Risk Of Derailment Research Articles

Dynamic Response Analysis of Ballasted Railway Track–Ground System under Train Moving Loads using 3D Finite Element Numerical Modelling

The faster and heavier trains in modern railway traffic are getting popularity in the public transportation authorities of many countries. Such trains cause higher stresses and excessive deformations in the ballasted railway track substructure under train dynamic loadings, which raises the risk of track damage and derailment. It is thus essential to investigate the impact of different influencing factors on the dynamic response of ballasted railway track–ground systems. In this study, a sophisticated three-dimensional finite element model simulating realistic train moving loads is presented and used to investigate the dynamic response of ballasted railway tracks in terms of stress transmission and track deflections under various train–track–ground conditions. The influencing factors considered in this study include the modulus and thicknesses of track substructure layers, the amplitude of train moving loads and the train speed. The outcomes of this study encompass important guidance to railway engineers to assist in finding the best possible scheme for the design of ballasted railway tracks and lifetime maintenance.

Development and Validation of a Weigh-in-Motion Methodology for Railway Tracks.

In railways, weigh-in-motion (WIM) systems are composed of a series of sensors designed to capture and record the dynamic vertical forces applied by the passing train over the rail. From these forces, with specific algorithms, it is possible to estimate axle weights, wagon weights, the total train weight, vehicle speed, etc. Infrastructure managers have a particular interest in identifying these parameters for comparing real weights with permissible limits to warn when the train is overloaded. WIM is also particularly important for controlling non-uniform axle loads since it may damage the infrastructure and increase the risk of derailment. Hence, the real-time assessment of the axle loads of railway vehicles is of great interest for the protection of railways, planning track maintenance actions and for safety during the train operation. Although weigh-in-motion systems are used for the purpose of assessing the static loads enforced by the train onto the infrastructure, the present study proposes a new approach to deal with the issue. In this paper, a WIM algorithm developed for ballasted tracks is proposed and validated with synthetic data from trains that run in the Portuguese railway network. The proposed methodology to estimate the wheel static load is successfully accomplished, as the load falls within the confidence interval. This study constitutes a step forward in the development of WIM systems capable of estimating the weight of the train in motion. From the results, the algorithm is validated, demonstrating its potential for real-world application.

Combining wavelet analysis of track irregularities and vehicle dynamics simulations to assess derailment risks

Guaranteeing operational safety is mandatory for railways worldwide. As track deteriorates, its geometry deviates from ideal conditions (e.g. perfectly aligned and levelled), which creates undesired vibration and oscillations to the vehicle, increasing dynamic loads and derailment risk. Although current standards establish nominal limits for the track geometry, such point-wise comparisons may overlook relevant track features that can lead to unsafe conditions. The proposed investigation is a contribution to the study of the response of the rail vehicle to the track quality, aimed at identifying track irregularities that produce high track forces and unsafe vehicle responses. To fulfil this aim, Wavelet Analysis is combined with Vehicle Dynamics Simulations to evaluate how the track irregularities, filtered in various wavelength ranges and reconstructed with different wavelets and coefficients' amplitudes, impact vehicle safety in terms of the Nadal safety criterion Y/Q. The simulations demonstrate that defects occurring in some scales/frequencies are more harmful than others, and the similarity between the geometric defects and the shape of the wavelets may be used to identify track locations that require maintenance. These findings suggest that it is possible to create ‘stamps’ of track irregularities that can be used by infrastructure managers to improve their maintenance strategies.

On-board measurement of aerodynamic loads for high-speed trains negotiating transitions in windbreak walls

The safety risk of a high-speed train due to the fluctuation of aerodynamic loads cannot be neglected, especially for transitions in the windbreak walls. In this study, the dynamic response of a high-speed train under cross winds is exploited to identify the aerodynamic loads. Firstly, the full-scale testing of a high-speed passenger train under cross winds is introduced to make insight into the wind-induced safety issues. Significant carbody lateral, roll and yaw motions can be observed in the secondary suspension and wheel-rail interface. Secondly, a new measurement approach of the aerodynamic loads is proposed based on the inertia and suspension loads. The comparison of identified aerodynamic loads shows good coincidence in the time history with that from the field testing. Then, a simplified aerodynamic load function with the damped sinusoid characteristic is applied to the vehicle dynamic simulations. The calculated derailment coefficient and wheel unloading ratio show good coincidence with that of the tested results. The parametric studies show that the overturning and derailment risks are of great relevance to the amplitude and frequency coefficients in the aerodynamic load waveform. Both the overturning and wheel climbing derailment risks are necessary to be evaluated for railway vehicles under transient aerodynamic loads.

A domino-like localized cascade toehold assembly amplification-based DNA nanowire for microRNA imaging in living cells.

High sensitivity and specificity imaging of miRNA in living cells plays an important role in understanding miRNA-related regulation and pathological research. Localized DNA circuits have shown good performance in reaction rate and sensitivity and have been proposed for sensitive imaging of miRNA in living cells. However, most reported localized DNA circuits have a high risk of derailment or a limited loading rate capacity, which hinder their further application. To solve these issues, we herein developed a domino-like localized cascade toehold assembly (LCTA) amplification-based DNA nanowire to achieve highly sensitive and highly specific imaging of miRNAs in living cells by using DNA nanowires as reactant delivery vehicles and confining both reactant probes in a compact space. The LCTA is constructed by interval hybridization of DNA double-stranded probe pairs to a DNA nanowire with multiplex footholds generated by alternating chain hybridization. Due to the localized effect, the LCTA showed high reaction kinetics and sensitivity, and the method could detect miRNAs as low as 51 pM. The LCTA was proven to be able to accurately distinguish the miRNA expression difference between normal cells and cancer cells. In particular, the developed LCTA could be used to construct an OR logic gate to simultaneously image the total amount of multiple miRNAs in living cells. We believe that the developed LCTA can be an effective intracellular nucleic acid imaging tool and can promote the development of nucleic acid-related clinical disease diagnosis and DNA logical sensors.

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.

Safety of a high-speed train passing by a windbreak breach under different wind speeds

A derailment phenomenon could take place on the windward side of a 120 km/h high-speed train when it runs by a breach, between two windbreak walls, subjected to a normal wind speed of 32 m/s. To study the safety of a high-speed train under different normal speeds of crosswind, six wind speeds are investigated; 32 m/s, 28 m/s, 25 m/s, 20 m/s, 15 m/s, and 10 m/s. The wind forces and moments of the moving train are calculated using the Unsteady Reynolds-averaged Navier-Stokes (URANS) model, which are then applied to the train multi-body dynamics. The pressure fields around the train passing by the breach are analysed, which gives a reasonable explanation for the fluctuation of the wind loads. After an analysis on the response of the train, it is apparent that the risk of derailment on the windward side is much greater than the risk of overturning. The lateral distance of the first wheelset increases towards the windward side as along with the yaw angle of the wheelset, which increases as well with wind speeds of higher than 20 m/s.

Influence of the railway vehicle properties in the running safety against crosswinds

The aim of the present study consists of evaluating the influence of the most relevant geometric, mechanical and aerodynamic vehicle properties in the risk of derailment caused by crosswinds. To achieve this objective, a vehicle-structure interaction model is used to carry out non-linear dynamic analyses to assess the train-track coupling behaviour in the presence of winds. By computing the wheel-rail contact forces, the derailment risk is evaluated based on the unloading criterion, as suggested by the European Norm EN 14067–6 (2016), for several scenarios with different train and wind speeds. The wind is simulated with a stochastic model that allows the generation of turbulent wind time-histories based on power spectral density functions. The reference vehicle adopted in this work corresponds to the European InterCity Express 3 (ICE-3) train, whose original properties were parameterized in order to evaluate their influence in the vehicle's stability. The parametric study focused on several properties of the vehicle, namely the carbody mass, height of the gravity centre, aerodynamic coefficients, and stiffness and damping of the suspensions. Apart from the suspensions' properties, which prove to have a negligible influence in the vehicle's stability, the remaining parameters have a significant impact in the running safety against crosswinds.

Analysis of the ‘dynamics of railway vehicles’ research field development using scientometric approach

The paper demonstrates the possibilities of a scientometric approach using CiteSpace II software analysis of the field of railway dynamics with detection of research front, main clusters of cross-cited papers, their evolution and pivotal points (see terms in Sections 2.1 and 2.2). The initial database contained 5126 Web Of Science records published between 1975 and 2019 (45 years). The linguistic analysis determined the evolution of burst terms and grouped the papers in 14 clusters that corresponded with the view of the specialists in the field. ‘Railway vehicle’, ‘Curved track’ (hunting stability and derailment risk), ‘Unconventional railway truck’, ‘Railway turnout (crossing)’ and ‘Polygonal wear’ clusters were analysed in more detail with a determination of top-cited papers in each cluster and papers that determined connections between clusters (pivotal papers). Two pivotal papers were verified with their authors.

Assessment of derailment risk in railway turnouts through quasi-static analysis and dynamic simulation

Train derailments in railway switches are becoming more and more common, which have caused serious casualties and economic losses. Most previous studies ignored the derailment mechanism when vehicles pass through the turnout. With this consideration, this work aims to research the 3D derailment coefficient limit and passing performance in turnouts through the quasi-static analysis and multi-body dynamic simulation. The proposed derailment criteria have considered the influence of creep force and wheelset yaw angle. Results show that there are two derailing stages in switch panel, which are climbing the switch rail and stock rail, respectively. The 3D derailment coefficient limit at the region of top width 5 mm to 20 mm is much lower than the main track rail, which shows that wheels are more likely to derail in this area. The curve radius before the switch rail is suggested to be set as 350 m. When the curve radius before turnout is 65 m, the length of the straight line between the curve and turnout needs to be larger than 3 m. This work can provide a good understanding of the derailment limit and give guidance to set safety criteria when vehicles pass through the turnout.

Application of a decision support tool for the risk management of a metro system

ABSTRACT Risk Management assumed over years a central role of safe management of metro railway operation. Since exposure of passengers to hazards cannot be avoided, risk cannot be cancelled but controlled and brought back to acceptable levels. The quantification of system risk level and of the effects of any decision on infrastructural or operational changes must be carefully evaluated. A methodology for in-depth risk analysis within a risk-based decision management is crucial not only to identify the risk, but especially to assess and manage it. This work introduces a complete Risk Management methodology which quantitatively analyses the causes and consequences, assessing all the influence factors of metro safety. Using as example the derailment risk level, an application to an operating metro is presented assessing the effects in terms of safety risk of three different management decisions and highlighting the impact that those choices have on safety.

Dynamic Railway Derailment Risk Analysis with Text-Data-Based Bayesian Network

In recent years, transportation system safety analysis has become increasingly challenging and highly demanding. Unstructured data contain sufficient information from which inherent interactions can be extracted. Determining how to process and fuse a large amount of unstructured data is a challenging task. In this paper, we propose a text-based Bayesian network (TBN) method to establish a Bayesian network (BN) based on text records, where the BN’s arcs are obtained from barrier relationships identified by a graphical model and its prior probabilities stem from fault trees. The comparative experimental results illustrate that the text-based method in TBN is efficient. The precision, recall and F-measure of TBN are 8.64%, 10.70% and 9.84% higher, respectively, than the most frequent (MF) result. Moreover, compared to the traditional BN, whose prior probabilities are frequently acquired from experts, the prior probabilities of the proposed text-based BN (TBN) have a high confidence. The experimental results of a train derailment accident case study show that with changes in the train derailment probabilities and the safety potentials of the barriers, the TBN generates quantitative results and reveals the critical risks of derailment accidents. Additionally, this work demonstrates relevant nonlinear relationships to improve the assessment results. Therefore, based on text-based data, this study reveals that barrier safety analysis has the potential to identify high-risk barriers, which can guide managers to enhance these barriers.

A GIS approach to the development of a segment-level derailment prediction model

Train related accidents, particularly derailments, can lead to severe consequences especially when they involve injuries or fatalities or when they involve hazardous materials that might result in environmental impacts. Whereas numerous road safety studies have suggested appropriate approaches to predicting vehicle-to-vehicle collisions, very few railway safety studies have considered predicting the number of derailments on rail tracks in North America. In addition, the existing few rail safety assessment and derailment prediction models have often been constrained by aggregated data limiting the safety assessments by, for example, failing to consider segment-level characteristics.This paper focused on the development of an integrated database for the development of a segment-level derailment prediction model for Canada’s rail network. The primary objective of this paper is to report how challenges in the data integration process were overcome and also to develop a network screening tool to identify segments with high derailment risk in Canada's rail network. Negative binomial regression and the Empirical Bayes technique were used to estimate the predicted number of derailments on Canada’s rail network at the segment level. A network screening process was then successfully applied to identify key segments of safety concern: the top ten segments of concern accounted for approximately 1% of the rail network allowing decision makers to focus their derailment mitigation efforts on a manageable part of Canada’s vast rail network. The data processing approach and analysis in this study have strong implications for advancing research on rail safety in North America.

Running safety evaluation of a 350 km/h high-speed freight train negotiating a curve based on the arbitrary Lagrangian-Eulerian method

To adapt to the rapid growth of the logistics market and further improve the competitiveness of railway transportation, the high-speed freight train with a design speed of 350 km/h is being developed in China. The safety of the train under great axle load of 17 t and dynamic load is unknown. This paper is aimed to study the running safety of the high-speed freight train coupled with various cargo loading conditions negotiating a sharp curve at high velocity. A numerical model integrated a fluid-structure coupled container model and the nonlinear high-speed freight train was set up by the software of LS-DYNA. The fluid-structure interaction model between the container and fluid cargo was established using the Arbitrary Lagrangian-Eulerian (ALE) method. Two influencing parameters, including the cargo state in the container and the fill level, were selected. The study results showed that the wheelset unloading ratio and overturning coefficient could be significantly affected by the liquid sloshing, while the influence of sloshing on the risk of derailment was slight. In general, increasing the cargo filling rate would contribute to vehicle operation safety. In conclusion, this study would provide theoretical help for the running safety of the newly designed high-speed freight train.

Identify severe track geometry defect combinations for maintenance planning

ABSTRACT Combined track defects (multiple types of track defects occurring in the same vicinity of a track section) pose greater challenges and risks for train operational safety. This study proposed a method to identify severe track defect combinations that pose greater risks for vehicle derailments. The method includes three main stages. The first stage uses literature review, industry survey, and Track Recording Car data analysis to determine track defect combinations that exist in reality and are of interest to the infrastructure managers. The second stage uses single vehicle simulations to further fine-tune the focus and select the more severe combinations. The third stage uses comprehensive simulations to determine the increases of derailment risks due to combined track defects. More than 5,000 simulations were conducted in this study using supercomputers. A tabular tool was developed to help infrastructure managers to adjust maintenance reactions when track defects are found in combinations.

Development of multilevel models for assessment of risk of train derailment

The paper presents a multilevel model for assessing risk of train derailment. The model is based on the toolkit of Bayesian nets and allows accounting for the influence of human and organizational factors as well as factors of safety regulation regimes on the occurrence of stochastic events that compile various scenarios of railroad accidents.

Dynamic analysis of railway vehicle derailment mechanism in train-to-train collision accidents

Train collision-induced derailment may result in serious casualties. This study investigates the railway vehicle derailment behaviour and explores the derailment causes in train-to-train impacts. A train-track coupled dynamic model is developed and validated. The lateral ( Yde) and vertical ( Zde) relative displacements of the wheel/rail pair are used for the derailment evaluation. The results show that the wheelset jumping derailment and the saw-tooth buckling mode may occur during the high-speed collisions. Derailment is mainly caused by car body yawing rotation and wheelset lateral and vertical displacements. Yawing and pitching motions of car body influence wheelset displacement significantly. Vehicles with the higher velocity generate more severe derailment behaviour. Under circumstance of the same train impact energy, the higher vehicle mass and greater car numbers have the stabilizing influence for reducing the derailment risk. Increasing the force on the main energy-absorbing structure which is set in the front-end crushing zone of a vehicle to dissipate the train impact energy and the damping coefficient of the secondary yaw damper can decrease the derailment risk. The train safety operation areas and derailment boundaries indicate that the reliability of the Yde criterion is higher.

Risk-informed sustainable asset management of railway tracks

Railway track infrastructure asset management is a challenging problem with added values on safety, society and environment. With railways serving as a key sustainable mode of transportation for passengers and freight, the industry is facing an increasing demand to expand its capacity, availability and speed, resulting in faster deterioration of the ageing railway track infrastructure. Given the constrained maintenance budgets and the environmental challenges posed by climate change, railway asset managers have to identify economically and environmentally justifiable track maintenance strategies without compromising on safety. To this end, this paper proposes a risk-informed approach to arrive at sustainable railway track maintenance strategies while considering the associated track maintenance costs and impacts on train operation (environmental emissions and risk of derailments). Monte Carlo simulation is employed to address data uncertainties associated with track quality data, the costs and benefits of track maintenance and train operation. The proposed approach is successfully applied to the heavy-haul railway lines in Sweden and Australia to compare some alternative maintenance strategies and identify the sustainable one.

Running safety evaluation of a train moving over a high-speed railway viaduct under different track conditions

This paper addresses the evaluation of the running safety of high–speed (HS) train moving over a continuous viaduct with different track conditions, ranging from very well-maintained to the worst condition possible according to the European recommendations, referred to as the safety limit. The case study focuses on the “La Scarpe” viaduct, which consists of a continuous nine-span steel–concrete composite bridge belonging to the French HS railway line TGV Nord, and on the German HS train ICE3 composed by eight independent cars. Firstly, the analysis is carried out considering the flexibility of the viaduct through train–bridge interaction (TBI) coupling system, where the running safety is analyzed according to Nadal, Prud'homme and Unload criteria. The results are then compared with those obtained using a rigid structure, which allowed to draw important conclusions regarding the effects of the viaduct’s vibrations. From the results it was possible to conclude that the criteria have shown a good agreement with the limits laid down in the European norms. In addition, it was also possible to assume that the viaduct flexibility did not influence the results with respect to the derailment risk. Thus, for this particular case study, the train running safety assessment could be carried out using a simpler rigid structure model, which considerably reduces the degrees of freedom and the problem complexity without losing accuracy.

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.