• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.415-418
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• 1998

The maleate copolyrner($C_{18}MA-VE_2$) is used as sensitive materials and deposited on the slide-glass substrates at room temperature using Langmuir-Blodgett(LB) method. The results of current-time(1-t) measurements are performed to investigate the gas-detection characteristics of the sensitive LB films in the presence of organic gases just as chloroform, acetone, ethanol, methanol using the apparatus for the gas-detection measurement. Several interesting responses are observed at room temperature, such as reversible response, sensitivity and response time. Response time and sensitivities are evaluated 160~220[sec], minimum 6[times], maximum 70[times] for each organic gas by adsorption and penetration of the organic gases in the relation concentration of 100[%], respectively.

• 한국분무공학회지
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• 제17권4호
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• pp.205-209
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• 2012

This study focused on comparing macroscopic characteristics of DME and diesel fuel experimentally. DME fuel is one of the most promising alternative fuels because of its superiority in atomization characteristic and clearness in terms of exhaust gas compared with existing fossil fuels. In addition, DME fuel has high cetane number so it could be applied to compression ignition engine. However because DME fuel exists in gas phase at room temperature and atmospheric pressure, and it corrodes rubber parts of fuel line, DME fuel is hard to apply to commercial vehicles. To establish knowledge about DME fuel and furthermore, to develop commercial DME vehicles such as passenger cars, many research have been proceeded steadily. The present study, by comparing spray characteristics of DME fuel to those of diesel fuel, improved atomization characteristics in DME were revealed. Injection quantity measurement and spray visualization experiment were progressed and it was revealed that DME fuel shows small injection quantity than that of diesel fuel and axial development of spray in terms of spray tip penetration decreases when DME fuel was injected.

• 한국항공우주학회지
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• 제45권6호
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• pp.447-454
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• 2017

난류 유동장으로 분사되는 두가지 형태의 액체 제트 (수평분사는 디젤연료와 수직분사는 물)의 액주 분열과 미립화 현상에 관한 이상(Two-phase) 유동에 대해 3차원 LES 수치해석을 수행하였다. 기체상태의 공기 유동은 오일러리안 해법을 사용하고, 액체 제트의 액적 추적은 라그랑지안 해법을 사용하여 기체-액체간 이상유동 해석을 수행하였다. 두 종류의 확률론적 분열 모델(Stochastic breakup model)을 사용하여 액적 분열을 모사하였으며, 액체제트의 침투깊이와 액적 분포(Sauter Mean Diameter)를 실험결과와 비교하여 미세하게 분열되는 액체 제트의 분열 현상에 대해 확률론적 분열 모델링의 적합성을 제시하였다.

• Journal of Welding and Joining
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• 제21권2호
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• pp.57-63
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• 2003

Since new types of vehicles or structures made from thin aluminum alloy are under rapid development and some products are already on the market, welding of aluminium sheet is increasing. MIG(Metal Inert Gas), MIG-Pulse, TIG(Tungsten Inert Gas) welding are the typical Ai welding. MIG welding has the advantage of high speed, but it is difficult to apply to the thin plate, because of bum-through by the high heat input and spatter. MIG-Pulse welding can weld without spatter and burn-through, but when the gap exists at the welding joint, there is quite a possibility of bum-through. TIG welding is difficult to weld at a high speed. AC Pulse welding alternates between DCEP(Direct Current Electrode Positive) and DCEN(Direct Current Electrode Negative). DCEN is higher wire melting rate than DCEP, while lower temperature of droplet than DCEP. In AC Pulse welding, far fixed welding current, wire melting rate increases as the EN ratio increases. For fixed wire feed rate, welding current decreases as the EN ratio increases. Because of these features, the temperature of droplet, the depth of penetration, the width of bead decrease and the reinforcement height increases as EN ratio increases, and these are able to weld at a high speed, lower heat input. It is the purpose of this study that design of AC pulse current waveform for MIG welding of Al sheet and estimation of output characteristic.

• 한국정밀공학회지
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• 제19권4호
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• pp.132-139
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• 2002

In GMAW(Gas Metal Arc Welding) processes, bead geometry (penetration, bead width and height) is a criterion to estimate welding quality. Bead geometry is affected by welding current, arc voltage and travel speed, shielding gas, CTWD (contact-tip to workpiece distance) and so on. In this paper, welding process variables were selected as welding current, arc voltage and travel speed. And bead geometry was reasoned from the chosen welding process variables using neuro-fuzzy algorithm. Neural networks was applied to design FL(fuzzy logic). The parameters of input membership functions and those of consequence functions in FL were tuned through the method of learning by backpropagation algorithm. Bead geometry could be reasoned from welding current, arc voltage, travel speed on FL using the results learned by neural networks. On the developed inference system of bead geometry using neuro-furzy algorithm, the inference error percent of bead width was within $\pm$4%, that of bead height was within $\pm$3%, and that of penetration was within $\pm$8%. Neural networks came into effect to find the parameters of input membership functions and those of consequence in FL. Therefore the inference system of welding quality expects to be developed through proposed algorithm.

• Journal of Welding and Joining
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• 제30권2호
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• pp.70-75
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• 2012

In this study, effect of nitrogen volume in the shielding gas of Ar-$N_2$ mixing gas on the bead shape, hardness and microstructure of GTA welds of 3mm thick Commercial Pure Ti was investigated. As the nitrogen volume increased, the welding current for full penetration was reduced and hardness in the fusion zone significantly increased compared with that of the base metal, but there is no difference in the hardness of HAZ. Microstructure in the fusion zone with pure Ar gas changed from equiaxed alpha of the base metal to serrated alpha. On the other hand, microstructure using Ar-$N_2$ mixing gas changed to acicular alpha. With the increasing of nitrogen content, the amount of acicular alpha increased and the size of that was fine.

• 동력기계공학회지
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• 제9권4호
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• pp.209-213
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• 2005

The effects of density change of ambient gas on mixture formation process have been investigated in high temperature and pressure field. To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Ambient gas density was selected as experimental parameter. The ambient gas density was changed from $r_a=5.0kg/m^3\;to\;r_a=12.3kg/m^3$ with a high pressure injection system(ECD-U2). For visualization of the experiment phenomenon, a CVC(Constant Volume Chamber) was used in this study. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas.

• Journal of Welding and Joining
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• 제31권3호
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• pp.60-65
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• 2013

Ar, $N_2$, and He are the conventional kind of shield gas that are used for laser welding. Many researches on the impact of laser welding shield gas have been done, and it is on going until now. However, there are few studies that analyze the changes and differences of the plasma emission signal. Therefore, in this study, we evaluated the change in the penetration characteristics according to the type of shield gas during fiber laser welding impacts to the plasma signal. As a result, if was checked that the difference in molecular weight of Ar, $N_2$, and He affects to the amount of spatter, and also found that the measured plasma radiation signal changes similar to the order of the molecular weight of the gases. Especially, clear change on the signal intensity per each shield gas was measured through RMS, and found that the shield gas was nothing to do with the FFT analyzed result.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.2020-2022
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• 2000

The cross-linked polyethylene(herein after XLPE) insulated power cable emit the methane($CH_4$)gas in the course of chemical cross-linking process. The general stranded conductor easily discharge this methane gas through the gap of each stranded wires. But the special stranded conductor that filled with semi-conducting rubber compound to prevent water penetration which is applied to water proof type of cable(22.9kV CN/CV-W), disturb the methane gas emission. The pre-mold type cable joint shall be expanded gradually by emit of gas left in XLPE insulation. For example, sometimes the corona problem outbreak on a new power distribution line, resulted from the gap between the sleeve and semi-conductive layer of cable joint. If above mentioned problem especially happened on the way of operating. We have to shut down the line and try to discharge the methane gas in cable joint. In this point, we would like to explain the mechanism of methane gas & cable joint and our test result briefly. At last, we are pleased to introduce the solution for preventing reoccurrence of this problem.

• International Journal of Korean Welding Society
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• 제1권2호
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• pp.30-35
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• 2001

Nowadays, repair welding on in-service natural gas pipeline is a matter of primary concern of gas company. The main purpose of this study is to investigate the effects of welding conditions on the allowable heat input for crack-free welds and welds without burn-through onto in-service natural gas pipeline. First of all, single pass weld bead on plates of the various thickness was deposited to evaluate the penetration of weld metal, the depth of heat affected zone and the hardness of repair weld under various welding conditions. Also, finite element analysis has been conducted to validate experimental results of bead-on plate welds and to develop appropriate model for repair welding. The welding experiments of bead-on-plate weld confirmed the influence of plate thickness, heat input and welding process on safety. And, the finite element model was demonstrated by comparing experimental results. The agreement between the computed and measured values was shown to be generally good. Therefore, It is possible to predict the safety of repair welding under various welding conditions with experimental results and finite element analysis model.