Operation Of Railway Systems Research Articles

Dynamic inspection of a rail profile under affine distortion based on the reweighted-scaling iterative closest point method

The precision and efficiency of rail inspection are of vital importance to the operation and safety of railway systems. However, because of vibrations that occur in the rail inspection vehicle and installation error of the line laser sensor, the collected rail profile is distorted. As a result, the accuracy and robustness of conventional registration and inspection methods cannot be guaranteed. In this paper, an accurate and robust calibration method for measuring rail profile distortion is proposed. In this study, the impact of vibration on the rail profile, which was obtained with a laser sensor, was analyzed. Then, the collected rail profile was divided into two segments according to the actual condition where only the upper part of the rail was subjected to wear. An accurate and robust reweighted-scaling iterative closest point algorithm was proposed to calibrate the distorted rail profile, and the upper and lower boundaries of the scale ratio were used as constraints to solve the registration problem effectively and efficiently. Finally, the Hausdorff distance method was introduced to clearly visualize the rectified rail profile and wear. The experimental results demonstrated that the proposed method can realize the affine transformation of the distorted rail profile with a high precision and robustness. Additionally, it can achieve an online dynamic calibration and inspection of the rail by comparing the data with the conventional iterative closest point, scaling iterative closest point, and Calipri.

Analysis of configuration data errors in Communication-based Train Control systems

Communication-based Train Control (CBTC) systems combining intelligent instruments and wireless communications are increasingly used in modern metros and other railway systems, because they can help optimizing railway traffic management and minimizing headways between running trains. Despite the potential benefits, CBTC systems functionality and availability can be affected by their configuration data errors, induced by human errors, instruments physical degradations and cyber communication interventions. In this paper, we identify and classify configuration data errors in CBTC systems, and propose a Monte Carlo (MC) simulation-based exploration approach, with safety margins estimation, for the primary purpose of verifying and assessing the data error effects on system functionality. The approach is illustrated with reference to a CBTC model prototyped from a Beijing Mass Transit Railway (MTR) operation system. Potentially risk-significant data errors of random magnitudes and running positions are injected by a Monte Carlo-driven engine and the system functional response is assessed.

Quantification of ground-vibrations generated by high speed trains in ballasted railway tracks

Abstract Ground vibration generated by high speed trains is one of the major challenges in the operation of high speed railway systems. The transit of high speed trains proximate to vibration sensitive structures pose a risk to the structural health of the buildings, especially when the ground vibrations reaching the structure get amplified through the height of the structure at resonant frequencies. A precise quantification of the peak particle velocities (PPVs) is required for analysis of ground vibrations propagating away from the railway track, which also aids in the implementation of suitable vibration mitigation measures if the vibration levels surpass the vibration safety criteria for various classes of buildings. This study investigates the ground vibrations generated by a high speed train wheel in the component strata of a railway embankment during transit at the speed of 200 km/h. Transient numerical analyses were conducted in full scale 3-D railway track models, developed with the geometric cross-sections specified by RDSO, Ministry of Railways in India, for operation of trains in the broad gauge railway track sections. The quantification of vibration velocities were performed in the vertical, longitudinal and lateral axes, and the resultant peak particle velocities were estimated for various strata in the railway embankment and supporting ground. The ground vibrations were found to be oriented mainly in the vertical direction, and the highest vibrations were recorded at the locations when the wheel load was located vertically on top of the section. It was observed that PPVs attenuate with increase in depth from the track level, and with increase in lateral distance from track centreline. High magnitudes of vibration were estimated in the railway embankment and ground when the effect of multiple train wheels superpose. The results also highlight that the horizontal components of ground vibration are significant at farther distances away from the track, implying that foundations of buildings proximate to railway tracks are subject to strong excitations in the horizontal direction.

A Link Stability Based Adaptive Clustering Routing Algorithm for HAP-Based Vehicle Ad Hoc Networks

In order to build a railway operation system capable of large-scale monitoring and comprehensive decision-making support, the HAP-based VANET is proposed. The traditional networking and routing mechanism can't be applied directly to the integrated network. This paper proposed a link stability based adaptive clustering routing algorithm (LSACR), which performs well in case of end-to-end delay and packet loss rate when the speed of nodes goes up.

Analyzing uncertainties in model response using the point estimate method: Applications from railway asset management

Predicting current and future states of rail infrastructure based on existing data and measurements is essential for optimal maintenance and operation of railway systems. Mathematical models are helpful tools for detecting failures and extrapolating current states into the future. This, however, inherently gives rise to uncertainties in the model response that must be analyzed carefully to avoid misleading results and conclusions. Commonly, Monte Carlo simulations are used for such analyses which often require a large number of sample points to be evaluated for convergence. Moreover, even if quite close to the exact distributions, the Monte Carlo approach necessarily provides approximate results only. In contrast to that, the present contribution reviews an alternative way of computing important statistical quantities of the model response. The so-called point estimate method, which can be shown to be exact under certain constraints, usually (i.e. depending on the number of input variables) works with only a few specific sample points. Thus, the point estimate method helps to reduce the computational load for model evaluation considerably in the case of complex models or large-scale applications. To demonstrate the point estimate method, five academic but typical examples of railway asset management are analyzed in more detail: (a) track degradation, (b) reliability analysis of composite systems, (c) terminal reliability in rail networks, (d) failure detection/identification using decision trees, and (e) track condition modeling incorporating maintenance. Advantages as well as limitations of the point estimate method in comparison with common Monte Carlo simulations are discussed.

Protection of 25 kV electrified railway system

Improving the reliability of an electrified railway operation system requires protection against overvoltage, particularly those of atmospheric origin. The most serious threat to the traction system is lightning when it strikes the mast or conductors. The ZnO arresters are used to protect a system from this phenomenon. In the present investigation the system under study is developed and each element is represented by a model corresponding in EMTP program and some elements are modelled using the models section in ATP EMTP. Protective effect of the surge arrester and discharge current which passes through it is analysed and discussed in case lightning strikes a mast. The simulation results have shown that the surge arrester reduces overvoltage in primary power transformer traction below the basic insulation level, under critical conditions.

Reliability of FTA general vibration assessment model in prediction of subway induced ground borne vibrations

One of the main factors in the design of subways is the level of subway-induced vibrations. The ground borne vibrations are usually estimated by prediction models among which the FTA (Federal Transportation Association) general vibration assessment model is the most popular one. Although FTA approach/model is vastly used in the design and operation of underground railway systems, its reliability has not been sufficiently evaluated in the available literatures. This is addressed in this research. For this purpose, a comprehensive experimental investigation (both in the time and frequency domains) was conducted in three newly constructed subway lines in the Iranian underground railway (subway) network. The track and soil characteristics as well as ground borne vibrations were measured. The reliability and accuracy of the FTA model was assessed through comparisons of the experimental results obtained here with the FTA predictions. Contrary to the current belief, considerable underestimations of subway ground borne vibrations in the FTA model predictions were shown in this research. The results obtained indicate up to 20 dB differences between the experimental results and those of FTA predictions. Based on the field measurements obtained here and the theoretical background, the FTA model was improved/optimized, leading to increase the reliability of FTA model predictions in subway systems.

Computer vision–based automatic rod-insulator defect detection in high-speed railway catenary system

Maintenance of catenary system is a crucial task for the safe operation of high-speed railway systems. Catenary system malfunction could interrupt railway service and threaten public safety. This article presents a computer vision algorithm that is developed to automatically detect the defective rod-insulators in a catenary system to ensure reliable power transmission. Two key challenges in building such a robust inspection system are addressed in this work, the detection of the insulators in the catenary image and the detection of possible defects. A two-step insulator detection method is implemented to detect insulators with different inclination angles in the image. The sub-images containing cantilevers and rods are first extracted from the catenary image. Then, the insulators are detected in the sub-image using deformable part models. A local intensity period estimation algorithm is designed specifically for insulator defect detection. Experimental results show that the proposed method is able to automatically and reliably detect insulator defects including the breakage of the ceramic discs and the foreign objects clamped between two ceramic discs. The performance of this visual inspection method meets the strict requirements for catenary system maintenance.

Imitation forecast of railway system operation in a macroregion

Imitation forecast of railway system operation in a macroregion

Optimal Operation of Electric Railways With Renewable Energy and Electric Storage Systems

This paper proposes a methodology for optimal operation of railway electric energy systems considering renewable energy sources (PV panels and wind turbines), regenerative braking capabilities and hybrid electric energy storage systems (ultracapacitors and batteries). The uncertainties associated to renewable energies are taken into account through a scenario tree approach. All these elements are integrated into a multi-period AC optimal power flow problem. This problem is then cast as a large-scale nonlinear optimization problem. The aim is to study the potential for energy and economic savings of the railway operation as well as energy storage systems behavior. A real case study is analyzed for a Spanish high-speed railway line. Results are reported for several cases comparing four different operation modes.

Inductive influence of 25 kV, 50 Hz electrified single rail traction system

The paper presents the methodology for calculation and measurement of induced voltage caused by railway system operation on the sensitive metallic structures. The arrangement and characteristics of railway system 25 kV, 50 Hz are provided. The procedures of short-circuit current calculation and supply current measurement in the railway system are described. The basic theoretic background of inductive interference is explained. The reduction factors of the communication cable, railway system and environment are mentioned and clarified. On a case study, the results of the induced voltage calculation and measurement is compared. It is proved that induced voltage directly depends of supply current or shortcircuit value.

Comparative analysis of experimental and calculation methods for determination of the traction current harmonics distribution in rails

The purpose of this work is to perform the comparative analysis of experimental and calculation methods for determination of the distribution of traction current harmonics in rails. To investigate the distribution of traction current in the rails, the special marks (flags) were set up at a certain distance (100, 300 and 500 m) from the point of measurement along the track. The moments of passing the train past the flags were recorded in a computer due to a sound signal from the train, as well as visual observation. The train was moving in the measuring section in a quasi-stationary mode with an average speed of about 48 km/h. Traction current was measured in circuit of the inter-throttle jumper with using an inductive contactless sensor and registered using computer.The distribution of the return traction current harmonics in rails for AC feeding systems were modeled by using the multi-conductor transmission line (MTL) model.Some discrepancies in the results of experimental and calculation methods were observed. One of main reason of measurement errors were an inaccuracy in determining distances from the train to the measurement point. Calculation errors were related mainly with using inaccurate electrical parameters of track in model, in particular, the track ballast resistance and the ground resistances.However, in general, the considered model can be used for investigation of the traction current harmonic propagation in rails from train, and their influence on the track circuits receivers for different cases including the variation of the track circuits electrical parameters, as well as the number of rolling stock units in the feeder zone. Such analysis of harmonic in rails is important for revealing the causes of failures in railway signalling system operation under simultaneous affecting on it several factors adverse to safe operation.

Self-powered triboelectric nano vibration accelerometer based wireless sensor system for railway state health monitoring

Vibration exists everywhere especially in the public railway operation system. The vibration acceleration is the key factor to monitor and evaluate the structure health of the railway equipment. In this paper, a kind of self-powered triboelectric nano vibration accelerometer (TEVA) is presented. A low frequency spring mass vibration model is built to calculate the vibration sensitive performance and the electric output of the TEVA. The prototype of the TEVA is demonstrated and characterized through the railway vibration simulation platform. It has been testified that TEVA can successfully harvest the low frequency vibration energy and convert it to electrical power to achieve the self-powered vibration acceleration monitoring system. The output current and voltage of TEVA are also sensitive to the vibration acceleration from 1.07m/s2 to 1.25m/s2 linearly. Hence it can be used as a self-powered nano vibration accelerator for the fault diagnosis. In addition, the generated electricity is used for charging the lithium battery (from 1.5V to 3.1V) which supplies power to the ZigBee module. The experiment shows that the charged battery through TEVA can support the wireless communication between ZigBee modules, with temperature and humidity sensors embedded on it. The temperature and humidity on the train are 22°C and 35%RH respectively. Therefore, the vibration energy can be harvested and stored for the power supply of wireless sensor network nodes in the near future.

Maximum Safety Regenerative Power Tracking for DC Traction Power Systems

Direct current (DC) traction power systems are widely used in metro transport systems, with running rails usually being used as return conductors. When traction current flows through the running rails, a potential voltage known as “rail potential” is generated between the rails and ground. Currently, abnormal rises of rail potential exist in many railway lines during the operation of railway systems. Excessively high rail potentials pose a threat to human life and to devices connected to the rails. In this paper, the effect of regenerative power distribution on rail potential is analyzed. Maximum safety regenerative power tracking is proposed for the control of maximum absolute rail potential and energy consumption during the operation of DC traction power systems. The dwell time of multiple trains at each station and the trigger voltage of the regenerative energy absorbing device (READ) are optimized based on an improved particle swarm optimization (PSO) algorithm to manage the distribution of regenerative power. In this way, the maximum absolute rail potential and energy consumption of DC traction power systems can be reduced. The operation data of Guangzhou Metro Line 2 are used in the simulations, and the results show that the scheme can reduce the maximum absolute rail potential and energy consumption effectively and guarantee the safety in energy saving of DC traction power systems.

STRUCTURAL ANALYSIS OF RAILWAYS BOLSTER-BEAM UNDER COMMERCIAL OPERATION CONDITIONS: OVER-TRACTION ANDOVER-BRAKING

The conditions for the operation of railway systems are closely related to the increase of the commercial demand; as a consequence, the performance of the structural elements of railways changes. The present paper focuses on a study of the structural behaviour of bolster-beams under commercial operation conditions of railway systems, specifically in the dynamic conditions generated in events of over-traction and over-braking on the vehicle running. The proposed work is constructed based on the following phases: (i) analysis of the kinematics of the vehicle; (ii) development of numerical models, a model based on the multibody theory, and a Finite Elements model; (iii) development of experimental field tests; and (iv) development of simulations for a detailed analysis of the structural behaviour for a study of the strain distribution in the main bolster-beam. This study is applied to a particular case of a railway system that provides commercial service to passengers.

LSTM-Based Temperature Prediction for Hot-Axles of Locomotives

The reliability of locomotives plays a central role for the smooth operation of railway systems. Hot-axle failures are one of the most commonly found problems leading to locomotive accidents. Since the operating status of the locomotive axle bearings can be distinctly reflected by the axle temperatures, online temperature monitoring has become an essential way to detect hot-axle failures. In this work, we explore the feasibility of predict the hot-axle failures by identifying the temperature from predicted nominal values. We propose a data-driven approach based on the Long Short-Term Memory (LSTM) network to predict the sensor temperature for axle bearings. The effectiveness of the prediction model was validated with operation data collected from commercial locomotives. With a prediction accuracy is within a few percent, the proposed techniques can be used as a dynamic reference for hot-axle monitoring.

Capacity analysis of railway lines in Germany – A rigorous discussion of the queueing based approach

The operation of railway systems requires detailed information on infrastructure capacity. A major challenge, especially in long-term planning, is assessing the quality of operations given very limited information on schedules is available. To this end, analytical models based on a stochastic description of railway systems have found widespread application. We discuss a model for the capacity analysis of railway lines relying on single channel queueing systems. By identifying knock-on delays with waiting times delays can be estimated using methods from stochastics and queueing theory. Mean knock-on delays are used as a quality-dependent indicator of capacity allowing to determine the admissible number of trains for a prescribed level of service.Though being widely used in Germany the model has not been made fully available to the research community. In this paper two main contributions are made: A new, mathematically rigorous derivation of the pivotal “Strele Formula” for the estimation of knock-on delays, which is based on the convolution of delay distribution functions, is provided. Unlike existing discussions our approach is valid for general independent buffer times. Additionally, we critically review the model assumptions and investigate the “triangular gap problem”, an overestimation of capacity resulting from the model’s limitation to pairwise correlations.

Rolling contact fatigue cracking in rails subjected to in‐service loading

AbstractRolling contact fatigue (RCF) is one of the most important failure mechanisms in rails with significant cost‐ and safety‐related implications on the operation of railway systems. In this work, a metallurgical analysis of RCF crack initiation and propagation, including geometrical characteristics of RCF cracks – length, depth from surface, angle of propagation and spacing between cracks, is presented. The role of proeutectoid ferrite in crack initiation has been studied. Analysis of the fracture surface of an RCF crack revealed a ductile initiation zone followed by a quasi‐cleavage crack propagation. Iron oxide formed in the interior of all cracks in rails exposed to stagnant water with implications to crack propagation rate because of crack closure effects. Sequential sectioning parallel to the rolling surface revealed that RCF cracks possess convoluted surfaces. The crack trace expands with depth from the rolling surface. Subsurface crack initiation has also been documented.

Operation analysis of AC traction motors in terms of electromagnetic torque capability on sustainable railway vehicles

Sustainable operation of electric railway systems represents a significant purpose nowadays in the development of high power and high speed locomotives and trains. At present, high speed electric vehicles mostly work with three-phase induction motors or three-phase synchronous motors as traction motors. The two electric machine types have different efficiencies at different operation points, and experience differences with respect to safety, speed and power, energy use and exergy efficiency. An important issue that correlates these aspects is the electromagnetic torque developed by an electric traction motor. In order to provide an overview of the technical performance of the operation of sustainable railway systems, a detailed analysis is carried out of the electromagnetic torque capability of AC electric motors utilized as traction motors in modern locomotives of high power and/or high speed. The results of this work may help in enhancing the main criteria for optimising the safe and sustainable operation of electric railway traction systems.

A Holistic Approach for Estimating Carbon Emissions of Road and Rail Transport Systems

ABSTRACTEnvironmental issues have become of crucial importance in the transport sector. Transport is the second biggest greenhouse gas emitting sector after energy and is responsible for 25% of the EU's total emissions. The challenges posed by climate change have added to the urgency for developing low-carbon transportation. In this paper, estimation of greenhouse gas emissions was conducted over the construction and the operation of the main road and rail axes infrastructure in Greece. The objective of this analysis is to better understand the significance of these emissions and their possible influence on designing optimal routes in order to achieve long-term greenhouse gas reductions from transport. The present study shows that the environmental impact due to the highway construction is smaller than that of the railway construction. However, the railway system operation is more environmentally friendly than the highway operation.