Actual Railway Research Articles

Influence of vibration on sub-ballast layer induced by loading application on a fouled track ballast

The railway track’s sub-ballast layer is important, but it is often neglected, leading to the contamination and blockage of voids, as well as track deformation and degradation. These issues occur when fouling materials infiltrate the subballast due to load-induced vibration. The purposes of this paper are to investigate the influence of vibration on the sub-ballast layer when loads are applied to a fouled ballast and to determine whether sub-ballast saturation should be ignored. A ballast box was fabricated to represent actual railway conditions and filled with 100 kg of ballast aggregates containing fouling materials (crushed ballast, sand, clay, and coal) proportional to the ballast weight. In addition, a vibratory compactor plate machine was used to simulate load on the fouled ballast, inducing vibrations that caused fouling materials to migrate into the sub-ballast. The results indicate that 18% of crushed ballast, 20% of sand, 20.7% of clay, and 15% of coal infiltrated the sub-ballast due to loading-induced vibration, and fouling infiltration percentages rose as vibration from loading increased. These percentages exceeded the standard 10% weight of fouling infiltration into the sub-ballast, indicating an unfavourable subballast condition and showing that sub-ballast saturation should not be ignored. These findings have significant implications for maintenance engineers, as they underscore the need for continuous monitoring and upkeep to ensure optimal sub- ballast performance.

Recreating horizontal alignments of existing railways with a hybrid analytic and harmony search algorithm

After operating a long time, existing railway tracks gradually deviate from their initially designed alignments due to the wheel-track interaction, thereby compromising operational performance and safety. Therefore, existing railway alignments should be recreated through periodic maintenance to enhance train operations and guarantee operational safety. Currently, most methods in this field first identify tangent alignment sections and then curves based on measured points along the railway. Afterward, these identified geometric components are optimized to fit the actual alignment. However, for existing railways that are fairly circuitous, the above strategy is limited since the curves’ geometric characteristics dominate those of tangents in recreating alignments. Thus, the precision of geometric identification is reduced and the recreated alignment may significantly deviate from the actual railway. To solve this problem, a three-stage optimization method is proposed. At the first stage, a dynamic threshold method is developed to flexibly identify the geometric attributions of all measured points based on the existing railway. For the second stage, an adaptive analytic method is proposed which combines two geometric recreation approaches that are devised for curves and tangents to determine a preliminarily recreated horizontal alignment. Moreover, to enhance the recreation accuracy of local alignment sections, a harmony search algorithm is customized as the third stage to further optimize the recreated alignment. Finally, the effectiveness of the proposed method is verified through detailed data and sensitivity analyses applied to a real-world case.

A Methodology of Condition Monitoring System Utilizing Supervised and Semi-Supervised Learning in Railway.

In this paper, research was conducted on anomaly detection of wheel flats. In the railway sector, conducting tests with actual railway vehicles is challenging due to safety concerns for passengers and maintenance issues as it is a public industry. Therefore, dynamics software was utilized. Next, STFT (short-time Fourier transform) was performed to create spectrogram images. In the case of railway vehicles, control, monitoring, and communication are performed through TCMS, but complex analysis and data processing are difficult because there are no devices such as GPUs. Furthermore, there are memory limitations. Therefore, in this paper, the relatively lightweight models LeNet-5, ResNet-20, and MobileNet-V3 were selected for deep learning experiments. At this time, the LeNet-5 and MobileNet-V3 models were modified from the basic architecture. Since railway vehicles are given preventive maintenance, it is difficult to obtain fault data. Therefore, semi-supervised learning was also performed. At this time, the Deep One Class Classification paper was referenced. The evaluation results indicated that the modified LeNet-5 and MobileNet-V3 models achieved approximately 97% and 96% accuracy, respectively. At this point, the LeNet-5 model showed a training time of 12 min faster than the MobileNet-V3 model. In addition, the semi-supervised learning results showed a significant outcome of approximately 94% accuracy when considering the railway maintenance environment. In conclusion, considering the railway vehicle maintenance environment and device specifications, it was inferred that the relatively simple and lightweight LeNet-5 model can be effectively utilized while using small images.

Life-Cycle Seismic Reliability Analysis of a Railway Cable-Stayed Bridge Considering Material Corrosion and Degradation

To study the life-cycle seismic reliability analysis (SRA) of cable-stayed bridges (CSBs) taking into account chloride-induced corrosion and degradation of components, an actual railway CSB with uncertainties in structural geometry and material corrosion coefficients was employed in this investigation, and time-dependent models of CSB components at different service times were studied. Based on the OpenSees batch program, we adapted a mass numerical computation to obtain time-dependent non-linear seismic response and probability density function (PDF) of response via the multiplier dimensional-reduction method (MDRM) and the maximum entropy method with fractional moments (FM-MEM). Next, the time-dependent failure possibility of every component and the association coefficient between the failure modes of different parts were acquired. In the end, the product of the conditional marginal (PCM) approach was employed to obtain the life-cycle failure possibility of the CSB system. The results showed that the system failure possibility of the CSB in a corrosive environment increases significantly with increasing servicing time.

Multi-vehicle accessed railway vehicle-grid system stability analysis and optimization based on OLTC

The interaction between Electric Multiple Units (EMUs) and the traction network can lead to oscillation problems due to electrical mismatch. The stability between the EMUs and the traction network is difficult to ensure because of the multiple operation points and variable operation modes of EMUs. To analyze the system stability, impedance-based methods are commonly used. However, existing impedance-based stability analysis methods require identifying system transfer functions, which can introduce under- or over-fitting problems. To address this issue, this paper introduces an optimized open-loop based stability analysis method for multi-vehicle accessed vehicle-grid system, which effectively assesses the impact of vehicle operating points and modes on system stability. In addition, we propose an On-Load Tap Changer based method to enhance the voltage stability of railway traction networks. By optimizing traction network voltage, the impedance characteristics of vehicles are also modified, thus enhancing system stability. Finally, we validate the efficacy of the proposed method through case studies based on an actual railway train schedule diagram.

Realizing a Quick Partial BIM Update of Subgrade in Railway Stations

A railway station subgrade (RSS) is a complex earth structure for supporting various railway facilities and its building information modeling (BIM) is an essential task in a railway station project. During the entire life cycle of an RSS BIM model, it will be frequently updated according to the progress of the project. However, the current way of updating an RSS model is commonly conducted in a complete rebuild, which is very inefficient and time-consuming. To address this issue, we propose a novel approach for realizing a partial BIM update driven by model changes, through which a quick update for an existing RSS BIM model can be achieved. A partial updating strategy that is triggered by a model change is developed to locate a minimum influenced domain of the original model and update it in that domain. An actual railway station case is used for demonstrating the validity of the approach, through which a quick partial update to an existing RSS model is achieved by skipping the redundant computations in the process of a complete rebuild.

The performance of top-of-rail products under water contamination

Top-of-rail products are commonly used for friction modification in wheel-rail contact. However, the effect of environmental conditions and contaminants on their performance remains unclear. In this study, three commercial top-of-rail products were contaminated by different amounts of water. The laboratory tribometer in ball-on-disc configuration was used to measure the coefficient of adhesion in contaminated contact. The results show that water influenced tested top-of-rail products significantly. A very low coefficient of adhesion occurred in tests with oil-based top-of-rail products suggesting that water could cause traction problems on the actual railway where friction modification is being used. Water-based top-of-rail products showed more resistance to water contamination.

FATIGUE REAL SCALE TEST COMPARISON WITH ACTUAL BRIDGE MONITORING

In railway bridges, special attention needs to be paid to the interaction between the railway track and the bridge. Forces occur in the rails, as well as in the deck and the bearings of the bridge. These forces result in additional stresses, which need to be kept sufficiently low. Peak stresses due to e.g., temperature variations and bridge deck bending are especially to be feared at the bridge/abutment transition. Special rail fastening systems may be used to limit these additional stresses. Real scale tests were performed to verify the behavior of the track and the bridge equipped with such modified fasteners, which are designed to limit the transfer of longitudinal forces to the bridge. Based on the data from these tests, a detailed finite element model is constructed in this research paper. In contrast to the generally accepted modeling approach prescribed by international norms such as Eurocode NBN EN 1991-2 and UIC Code 774-3R, this research is performed, assuming the fact that the behavior due to track-bridge interaction can be simulated by a rail model supported by springs, i.e., without the need to model the actual bridge structure in detail. The results of these finite element model simulations are compared with data of a long-term monitoring program using strain gauges on all elements of the rails and support structure of an actual railway bridge in Belgium.

Practical wheel/rail tangential contact force model for vehicle dynamics analysis combining Levi-Chartet’s formula with adhesion coefficient-velocity relational expression

This paper describes a practical wheel/rail tangential contact force model for railway dynamics analysis under running in rainy conditions. In our previous studies, it was confirmed that experimental results of tangential contact force measurement are agree well with Kalker’s rolling contact theory under dry condition with low humidity around contact surfaces. Here, it can be considered that if the ambient humidity around the contact surface become high infinity, the contact surface is under wet lubrication conditions. On the basis of this assumption, in this study, a practical estimation model for characteristics of tangential contact force under running in rainy conditions is proposed by combining the relationship between the adhesive coefficient and velocity measured on running experiments using actual railway vehicles and Kalker’s linear rolling contact theory. Therefore, to verify the proposed model, the tangential contact force measurement experiment using a twin-disk rolling sliding machine was carried out. As a result, it is confirmed that estimated formulae based on the proposed model are well agreed with experimental results even under different velocity conditions, comparing the relationship between tangential contact force coefficient and slip ratio. From these verified results, the proposed model is considered to be a practical wheel/rail tangential contact force model for vehicle dynamics analysis under rain conditions, because the proposed model has the advantage of low calculation cost and can be easily applied to vehicle dynamics analysis based on multi-body dynamics theories.

Role of ambient temperature in the adhesion and damage characteristics of wheel/rail interface during rolling-sliding contact

A systemic evaluation in laboratory were conducted to explore the effect of extreme temperature environment (−50 °C–60 °C) on the tribology properties of the wheel/rail rolling contact. Systemic analysis revealed the evolution rule of adhesion capacity of wheel/rail contact, the performance changes of wheel surface (including plastic deformation, hardening behavior, residual stress), and the damage morphology of the wheel surface and subsurface. The results showed that the seasonal damage to actual railway in the frigid zone can be reproduced through lab tests. The interface behavior and wear mechanism were affected by the service temperature. The adhesion capacity of the wheel/rail interface decreased with the increasing temperature, whereas it was relatively stable at low temperature and fluctuates obviously at high temperature. The high temperature accelerated the tribo-oxidation between the wheel/rail interface, but the brittleness of wheel material and the surface residual stress of worn surface increased as a result of the intensified surface shear action at cold environment. The wear mechanisms gradually transformed from abrasive wear, oxidation and adhesive wear to fatigue wear accompanied by the decrease of temperature.

Role státu ve výstavbě a provozu železnice od 30. let 19. století do 20. let 20. století v interakci s vývojem ekonomického myšlení v českých zemích

The topic of this study is historical analysis of the construction of the Czech railway network and the role of the state in its development in comparison with economic thought of the time. The aim of this study is to present relations between the development of theoretical economic foundations and the actual railway construction in the Czech lands from the middle of the 19th to the beginning of the 20th century. During this time, the railway network was constructed in the shape it functions until these days. The topic is examined as a historical sequence of interactions between actual railway construction and operation and economic opinions regarding the role of the state in construction and running of railways. The history of the relationship between the state and the railway went through a few periods differing in the approach of the state to ownership and operation. We can trace the private beginnings from the 1830s, to first state railways from 1841 to 1848, to privatization and indirect state subsidies, to the victorious definite idea of solely state railways in the last third of the 19th century. The study follows detailed discussions of the era together with connections to economic thought of the era.

Energy-Management Method to Reduce the Capacity of Lithium-Ion Batteries in Hybrid-Voltage-Source Three-Level Inverter for DC-Electrified Railway Vehicles

The hybrid-voltage-source three-level inverter is a traction circuit system aimed at realizing energy savings with lithium-ion batteries for direct-current-electrified railway vehicles. However, this system has the limitation of being unable to freely control the power flow of the batteries owing to the pulse width modulation. However, because this system has batteries, energy management is required for the batteries. Therefore, it is necessary to propose an energy-management method that achieves the required energy-saving effect while considering the constraints of the battery power control. In this paper, a management method is proposed to control the power flow of the batteries by determining the pulse mode of the inverter and the modulation wave offset based on the state of the charge and inverter frequency. In a 0.75-kW class mini-model verification, the effectiveness of the proposed energy-management method is then confirmed based on the state of the charge, inverter frequency, offset, and battery power. Subsequently, we evaluate the energy-saving effect of this hybrid system using a numerical simulation while considering an actual railway vehicle. In addition, the optimal capacity of the batteries is investigated. As a result, the best energy-saving effect is obtained when two of the assumed batteries are connected in series and three in parallel, and the power consumption is reduced by approximately 21%.

Practical wheel/rail tangential contact force model for vehicle dynamics analysis under running in rainy conditions

This paper describes a practical wheel/rail tangential contact force model for railway dynamics analysis under running in rainy conditions. In our previous studies, it was confirmed that experimental results of tangential contact force measurement are agree well with Kalker’s rolling contact theory under dry condition with low humidity around contact surfaces. Here, it can be considered that if the ambient humidity around the contact surface become high infinity, the contact surface is under wet lubrication conditions. On the basis of this assumption, in this study, a practical estimation technique for characteristics of tangential contact force under running in rainy conditions is proposed by combining the relationship between the adhesive coefficient and velocity measured on running experiments using actual railway vehicles and Kalker’s linear rolling contact theory. Therefore, to verify the proposed technique, the tangential contact force measurement experiment using a twin-disk rolling sliding machine was carried out. As a result, it is confirmed that estimated formulae based on the proposed technique are well agreed with experimental results even under different velocity conditions, comparing the relationship between tangential contact force coefficient and slip ratio. From these verified results, the proposed technique is considered to be a practical wheel/rail tangential contact force model for vehicle dynamics analysis under rain conditions, because the proposed technique has the advantage of low calculation cost and can be easily applied to vehicle dynamics analysis based on multibody dynamics theories.

Study on seismic behavior of a self-centering railway bridge pier with sacrificial components

Railway bridge pier with large cross-section will vibrate significantly during strong earthquake events. Sacrificial components can be used to improve the lateral stiffness and control the initial uplift of the self-centering pier during earthquakes. This study investigated the seismic isolation mechanism and behavior of a self-centering railway bridge pier with sacrificial components by experimental and numerical methods. Based on an actual railway bridge, a 1/30 scaled bridge pier model was designed for pseudo-static test. Constant axial load and cyclic lateral load were applied for the scaled bridge pier model. Test results showed that sacrificial components were fractured when the loading displacement exceeded 25 mm. The hysteretic behaviors of the self-centering pier exhibited significant difference before and after the failure of sacrificial components. It was found that the bridge pier concrete cracked but steel bars did not yield during the test. This indicated that the failure of sacrificial components of the self-centering bridge pier can effectively protect the pier from severe damage during earthquakes. Furthermore, a Four-spring model was proposed with assistance of the Opensees software platform, and it was verified by pseudo-static test results. It is demonstrated that the proposed model can simulate the self-centering piers with sacrificial components under cyclic lateral loading.

철도차량 속도구간별 가감속 특성의 객체지향 모델링 기법

Railway vehicles have different traction and braking forces depending on their speed, which can be divided into constant torque areas, constant power areas and characteristic areas. The 4th order Runge-Kuta method was applied as a method for simulating these characteristics, and object model for railway vehicle was constructed using the overloading function of the function. The characteristics of the vehicle were calculated and compared with the actual values by applying the constructed model. We also calculated TPS (Train Performance Simulation) from the actual railway rail data and confirmed that it was similar to the characteristics of the actual railway vehicle.

Development of Scott Transformer Model in Electromagnetic Transients Programs for Real-Time Simulations

This paper presents a Scott transformer model to be applied in electromagnetic transients (EMT) programs, particularly in the absence of a detailed Scott transformer model for performing real-time simulations (RTS). Regarding a Scott transformer, a common topology for converting a three-phase network into two single-phase networks, the transformer model in EMT programs is essential to simulate large-scale electric railway systems. A code-based model has been developed to simulate the transformer in RTS directly and contain the transformer’s actual impedance characteristics. By establishing a mathematical foundation with the current injection method, we presented a matrix representation in conjunction with a network solution of EMT programs. The proposed model can handle more practical parameters of Scott transformers with a relatively low computational load. Thus, it supports the flexible computation of real-time simulators with a finite number of processor units. The accuracy of the model is verified by simulating it and comparing the simulation results with an industrial transformer’s certified performance. Furthermore, a case study involving a comparison of the results with the field measurement data of an actual Korean railway system demonstrated the efficacy of the model.

Simulation of Energy Absorption Performance of the Couplers in Urban Railway Vehicles during a Heavy Collision

Railway vehicles are generally operated by connecting several vehicles in a row. Mechanisms connecting railway vehicles must also absorb front and rear shock loads that occur during a train’s operation. To minimize damage, rail car couplers are equipped with a buffer system that absorbs the impact of energy. It is difficult to perform a crash test and evaluate performance by applying a buffer to an actual railway vehicle. In this study, a simulation technique using a mathematical buffer model was introduced to overcome these difficulties. For this, a model of each element of the buffer was built based on the experimental data for each element of the coupling buffer system and a collision simulation program was developed. The buffering characteristics of a 10-car train colliding at 25 km/h were analyzed using a developed simulator. The results of the heavy collision simulation showed that the rubber buffer was directly connected to the hydraulic shock absorber in a solid contact state, and displacement of the hydraulic buffer hardly occurred despite the increase in reaction force due to the high impact speed. Since the impact force is concentrated on the vehicle to which the collision is applied, it may be appropriate to apply a deformation tube with different characteristics depending on the vehicle location.

유연수요반응을 제공할 수 있는 역사 내 부하 활용 방안 연구: 도시철도 역사 사례 분석

유연수요반응을 제공할 수 있는 역사 내 부하 활용 방안 연구: 도시철도 역사 사례 분석

Field Tests for Evaluating the Inherent High-Order Harmonic Resonance of Traction Power Supply Systems Up to 5000 Hz

The inherent resonant frequency of a traction power supply system (TPSS) needs to be accurately identified in order to provide crucial information for resonance suppression, safe operation, and system optimization of electrified railways. In this paper, implementation of experiments was carried out in actual railway systems to evaluate the inherent harmonic resonances of the TPSS. The field tests were based on a harmonic generator (HG) constructed with cascaded H-bridge converters (CHBCs). Compared to other experimental setups, the field tests of this paper, which were performed in the 25kV practical system, can provide straightforward results in a wide frequency range up to 5000 Hz. Such a wide frequency range is necessary for assessing and taking effective measures to address the harmonic resonance problem. The results of this paper will supply valuable data for the modeling of TPSSs and the stability analysis of train converters contributing to improvement of the power quality of electric railways.

Prediction of railway wheel load unbalance induced by air suspension leveling valves using quasi-steady curve negotiation analysis procedure

While air suspensions are widely utilized for passenger railway vehicles as secondary suspension, initial lever angle setting of the air spring levelling valve can make a non-negligible impact on the residual wheel load unbalance in curve negotiation on small radius curved tracks. To enable accurate and quick prediction of the levelling valve-induced residual wheel load unbalance for vehicle safety evaluation, this study proposes a new quasi-steady curve negotiation analysis procedure considering the detailed thermodynamic air suspension system model that accounts for the nonlinear airflow characteristics of levelling valve and differential pressure valves. This approach allows for eliminating a limitation of existing full dynamic simulation models associated with high computational intensity that prevents quick safety evaluation with long-distance simulation under actual railway operating scenarios. A co-simulation scheme for the quasi-steady vehicle motion solver is also proposed to further improve the computational efficiency with explicit force–displacement coupling. Several numerical examples are presented to demonstrate the proposed quasi-steady vehicle motion solver for prediction of levelling valve-induced residual wheel load unbalances in small radius curved tracks. The numerical results are compared with those of the dynamic simulation model and validated against the test data. It is demonstrated that computational time is substantially decreased by the proposed approach while accurately predicting the levelling valve-induced residual wheel load unbalance caused by the initial offset of lever angles on small radius curved tracks.