• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.19-27
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• 2014

Urban railway vehicles operate in downtown areas. Due to increases in the number of passengers and changes in the service plans, railway vehicles are expected to operate on sharp curved tracks. However, on these tracks, the running stability of the railway vehicles is significantly decreased and the creepage is increased. Creepage causes the wheel/rail to wear and vibration. Therefore, reducing the creepage helps ensure the running stability and can be beneficial for the environment and cost. In this paper, the longitudinal creepage is analyzed using a railway vehicle model on a sharp curved track. Furthermore, in order to minimize the problems when a railway vehicle runs on a sharp curved track, the characteristics of a bogie are optimized using response optimization.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.75-82
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• 2011

There is the uncertain period of the construction in case of the products meeting the quality standard of KS M 6080, the quality is degraded because of the abrasive loss of the paint caused by vehicle tires as the traffic amount increases and of the loss and detachment of the glass beads providing the retroreflective function. The abrupt degradation of visibility causes the high frequency of traffic accidents at night and increases the traffic accident rate. Additional supplementary construction induces the direct material and construction costs. As the more cost induction effect than the direct cost, the traffic jam caused by the additional construction increases the indirect social costs such as time cost and vehicle cost. Hence, the study is concerned with performing the abrasion resistance test based on the EN 1436 standard to check and improve the quality of various road marking materials resulting in improving the durability of road marking materials. However, even though the difference in the durability lifetime of resins(binders) is bibliographically or theoretically clear, there was no difference in the durability lifetime (retroreflectivity aspect) of the road marking paint using these binders. The reason is that the bonding of beads was very insufficient or that the cross density caused by crack or freshness was low. Moreover, the measured wet retroreflectivity was distributed as the Rw3 or higher class in average on the basis of EN 1436 but was very insufficient on the basis of the minimum wet threshold retroreflectivity with 100mcd/($m^2{\cdot}lx$) managed overseas.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.697-704
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• 2017

This study was carried out to investigate and alleviate the vibration problem of commercial high-speed trains. First, the measurement of the carbody vibration was performed, in order to determine the vibration level of the high-speed train. The measurement result showed that the vibration level of the driver cab was higher than that of the passenger car and that the vibration became bigger toward the trailing end of the train. The vertical vibration of the driver cab and passenger car was larger than the transverse vibration, and the maximum value of the vibration in the ballast section was larger than that in the concrete section. A dynamic analysis was carried out to improve the vibration of the KTX-Sancheon train. The results of the analysis showed that it is necessary to reduce the vibration of the driver cab and both ends of the passenger cars. To reduce the vibration of the driver cab, it was recommended that the stiffness of the secondary coil spring be reduced and the damping coefficient of the secondary vertical damper be increased. It was found that the failure of the suspension system could be the origin of the vibration problem of the high-speed train. The proper management of wheel wear plays an important role in the improvement of the operation efficiency and reduction of the carbody vibration of high-speed trains, and research is underway to change the present wheel profile to increase the mileage between wheel turning.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.7
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• pp.529-534
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• 2016

During the past few years, several incidents of freight car wheel failure during operation have occurred due to fatigue crack and overheating from braking. Tensile residual stress on the wheel tread creates an environment conducive to the formation of thermal cracks that may threaten the safety of train operations. It is important to investigate the residual stress on wheels in order to prevent derailment. In the present paper, the residual stress on wheels is measured using the x-ray diffraction system and the residual stress is analyzed using FEM. The result shows that the residual stress on the wheel rim is lower than that on the wheel tread center and the stress on over-braked wheels changes from compression residual stress to tensile residual stress.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.442-449
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• 2000

Before the complete construction of new high-speed line between Seoul and Pusan, KTX is going to operate on both new high-speed line between Seoul and Daegu and electrified conventional lines between Daegu and Pusan. Then, the wheels of KTX are going to operate on various rails such as KS50N and KS60 of conventional line as well as UIC60 of high-speed line. Also, conventional line will have a mixed traffic mode with various types of trains operating on it, such as Saemaul and Mugunghwa. Hence, this study reviews the wear phenomena of wheels and rails in geometrical point of view by comparing their profiles. The analyses of the results show that because UIC60 rail is designed for KTX, KS50N rail whose profile is similar to that of UIC60 will not have any impact on the shape of wheel wear. On the other hand, KS60 rail is expected to have partial wear on both the flange of KTX wheel and the gauge corner of the rail in the initial stages. However, the operation of the trains whose wheels have 1/20 conicity will cause partial sidewear on the inside of the rail and the movement of the contact point between KTX wheel and the rail toward the inside of the track. As a result, the flange wear of KTX wheel will be reduced and the formation of wear-equilibrium profile will be faster.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.603-610
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• 2016

Over 12 years have passed since the first commercial operation of a Korean high-speed train. Since then, the transport capacity of the high-speed lines has become almost saturated. Therefore, studies have been carried out to increase the operating speed of the trains in order to increase their transportation capacity. This study was carried out to improve the critical speed of the KTX-Sancheon, Korean high-speed train, in order to increase its operating speed. A dynamic analysis of the KTX-Sancheon train was performed using the contact data obtained from the wheel wear profiles that were measured from a KTX-Sancheon train in commercial operation. The analysis results were verified by comparing them with the measurement acceleration data obtained from KTX-Sancheon. The suspension parameters were optimized to improve the operation speed. The critical speed of KTX-Sancheon was increased by 9.4% after the optimization by the response surface method. The optimized suspension parameters are expected to be used for the new bogie design to increase the operating speed of KTX-Sancheon from 300km/h to 350km/h.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.797-803
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• 2019

This study was carried out to reduce the lateral vibration of high-speed electric multiple units. In the study, the high-speed electric multiple unit prototype (HEMU-430X) has a high lateral vibration at low equivalent conicity regardless of the wheel profiles (XP55, GV40, S1002). As wheel wear progresses and the equivalent conicity increases, the lateral vibration tends to decrease. The reason is that a combination of the suspension characteristics causes the body and bogie to resonate at a frequency of 1.4 Hz when the equivalent conicity is low, resulting in body hunting. An investigation of the lateral vibration of overseas high-speed trains showed that a decrease in the hydraulic stiffness of the yaw damper could improve the vibration. The series stiffness of the yaw damper is a combination of the hydraulic stiffness and elastic joint. In this study, an attempt was made to improve the lateral vibration by lowering the stiffness of the elastic joint. The series stiffness of the adjusted yaw damper was approximately 60% compared to the original one. The on track test results showed improvement in the lateral vibration for both running directions. The vibration reduction method of this study can be used for EMU-250 and EMU-320 in future commercial operations.

• Journal of the Korean Society for Railway
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• v.20 no.3
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• pp.311-319
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• 2017

The primary suspension system of a railway vehicle restrains the wheelset and the bogie, which greatly affects the dynamic characteristics of the vehicle depending on the stiffness in each direction. In order to improve the dynamic characteristics, different stiffness in each direction is required. However, designing different stiffness in each direction is difficult in the case of a general suspension device. To address this, in this paper, an optimization technique is applied to design different stiffness in each direction by using a conical rubber spring. The optimization is performed by using target and analysis RMS values. Lastly, the final model is proposed by complementing the shape of the weak part of the model. An actual model is developed and the reliability of the optimization model is proved on the basis of a deviation average of about 7.7% compared to the target stiffness through a static load test. In addition, the stiffness value is applied to a multibody dynamics model to analyze the stability and curve performance. The critical speed of the improved model was 190km/h, which was faster than the maximum speed of 110km/h. In addition, the steering performance is improved by 34% compared with the conventional model.