Discrete element simulation provides some insight into the alteration of railway ballast after repeated train passings. The present Part 1 is devoted to a 2D model of this granular layer interposed between the deformable ground and the rail sleeper, to which a large number of loading cycles is applied. Ballast grains are modelled as indeformable polygonal solids. A detailed account of the application to this frictional dynamical problem of the Non-Smooth Contact Dynamics numerical method is given. Validation is obtained through comparison with physical experiments performed on assemblies of prismatic mineral grains. Numerical results on the settlement of a track submitted to 20,000 loading cycles or more are presented.
Rolling noise is the main source of noise from railway operations at conventional speeds, and even at 300 km/h, it is at least as important as aerodynamic noise. In the last decade, several large research projects have been carried out across Europe with the aim of reducing wheel/rail rolling noise at source. Much of the research has concentrated on freight traffic as this has been perceived as the major source of nuisance because of its relatively high noise levels and the operational necessity of running at night. The solutions considered have included means of reducing wheel and rafl surface roughness, improved wheel and track designs for low noise generation, and local shielding applied to the vehicle and track. These have demonstrated a number of successful concepts, including wheel shape optimization, wheel damping, rail damping, bogie shrouds, low barriers, and modified tread braking. This article summarizes the main results obtained and discusses the prospects for implementation of the technology in practice.
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