Tyre Noise over Impedance Surfaces - Efficient Application of the Equivalent Sources Method

Doctoral thesis, 2003

Reduction of the transportation noise nuisance has become an important challenge in today's societies. As a consequence of engine noise reduction, tyre / road contact noise is now the main source of traffic noise under normal driving conditions. In this respect, the aim of the present work is to understand and to control the mechanisms of tyre radiation by designing accurate tools to predict the tyre noise radiation over arbitrary impedance surfaces. Tyre radiation is modelled using the Equivalent Sources method. Besides low frequency limitations because of two--dimensional simplifications, this model is proved to be an accurate tool for predicting tyre noise over acoustically rigid surfaces. Ground effects induced by absorbing surfaces are only approximated. Therefore, a model for the propagation of sound due to an arbitrary order source over an arbitrary impedance plane is developed. It is mainly an alternative to integral equation methods. In addition, the exact solution to this problem is presented. Based on the two previous models, an iterative model of the tyre radiation over arbitrary impedance surfaces is implemented. Comparison with horn effect sound amplification indicate that this model is accurate for homogeneous as well as inhomogeneous absorbing surfaces. Using this model, trends for the tyre radiation over absorbing surfaces are discussed in a parametrical study. The work presented in this thesis gives further insights into the mechanisms of tyre / road noise radiation; furthermore, it allows to study the possibilities of reducing traffic noise by the use of so--called "low--noise" road surfaces.