Beyond the advantages in design of running gear and railway vehicles itself and introducing the active wheelset steering control systems many railroads and tram companies still use huge number of old fashion vehicles. Dynamic performance, safety and maintenance cost of which strongly depend on the wheelset dynamics and particularly on how good is design of wheel and rail profiles. The paper presents a procedure for design of a wheel profile based on geometrical wheel/rail (w/r) contact characteristics which uses numerical optimization technique. The procedure has been developed by Railway Engineering Group in Delft University of Technology. The optimality criteria formulated using the requirements to railway track and wheelset, are related to stability of wheelset, cost efficiency of design and minimum wear of wheels and rails. The shape of a wheel profile has been varied during optimization. A new wheel profile is obtained for given target rolling radii difference function ' r y ∆ − ' and rail profile. Measurements of new and worn wheel and rail profiles has been used to define the target ' r y ∆ − ' curve. Finally dynamic simulations of vehicle with obtained wheel profile have been performed in ADAMS/Rail program package in order to control w/r wear and safety requirements. The proposed procedure has been applied to design of wheel profile for trams. Numerical results are presented and discussed.
Worldwide, metallurgical rail welds are being geometrically assessed by the principle of vertical deviations satisfying given tolerances, measured with steel straightedges or occasionally with digital/electronic straightedges. In this approach, the geometrical shape of the weld in longitudinal direction has no real influence, although it has a direct relation with the dynamic wheel -rail interaction forces, which are responsible for track deterioration. In this article, different new assessment methods for rail welds are proposed and evaluated in practice, after which a choice is made for the best method. This is done in line with the situation in the Netherlands, where the chosen new method was recently introduced and standardized (2005). The proposed method is based on a limitation of the gradient of the discrete measurement signal, implying a limitation of the wheel -rail dynamic contact force.
The primary mechanisms playing a role in the dynamic wheel-rail response to rail weld irregularities in a ballasted track are pointed out. The concept of P1 and P2 forces for metallurgical rail welds, introduced in a first paper [1] concerning the present research, is further elaborated. The dynamic wheel-rail response is simulated for a number of geometrical rail weld measurements. Results show a good correlation between the gradient of the rail weld geometry and the maximum dynamic wheel-rail contact forces, whereas the correlation with vertical peak deviations is shown to be very poor. Therefore, an assessment method based on the gradient (introducing a speed-dependent quality index [1]) is more consistent than a method based on vertical tolerances. An approximate formula is presented to calculate the maximum dynamic wheel-rail contact force as a function of the train velocity and the maximum gradient of the weld geometry, in analogy to Jenkins' formulae for calculating P1 and P2 forces at dipped rail joints.
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