Pierre-Etienne Gautier

Assessment of a semi-Hertzian method for determination of wheel–rail contact patch

Wheel–rail contact calculations are essential for simulating railway vehicle dynamic behavior. Currently, these simulations usually use the Hertz contact theory to calculate normal forces and Kalkers ‘FASTSIM’ program to evaluate tangential stresses. Since 1996, new methods called semi-Hertzian have appeared: 5 7 (STRIPES). These methods attempt to estimate the non-elliptical contact patches with a discrete extension of the Hertz theory. As a continuation of 2, a validation of the STRIPES method for normal problem computing on three test cases is proposed in this article. The test cases do not fulfill the hypothesis required for the Hertz theory. Then, the Kalkers FASTSIM algorithm is adapted to STRIPES patch calculus to perform tangential forces computation. This adaptation is assessed using Kalkers CONTACT algorithm.

Synthesis of Noise of Operating Vehicles: Development within SILENCE of a Tool with Listening Features

The European Integrated project SILENCE is dedicated to the reduction of railway and road noise in urban areas. Within this context, SNCF and LMA collaborate in the sub-project B in order to develop a pass-by sound simulation software. This global modelling tool will support parametric studies on the reduction of the noise of a train or a car pass-by, by providing standard indicators (time signature, sound pressure level) and sound samples. It will be used to determine the best combination of optimised sources, developed by manufacturers, in order to reduce the global pass-by noise. In the software, each simulation is based upon the definition of the acoustic sources and the pass-by scenario. Each physical acoustic source on the vehicle is represented by one or several point sources. These point sources radiate either pure tones or broadband noise. A dedicated algorithm is used to simulate each type in an efficient way to reduce the computation time. The characteristics of the sources are obtained either from numerical models, or from standstill and pass-by antenna measurements (carried out in the SILENCE project). As a large source such as a cooling system can not be modelled by several point sources located at close positions, a radiation pattern is allocated to the point source. Dedicated studies are in progress to measure the radiation pattern of classical sources on a train (two series of measurements on a 1:14 scale-model and on a train).

Vibration du ballast ferroviaire : Une étude expérimentale à échelle réduite

ABSTRACT An experimental set-up at a reduced scale was carried out in laboratory. This device reproduces the action of tamping on ballast. In these experiments, we highlight the frequency influence. Three different behaviours were observed depending on the frequency: a stiff behaviour at low frequencies: the grains motion is mainly due to the tightening loading effect. A liquid behaviour at high frequencies: vibrations effects are very significant, ballast opposes therefore little resistance to the tightening loading. A viscous behaviour at intermediate frequency: for this range of frequencies, vibrations and tightening force have the same importance.

Granular Media and Ballasted Railway Tracks Milieux Granulaires Et Voies Ballastées

Since the beginnings of the railway track, ballasted track is widely employed because of its mechanical properties and its exibility for construction and maintenance but also for their capacity to fulfil the mechanical requirements fixed by the transport of heavy loads at a long distance. The study of the track deterioration is one of the principle assignments in railway engineering, specially for SNCF to preserve a good quality of track and to ensure the comfort and the safety of circulation.

Numerical Simulation and Experimental Investigation of the Side Loading on a High Speed Train

An assessment of train safety whilst simultaneously traveling at high speed and being subjected to strong cross winds requires the knowledge of the aerodynamic load on the train. This situation currently affects the French high speed double decker train (TGV Duplex) that travels on the “TGV Mediterranee” line between Paris and Marseille. For safety reasons, the SNCF has investigated the cross wind sensitivity of the TGV Duplex operating on this line using both reduced scale wind tunnel and hydraulic tank tests and numerical methods. Comparisons between experimental and numerical side and lift forces and lee rail rolling moments acting on the TGV have been made. The leading vehicle experimental pressure distributions have also permitted further comparisons between the experimental and numerical results. Overall, these comparisons showed good agreement between the two sets of results for TGV / wind relative flow angles of 30° or less. Beyond this, the differences between the results are more pronounced with a maximum difference occurring for a relative flow angle of approximately 60°.