Towards Optimization of Railway Turnouts

Licentiatavhandling, 2011

The turnout (Switch & Crossing) is a vital component in railway networks as it provides flexibility to traffic operation by allowing trains to switch between tracks. The flexibility comes at a cost as the common lack of a transition curve in the diverging route together with the variation and discontinuities in rail profiles result in higher rail degradation rates than in regular track. In this thesis, dynamic interaction between vehicle and turnout is studied using numerical tools for multibody dynamics with focus on laying a foundation for robust optimization of turnout geometry. Considering a stochastic spread in traffic parameters, quantitative and qualitative estimates of rail profile degradation are computed. The influence of wheel profile wear on wheel–rail interaction in a turnout is studied, and it is concluded that equivalent conicity is the wheel profile characterization parameter with the best correlation to rail damage of the investigated parameters. In addition, the influence of hollow worn wheels on rail damage is investigated and it is found that such wheel profiles display a significantly different and potentially more harmful running behaviour at the crossing. The influence of wheel–rail friction coefficient is studied and it is shown that friction correlates strongly to lateral contact forces and wear in the diverging route. Wheelset steering, considering the turnout specific configuration of rail profiles and the presence of check rails, is discussed. One of the track models studied is a discretized mass-spring-damper model with nine degrees-of-freedom. This track model can be tuned to capture the large phase delay at low frequencies found in measurements of dynamic track stiffness, while remaining sufficiently resilient at higher frequencies. Good agreement between the simulation model and field measurement data has been observed. It is concluded that the use of more resilient rail pads can reduce wheel–rail impact loads during the crossing transition.