Doctoral thesis presented by Eleonora Lind Nordgren

A study of tailoring acoustic porous material properties
when designing lightweight multilayered vehicle panels

Submitted September the 7th 2012 to the thesis committee:

Olivier DAZEL LAUM, Le Mans, France Rapporteur
Wim DESMET Katholieke Universiteit Leuven, Belgium Rapporteur
Peter DAVIDSSON CREO Dynamics, Linköping, Sweden Examinateur
Ulf OLOFSSON Royal Institute of Technology (KTH), Stockholm, Sweden Président
Peter GÖRANSSON Royal Institute of Technology (KTH), Stockholm, Sweden Directeur de thèse
Jean-François DEÜ Cnam Paris, France Co-directeur de thèse
Nils-Erik HÖRLIN Royal Institute of Technology (KTH), Stockholm, Sweden Co-encadrant

Abstract:

The present work explores the possibilities of adapting poro-elastic lightweight acoustic materials to specific applications. More explicitly, a design approach is presented where finite element based numerical simulations are combined with optimization techniques to improve the dynamic and acoustic properties of lightweight multilayered panels containing poro-elastic acoustic materials.

The numerical models are based on Biot theory which uses equivalent fluid/solid models with macroscopic space averaged material properties to describe the physical behaviour of poro-elastic materials. To systematically identify and compare specific beneficial or unfavourable material properties, the numerical model is connected to a gradient based optimizer. As the macroscopic material parameters used in Biot theory are interrelated, they are not suitable to be used as independent design variables. Instead scaling laws are applied to connect macroscopic material properties to the underlying microscopic geometrical properties that may be altered independently.

The design approach is also combined with a structural sandwich panel mass optimization, to examine possible ways to handle the, sometimes contradicting, structural and acoustic demands. By carefully balancing structural and acoustic components, synergetic rather than contradictive effects could be achieved, resulting in multifunctional panels; hopefully making additional acoustic treatment, which may otherwise undo major parts of the weight reduction, redundant.

The results indicate a significant potential to improve the dynamic and acoustic properties of multilayered panels with a minimum of added weight and volume. The developed modelling techniques could also be implemented in future computer based design tools for lightweight vehicle panels. This would possibly enable efficient mass reduction while limiting or, perhaps, totally avoiding the negative impact on sound and vibration properties that is, otherwise, a common side effect of reducing weight, thus helping to achieve lighter and more energy efficient vehicles in the future.



Laboratoire de Mécanique des Structures et des Systèmes Couplés - LMSSC