In this work a general methodology for the description of fully three dimensional track geometries is used. Any descriptive form of parametric curves is dealt within a pre-processor while the dynamic analysis program only has to proceed with linear interpolations of the rail databases. By ensuring that the arc-length step is small enough, the linear interpolation procedure does not introduce any significant errors in the geometric description of the rails. An efficient formulation for the accurate prediction of the contact points location on the wheel and rail surfaces is used. The coordinates of the contact points are predicted online, during dynamic analysis, by introducing surface parameters that describe the geometry of the contact surfaces. This method is applied to study specific problems inherent to the railway dynamics such as the two points of contact scenario. The dynamic analyses results show that the contact forces are sensitive to the parameterization procedures used for the representation of the wheel and rail profiles. It is shown that the Akima splines interpolation scheme is not recommended since it might produce unrealistic results. This is explained by the fact that the Akima splines only have Cl continuity and, consequently, it does not guarantee the necessary geometric continuity conditions. It was also shown that the undesired wiggles in the contact forces results are higher in the wheel and rail profiles parameterized with cubic splines than when using the shape preserving splines. Such results allow recommending the use of shape preserving splines for the wheel and rail profile representation. The methodology developed here to look for the contact points between wheel and rail surfaces requires that these are convex. Therefore, the small concave region in the transition between the wheel tread and flange is neglected. When running on tangent tracks, with forward velocities below the critical speed, or when negotiating large radius curved tracks, flange contact is unlikely to occur. For such cases, the above mentioned simplification is not meaningful since the contact point is far from the flange area. Future research work should be directed towards the development of a new algorithm to look for contact points between concave surfaces. Another problem that arises, when studying the wheel-rail contact in the concave region of the wheel profile, is that the contact is conforming. In this case, the Hertz theory is not valid and, therefore, all creep force laws based on such assumption cannot be applied. The development of a new creep force law that deals with conforming contact is also foreseen as future research.
Influence of the wheel and rail interpolation scheme on the contact evaluation in railway dynamics
Einfluss des Interpolationsschemas Rad/Schiene auf die Kontaktbewertung in der Eisenbahndynamik
2005
12 Seiten, 17 Bilder, 3 Tabellen, 30 Quellen
Conference paper
English
Dynamics of Railway Vehicles and Rail/Wheel Contact
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