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Content archived on 2024-05-21

Road and tyre interaction noise (RATIN)


A tyre model for the prediction of tyre vibrations was developed and implemented. The model calculates the normal and tangential vibration of the tyre due to normal and tangential force excitation. The tyre is modelled as a two-layer plate with appropriate boundary conditions. The one layer corresponds to the tyre structure and the second one to the tyre tread. By doing this, the local deformation of the tyre tread by roughness indenting is included, which is an important feature as far as contact modelling is concerned. The model was validated towards mobility measurements with good agreement.
A rolling contact model was implemented in order to describe the tyre/road contact interaction in rolling conditions. The three-dimensional contact problem is solved by classical contact mechanics using an elastic half-space. In order to solve contact problem, the impulse response functions of the tyre are required. As being the central part of any tyre/road noise prediction models, the rolling contact model was made modular, which means that it can use impulse response functions coming from any tyre models including, or not, the local deformation of the tread and that it can produce input data for various radiation models. As output, the model calculates dynamic contact forces, which can be used for hybrid tyre/road noise prediction models, and vibration velocity fields, which can be used as input to radiation models. Additionally, the calculation of the local deformation of the tyre tread under rolling conditions makes it possible to produce input data for the calculation of air pumping generated noise to adequate radiation models.
An analytic dynamic model of a pneumatic tyre was developed to operate from static behaviour to 3kHz, the upper frequency required for radiated noise. The model gives the tyre motion in the normal and tangential directions at any point on the tyre surface arising from a normal or tangential input force. This transfer function is expressed in terms of the average geometric and material properties of the tyre cross section. Another low frequency model was also made to give the: contact length and normal and tangential force distribution in the contact zone. The most influential tyre parameter on the force distribution is the contact stiffness between the tread and road surface, which is largely controlled by the surface roughness. A mathematical expression for this contact stiffness was obtained as a function of static load, air pressure and the road geometry. The tyre model and contact stiffness models were confirmed experimentally. The contact model was further developed to give the dynamic friction functions for a single asperity on a rubber surface, as a function of slip speed, material properties, static load, and adhesion due to air pressure. The main benefit of these analytic models is in research to provide physical insight to the mechanisms at work. They will also be used in future work to predict the vibration to rolling, and will be used in an investigation of tyre slip and traction.
A mixed approach for the computation of noise radiated by tyres has been developed. It combines the velocity on the tyre (obtained by models from other partners or any other) and elementary acoustic solutions (known as Green functions) between receiver and points on the tyre surface. The Green function has been computed either using the ICARE software, based on a ray tracing algorithm, or using BEM (Boundary Element Method). ICARE takes into account the curvature of the tyre and diffracting edges. Also it enables the computation of the solution including the car body even at high frequencies. BEM has also been employed to validate the ICARE tyre modules. An original mixed BEM/ray tracing approach has been developed. Parametric studies have shown that the presence of the car body significantly modifies the radiation patterns. Comparisons with measurements made by Goodyear have been made for 3 road types and 4 different tyres. RATIN has therefore provided a first step towards a general numerical tool, which offers a means to reduce noise radiated by tyres.
A contact model was implemented in order to describe the tyre/road contact interaction in rolling conditions. The three-dimensional contact problem is solved by classical contact mechanics using an elastic half-space. The solving of the contact problem for each time step requires an iterative algorithm. The input required by the model are the road roughness, the tyre tread profile, and the impulse response functions of the tyre, which can be obtained from the various tyre models developed in the project. The output of the model are the dynamic contact force at the contact patch and even the local deformation of the tyre tread due to roughness indenting. The contact model was validated towards measurements with good agreement for a variety of tyres and rolling speeds.
To face the requirements related to building tyre noise radiation models, Free Field Technologies has extended the infinite element method implemented in its ACTRAN general purpose acoustic simulation software. Among the numerous improvements developed in the context of RATIN and made available to all current and future users of ACTRAN are: - A stabilized interpolation scheme removing any limit on the radial interpolation order of the infinite elements; - A time-domain version of the infinite element library complementing the frequency domain implementation; - The correct and automatic handling of absorption on infinite surfaces; - Simulation of convected wave propagation (propagation in moving fluids). The new infinite element module of ACTRAN is obviously well applicable to tyre noise radiation but also found applications in numerous other domains of acoustic design like: aircraft engine noise modelling, power train radiation analysis, loudspeaker design ans more.
A tyre model has been developed, which allows prediction of the vibration of a car tyre that results from the forces arising at the contact to a rough road. The modal is special in that it is computationally efficient and in that it models the air contained in the tyre. Moreover, damping and other material parameters may vary within the structure and with frequency. The development of this model has engaged many undergraduate students and two PhD students who have received an excellent training on this challenging structure. Also, they have become aware of standards and practice in leading European industrial companies. The model will allow simulation of the mechanism that leads to noise generation in tyres. Thus, it will facilitate the development of quiter tyres.

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