Contact stiffness in tyre/road noise modelling and speed dependencies of tyre/road noise generation mechanisms

Doctoral thesis, 2017

Tools for simulating tyre/road noise are highly valuable in the efforts to limit the negative consequences of road traffic noise. A numerical tyre/road noise simulation tool was in this study used to investigate how the contact stiffness parameter affects the predicted tyre/road noise. It includes a contact model with contact springs that accounts for the effect of local small-scale tread deformation. Results showed that simulated noise was sensitive to the value of the spring stiffness, primarily as it affected the total contact force. A non-linear contact spring formulation resulted in a reduction of the high-frequency content in the contact forces and simulated noise. Aspects of small-scale tread dynamics were evaluated by simulating the detailed contact between an elastic layer and a rough road surface using a numerical time domain contact model including non-linear contact springs to account for small-scale roughness. Contact stiffness increased as the number of contact points grew as well as the deformation of their non-linear contact springs. The results imply that dynamic properties of the local tread deformation may be of importance when simulating contact details during normal tyre/road interaction conditions, but that effects of damping could, as a first approximation, be included as an increased stiffness in a quasi-static tread model. The speed dependency of measured and simulated tyre/road noise was analysed. A large part of the noise had a high speed exponent, traditionally connected with air-pumping. However, the results showed that tyre vibrations can generate noise with a speed exponent that verges on what is expected from air-pumping. Due to the overlap in the speed exponents of the main generation mechanisms, they cannot be distinguished through a speed exponent analysis. The most important contribution of this work is an increased understanding of how the contact spring formulation affects the simulated noise. The work has also provided insights into the speed dependency of tyre/road noise generation mechanisms.