Advanced Techniques for Time-Domain Modelling of High-Frequency Train/Track Interaction

Abstract

The aim of the present Thesis is to develop models for the study of very highfrequency phenomena associated with the coupled dynamics of a railway vehicle with the track. Through these models, this Thesis intends to address squeal noise as a particular case of rolling noise when the train negotiates a small radius curve.Wheel/rail interaction is the predominant source of noise emission in railway operations. Rolling contact couples the wheel and the rail through a very small area, characterised by strongly non-linear and non-steady state dynamics that differentiates rolling noise from any other noise problem. Wheel/rail contact problem is studied based on Kalker's variational theory and the local falling behaviour of the coefficient of friction is introduced by means of a regularisation of Coulomb's law. Its implementation shows that the influence of the falling friction on the creep curves can be assumed negligible, thus rolling contact is finally modelled using a constant coefficient of friction.Flexibility is introduced in railway substructures through the Finite Element (FE) method in order to cover the high-frequency range. This work adopts a rotatory wheelset model that takes computational advantage of its rotational symmetry. It also develops a cyclic flexible rail model that fixes the translational contact force in a spatial point of the mesh through a technique called Moving Element (ME) method. A modal approach is used to reduce significantly the number of degrees of freedom of the global problem and a diagonalisation technique permits to decouple the resulting modal equations of motion in order to reduce the computational requirements of the time integrator.Simulations in curving conditions in the time domain are carried out for constant friction conditions in order to study if the proposed interaction model can reproduce squeal characteristics for different curve radii and coefficients of friction.Keywords: train/track dynamic interaction, rotatory wheelset, cyclic track, wheel/rail rolling contact, falling friction, regularisation of Coulomb's law, Moving Element Method, decoupling techniques, curve squeal. iii ResumenEl objetivo de la presente Tesis es desarrollar modelos para el estudio de fenómenos de muy alta frecuencia asociados a la dinámica acoplada de un vehículo ferroviario con la vía. A través de estos modelos, esta Tesis pretende abordar el fenómeno de los chirridos como un caso particular de ruido de rodadura en condiciones de curva cerrada.La interacción rueda/carril es la fuente predominante de ruido en las operaciones ferroviarias. El contacto es el responsable del acoplamiento entre la rueda y el carril a través de un área muy pequeña caracterizada por una dinámica fuertemente no lineal y no estacionaria. El problema de contacto rueda/carril se estudia mediante la teoría variacional de Kalker y la caída local del coeficiente de fricción se introduce por medio de una regularización de la ley de Coulomb, que muestra que su influencia sobre las curvas de fluencia se puede despre...

Study of railway curve squeal in the time domain using a high-frequency vehicle/track interaction model

“…A continuous support is modelled under the rail through a viscoelastic Winkler foundation with a uniform distribution of vertical stiffness and damping equivalent to discrete rail supports (railpads + ballast). The dynamics associated with the model is similar compared to the beam resting on discrete supports in the high-frequency band [14] in which squeal phenomenon takes place. In this section, the generalised force associated with the Winkler foundation W F is obtained through the formulation of the virtual work for the elastic and viscous forces.…”

“…Due to the periodicity of the structure and the loading conditions, the study is reduced to a single section having finite length L, whose value is set large enough to avoid interaction between the vehicles. This interaction appears as reflection waves in the receptance function of the rail between 500 Hz and 2 kHz, which are mitigated when increasing the length; from 40 m, those can be considered negligible [14]. The method allows positioning the wheel/rail contact area at a fixed railhead element avoiding the vehicle exceeding the 'downstream' boundary ends since; it also permits to implement a mesh with greater refinement around this region, where forces and displacements are higher, contributing to reduce the computational cost.…”