Keywords: railway dynamics, multibody systems, track irregularities, vehicle-track interaction, wheel-rail contact.

In this chapter, a methodology for the accurate representation of three-dimensional track geometries is presented. It involves, not only the description of the design track layout, but also the representation of its irregularities. For this purpose, a methodology that includes the track imperfections, measured experimentally by the railroad companies, in the definition of the track model is developed. This approach allows one to tackle some sensible issues in the railway industry that involve the damage to vehicles caused by the track conditions and the infrastructure deterioration arising from the trainsets' operation. A multibody formulation is used here to describe the vehicle model. The complex interaction that is developed between the wheels and rails is studied using a generic wheel-rail contact model.

The methodologies described in this work are applied to study the dynamic behaviour of the railway vehicle ML95. The studies are performed in real operating conditions as the track irregularities, which are obtained experimentally, are considered. It is observed that the track irregularities increase the wheel-rail contact forces. If these forces reach sufficiently high values, they will contribute to increase the track imperfections, which originate higher contact forces. Hence, the reduction of the track irregularities allows a limit on the loads applied on the rolling stock, reducing the structural fatigue in the mechanical elements and reducing the wear on wheels and rails.

The comparison of the dynamic analysis results with the data available from experimental tests and obtained with the commercial code ADAMS/Rail, allows the conclusion that the models and methodologies developed here are not only qualitatively but also quantitatively correct. It is believed that the differences that are observed result from uncertainties associated with the experimental tests and to the modelling methodologies.

The case tested in this work showed that the proposed methodology provides a reliable and accurate track model. This methodology is appropriate to the needs of the railway operators since the required input data is the information that is standard in the railway industry. It is also shown that the formulation integrates, in an efficient way, the main requirements associated with the dynamic analysis of railway vehicles. Therefore, the models allow results to be extracted that would be either impossible to measure experimentally or for which very costly experimental procedures would be required.

Another advantage of the proposed track model is that the time required for the dynamic simulation of the rail-guided vehicles is completely independent of the track complexity. Any descriptive form of parametric curves is dealt with within the track 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 error in the geometric description of the rails.

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