Korean High Speed Train Research Articles

Unsupervised anomaly detection for earthquake detection on Korea high-speed trains using autoencoder-based deep learning models

We propose a method for detecting earthquakes for high-speed trains based on unsupervised anomaly-detection techniques. In particular, we utilized autoencoder-based deep learning models for unsupervised learning using only normal training vibration data. Datasets were generated from South Korean high-speed train data, and seismic data were measured using seismometers nationwide. The proposed method is compared with the conventional Short Time Average over Long Time Average (STA/LTA) model, considering earthquake detection capabilities, focusing on a Peak Ground Acceleration (PGA) threshold of 0.07, a criterion for track derailment. The results show that the proposed model exhibit improved earthquake detection capabilities than STA/LTA for PGA of 0.07 or higher. Furthermore, the proposed model reduced false earthquake detections under normal operating conditions and accurately identified normal states. In contrast, the STA/LTA method demonstrated a high rate of false earthquake detection under normal operating conditions, underscoring its propensity for inaccurate detection in many instances. The proposed approach shows promising performance even in situations with limited seismic data and offers a viable solution for earthquake detection in regions with relatively few seismic events.

Analysis for AC Loss by Electromagnetic Disturbance in HTS Magnet for Maglev Train

Research on Hyper Tube, a Korean high-speed HTS Maglev train, has reached the verification stage for actual operation, and electromagnetic dynamic characteristics analysis of the train is required accordingly. Depending on the winding type of the propulsion armature, the HTS magnet experiences the harmonic that causes AC loss. Beside the static thermal losses by thermal conduction, current leads et al., the AC loss should be take account for the thermal battery design depending on operation conditions. This study describes the AC loss analysis of the HTS magnet induced by the harmonic using the homogeneous <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T-A</i> formulation widely used in recent. In consideration of acceleration and cruise conditions, the effect of the AC loss by harmonics on the capacity of the solid nitrogen thermal battery was discussed.

Characteristics of the air flow underneath high-speed trains running on the ballast track

The air flow underneath high-speed trains have been measured at full-scale for three types of high-speed trains running on two types of ballasted tracks, and the characteristics of the flow have been investigated and comparatively analyzed related to the train and track types. 6 Kiel probe rakes vertically distributed in 40 mm interval from just above the track surface have been employed to measure the temporal histories of wind velocity during the passage of train. The results show that the flow under test trains reached fully-developed state before the end of the second vehicle and maintains until the start of the last vehicle, and average velocities over the fully-developed region show very good consistency for no more than 3 repeated samples. The vertical profile of average velocity over the fully-developed region has been suggested as a useful model to represent the characteristics of the flow underneath high-speed trains, and equivalent roughness of the test trains and tracks have been obtained by introducing the analytical solution of the turbulent Couette flow. The resulting values of equivalent roughness of Korean high-speed trains ranged from 50 mm to 150 mm, and that of the ballast track was 150 mm.

Investigation of low damped carbody oscillation for Korean high-speed EMU experimental train

This study describes the low damped carbody oscillations of the HEMU-430X, a high-speed electric-multiple-unit experimental train of Korea. The HEMU-430X had already undergone a kind of hunting problem in the test period, but it was effectively suppressed through several measures and the test was finished successfully. However, recently, the HEMU-430X again experienced the similar but slightly different problem after its wheel profile was changed to XP55, which is widely used in high-speed trains in Korea. In this paper, the eigenbehavior and system damping ratio are analyzed using a linearized vehicle model to more systematically investigate the cause of the carbody oscillation of the HEMU-430X. The results show that the bogie lateral movement coupled with carbody upper sway has the least damping ratio in the case of the HEMU-430X and the magnitude of yaw directional constraints of the bogie plays an important role in causing the carbody oscillation. Parametric studies for suspension, equivalent conicity and creep coefficients are carried out. A solution is suggested and it is validated using field tests.

Prediction of Theoretical Derailments Caused by Cross-Winds with Frequency

In this paper, theoretical derailment equations for cross-wind with frequency were derived to assess running safety. For a KTX (Korean high-speed train) unit, the wheel unloading ratios, which are the criteria for evaluating derailments in UIC (International union of railways) and TSI (Technical Specification for Interoperability) regulations, were calculated through the formula under the driving regulations according to cross-wind speeds, and the theoretical results were compared and evaluated through a multibody dynamics (MBD) simulation. In addition, the wheel unloading ratios were calculated for various frequencies of cross-winds. As a result of the formula and MBD, the wheel unloading ratios were shown to increase rapidly regardless of the dampers in suspension when the cross-wind frequency and the natural frequency of a vehicle were in agreement. Finally, we calculated the changes of wheel unloading ratio for different track gauges and found that these theoretical equations could calculate more accurate results than the existing Kunieda’s formula. The formula derived in this study has the advantage of considering various variables, such as fluctuant cross-winds, rail irregularities, and derailment behaviors, which were not considered in previous studies or Kunieda’s formula. It could be used for setting suspensions or railway vehicle specifications in the initial design stage.

Modelling and analysis of the dynamic response of a railway viaduct using an accurate and efficient algorithm

This article describes the simulation of the Korean high-speed train passing over a single-track viaduct and the influence of track isolated defects on the dynamic behaviour of the system. The model of the viaduct is validated and calibrated using a finite element model updating technique, and a three-dimensional (3D) model is used to account for the local deformations of the slab accurately. The direct method, an efficient vehicle-structure interaction algorithm previously developed by the authors, is used to solve the dynamic problem. It proved to be significantly more efficient than the widely used finite element software ANSYS® when solving large and complex problems. The computational time has been reduced by more than ten times. The results obtained show that the shape of the isolated defects and the local deformations of the slab strongly influence the dynamic behaviour of the system. Neither is taken into account in the current standards, and hence further research is necessary.

Realization and Demonstration of Enhanced Korean High-speed Train Navigation System with Noise Filtering Schemes

A precise train navigation system for Korean high-speed trains having a maximum speed of 400km/h or higher was developed in 2015. The navigation system employs multi-sensor fusion technique, and until now, the target performance of 1-meter instantaneous positioning accuracy in all environments including the Global Positioning System (GPS)-denied environments such as tunnels has been demonstrated using only simulations for various scenarios. In this paper, we demonstrate that the train navigation system achieves the target positioning accuracy in real train environments, which is the first train navigation system that the performance of sub-meter accuracy is demonstrated with real data in the literature. We also introduce additional filtering schemes applied to the various sensors of the train navigation system to enhance the sensor data corrupted by large unexpected noises often observed in the train environments. The train navigation system is properly modified for real train environments to employ the filtering schemes.

A study on the resistance force and the aerodynamic drag of Korean high-speed trains

ABSTRACTThe resistance force as well as the aerodynamic drag of Korean high-speed trains including two commercial trains, the KTX and the KTX-Sancheon (KTX-II) and two experimental trains, the HSR-350X and the HEMU-430X have been studied comprehensively. To deduce the aerodynamic drag of the trains, the coefficients of the Davis equation, which is a universal formulation to represent the resistance to motion of the train, have been calculated using the coasting test method and analysed in comparison with those by empirical prediction methods. In case of HEMU-430X train, the equations of resistance to motion have been calculated by an alternative regression method that is established in this study. The results show that the suggested method can successively yield the resistance to motion equation from the coasting test measurements with varying air density by separating the aerodynamic drag from the total resistance of train. It also prevents from improper coefficients which are occasionally taken by normal regression method in irregular coasting condition. After yielding the aerodynamic drag of the trains from the resistance to motion equations, characteristics of the aerodynamic drag have been analysed and compared between the trains.

A study on the Dynamic Behavior Enhancement of the Korean High-speed Train

A study on the Dynamic Behavior Enhancement of the Korean High-speed Train

Critical speed enhancement of a Korean high-speed train through optimization with measured wheel profiles

This study describes the critical speed enhancement of the KTX-Sancheon, a Korean high-speed train, using measured wheel profiles. The wheel wear shape of the commercial high-speed train was measured according to mileage, and the relationship between conicity and mileage was investigated. The critical speed of the KTX-Sancheon power car was analyzed numerically with the measured wheel profiles. The suspension parameters were optimized to increase the critical speed of the KTX-Sancheon. As a result, the critical speed of the power car increased by 34.1% compared to its initial condition. The results are being used for a new design of the power bogie.

Investigation on aerodynamic drag of Korean high speed train (HEMU-430X) due to roof apparatus for electrical device

To explore the need for a roof apparatus for an electrical device, such as a pantograph cover or additional cover, the total aerodynamic drag of HEMU-430X, which is a high-speed train developed in South Korea with a maximum speed of more than 400 km/h, was experimentally analyzed using wind-tunnel testing. Experimental models were selected to a 1/20-scale, 5-car HEMU-430X model and three types of pantograph covers (A streamlined type and two wedge types), along with an additional cover. The experimental Reynolds numbers were 370000–620000. The aerodynamic drag of each car was simultaneously measured using load cells. First, the aerodynamic drag of each car without any roof apparatus was analyzed as the baseline model. Second, according to the variations in the three types of pantograph cover configurations, the aerodynamic drag of each car with pantograph covers was compared with the aerodynamic drag of the basic model. Third, the aerodynamic drag of each car with a pantograph cover and additional cover was compared with the results of the baseline model and baseline model with the pantograph cover. Finally, the aerodynamic drag due to the roof apparatus for an electrical device was investigated and analyzed.

Analysis of Aerodynamic Noise at Inter-coach Space of High Speed Trains

A numerical analysis method for predicting aerodynamic noise at inter-coach space of high-speed trains, validated by wind-tunnel experiments for limited speed range, is proposed. The wind-tunnel testing measurements of the train aerodynamic sound pressure level for the new generation Korean high-speed train have suggested that the inter-coach space aerodynamic noise varies approximately to the 7.7th power of the train speed. The observed high sensitivity serves as a motivation for the present investigation on elucidating the characteristics of noise emission at inter-coach space. As train speed increases, the effect of turbulent flows and vortex shedding is amplified, with concomitant increase in the aerodynamic noise. The turbulent flow field analysis demonstrates that vortex formation indeed causes generation of aerodynamic sound. For validation, numerical simulation and wind tunnel measurements are performed under identical conditions. The results show close correlation between the numerically derived and measured values, and with some adjustment, the results are found to be in good agreement. Thus validated, the numerical analysis procedure is applied to predict the aerodynamic noise level at inter-coach space. As the train gains speed, numerical simulation predicts increase in the overall aerodynamic sound emission level accompanied by an upward shift in the main frequency components of the sound. A contour mapping of the aerodynamic sound for the region enclosing the inter-coach space is presented.

기존선을 통과하는 고속차량의 적절한 주행속도에 관한 연구

KTX (Korea Train eXpress) is the first high-speed train operated in Korea and its highest speed reaches 300 km/h. Korean high-speed trains are mostly operated on the railroads exclusively designed for high-speed trains, but the sections of Seoul~Gwangmyeong, nearby of Daejeon station and Dongdaegu are operated on the existing tracks having the speed less than 150 km/h. With this paper, we’d like to analyze the lateral force that occurs between the wheels and the rail when high-speed trains were operated on the existing track section to suggest an appropriate driving speed for high-speed trains. As the rigid wheel base of the high-speed train is 3m which is about 50% longer than normal vehicles, it works as an advantage for high-speed driving. However, as the lateral force becomes higher than normal vehicles when driving on curves, plans to reduce wear-outs on the wheels are required.

Experimental studies on the aerodynamic characteristics of a pantograph suitable for a high-speed train

The aerodynamic properties of a pantograph that is under consideration for application on Korean high-speed trains are experimentally investigated. The selected experimental models were one-quarter scale pantographs (a double-arm pantograph, single-arm pantograph and a periscope pantograph) with either a rectangular panhead or a panhead with an optimized streamlined shape. To increase the performance and the robustness of the pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack are simultaneously minimized. In order to confirm the aerodynamic enhancement of the pantograph due to the optimized panhead, the aerodynamic forces are compared with those of a pantograph with a rectangular panhead. To investigate the aerodynamic force distribution of a pantograph, the aerodynamic forces of the lift and drag of the pantograph are measured in wind tunnel tests and analyzed in terms of the pantograph’s components. In addition, wake flows are examined based on variations of the shape of the panhead.

장대레일 좌굴 신뢰도에 기반한 국내 고속열차 운행속도 제한의 신뢰도 평가

혹서기에 궤도 좌굴을 방지하고 열차의 주행 안정성을 확보하기 위하여 국내 고속열차 구간에서는 2004년부터 고속철도 안전관리를 위해 레일온도에 따른 혹서기 열차 운행속도 제한을 시행하고 있다. 그러나 이에 대한 개념적, 이론적 배경이 불명확하다. 본 논문에서는 기존 본 연구진에 의해 개발된 장대레일 좌굴확률 평가프로그램에서 허용온도 계산 시 상한 및 하한좌굴온도를 고려하도록 개선하였으며, 국외 연구의 이론적 배경과 국내 선로조건이 고려된 좌굴확률을 근거로 국내 고속열차 운행속도 제한의 타당성과 신뢰성을 고찰하였다. In order to prevent the track buckling in the hot summer and ensure the safety of the running train, as a part of the safety control plan for high-speed railway, the train speed restriction according to the rail temperature was introduced in 2004. However, the conceptual and theoretical background of train-speed restriction is unclear. In this paper, the buckling probability evaluation program( ProCWR) developed by this researchers was improved to take maximum and minimum buckling temperature into account for the calculation of allowable temperature. From the theoretical background of the international research and the buckling probability considering domestic railroad conditions, the validity and reliability of Korean high-speed train speed reduction scheme were investigated.

고속철도차량 감속구동장치 진동특성 분석

The gear-reduction units of Korean high-speed trains consist of a motor reduction unit, an axle gear box reduction unit, and a tripod joint shaft. A reduction gear unit is a gearbox used to reduce the rotational speed of the input shaft to a slower rotational speed on the output shaft. This reduction in output speed helps to increase torque. Defective reduction gear units in high-speed trains are caused by damage to the gear or by gear fatigue. To diagnose potential problems, it is important to know the vibration characteristics of the reduction gear units. In this study, we analyzed the vibration characteristics of reduction gears under various conditions. The test setup included a full-scale test rig to evaluate reduction gear under both normal and extreme operating conditions.

차륜-레일 구름접촉을 적용한 철도차량 유한요소 모델의 충돌 기인 탈선거동 해석

In this paper, a finite element analysis technique of rolling stock models for collision-induced derailments was suggested using rolling contacts for wheel-rail interaction. The collision-induced derailments of rolling stock can be categorized into two patterns of wheel-climb and wheel-lift according to the friction direction between wheel flange and rail. The wheel-climb derailment types are classified as Climb-up, Climb/roll-over and Roll-over-C types, and the wheel-lift derailment types as Slip-up, Slip/roll-over and Roll-over-L types. To verify the rolling contact simulations for wheel-rail interaction, dynamic simulations of a single wheelset using Recurdyn of Functionbay and Ls-Dyna of LSTC were performed and compared for the 6-typical derailments. The collision-induced derailment simulation of the finite element model of KHST (Korean High Speed Train) was conducted and verified using the theoretical predictions of a simplified wheel-set model proposed for each derailment type.

방향틀림이 KTX 주행거동에 미치는 영향 분석

궤도틀림은 철도차량의 주행안전성 및 승차감에 매우 큰 영향을 미치는 중요 인자 중 하나이다. 따라서, 차량의 주행안전성과 승차감의 확보를 위해서는 주행속도, 차량의 동적특성, 궤도틀림 검측차의 검측특성, 검측주기등을 고려하여 적정한 궤도틀림 기준을 설정하고, 관련 기준에 따라 궤도틀림을 철저히 관리하여야 한다. 본 논문에서는 궤도틀림 중에서 방향틀림이 KTX 차량의 거동에 미치는 영향을 조사하기 위하여 철도차량 동특성 해석프로그램인 VAMPIRE를 이용하여 방향틀림의 파장과 진폭에 대한 매개변수해석을 수행하였다. 방향틀림 크기와 파장에 따른 KTX의 탈선계수, 대차가속도, 차체가속도 및 궤도횡압 등의 주행거동을 조사하였으며, 방향틀림이 KTX차량의 주행안전성과 승차감에 미치는 영향을 분석하였다. 방향틀림은 차량주행안전성에 미치는 영향이 크며, KTX 주행안전성 확보를 위하여 방향틀림을 엄격하게 관리하여야 함을 알 수 있었다. Track irregularities is one of the key factors influencing the running behavior of trains. In order to ensure safety and ride comfort of train, the criteria for track irregularities should be adequately established regarding vehicle velocity, vehicle characteristics, characteristics of the track recording car, and measurement interval. Also, track maintenance should be carried out thoroughly according to the criteria for managing track irregularities. Numerical analysis was conducted to investigate the influence of track alignment on the running behavior of Korean high speed train(KTX). Various wavelengths and amplitudes of lateral alignment were considered as parameters for this study using the Vampire program, a vehicle dynamics modeling package in railway environment. Derailment, lateral load, bogie acceleration and body acceleration of numerical analysis results due to alignment were investigated. Finally, the influence of the alignment on safety and ride comfort for the KTX was evaluated. This study indicates that alignment irregularities have significant impacts on running safety, and that the criteria used to manage alignment irregularities should be restrictive to ensure the running safety of the KTX.

고속철도차량 감속구동장치의 이상진단을 위한 진동특성분석

The reduction unit is one of the most important components for railway vehicles because the torque of the motor must be transmitted to the wheels of the vehicle by the reduction unit. The faults in the reduction units of high-speed trains are caused by damage such as gear, fatigue. These have serious impacts on safety of the train during operation. To address this development of a system for monitoring, fault diagnosis of the reduction unit is needed to keep the vehicle running safely. Before that can be accomplished, it is most important to understand the vibration characteristics of the reduction unit in a normal state. Vibration diagnosis technology using characteristic-analysis of vibration waveform and frequency is known to be the most effective method for fault diagnosis. In this paper, we analyzed the vibration characteristics of the reduction units two Korean high-speed trains (KTX and KTX II), under normal conditions, by two test methods (driving gear test, full-vehicle test).

Investigation of noise sources in high-speed trains

In this paper, the quantification of the external noise sources in high-speed trains is discussed. A thorough understanding of the underlying causes of noise generation in high-speed trains is needed to develop effective noise control measures. However, because high-speed trains produce a complex array of sounds, it is very difficult to determine each individual source of noise. In this study, the delay-and-sum beamforming method, which uses microphone arrays, was used to separate the noise sources and analyze the sound characteristics of high-speed trains. A new microphone array with 96 microphones was designed to measure the noise produced by high-speed trains. Performance verification tests were conducted to ensure the reliability of the results obtained from the array. Then, the system was used to measure the sounds produced by Korean high-speed trains traveling at speeds between 150 and 300 km/h. Sound maps were then produced using the beamforming technique. The study determined that the majority of the noise produced by the high-speed trains originated from the front nose, bogie, pantograph and inter-coach spacing. Finally, the beampower spectra of the aerodynamic noise sources originating in the front nose, pantograph and inter-coach spacing were deduced from frequency conversion. From these results, the aerodynamic noise characteristics of the major sources of noise in high-speed trains were determined.