Study On High-Speed Train Derailment Mechanism In Severe Environment

The mechanism of train derailment is quite complicated and involved in many uncertain influencing factors. Fully understanding and solving it is still a very difficult theoretical and technological project in railways all over the world. Now the environmental state of natural disasters and the failure of the key parts of railway vehicle and track is a threatening to the safety operation of high-speed trains, and in the past caused many serious derailment occurring. So far, the dynamical behavior and characteristics of high-speed operating trains in such a severe environmental state cannot be clearly described by using the existing coupling dynamics theories of railway vehicle and track, especially the transient process of derailing and its mechanism understanding. In addition, railways around the world have not reached a consensus on the widely used derailment criteria and operation safety estimating standards of high-speed trains. The railways of different countries and areas hire the different derailment criteria and operation safety estimating standards, some of which are deficient, unscientific and even unreasonable. People don’t understand their internal relations even if the application purposes of them are the same. The most of them consider a single influencing factor or few influencing factors only. Usually one or two of them is alonely used in evaluating the safety operation of high-speed trains and the obtained consequences have been doubted. Hence, it is very necessary to further make an investigation into the derailment mechanism of high-speed trains operating in the severe environmental state, the boundaries between derailment occurring and safety operation areas, and the internal relation and difference of the existing derailment criteria.The thesis is funded by the National Natural Science Foundation Projects of China’Study on Mechanism of High-speed Train Transient Derailment in Severe Environmental State (50875218)’and’Research on Key Problems of Science and Technology of High-speed Trains in Satety Operation (50821063)’, and’Science and Technology Planning Project in Sichuan Province (2010JY0070)’. The following researches were conducted.(1) A whole model of the transient derailment mechanism of high-speed train and its matching computational code are developed. This model considers the five subsystems:a railway vehicle, a track, wheel/rail in transient rolling contact, the boundary excitations of the vehicle/track coupling system and a new system of estimating safety operation of high-speed trains. According to the characteristics of the defined severe environmental state, they are included in the dynamics model of a high-speed train coupled with a track as general boundary conditions.(2) The developed model of railway vehicle considers both single vehicle and multi-vehicles. The single vehicle model has35degrees of freedom and the multi-vehicle model considers8vehicles with42degrees of freedom for each vehicle, which are the rigid multi-body models. All the parts of the vehicle in service neglect their deformation, the operation speed is assumed to be a constant and the accelerations and decelerations of the vehicle parts are also ignored in the modeling. The connections between the parts are replaced with the equivalent spring/damper systems. The nonlinear connections are characterized with piecewise linearities.(3) This thesis improves the ballasted track dynamics model with three layers (rails-sleepers-ballast) and the slab track dynamics model which uses the finite element method to model the slabs. The infrastructure of the rails is treated as a discrete system with sleeper supporter units, in which the variation of the track stiffness along the track is considered. A pair of rails is modelled by using the finite Timoshenko beam with discrete supporters which takes the vertical and lateral motions and rotation of the rail into account. In modeling the ballasted track, a sleeper is treated as the Euler beam the vertical and lateral motions and rolling of which are considered. The ballast bed is replaced with equivalent discrete mass bodies. Each support unit of the track consists of dual-mass (sleeper and ballasted body) and three-layer spring-damper system (rail-sleeper-ballast bed-roadbase). In modelling the slab track, the slab is modeled by using three-dimensional solid finite elements, the fasteners and the CA screed are replaced with periodically discrete viscoelasticity unit systems.(4) A new spatial calculation model of wheel/rail in transient rolling contact is developed, in which the wheel/rail contact points are still determined based on the traditional "tracing method" and the traditional "minimum distance method ". The model considers the effect of the track transient responses on the wheel/rail contact geometry and the interaction of the wheel/rail. The normal forces are calculated by using the improved formula of wheel/rail normal approaching and the nonlinear spring based on Hertzian contact theory. The wheel/rail tangent forces are determined by using the model of Shen-Hedrick-Elkins.(5) In the modelling a train operating along a track a "Tracking Window" technique is adopted to simulate the train moving with respect to the track (tangent and curved tracks) at a constant speed. This is a new vehicle/track interaction model. In this model, the constant speed of the train is available and it is assumed that the infrastructure of the rails moves at a constant speed of the train with respect to the train that is assumed to be in a static state in the window. The longitudinal motion variation of all the parts of the vehicle and the track is neglected. The infrastructure contains fasteners, slabs or sleepers, ballast, CA layer replacement, subgrade and irregularity between wheel/rail.(6) In estimating the dynamical behaviour and the safety operation of a high-speed train, two more derailment criteria are put forward based on the lateral location of wheel/rail contact point and the wheel rise with respect to the rail, which are obtained through the calculation by using the improved model of wheel/rail in transient rolling contact. A new evaluation system for estimating the safety operation and the derailment occurring of high-speed trains in severe environmental state is developed. The basic idea of the estimating system is that the effect of the key influencing factors in changing on the dynamical behavior and derailment occurring process of a high-speed train operating in several severe environmental state is numerically reproduced by using the transient derailment model of a high-speed train with a track, in which the safety operation area, the derailment occurring area and their boundaries are obtained through the detailed numerical calculation. These areas are constructed by using the key influencing factors and the limits of all the considered derailment criteria in the present paper and their internal relationships are shown clearly in these areas. They are very useful for estimating the safety operation of high-speed trains.Using the above models and methods analyze the dynamical behavior and derailment occurring process of a high-speed train operating in several severe environmental states which includes fastener failure, track buckling, strong crosswind and earthquake.(1) The transient derailment model of high-speed vehicle operation under the condition of fastener failure is developed, and used to analyze the effect of the failure of fasteners on the dynamical behaviour, the safety operation and the derailment occurring of a high-speed vehicle. The analysis considers the cases that the failure of different fasteners occurs, respectively, on the high rail, the low rail and both the high and low rails of the tangent and curved ballasted tracks. In the analysis, the two key influencing factors are, respectively, the number of the failed fasteners and the operation speed of the vehicle, which are used to construct the safety operation and derailment occurring areas and their boundary of the vehicle, and also the limits of all the considered derailment criteria shown in the areas.(2) The transient derailment model of high-speed vehicle operation under the condition of track buckling is developed, and used to analyze the effect of the track buckling on the dynamical behaviour, the safety operation and the derailment occurring of a high-speed vehicle. The analysis considers the2cases that the buckling occurs, respectively, on a tangent and curved ballasted tracks. In the analysis, the three key influencing factors are, respectively, the wavelength and amplitude of the track buckling and the operation speed of the vehicle, which are used to construct the safety operation and derailment occurring areas and their boundary of the vehicle, and also the limits of all the considered derailment criteria shown in the areas.(3) The transient derailment model of high-speed vehicle operation under the condition of strong crosswind is developed, and used to analyze the effect of strong crosswind on the dynamical behaviour, the safety operation and the derailment occurring of a high-speed vehicle operating on a tangent track. In the analysis, the three key influencing factors are, respectively, the wind speed, the wind angle and the operation speed of the vehicle, which are used to construct the safety operation and derailment occurring areas and their boundary of the vehicle, and also the limits of all the considered derailment criteria shown in the areas.(4) The transient derailment model of high-speed vehicle operation under earthquake is developed, and used to analyze the effect of earthquakes on the dynamical behaviour, the safety operation and the derailment occurring of a high-speed vehicle operating on a tangent track. In the analysis, the four key influencing factors are, respectively, the earthquake intensity, the direction of earthquake wave propagation, the vehicle speed, and earthquake spectrum characteristics. The former three factors are used to construct the safety operation and derailment occurring areas and their boundary of the vehicle, and also the limits of all the considered derailment criteria shown in the areas.