Mitigating train derailments due to sharp curve and overspeed

Each year around the world there are still several cases of train derailments on the curved tracks due to overspeed, leading to big casualties and costs to the rail industries. With the ongoing increase on the speed, the possibility of train derailment will increase, especially on the sharp curved tracks. Two guard rails (or check rails) are usually required to be placed inside and parallel to two running rails along restrictive clearance areas of the bridge, tunnel, and turnout, preventing the rail vehicle wheels from turning over the rails in case of derailment. However, the investigation on the guide rail which is used to mitigate the train derailment due to a curved track and overspeed is carried out in this paper through the simulations. On sharp curved tracks, one guard rail can be placed inside the low rail, where it engages the back of the wheel flange. The simulations demonstrate that the guard rail can reduce the train derailment potential caused by a sharp curve and overspeed. The lateral clearance between wheel rim back and guard rail, as well as the height over the low rail top, is crucial in the effectiveness of guard rail. Their optimal selections could be obtained through the further simulations

Importance of track modeling to the determination of the critical speed of wagons

This paper presents the application of a three-dimensional wagon-track system dynamics (3DWTSD) model to examine the hunting characteristics of wagons containing three-piece bogies running on tangent track. In the 3DWTSD model, two types of track subsystem were considered--one as a layered viscoelastic track subsystem and the other as a 'rigid' track subsystem. Both the critical speed of wagons and the hunting frequency obtained using the viscoelastic track subsystem are smaller than those using 'rigid' track subsystem. The influence of the wheel profiles to the hunting characteristics is also examined. The worn wheel profile was found to incrrease the critical speed of wagons in addition to changing the hunting characteristics

Wagon–track modelling and parametric study on rail corrugation initiation due to wheel stick-slip process on curved track

For the investigation of rail corrugation formation due to the wheel stick-slip process on curved tracks, a nonlinear wagon–track model is presented in this paper. In this model, the wagon movements were described using up to 78 degrees of freedom (Dofs). The two wheels in a wheelset are coupled through the stiffness coefficients corresponding to the natural torsional and bending modes of wheelset. The track is considered as a discretely supported distributed-parameter track modelling with one layer. In the wheel–rail interface, before the creep saturation point µsNc (μs, static wheel–rail friction coefficient; μc, normal force), the creep forces and moments are calculated using Kalker’s linear creep theory. After that point, the wheel slides on the rail and the friction force will be μkNc (µk—kinetic friction coefficient). The simulations show that the frequency of wheel stick-slip process is composed of a basic frequency, which matches the sleeper-passing frequency and the combined torsional and bending frequency of the wheelset, forming the wavelength of rail corrugation at different situations. Generally, the wheel stickslip process on the high rail oscillates at the basic frequency whilst the dominant frequency on the low rail is double the basic frequency. The effects of the curved track parameters, the wheel–rail friction characteristics and the wheel–rail profiles on the wheel stick-slip process were investigated

Finite element modeling and analysis of friction wedge damping during suspension bounce modes

A two-dimensional finite element model (2D FEM) has been developed to improve the modeling and understanding of the friction damping characteristics of freight bogie suspensions. The specific suspension considered utilizes friction dampers with constant pre-load force as are widely used in three-piece bogie wagons in Australia. Unlike simpler models commonly used in rail vehicle dynamics, the FE model developed can accommodate distributed normal forces across the wedge surfaces. The model was tested in bounce modes and compared with the normal equations used to model wedge friction forces, which treat the forces on the wedge as a static problem. The simulation results using the 2D FEM model showed that the friction damping force is not constant and changes when the suspension is in motion. It was also shown that the force changes magnitude during the loading and unloading situations. The factors, which affect the change in friction force, are the friction characteristics on wedge contact surfaces, the direction and change in tangent force on wedge angular surface, the elastic deformation of the wedge, the wedge relative movement, and the wedge structure arrangement. The FE model assumptions are investigated and insights on wedge friction and creepage discussed (DOI: 10.1115/1.3207338

Vertical dynamic behavior of three-piece bogie suspensions with two types of friction wedge

There are two common types of friction wedge in the suspension system of a three-piece bogie—the “constant damping” wedge and the variable damping wedge. A generic wagon–track dynamics interaction model has been developed to investigate the dynamic behaviour of suspension systems with these two wedge types .The model differs from usual approaches in two aspects: (1) the mass of the wedge is considered in the model and, (2) the track is modelled as a flexible element with multiple degrees of freedom modelling sleepers, ballast and subgrade. The dynamic response characteristics of the two suspension-wedge systems are simulated, compared and discussed for different wedge friction conditions and track input frequencies

The effect of wedge friction conditions on the dynamic wheel-rail contact force on short wavelength defects

For wagons with three-piece bogies, the suspension dynamic characteristics are largely dependent on the friction condition of the wedge dampers. The influence of changes in wedge friction conditions on the dynamic wheel load is investigated. Comprehensive wagon-track modelling has been developed for the analysis. Simulations show that a small friction coefficient on the wedge contact surfaces can lead to the severe resonance of suspension system, causing large dynamic wheel loads and high levels of wheel unloading while with a large friction coefficient, suspension resonance is restricted, leading to smaller dynamic wheel loads

Vehicle-track modelling for rail corrugation initiation investigation

As a part of Australian Rail CRC Project #82 - Bogie Rotation Friction Management, the investigation on rail corrugation initiation has been carried out. This paper reports the progress made on this research. At present, the literature review and the vehicle-track modelling for rail corrugation have been finished. A three-dimensional vehicle-track system dynamics model is developed for the simulations, in which the vehicle dynamics is described using up to 78 degrees of freedom (DOF). The wheelsets are considered as flexible bodies. The track is modeled as one-layered, two rail beams on elastic foundation or two-layered, sleepers included structure. The effect of wheel-rail profiles, wheel-rail interface conditions, curved track parameters, wheelset design parameters and centre bowl rotation friction on the rail corrigations will be examined

Nonlinear three-dimensional wagon–track model for the investigation of rail corrugation initiation on curved track

A nonlinear wagon–track model on curved track has been developed to characterize rail corrugation formation due to self-excitation of the wheel–rail stick–slip process. In this model, wagon movements were described using up to 78 degrees of freedom (DOFs) to model a three piece freight bogie. Innovatively, the wheelset movements are described using nine DOFs, including torsional and bending modes about the longitudinal and vertical directions. The track modelling is considered as a one-layer structure (two rail beams on discrete spring and damper elements). The wheel sliding after creepage saturation is considered in the wheel–rail interface modelling. Simulation of a case study shows that the frequencies of the wheel stick–slip process are composed of the basic frequency, which might come from the combined effect of sleeper-passing frequency and one third of the combined torsional and bending frequency of the wheelset, and the double and triple basic frequencies, which form the wavelengths of rail corrugation at different situations

A dynamic model for the vertical interaction of the rail track and wagon system

With the advent of high-speed trains, there is a renewed interest in the rail track–vehicle interaction studies. As part of an ongoing investigation of the track system optimisation and fatigue of the track components, a dynamic model is developed to examine the vertical interaction of the rail track and the wagon system. Wagon with four wheelsets representing two bogies is modelled as a 10 degree of freedom subsystem, the track is modelled as a four-layer subsystem and the two subsystems are coupled together via the non-linear Hertz contact mechanism. The current model is validated using several field test data and other numerical models reported in the literature by other researchers

Wagon-track modelling and parametric study on rail corrugation initiation due to wheel stick-slip process on curved track

As a result of the rail corrugation formation due to the wheel stick-slip process, a nonlinear wagon-track model on curved track has been developed. In this model, wagon movements were described using up to 78 degrees of freedom (Dofs). Two wheels in a wheelset are coupled through the stiffness coefficients corresponding to the natural torsional and bending modes of wheelset. The track is considered as the discretely supported distributed-parameter track modelling with one layer. In the wheel-rail interface, before the creep saturation point sNc (s - static wheel-rail friction coefficient, Nc - normal force), the creep forces and moments are calculated using Kalker’s linear creep theory. After that point, the total wheel contact patch slides on rail, and the friction force will be kNc (k - kinetic friction coefficient). Simulations show that the frequency of wheel stick-slip process is composed of a basic frequency, which matches the sleeper-passing frequency and the combined torsional and bending frequency of the wheelset. The later appears as double or triple frequency of the basic frequency, and forms the wavelength of rail corrugation at different situations. Generally, the wheel’s stick-slip process on the high rail oscillates at the basic frequency. The dominant frequency of wheel’s stick-slip process on the low rail is double basic frequency. The effects of the wheel-rail friction characteristics, the wheel-rail profiles, the wheelset’s torsional and bending frequencies, and the curved track parameters such as curvature and cant on wheel stick-slip process have been investigated