A fast method for computing convolutions with structural Green's functions: application to tyre dynamic contact problems

International audienceTyre/road contact is the main source of car noise at speeds greater than 50 km/h. In this context, we have developed a new approach for modelling tyre vibrations and contact with rigid road surfaces during rolling. For tyres, a periodic model is used to compute Green's functions. The response of tyres can, thus, be modelled over a large frequency range. Then, a fast convolution and a new contact model are developed and examples of computations of contact stress are given for real road textures. Spectra of stress for different tyre velocities are also compute

A fast algorithm for computing dynamic tyre road contact forces

International audienceTire/road contact is the principal source of car noise at speeds greater than 50 km/h. In this context, we have developed a new approach for modelling the tire vibrations and the contact with the rigid road surfaces during rolling. For the tire, a periodic model is used to compute Green's functions. The response of the tire can thus be modelled over a large frequency range. Then a fast convolution and contact model is developed and examples of computations of contact forces are given for real road textures. Spectra of forces for different tire velocities are also computed

Une méthode rapide pour calculer un produit de convolution avec une fonction de Green : application au problème de contact dynamique

International audienceDans ce travail, nous proposons une nouvelle démarche pour calculer le produit de convolution de façon rapide et efficace. L'idée est de simplifier la fonction de Green dans le domaine fréquentiel en la décomposant dans une base modale. Les paramètres modaux identifiés sont ensuite utilisés pour construire une convolution rapide. Cette démarche a été adaptée au problème de contact dynamique. Pour illustrer l'efficacité de la méthode, deux exemples sont présentés. Les déplacements et les forces de contact obtenus par cette méthode sont comparés à ceux obtenus à l'aide de la convolution classique

Numerical evaluation of tyre/road contact pressures using a multi-asperity approach

International audienceThe interaction between the tyre and the road surface is responsible for many physical problems such as skid resistance, rolling resistance or noise generation. This paper deals with the numerical study of tyre/road contact. A two-scale iterative method is used for solving the contact problem between a multi-asperity road surface and an elastic half-space. This method has been used successfully for idealized rough surfaces. However, for efficient applications to real surfaces, an appropriate partition of the surfaces is required. A partitioning method is proposed to describe road surfaces using classical image processing and a new load/penetration relation for a single road asperity is introduced. In order to evaluate the efficiency of the method, numerical results for a small sample of road are compared to a classical matrix inversion method, which show at macro-scale a rather good accuracy to predict tyre/road noise. At micro-scale both methods give the same results, but the multi-asperity method is much less time-consuming. Then numerical evaluation of tyre/road static contact pressures for different road textures at full contact area is presented. This approach with new preconditioning can be a reliable and efficient method to simulate contact problems with large surfaces

A new algorithm for computing the indentation of a rigid body of arbitrary shape on a viscoelastic half-space

In this paper the contact problem between a rigid indenter of arbitrary shape and a viscoelastic half-space is considered. Under the action of a normal force the penetration of the indenter and the distribution of contact pressure change. We wish to find the relations which link the pressure distribution, the resultant force on the indenter and the penetration on the assumption that the surfaces are frictionless. For indenters of arbitrary shape the problem may be solved numerically by using the Matrix Inversion Method (MIM), extended to viscoelastic case. In this method the boundary conditions are satisfied exactly at specified "matching points" (the mid-points of the boundary elements). It can be validated by comparing the numerical results to the analytic solutions in cases of a spherical asperity (loading and unloading) and a conical asperity (loading only)

ODSurf : Modélisation et réalisation d'une couche de roulement de chaussée optimisée, dense et peu bruyante

ODSurf project is following a previous P2RN project dealing with the emission and propagation of rolling noise, carried out in the framework of the German-French collaboration DEUFRAKO. During P2RN, an optimum pavement texture in terms of the noise emission was calculated. The current ODSurf project was mainly dedicated to the development and implementation of low noise new technologies and new materials adapted to urban environment. Original solutions have been investigated, implemented and tested on-site. In parallel to these technological approaches, new models have been developed to better characterize various physical phenomena produced when a tyre is rolling on a textured pavement. Vibration phenomena, air pumping and the horn effect were specifically studied and the main results are detailed in this document. In addition to the modelling approach, this project includes a strong experimental component useful for model validation and also to allow an acoustic classification of road surfaces. The measures presented in this report were carried out both on test tracks and actual site on which were positioned the optimized conventional or industrially designed coatings, both in France and Germany. Finally, this report is ending with the common database "DEUFRABASE". It includes the noise produced by light and heavy vehicles running on a large panel of French and German road surfaces for various propagation configurations. Updated at the end of the project, this database posted on the Ifsttar server will be soon freely available online. From its current design, it will easily allow regular updates in terms of site configurations and new road surfaces. It thus will be a good tool to estimate the acoustic impact of traffic for many suburban and urban situations. Following the results achieved during the project, the next steps will concern on one hand, the improvement and integration of the various modelling approaches of different tyre noise generation phenomena in a "unique" tool in order to have an overall estimation of the impact of road surfaces on the sound level produced by road traffic and secondly, to extend the DEUFRABASE to more realistic situations.Le projet ODSurf fait suite à un précédent projet P2RN, relatif à l'émission et la propagation du bruit de roulement, réalisé dans le cadre de la collaboration franco-allemande DEUFRAKO. Au cours de P2RN, une texture de chaussée optimale du point de vue de l'émission sonore avait été calculée. L'actuel projet ODSurf a été principalement dédié à l'élaboration et la mise en oeuvre de nouvelles technologies à faible bruit et de nouveaux matériaux adaptés au milieu urbain. Des solutions originales ont été imaginées, mises en oeuvre sur site et testées. Parallèlement à ces approches technologiques, de nouveaux modèles ont été développés pour mieux caractériser les divers phénomènes physiques mis en jeu lors du roulement d'un pneumatique sur une chaussée texturée. Les phénomènes vibratoires, de pompage d'air ainsi que l'effet dièdre ont été plus particulièrement étudiés et les principaux résultats sont détaillés dans le présent document. Outre l'approche modélisation, ce projet a fait l'objet d'une forte composante expérimentale utile à la fois pour la validation des modèles mais aussi pour permettre une classification acoustique des revêtements routiers. Les mesures présentées dans ce rapport ont été réalisées à la fois sur pistes d'essai et sur site réel sur lesquels ont été mis en place les revêtements optimisés de conception classique ou industrielle, tant en France et qu'en Allemagne. Enfin, ce document se termine par la base de données commune « DEUFRABASE ». Elle regroupe les émissions sonores produites par le roulement de véhicules légers et lourds sur un large panel de revêtements routiers français et allemands pour diverses configurations de propagation. Mise à jour en fin de projet, cette base déposée sur le serveur de l'Ifsttar sera prochainement accessible gratuitement en ligne. De par sa conception actuelle, elle permettra aisément des mises à jour régulières tant en termes de configurations de sites que de nouveaux revêtements de chaussée. Elle permettra ainsi d'être un bon outil pour estimer l'impact acoustique du trafic routier pour de multiples configurations périurbaines et urbaines. A la lumière des résultats enregistrés au cours de ce projet, les étapes futures concerneront d'une part, l'amélioration et l'intégration des diverses approches de modélisation des différents phénomènes de génération de bruit de roulement dans un outil « unique » afin d'avoir une estimation globale de l'impact des couches de roulement sur le niveau sonore produit par le trafic routier et d'autre part, d'étendre la DEUFRABASE à un plus grand nombre de situations réalistes

CD40, autophagy and Toxoplasma gondii

Toxoplasmagondii represents a pathogen that survives within host cells by preventing the endosomal-lysosomal compartments from fusing with the parasitophorous vacuoles. The dogma had been that the non-fusogenic nature of these vacuoles is irreversible. Recent studies revealed that this dogma is not correct. Cell-mediated immunity through CD40 re-routes the parasitophorous vacuoles to the lysosomal compartment by a process called autophagy. Autophagosome formation around the parasitophorous vacuole results in killing of the T. gondii. CD40-induced autophagy likely contributes to resistance against T. gondii particularly in neural tissue

Rolling resistance modelling

In this study, a rolling contact model is proposed for quantifying the part of rolling resistance originating from hysteretic energy dissipation at the interface between a viscoelastic solid and a rigid surface. A viscoelastic half-space assumption is made and a 3D time dependent algorithm is used to solve the problem. This approach is validated for a viscoelastic sphere rolling on a rigid flat surface and agrees with previous results of the literature. Then the model is applied to the NBR solid wheel implemented on a small-scaled test rig developed for the experimental evaluation of rolling resistance by Roskilde University. Contact calculations are firstly performed in static conditions and show that contact stiffness increases with surface roughness. Then rolling of the wheel on a perfectly flat surface and two rough sandpapers is considered. On the flat surface the steady-state contact pressure distribution is asymmetric along the rolling direction due to viscoelasticity. It is observed that steady-state rolling resistance coefficient increases with the total load and with the rolling speed. Regarding rolling on sandpapers, the averaged rolling resistance coefficient increases with surface roughness, especially at higher speeds. Taken as a whole, these numerical results are similar to experimental trends observed with the test rig, but further investigations should be made on the input data to improve the comparisons

Contact analysis of road aggregate with friction using a direct numerical method

This paper deals with the contact of road surface aggregates with tangential tractions. The problem is modeled in static conditions with Coulomb's friction. The aggregate is assumed perfectly rigid and is loaded on an incompressible elastic half-space. The contact problem is solved by means of a direct numerical method which is successfully validated for a spherical indenter. Then, the method is applied to three real road aggregates which surfaces were measured. The normal and tangential stresses at the contact interface are studied. The contact on a single aggregate is similar to multi-asperity contact and the contact areas can be finely observed. The adhesive and sliding contact areas were also identified on each contacting asperity. Relationships between the total force and displacement can be approached by simple functions and ranged between the solutions for a sphere and a cone. The conclusion is that the developed numerical method and the identified contact relationships could be used for further study of contact stresses at the full tyre/road interface

Bruit de roulement automobile : influence du revêtement de chaussée

Le bruit de roulement automobile ou bruit de contact pneumatique-chaussée constitue la source prépondérante de bruit d'un trafic routier. Sa réduction nécessite en priorité d'optimiser les revêtements de chaussées. Mais au préalable, il convient de connaître les phénomènes physiques responsables de la génération de bruit. Les méthodes expérimentales pour la mesure du bruit de roulement sont présentées, avec une revue exhaustive des modèles de prévision du bruit engendré. Enfin, les différents revêtements peu bruyants sont présentés, leur typologie, leur emploi et leur intérêt pour la réduction du bruit routier