Keywords: railway ground vibrations, multibody model, finite-infinite element method, vehicle dynamics, wheel-rail contact, track deflection.

Nowadays the railway represents an interesting modal transfer, especially in the dense cities where the road traffic, often saturated, is associated with environmental and sociological problems. However, the train also brings its own nuisance, among which is ground vibration. As for the noise, the vibration problem must be addressed from the first steps of the vehicle design to obtain an efficient reduction of the nuisance. This paper presents numerical results of ground vibrations and the influence of the rolling stock dynamics on the transmitted ground vibration level. Four vehicle types (Thalys, German ICE, Eurostar and Belgian freight trains) are modelled using the multibody approach. The simulation of each model is made with a flexible track on which the vehicle rides at constant speed. The track model is built so as to properly estimate its deflection and therefore the forces transmitted to the ground surface. The Euler-Bernoulli theory is chosen for the rail flexibility. Discrete masses are associated to the sleepers. The dynamic behaviour of the pads between rail and sleepers is taken into account through spring and damper systems. The subgrade is also modelled with a spring and damper system for the ballast and a coupled lumped mass model for the foundation [1]. The latter includes the direct impedance of the foundation but also the coupling between the sleepers through the soil. The adopted strategy permits the vehicle-track simulation from the soil simulation without loss of accuracy [2]. The ground wave propagation is afterwards calculated, knowing the reaction of the ballast on the soil surface. The finite element method is used in this case, with specific boundary conditions at the border of the domain, to minimize numerical reflecting waves. This method has been thoroughly validated in the past, in the case of low and high speed, with local and overall track irregularities, respectively. The numerical results presented here reveal that the vehicle dynamics influences the track deflection and the soil velocity, both in time domain and in frequency content. Each curve is compared to the static contribution one, showing the effect of the dynamic wheel-rail interaction and the bogie periodicity. A special emphasis is paid on the comparison of a normalised indicator, defined here as the ratio between the peak particle velocity and the nominal axle load. From this study, it appears that the track irregularity, coupled with the rolling stock dynamics, and the geometrical configuration play a non-negligible role in the railway-induced ground vibrations.

1

G. Kouroussis, G. Gazetas, I. Anastasopoulos, C. Conti, O. Verlinden, "Discrete modelling of vertical track-soil coupling for vehicle-track dynamics", Soil Dynamics and Earthquake Engineering, 31(12), 1711-1723, 2011. doi:10.1016/j.soildyn.2011.07.007

2

G. Kouroussis, O. Verlinden, C. Conti, "A two-step time simulation of ground vibrations induced by the railway traffic", Journal of Mechanical Engineering Science, 226(2), 526-544, 2012. doi:10.1177/0954406211414483

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