Doctoral thesis presented by Martin Östberg

Modelling tools for quieter vehicles: Waves in poro- and visco-elastic continua

Submitted June the 7th 2012 to the thesis committee:

Sergey SOROKIN Aalborg University, Danmark Rapporteur
Olivier DAZEL LAUM, Le Mans, France Rapporteur
Sebastian STICHEL Royal Institute of Technology (KTH), Stockholm, Sweden Examinateur
Anders BOSTRÖM Chalmers University, Göteborg, Sweden Président
Leif KARI Royal Institute of Technology (KTH), Stockholm, Sweden Directeur de thèse
Roger OHAYON Cnam Paris, France Co-directeur de thèse
Jenny JERRELIND Royal Institute of Technology (KTH), Stockholm, Sweden Co-encadrant


New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro– and visco–elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two different ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco–elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode–matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro–elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three–dimensional problem is split up into several, much smaller, two–dimensional ones, radically decreasing the computational load.

Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures.

The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.