSc
Publicerad
2020
Författare
Panter, Pablo
Kåberger, Axel
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This thesis work addresses the finite-element-method (FEM) modelling of the sound
transmission and absorption properties of multi-layer systems including compressed
fibrous materials. The investigated system is a noise shield which is used for encapsulating
the engine in trucks. Today, the complex surface impedance is used to represent
this system in FEM modelling. With this method, the back face of the noise shield is
considered as fully reflective and there is no possibility to assess transmission through
the encapsulation. The present thesis work aims for improving the currently employed
methods by taking more complex information into account, specifically by applying
Biot’s theory in the modelling of poroelastic materials.
The results of different FEM models are compared to the results obtained fromtransfermatrix-
method (TMM) models and measured data. Three out of seven models have
been found to provide a good agreement between the FEM and TMM results as well as
to measured data of the absorption coefficient.
A mesh size sensitivity study indicates that six to seven linear elements per smallest
wavelength are sufficient to decrease the mesh-related error in the calculated sound
transmission loss to below1 dB for the investigated system. However, it has been found
that today there are still hindering limits in terms of computational power when modelling
soft poroelastic materials in FEM due to the small apparent wavelengths.
Beskrivning
Ämne/nyckelord
FEM, poroelastic, multi-layer, sound transmission, sound absorption