• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.1
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• pp.51-56
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• 2015

This paper presents an investigation of abnormal wear of a contact jig between a nail and a nail fixture in electric resistance welding. To perform an analysis on the abnormal wear phenomenon, several methods are provided. Based on the theory of electric resistance welding, are analyzed. Using microscopic analysis, surface craters are observed. In the measurement of the electric current flow in the nail fixture, the current flow distribution is measured. From several analyses, the cause of abnormal wear in the contact jig is measured using the electric discharge of high current density at the inflow point of the electric supply to the nail fixture. An alternative shape for normal wear is proposed.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2628-2631
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• 1999

One of the limitations of conventional ASCI for high-power induction motor drives is the high voltage that is produced in the commutation capacitors during the current commutation from one phase to another. Since the capacitor voltage appears directly on the semiconductor components, it increases their required voltage ratings. Also, the high-voltage spikes generated at the motor terminals may cause damage to the motor insulation. And we investigated how de input power is increased or decreased according to size of de link inductor. In this paper, de link inductor and clamping capacitor in GTO inverter suitable for induction motor drives are propose through experiment.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1416-1423
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• 2007

Dynamic instability of the railway bridge can cause track irregularities and be directly connected with unstable passenger comfort and derailment of the train. Europe and Japan had studied on this problem for a long time since 1960's, Results of those studies are reflected in recent Eurocode and the bridge design code of Japanese railway bridges. However, even though some traffic safety requirements were applied in Kyoung-bu highspeed railway by French engineers, we experienced many difficulties from insufficient information of criteria background and application procedures. In this paper, a investigation of recent traffic safety requirements of Europe and Japan for railway bridges will be introduced and application procedures for the estimation of dynamic performance will be proposed.

• Journal of Aerospace System Engineering
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• v.7 no.1
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• pp.1-7
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• 2013

Launch vehicles cause several shock events during their lift-off. The excessive shock loads in the several thousands of g's level can results in permanent damage to electronics, optics and other sensitive payload components. The shock can be attenuated by mounting a shock absorber. In this paper, we proposed a semi-active control logic to attenuate the shock so that the input acceleration to main instruments does not exceed the allowable maximum acceleration value. For the performance investigation, two elements model of variable damping and spring stiffness has been used and the analysis results indicate that the proposed semi-active control logic attenuates shock level better than an optimal passive and conventional semi-active on-off control system.

• Congress of the korean instutite of fire investigation
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• 2010.12a
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• pp.120-136
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• 2010

엔진 정지 중 발생한 자동차화재는 엔진 정지 전에 이미 화재가 발생해 있었으나 이를 모르고 엔진 정지 중에 화재가 발견되는 경우와 엔진 정지 후에 발생한 경우로 나눌 수 있다. 엔진정지 전 발생한 화재는 운행 중 화재가 발생할 수 있는 모든 원인에 의해 발생할 수 있고, 엔진정지 후 발생한 화재는 전기적인 원인에 의한 화재, 담뱃불에 의한 화재, 방화, 다른 곳에서 발화된 후 자동차로 확대된 화재 중의 하나로 압축할 수 있다. 그러므로 외부발화 또는 방화나 담뱃불에 의한 화재가 배제되는 경우는 전기적인 원인만을 생각할 수 있다. 엔진정지 전에 이미 엔진룸 등에 불이 붙어 있어도 주차 중 이를 인식하지 못하는 것은 엔진정지 시 화재의 규모가 작거나 눈에 띄는 이상징후가 나타나 있지 않고 또한 이를 관심 있게 확인하지 않기 때문이다. 엔진정지 전에 화재가 발생한 경우에는 일반적으로 주차 후 대략 10분 이내에 화재가 발견되고 있다. 따라서 주차 후 10분이 경과하지 않은 시점에 화재가 발견되었다면 엔진정지 전에 이미 화재가 발생하였을 가능성이 크다고 볼 수 있다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.148-149
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• 2017

Recently, South Korea is reaching aged society through ageing society. Accordingly, facility related to aged is increased consistently because of effort to improve the welfare of the elderly through elderly long term care insurance in 2008. however, the number of fires in the elderly facilities is increasing rapidly too. It is becoming bigger and higher and the characteristics of person who is unable to afford are mostly having difficult evacuation. so fire safety guildelines are urgently needed but korea research is insufficient. In this study, we propose a fire scenario through investigation of fire causes for fire safety guideline development of elderly facility, and describe to the fire safety countermeasure.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.56 no.1
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• pp.37-44
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• 2007

This paper describes characteristics for copper oxide growth of polyvinyl chloride(PVC) insulated wires by series arc. In this experiment, 600V IV wires were used, and characteristics of oxide growth and ignition process were analyzed in case load was 300W, 460W and 600W, respectively. In the result of experiment, covering materials were molten, carbonized and ignited, whereas, oxidized materials were grown in conducting material. During copper oxide was growing, contact voltages and power dissipations increased. When there is copper oxide growth, the waveform of current showed sinusoidal waveform, and the waveform of voltage showed modified waveform. Oxidized materials were heated at about $905^{\circ}C$, surface structure showed irregular shapes, and cross-section showed multiple cracks. And, the results of this experiment were applied to the fire cause analysis of fire evidence collected at the fire scene.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.373-375
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• 2003

The subway, a typical electrified transit, is operated by the 1500 V DC-powered system with the overhead positive feeder and the rails negative return. This return path would bring about considerable stray current circuits, that is, from the bottom of rails to sell and then to the station ground, unless the rail-to-soil resistance is sufficiently high. The stray current can cause electrolytic corrosion of subway metallic structures and adjacent underground utilities. In this paper, we reports on-site investigation of the stray current condition, especially influenced by drainage method. The drainage method including both forced drainage and polarized drainage, extensively adopted as a countermeasure for electrolytic corrosion of underground pipelines, was found out to exert a harmful influence upon rail components as well as the pipelines.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.271-281
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• 2010

Brazing fitting which is one of the aircraft hydraulic power system components is widely used for saving weight and achieving higher reliability. Any inherent defects or damage of fitting can cause system failure and/or physical damage of human body due to highly pressurized fluid. Radiographic testing(RT) technique and additional micro-structure investigation on cut-away surfaces have been accomplished to find out some defect-like-inhomogeneity in the fittings. The radiography results showed that some defect-like-inhomogeneity existed inside body. Additional micro-structure investigation on cut-away surface reveals that the inhomogeneity is due to internal voids. In this study, it can be is said that RT technique can be a useful tool for field acceptance test of hydraulic brazing fitting in short time.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.361-368
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• 1997

Summary of experiments for the investigation of a fire which caused an upward fire spread for over 12 floors through balconies in a high-rise apartment complex is reported. The experiments include indoor tests to obtain fire properties of vertical PMMA fences and outdoor ones with a full scale model of the balcony. The test results suggest significance of the increase of total flame height by the merging of flames and a cooperative effect of the burning of the PMMA fence and combustibles on the balconies for the generation of a tall flame enough to cause ignition on the upper floors.