• 한국추진공학회지
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• 제20권1호
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• pp.69-75
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• 2016

본 논문은 한국형발사체 연소기 연소시험설비의 구축과 시운전 결과를 다루고 있다. 이 시험설비는 2012년부터 2014년까지 구축되었고, 2014년 하반기에 시운전이 수행되었다. 시운전 과정에는 산화제 수류시험, 연료 수류시험, 냉각수 수류시험 등이 수행되었고, 이후 점화시험이 이루어졌다. 점화시험 결과는 연소기의 시동시퀀스를 설정하는데 적용되며, 저압연소시험과 설계점 연소시험을 위한 기초자료로 활용되게 된다.

• 한국해양공학회지
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• 제20권6호
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• pp.18-23
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• 2006

This paper introduces the results of the development of a new mobile digital DC-arc welding machine (DDWM). A simple PI controller is applied to the DDWM to control the output welding current that is tracking the constant setting current. Furthermore, a hot-start function, an anti-stuck function, a standby mode and an intelligential circuit breaker (ICB) are included in the DDWM. The DDWM increases welding quality and saves more power energy than a conventional welding machine. The DDWM is changed from ready mode into the standby mode, automatically, after 2-minute intervals from this unload start. Then, the DDWM is changed into ready mode, automatically, since it is reused for welding. Moreover, the DDWM increases welding quality, productivity and reduces costs of welding. So, the DDWM can make a considerable contribution to the mobile welding industries. The effectiveness of the DDWM was proven by the experimental results.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.71-72
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• 2006

This paper introduces the results of the development of a new mobile Digital DC-arc Welding Machine (DDWM). A simple PI controller is applied to the DDWM to control the output welding current tracking the constant setting current. Furthermore, a hot-start function, an anti-stuck function, a standby mode and an intelligential circuit breaker (ICB) are included in the DDWM. The DDWM increases welding quality and saves more power energy than a conventional welding machine. Because the DDWM is changed from ready mode into the standby mode automatically after 2 minutes interval from this unload start. Then the DDWM is changed into ready mode automatically since it is reused to weld. Mover, the DDWM increases welding qualify, productivity and reduces costs of welding. So, the DDWM can have a great of contribution to the mobile welding industries. The effectiveness of the DDWM was proven by the experimental results and durable test.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2003년도 춘계학술대회 논문집
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• pp.157-158
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• 2003

급증하는 자동차 수요로 인해 발생되는 배출량 증가는 자동차 운행의 특성상 대도시 대기오염의 주원인으로 작용하고 있다. 자동차 배출오염물질의 배출량 추정 및 관리에 있어 연간 배출량 뿐만 아니라 월별 기온변화에 따른 배출량의 시간분포 또한 고려되어야 한다. 본 연구에서는 Hot emission에 부가되는 Cold start emission과 Evaporative VOC emission의 산정에 있어서 차종/차령에 대해서 월별 배출량을 추정하여 보았다. (중략)

• 조명전기설비학회논문지
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• 제18권5호
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• pp.9-15
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• 2004

메탈핼라이드 램프의 가장 큰 단점중 하나는 아크튜브가 뜨거운 상태에서는 순시 재점등이 불가능하다는 것이다. 메탈핼라이드 램프의 점등중 고온의 아크튜브는 초기 램프가 차가운 상태에서의 방전 전압보다 재점등 방전전압이 높아 재점등 시키는데 압력과 온도가 감소되어지는 약5분정도의 시간이 소요 된다. 만약 램프가 뜨거운 상태에서 재점등시키려면 램프전극 양단에 약20[kV] 이상의 높은 전압펄스를 공급해야한다. 따라서 이러한 목적의 전자식 안정기는 EMII필터, PFC회로, 플라이백 컨버터, 하프브리지 인버터, 고전압 이그나이터 회로로 구성되는데 이것은 순시점등은 물론 램프가 뜨거운 상태에서도 20[kV]의 전압으로 램프를 점등/재점등 할 수 있다.

• 한국물환경학회지
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• 제27권3호
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• pp.357-363
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• 2011

In spite of numerous advantages in railroads such as mass transportation, high reliability, and environmental soundness etc., the value of railroad construction is relatively underestimated compared to road. This is because the current method of evaluation focuses mainly on economic effect. In this study, considering recent research results, the environmental value of railroad construction was assessed by calculating the effect of reduction of emissions and water contamination. With these two benefits, the environmental effect produced by railroads and road construction was calculated and compared to each other using EMME/3. As a result, the senario 4 which considers 'Hot/Cold start' condition and water contamination had highest benefits. Furthermore, the environmental effect produced by railroad is 55~101% higher than road construction. If the suggested method is used in the current appraisal system, the environment-friendly mode like railway would be highly valued, much more than before.

• Journal of Magnetics
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• 제16권3호
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• pp.300-303
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• 2011

The effect of the hot-compaction temperature on the microstructure and magnetic properties of anisotropic nanocrystalline magnets was investigated. The hot-compaction temperature was found to impact both the magnetic properties and the microstructure of die-upset magnets. The remanence of the isotropic precursor increases slightly with the improved hot-compaction temperature, and the grains start to grow on the flake boundary at higher hot-compaction temperatures. After hot deformation, it was found that the change in the magnetic properties was the inverse of that observed with the hot-compaction temperature. Microstructural investigation showed that die-upset magnets inherit the microstructural characteristics of their precursor. For the die-upset magnets, hot pressed at low temperature, scarcely any abnormal grain growth on the flake boundary can be seen. For those hot pressed at higher temperatures, however, layers with large equiaxed grains could be observed, which accounted for the poor alignment during the hot deformation, and thus the poor magnetic properties.

• Journal of Welding and Joining
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• 제20권2호
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• pp.82-89
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• 2002

In order to clarify hot cracking phenomena occurred in Inconel 690 welds and it's prevention, in this study, the cracking behavior and the influence of welding variables on cracking in Inconel 690 overlay welds on Mn-Ni-Cr-Mo steel(SA 508 cl.3) for pressure vessel were investigated by using mock-up test. The main results are as follows: The cracks in Inconel 690 overlay welds were mainly generated near the start and the end part of welding beads adjacent to STS 309L welded outside of Inconel 690 welds. Most of the cracks showed typical solidification crack, and also it was assumed that there was possibility of liquation cracking in HAZ. The existence of Nb constituents or concentration of Nb was recognized on the fracture facets of the solidification cracks in the welds by SMAW. Therefore Nb was considered to be the main factor of the solidification cracking. As the weld heat input was more increased and the weld bead length was longer, the extent of cracking was more increased. Moreover the extent of cracking was considerably decreased by changing of welding sequence to the start and the end part of welds. Hot cracking in welds by GTAW was considerably decreased as compared with that of SMAW. And cracks were well generated in the Inconel 690 overlay welds adjacent to 575 309L welds. This means that the hot cracking susceptibility of Inconel 690 welds was largely varied by chemical components and/or compositions of filter metals, base metals and neighboring welds.

• 한국대기환경학회지
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• 제21권6호
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• pp.649-655
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• 2005

Automotive exhaust is suspected to be one of the main reasons of the rapid increase in greenhouse effect gases in ambient air. Although methane emissions are generally orders of magnitude lower than emissions of $CO_{2}$, the global warming potential (GWP) of methane is greater than that of $CO_{2}$. The environmental impact of methane emissions from vehicles is negligible and is likely to remain so for the foreseeable future. In this study, in order to investigate greenhouse gas emission characteristics from gasoline passenger cars, 20 vehicles were tested on the chassis dynamometer and methane emissions were measured. The emission characteristics by model year, mileage, vehicle speed were discussed. Test mode is CVS-15 mode that have been used to regulate for light-duty vehicle in Korea. It was found that $CH_{4}$ emissions showed higher for cold start, old model year and long mileage than hot start, new model year and short mileage, respectively. These results were compared with IPCC emission factors and the overall our results were anticipated to contribute for domestic greenhouse gas emissions calculation.

• 대한기계학회논문집B
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• 제26권6호
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• pp.788-794
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• 2002

In liquid rocket engine, propellant feed rate is proportional to approximately square root of the pressure difference between injector head and combustion chamber. This ΔP depends on the engine design, but in general on the order of 50psi. However, during ignition period, especially for the pressurized feed system, combustion chamber pressure is almost atmospheric and large ΔP causes over flow of propellants which may lead to catastrophic accident due to hard start. Hard start may be prevented by applying cavitating venturi or/and two step ignition. In cavitating venturi, evaporated propellants near the venturi throat become chocked and flow rate depends on only upstream condition. In two step ignition propellants are supplied to the liquid engine in two different flow rate. First step, to avoid hard start, small amount of propellants are supplied to build up chamber pressure in safe zone, then full propellants to ensure design pressure. In this study, both cavitating venturi and two step ignition method were used for the hot test and hard start problem was completely solved.