Dynamic Derailment Research Articles

Evaluation of dynamic derailment in a railway switch considering the longitudinal impacts caused by vehicle retarder

The operating conditions at the railway marshalling station are quite complicated, featuring low-speed turnouts, sharp curves, and vehicle retarders. Train derailments frequently occur in the switch panel. However, the passive safety and derailment behaviour considering the longitudinal impacts are still not clearly understood. With this aim in mind, a three-dimensional freight wagon-track (turnout) dynamic interaction model considering the impacts between wagons in longitudinal direction is established. The braking of the vehicle retarder on wheels is also simulated. The comparative analysis between the simulation results and field observation for the derailment is presented. The derailment limits along the switch are assessed based on 3D quasi-static analysis and numerical simulation. The results show that the longitudinal impact from the rear wagon can significantly increase the derailment risk when an empty wagon located in the middle passes through the vehicle retarder and switch. As the side wear depth of the switch rail increases to 5 mm, the vertical wheel rise at the front of the switch increases from 0 to 4.73 mm even though the other parameters keep an ideal level. Proper measures such as rail grinding and lubricating are suggested to be adopted for optimizing wheel-rail contact relationships and improving running safety.

Effect of lateral misalignment defects of rail joints on dynamic derailment behaviour in railway turnouts

This study aims to investigate the mechanism of wheel jumping derailment in the railway switch panel after a freight wagon passes over a rail joint defect (RJD) situated before the switch. For this purpose, a 3D vehicle-track (turnout) coupled dynamic model that considers the elastic deformation of the rails and wheelsets has been established. Several extreme running conditions, including sharp curves, low-speed railway turnouts, lateral misalignment defects of RJs, and empty wagons are all considered in the simulation model. The vertical wheel rise limit for the railway switch panel is presented for the evaluation of a quasi-static derailment risk. The wheel-rail impact behaviour and the evolution of the derailment processes in the switch panel are revealed, and the effects of wagon load and misalignment width of RJ sections on the vehicle’s dynamic response and running safety are investigated. The results show that the root cause of the high derailment risk in the railway switch is a lower wheel rise limit at the front region of the switch rail when compared with the mainline. This dynamic derailment limit is sensitive to the car-body load and the misalignment width. Severe lateral defects of the RJ before the switch toe should therefore be avoided.

Investigation on train dynamic derailment in railway turnouts caused by track failure

Train derailments in low-speed railway turnout areas are very common due to poor track alignment and rail failures, and in extreme cases can lead to casualties and damage to infrastructure and railway vehicles. This study aims to explore the dynamic derailment behaviour caused by rail joint failures before the railway switch panel, and to understand the effects of crucial parameters on the operating safety of trains. To this end, a 3D dynamic coupled freight train-track simulation model is developed based on the MBS-FEM method. The model takes into consideration the lateral difference between rail joint sections that directly cause the wheel to rise. Flexible deformations of the rail and wheelset are modelled, and the derailment mechanism of wheel jumping and climbing in the railway switch panel is revealed. Results show that increasing the curve radius and distance between the rail joint and switch toe can effectively improve passing safety. When a sharp curve has to be placed before the switch panel due to site limitations, reducing the wheel-rail coefficient can also ensure better operating safety. This study indicates that the proposed MBS-FEM dynamic coupled derailment simulation model is able to efficiently evaluate the operating safety as a result of various wheel and track defects, and thus form a basis for providing a cost-effective platform for the future parameter optimization of railway tracks and vehicles.

Dynamic derailment behaviour of urban tram subjected to lateral collision

ABSTRACT The urban tram is theoretically likely to be laterally collided by the automobile during operation due to their shared right of roadway. The collision occurrence is fortuitous, but the consequence is commonly disastrous induced by the collision and subsequent derailment accidents. This article presents an investigation into the derailment performance of the tram when the automobile impacts laterally onto the tram flank. A comprehensive dynamic model to simulate derailment behaviours of the tram under this collision scenario is built, in which the complicated contact relation of wheel/rail system is treated. The contribution of several affecting factorsto the derailment response is reported. It is shown that the guardrails of the grooved rail track play a key role in preventing the tram derailments due to low-speed collision. The violent lateral and rolling motions of the tram body caused by the great lateral impact is the root cause of the derailments.

Influence of the motion conditions of wheelsets on dynamic derailment behaviour of a bogie in railway turnouts

Wheel climb derailment frequently occurs in turnouts. This is usually because track alignments in the turnout area are very poor and the cross-sections of switch rail are not uniform. Most previous studies focused on derailments in straight or curved lines. For this reason, understanding the derailment mechanism in turnouts and revealing the influence of the wheelset motion conditions on dynamic derailment behaviour are fundamental for the development of the required dynamic derailment criteria. For this paper, a half-vehicle multi-body dynamic model for derailment simulation was established and validated. Then, the effect of three different running cases with different wheelset motion conditions was further analysed. The results show that the variable cross-sections of switch rail along the longitudinal direction with a small contact angle are the root cause of the wheel climb derailment when compared with straight and curved lines. The wheels start climbing the switch rail at regions of rail top width from 5 to 20 mm. If the effect of the switch rail is ignored, the derailment risk in the guide curve is significantly reduced. This paper can contribute to the mitigation of derailment in railway turnouts as well as to the development of safety assessment criteria.

Numerical investigation of dynamic derailment behavior of railway vehicle when passing through a turnout

Wheel flange climb derailment of vehicles in railway turnouts is a serious safety issue. In particular, derailment accidents in smaller turnouts, caused by poor track alignment before the turnout or structural degradation, are becoming more and more frequent. Most of the previous research on derailment has focused on main track areas, while the dynamic derailment mechanism for turnouts is still not clear. For this reason, a field derailment investigation of freight wagons in No.6 symmetrical turnouts is presented in this paper. Taking this into consideration, a half-car multi-body dynamics model and flexible turnout model, subject to wheel flange climb derailment, has been established. In addition, a field test for wheel-rail interaction was carried out to verify the dynamic model. This model is capable of revealing derailment evolution of the front and rear wheelset for a bogie under critical derailment conditions. The influence of several sensitive parameters of the derailment model on critical derailment behavior has been carried out. Results show that the simulation results of the wheel climb derailment are very consistent with the filed investigation, and the safety of the bogie depends on the status of both front and rear wheelset. This work is a world first in providing a solid understanding of dynamic derailment behavior and motion posture, giving guidance on the prevention of wheel flange derailment in turnout areas.

Dynamic derailment simulation of an empty wagon passing a turnout in the through route

Turnouts are among the weakest links of railway lines, but the derailment risk of vehicles passing the through route of a turnout is seldom considered. The potential factors affecting derailment are screened according to field investigations of a train derailment case at the through route of a turnout. A detailed wagon-turnout interaction model considering the non-uniform cross-sections of turnout rails and the interaction between adjacent wagons is developed and validated. Through numerical simulation, the dynamic performance of an empty wagon passing the through route of turnout at a low speed is studied. When the wagon passes the turnout under the continuous lateral force condition, the wheels climb onto the rail head at the switch area in the facing direction, while the derailment occurs at the frog area in the trailing direction. Moreover, the possibility of derailment of the empty wagon increases with increasing coupler force and wheel-rail friction coefficient, and with decreasing speed. To improve the safety of empty wagons in the turnout area, rail lubrication should be implemented to reduce the wheel-rail friction coefficient, and large braking forces should be avoided. Furthermore, the wheel surface condition after re-profiling requires continuous attention.

Numerical investigation on the dynamic behaviour of derailed railway vehicles protected by guard rail

Train derailment can cause not only damage to the train itself but also secondary damage to surrounding structures. For this reason, guard rails are commonly used to prevent secondary damage caused by derailed trains on high-risk lines. In this paper, a 3D vehicle-track dynamics simulation model and a collision contact model were used to investigate the post-derailment dynamic behaviours of the train as well as the effectiveness of guard rail protections. Variables studied include derailer oblique angle, the gap between running rail and guard rail, the effect of derailing speed on the posture, and impact force after derailment. The study shows that the oblique angle has a strong influence on the dynamic derailment behaviours. At a large gap, the bogie generates a noticeable distortion, which is very detrimental to the derailed vehicles. It was found that when the gap is 200 mm, the derailed wheelsets roll on the sleepers stably. And high derailing speeds can also cause significant impact forces. These simulations further the theory of train running posture and impact response, and can inform good railway design and maintenance. This is particularly true for tracks on which guard rails are installed to reduce secondary damage.

Study on the derailment behaviour of a railway wheelset with solid axles in a railway turnout

ABSTRACTDynamic wheel–rail interaction in railway turnouts is more complicated than on ordinary track. In order to evaluate the derailment behaviour of railway wheelsets in railway turnouts, this paper presents a study of dynamic wheel–rail interaction during a wheel flange climbs on the turnout rails, by applying the elasticity positioning wheelset model. A numerical model is established based on a coupled finite element method and multi-body dynamics, and applied to study the derailment behaviour of a railway wheelset in both the facing and trailing directions in a railway turnout, as well as dynamic wheel–turnout rail interaction during the wheel flange climbing on the turnout rails. The influence of the wheel–rail attack angle and the friction coefficient on the dynamic derailment behaviour is investigated through the proposed model. The results show that the derailment safety for a wheelset passing the railway turnout in facing direction is significantly lower than that for the trailing direction and the ordinary track. The possibility of derailment for the wheelset passing the railway turnout in facing and trailing directions at positive wheel–rail attack angles will increase with an increase in the attack angles, and the possibility of derailment can be reduced by decreasing the friction coefficient.

Dynamic response of the train–track–bridge system subjected to derailment impacts

ABSTRACTDerailments on bridges, although not frequent, when occurs due to a complex dynamic interaction of the train–track–bridge structural system, are very severe. Furthermore, the forced vibration induced by the post-derailment impacts can toss out the derailed wagons from the bridge deck with severe consequences to the traffic underneath and the safety of the occupants of the wagons. This paper presents a study of the train–track–bridge interaction during a heavy freight train crossing a concrete box girder bridge from a normal operation to a derailed state. A numerical model that considers the bridge vibration, train–track interaction and the train post-derailment behaviour is formulated based on a coupled finite-element – multi-body dynamics (FE-MBD) theory. The model is applied to predict the post-derailment behaviour of a freight train composed of one locomotive and several wagons, as well as the dynamic response of a straight single-span simply supported bridge containing ballast track subjected to derailment impacts. For this purpose, a typical derailment scenario of a heavy freight train passing over a severe track geometry defect is introduced. The dynamic derailment behaviour of the heavy freight train and the dynamic responses of the rail bridge are illustrated through numerical examples. The results exhibit the potential for tossing out of the derailed trains from the unstable increase in the yaw angle signature and a lower rate of increase of the bridge deck bending moment compared to the increase in the static axle load of the derailed wheelset.

Theoretical cross-wind speed against rail vehicle derailment considering the cross-running wind of trains and the dynamic wheel-rail effects

In this paper, a theoretical formula was proposed that predicts the derailment index due to a cross wind applied to a rail vehicle considering the cross running wind condition of two running trains as well as the dynamic wheel-rail effects. The recently developed derailment theory on a wheelset was applied to this new cross wind derailment formula. Contrary to the conventional formulas, this new derailment formula was derived considering a dynamic derailment coefficient (Q/P) under normal running, the friction coefficient between the wheel and the rail, the wheel load variation, the cross running wind effects, and the cross wind. Using this proposed formula, the derailment pattern and the critical cross wind speed of derailment could be predicted for various cross running wind conditions of two running trains. Finally, for some typical examples, the results of this proposed formula were compared and verified with those of the conventional formulas and the numerical simulation of multi-body dynamics software, Recurdyn.

Research on the mechanics of high speed rails

In the preceding theme issue on'Current research progress on mechanics of high speed rails'(Acta Mechanica Sinica,30:846–909(2014)),we invited several authors in the fiel to present their research on high speed rails(HSR),including work on dynamic derailment analysis(Ling et al.[1]),load

Fast estimation of the derailment risk of a braking train in curves and turnouts

When a train runs through a turnout or a sharp curve, high lateral forces occur between the wheels and rails. These lateral forces increase when the couplers between the wagons are loaded in compression, i.e., a rear locomotive pushing a train or a front locomotive braking a train. This study quantifies these effects for a train that begins braking when steadily curving and for a train that brakes upon entering a turnout. Our approach allows distinguishing between the effects of braking and the transient effects of entering the turnout. The dynamic derailment quotient is mapped as a function of the vehicle speed and the braking effort. Then the dynamic derailment coefficient obtained from the dynamic simulations is compared to results from quasi statics. This allows determining a dynamic multiplication coefficient that can be used on the quasi static derailment coefficient to obtain a first estimate of the dynamic derailment coefficient.

Track geometry defect rectification based on track deterioration modelling and derailment risk assessment

Analysing track geometry defects is critical for safe and effective railway transportation. Rectifying the appropriate number, types and combinations of geo-defects can effectively reduce the probability of derailments. In this paper, we propose an analytical framework to assist geo-defect rectification decision making. Our major contributions lie in formulating and integrating the following three data-driven models: (1) A track deterioration model to capture the degradation process of different types of geo-defects; (2) A survival model to assess the dynamic derailment risk as a function of track defect and traffic conditions; (3) An optimization model to plan track rectification activities with two different objectives: a cost-based formulation (CF) and a risk-based formulation (RF). We apply these approaches to solve the optimal rectification planning problem for a real-world railway application. We show that the proposed formulations are efficient as well as effective, as compared with existing strategies currently in practice.

Development of a simulation model for dynamic derailment analysis of high-speed trains

The running safety of high-speed trains has become a major concern of the current railway research with the rapid development of high-speed railways around the world. The basic safety requirement is to prevent the derailment. The root causes of the dynamic derailment of high-speed trains operating in severe environments are not easy to identify using the field tests or laboratory experiments. Numerical simulation using an advanced train-track interaction model is a highly efficient and low-cost approach to investigate the dynamic derailment behavior and mechanism of high-speed trains. This paper presents a three-dimensional dynamic model of a high-speed train coupled with a ballast track for dynamic derailment analysis. The model considers a train composed of multiple vehicles and the nonlinear inter-vehicle connections. The ballast track model consists of rails, fastenings, sleepers, ballasts, and roadbed, which are modeled by Euler beams, nonlinear spring-damper elements, equivalent ballast bodies, and continuous viscoelastic elements, in which the modal superposition method was used to reduce the order of the partial differential equations of Euler beams. The commonly used derailment safety assessment criteria around the world are embedded in the simulation model. The train-track model was then used to investigate the dynamic derailment responses of a high-speed train passing over a buckled track, in which the derailment mechanism and train running posture during the dynamic derailment process were analyzed in detail. The effects of train and track modelling on dynamic derailment analysis were also discussed. The numerical results indicate that the train and track modelling options have a significant effect on the dynamic derailment analysis. The inter-vehicle impacts and the track flexibility and nonlinearity should be considered in the dynamic derailment simulations.

Study on the safety of operating high-speed railway vehicles subjected to crosswinds

A coupled vehicle-track dynamic model is put forward for use in investigating the safety effects of crosswinds on the operation of a high-speed railway vehicle. In this model, the vehicle is modeled as a nonlinear multi-body system, and the ballasted track is modeled as a three-layer discrete elastic support system. The steady aerodynamic forces caused by crosswinds are modeled as ramp-shaped external forces being exerted on the vehicle body. This model was used in a numerical analysis of the dynamic response and dynamic derailment mechanisms of high-speed vehicles subjected to strong crosswinds. The effects of the crosswind speeds, crosswind attack angle, and vehicle speed on the operational safety of the vehicle were examined. The operational safety boundaries of a high-speed vehicle subjected to crosswinds were determined. The numerical results obtained indicate that crosswinds at attack angles of 75° to 90° with respect to the forward direction of the vehicle have a great influence on the safety of operating high-speed railway vehicles. The wheelset unloading limit, which determines the position of the warning boundary dividing the safe operating area and the warning area, is the most conservative, i.e., the safest, criterion to use in assessing the high-speed operational safety of vehicles in crosswinds.

Effects of Rail Cant on Wheel-Rail Contact Forces in Slab Tracks

Rail cant parameter, applied in order to attain suitable movement of wheel on rail, directly influences in dy- namic interaction of track-vehicle. In this paper, the effect of geometrical parameters on the behaviour of dynamic interaction of wheel-rail is being investigated through a parametric study. A complex dynamic analyses using ADAMS/RAIL are being applied for one section of actual executed line and the records of geometrical parameters have been registered for this purpose. The necessary measurements have been recorded by KRAB measuring machine, safety levels and serviceability have been controlled based on these data. The results of the analysis show that non-conformity of the rail seat slope relative to its desired value, strictly influences on the coefficient of derailment (about 18 percent), horizontal dynamic forces (about 17 percent), and results in severe rail wear (about 18 percent). However, vertical dynamic forces and safety index are not of any concern form the derailment point of view, since it is within the acceptable range of the standards. The comparison of analyses' results in various operational speeds shows a remarkable impact on the vertical dynamic forces (up to 13 percent) and derailment index (up to 8 percent).

Development of high-speed railway vehicle derailment simulation – Part II: Exploring the derailment mechanism

Based on the exactly solution for the wheel/rail contact point and the contact force, a vehicle/rail coupling model for analyzing dynamic derailment is developed in MATLAB as DDSHV (Dynamic Derailment Simulation for High-speed Vehicle). The calculation process of the simulation system is presented in detail, and the best solution conditions are also discussed to quickly obtain results. Two common types of dynamic derailment are studied in DDSHV. There exists a critical point in the process of wheel climb, and the dynamic weakening effect will promote the wheel-climbing rail. Meanwhile, some main factors, such as the speed, the rail condition and the wheel unload rate, have been studied on the dynamic weakening effect. The collision speed of the wheelset is the most important factor affecting impact derailment. As time becomes shorter, the collision can be investigated using LS-DYNA. The results confirm the equation for the critical impact speed used in this paper. DDSHV can also be used to find the vehicle running stability. Through the design of uplink and downlink algorithms, two critical running speeds, the critical speed and the nonlinear critical speed have been found. Yet, the changes in suspension parameters will directly influence these critical speeds. Therefore, an accurate configuration in vehicle will help to reduce the disturbances while an inaccurate configuration may lead to an incident. Although it is dangerous and difficult to make a derailment online test, the effectiveness of DDSHV has been verified by the known dynamic cases and lab tests. In conclusion, DDSHV has assisted in understanding the process of derailment, finding the important factors affecting derailment and exploring the mechanism of dynamic derailment.

Development of high-speed railway vehicle derailment simulation – Part I: A new wheel/rail contact method using the vehicle/rail coupled model

With an increase in speed, a vehicle’s dynamic behavior becomes apparent. Increasing speed not only affects the sitting comfort, but also may lead to derailment. However, an accident is difficult to predict, because the derailment mechanism is not thoroughly understood. The reliability of derailment simulations are completely conditional to being able to accurately solve the wheel and rail contact problem. Thus, an improved three-dimensional contact trace method is presented to quickly obtain the correct point. Then, a fast and accurate method for obtaining the contact force, which includes the creep force and the normal force, is improved. The results correspond more closely to realitic solutions compared with those of current methods. Next, a dynamic model of the vehicle and the rail is established. The two models are not independent of each other. The wheel–rail contact calculation is the key consideration for coupling in the two models. Finally, all the dynamic models, which are called dynamic derailment simulation for high-speed vehicle (DDSHV), are developed in MATLAB. To identify two different types of derailment, derailment judgment is embedded in the program package. The simulation system can be used to study the dynamic derailment mechanism, analyze derailment conditions and influence factors, and determine the key cause of the incident.

Effect of tangent track buckle on vehicle derailment

In order to investigate the effect of a tangent track buckle on the dynamic derailment of a railway vehicle, a coupled vehicle/track dynamics model is developed, in which the vehicle is modeled as a 35 D.O.F. multibody system and the track is modeled as a 3-layer discrete elastic support model. Rails are assumed to be Timoshenko beams supported by discrete sleepers, and the effects of vertical and lateral motions and rolling of the rail on the wheel/rail creepages are taken into account. The sleepers are treated as Euler beams on elastic foundation for the vertical vibration, while as lumped masses in the lateral direction. A moving sleeper support model is developed to simulate the effect of the periodical discrete sleepers on the vehicle/track interaction. The vehicle and the track are coupled by wheel/rail contacts whereas the normal forces and the creep forces are calculated using the Hertzian contact theory and the nonlinear creep theory by Shen et al., respectively. The equations of motion of the coupled vehicle/track system are solved by means of an explicit integration method. A tangent track buckle is simulated with a cosine function, which describes the misalignment of the track with different lengths due to its buckling. In the analysis the effects of the buckle wavelength and amplitude and of the vehicle speed on the dynamic behavior of the coupled vehicle/track system are considered. The present paper analyzes in detail the conventional derailment coefficients which include the ratio of the wheel/rail lateral force to the vertical force, the wheel load reduction, and the new criteria indicating the wheel/rail contact point traces and the wheel rise with respect to the rail. These criteria are simultaneously used to evaluate the risk of derailment of the whole vehicle. The numerical results obtained indicate that the track misalignment caused by the buckle and the vehicle speed have a great influence on the whole vehicle running safety when the vehicle passes through the buckled tangent track.