• Journal of the Korean Society for Railway
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• v.18 no.2
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• pp.111-116
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• 2015

LED luminaires as a lighting system have attracted much research attention due to their high efficiency and long lifetimes. However, disappointing outcomes have been noted in terms of performance levels and lifetimes as compared to desired system requirements in practice due to certain electrical and thermal characteristics of LEDs. LM-80 and TM-21 established by IESNA are the best known standards for lifetime test procedures and estimation techniques. However, they only handle LED light sources without guaranteeing the LED luminaire in a reliability test. They also operate for more than 6,000 hours and undergo various stresses, such as the operating current and temperature. Therefore, a lifetime standard for LED luminaires has not yet been established. This paper proposes a conceptual design of a lifetime test system for LED headlamps depending on the operating environment. Eventually, this method can assist with evaluations of the validity of lifetime standard tests of LED headlamps.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.2319-2344
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• 2010

Accumulated deficits resulting from managing the Korean Railroad and debts from the construction of the KTX (Korea Train Express which is a high-speed rail system) have left the Korean Railroad faced with great troubles. Since it changed into a public corporation Korail on January 1st, 2005, the Korea Railroad has been making unceasing efforts to overcome the troubles and improve its management. However, even these efforts haven't worked in the face of the improved conditions of other transportation methods such as better networks of land roads and air ways. The Korea Railroad had its revenue from its railway transportation limited, and has tried to expand its business to non-transportational areas. In some metropolitan cities, the Korea Railroad made investments in real estate by constructing station buildings based on private money. Yet, in small and medium size cities, the Korea Railroad has little particular strategic projects for business development. Recently certain small and medium size regional cities began to plan on business developments for the ex-railway land, and some small towns have developed real estate on the ex-railway land. Nevertheless, there have been no systematic case studies to classify these real estate developments.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7934-7940
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• 2015

The raise of the acceleration can be one of possible methods to increase the scheduled speed of the metropolitan railway system. It is possible to raise the acceleration to the some point by increasing the traction power of the motor. However, there is a limit of the acceleration because the traction power over some level related to the adhesion causes a slip, which prevents from accomplishing the target acceleration. The running resistance is also an important factor to consider. Both the adhesion and the running resistance as well as the traction power vary according to the velocity. Therefore, the standardization of the acceleration needs the analysis of these factors as a function of velocity. In this study, we focus on the advanced urban transit unit(AUTS) for the standardization. We derive a novel equation of the adhesion suitable for the AUTS by investigation of the traction and adhesion equation as well as the experiment data. And finally we propose the standard of the acceleration based on this analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.1-11
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• 2016

The effect of the migration of nanoparticles near the wall of a channel on the convective heat transfer in a laminar flow of $SiO_2$ nanoparticle suspensions (nanofluids) under constant wall heat flux boundary conditions was numerically and experimentally investigated in this study. The dynamic thermal conductivity of the aqueous $SiO_2$ nanofluids was measured using T-type thermocouples attached to the outer surface of a stainless steel circular tube (with a length of 1 m and diameter of 1.75 mm). The nanofluids used in this study were synthesized by dispersing $SiO_2$ spherical nanoparticles with a diameter of 24 nm in de-ionized water (DIW). The enhancement of the thermal conductivity of the nanofluids (e.g., an increase of up to 7.9 %) was demonstrated by comparing the temperature profiles in the flow of the nanofluids with that in the flow of the basefluids (i.e., DIW). However, this trend was not demonstrated in the computational analysis, because the numerical models were based on continuum assumptions and flow features involving nanoparticles in a stable colloidal solution. Thus, to explore the non-continuum effects, such as the modification of the morphology caused by nanoparticle-wall interactions on the heat exchanging surfaces (e.g., the isolated and dispersed precipitation of the nanoparticles), additional experiments were performed using DIW right after the measurements using the nanofluids.

• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.43-51
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• 2014

In the earth structures of railways, large coarse granular materials are widely used as fill materials. However, experimental studies that consider the dynamic properties of these coarse granular materials have rarely been carried out in Korea due to the lack of a large scale test apparatus in this country. In this study, large scale cyclic triaxial tests were carried out for materials such as reinforced roadbed (subballast, graded crushed stone), transition zone gravel, and the upper subgrade of a railway. These specimens were prepared according to certain conditions (dry unit weight, grain size distribution, and so on) specified in the Korea railroad design standard. Based on these large triaxial test results, normalized shear modulus and damping ratio curves according to small strain level are suggested. A model and coefficients for each material are also proposed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.755-761
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• 2017

In railways powered by AC power, the main circuit breaker (MCB) is used for supplying the electric power to the catenary of the vehicle. Generally, the main circuit breaker is located between the pantograph and the main transformer, and the phase of the power applied to the vehicle changes according to the operation timing of the main circuit breaker. The operation of the main circuit breaker should be actively controlled according to the phase of the power source, since the phase of the power causes unintended transient states in the vehicle's electrical system in the form of an inrush current and surge voltage. However, the MCB has a delay time when it operates which is not constant. Therefore, an intelligent controller is needed to predict the operation delay time and control the opening and closing of the MCB.

• Journal of the Korean Society for Railway
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• v.20 no.5
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• pp.588-594
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• 2017

Permanent magnet assisted synchronous reluctance motors (PMa-SynRM) show higher efficiency and power density compared to conventional induction motors for high speed railroad traction systems. Furthermore, 5-phase PMa-SynRMs have lower torque ripple and higher power density than 3-phase systems. Therefore, the 5-phase PMa-SynRM is suitable for high-speed railway traction systems. In this study, 3kw 3-phase and 5-phase PMa-SynRM models were optimized using lumped parameter model and genetic algorithm, and their characteristics were compared. The optimized models are fine-tuned using finite element analysis. The final models of the 3-phase and 5-phase PMa-SynRMs are fabricated and tested to verify the analysis results.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.241-245
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• 2013

In the case of the existing train control system, the driver monitors the condition of the vehicle through a composite controller device that displays various information on a screen in the vehicle. However, when problems arise such as car trouble, it is difficult for the drivers to take action immediately. In addition, maintenance personnel have to manually save data one by one after storing the vehicle to analyze control information of the main devices such as the brake controller and auxiliary power. To improve these points, a system that sends and receives all information in real time should be established by installing a sensor communication network and a surveillance system. This study attempts to improve the safety and maintenance of rail vehicles by suggesting a standardized method for train control and surveillance system.

• Journal of the Korean Society for Railway
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• v.16 no.3
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• pp.163-168
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• 2013

The maintenance of an urban transit vehicle accounts for 60-70% of total costs over its entire life cycle, so it is critical to reduce maintenance costs and extend the life times of urban transit EMUs (electric multiple units) through research. For these researches, the reliability and availability data management system was constructed through the case study of several industries in the domestic and international in the field of reliability centered maintenance system. And we created a system to manage reliability and availability data for use in urban-EMU maintenance. In this work, we identified the major functions needed to successfully develop the system. Here we report the successful development of a reliability and availability data management system for maintenance of urban transit vehicles.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.257-262
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• 2003

Now, the population and economical power is deeply concentrated to Seoul-metropolitan region, therefoere the provinces is so lagging behind and the country cannot get balance development. And, like metropolitan region, the more outer the living area of local wide-area city is spreading, the more serious wide-region transportation problems are. But the railroads near wide-area city fun seldom commuter train, so they cannot absorb the transportation demand of wide-area city metropolitan region. To solve above transportation problem, local wide- area cities try to make a subway or a light rail transit. But it is so difficult because the limit of public finance and original small capacity of light rail. In the paper, I propose 'Local city wide-area electric railways' system of the consortium of 'Local wide-city and province transportation union', Korean National Railroad (KNR) and local capital. A 'Local wide-city and province transportation union' operates commuter railways directly using the facilities of KNR, and local capital invests to the stations of above railways system. Therefore the commuter railway system around local wide-city region will be constructed quickly and the stations will be the strong point of local development and investment.