• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.196-199
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• 2011

고압관, 가압관, 발사관으로 구성된 2단식 경가스 총을 사용하는 축소형 초고압 분사 시스템은 액체 제트를 초음속으로 생성할 수 있다. 이러한 초음속 액체 제트는 전방에 발생하는 충격파로 인한 액적 미립화를 촉진 시킬 수 있다. 본 연구에서는 초음속 액체 제트의 미립화 특성을 파악하기 위해 직선 원추형 노즐을 사용하여 기하학적인 형상 변화에 따른 실험을 진행하였다. 미립화 특성을 나타내는 SMD는 L/d가 증가할수록 $151.2{\mu}m$에서 $52.25{\mu}m$로 감소하는 경향을 나타내었다.

• 한국항해항만학회지
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• 제34권3호
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• pp.205-211
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• 2010

밸러스트수 처리를 위한 Plasma Gun의 전기적 특성과 오존 생성에 미치는 주요 운전변수들의 영향에 관해 실험실 규모 연구를 수행하였다. 방전개시전압보다 높은 전압이 인가되면 방전이 시작되고 오존이 생성되었으며 전압이 증가함에 따라 기체로 전달되는 에너지 및 오존 농도가 거의 선형적으로 증가하였다. 오존 생성 측면에서 최적의 에너지 효율성을 얻을 수 있는 전극간 거리가 존재하였으며 실험된 장치에서는 1.95 mm의 전극간 거리에서 최적 효율이 얻어졌다. 전기에너지 특성에 미치는 내부전극 재질의 영향은 무시할만한 수준이었으나 내부전극의 전기전도도와 열전도도 차이가 오존 생성에 큰 영향을 미치는 것으로 나타났다. 일정한 Plasma Gun 구조에서 오존 생성은 기체로 전달되는 에너지밀도에 의해 중요한 영향을 받는 것으로 나타났으며 유입되는 기체의 산소함량이 증가할수록 오존 생성이 증가하는 것으로 나타났다.

• 유통과학연구
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• 제16권4호
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• pp.83-88
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• 2018

Purpose - This study conducts an empirical analysis on gasoline pricing of Korean retail gas stations focusing on spatial effects. Unlike previous studies, the study uses an official land price for a proxy of the importance of location, and also allows the spatial effects from other competing gas stations as well. Research design, data, and methodology - In collection of data, we obtain more abundant data than those of previous studies. The gasoline prices used in the study are 909,084 observations as daily data from January 1 to July 31 of the year 2016. A proxy for the land price is collected by linking official public land price data with address information on each gas station. For the estimation, the study employs the Panel Spatial Dubin Model to make the best use of the collected location information. Results - As expected, spatial properties of gas stations have significant effects on the gasoline price. As the price per square meter increases by 100 thousands won, the price of gasoline rises 9 won per liter. Among other characteristics, the price increases by 16 won per liter if the station has a convenience store, and about 5 won if it has a car wash service. Gasoline price in Singapore accounted for 26% of variations in domestic gasoline prices. SK Energy and GS Caltex are the top brands in terms of price. The study also finds prices and other important properties of competing gas stations have significant effects on others' prices. Prices of competing gas station have a positive relationship with those of others. If a competing gas station raises the price, the gas station also raises the price, and lowering the price lower the price. Among brands, GS Caltex has the greatest downward pressure on nearby gas stations. Conclusions - The study confirms that location value of gas stations affect their gasoline prices, and the prices of the competing gas stations also have a significant effects on their prices. It suggests that the prices in the competing retail areas tend to be synchronized with each other.

• 한국수소및신에너지학회논문집
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• 제29권6호
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• pp.587-595
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• 2018

Recently, research is being conducted to use a fuel cell as a power source of unmanned aircraft. However, safety standards about applying fuel cells to unmanned aircraft are insufficient. In this paper, to improve the safety of the fuel cells for unmanned aircraft is experimentally studied. For this reason, standards for safety of fuel cells were analyzed. And influence of vibration among the evaluation items related to the safety of the fuel cell for unmanned aircraft was discussed. In order to, at constant intervals, vibration was applied to the fuel cell, then the performance was measured, the measurement items were gas tightness, polarization curve, frequency response analysis (FRA). A total of 220 hours was experimented at 20 hour intervals. the result of vibration test, gas leakage rate was a maximum of -0.04826 kPa/min and Polarization curve reached a maximum of 1.0103 times of the initial value, the charge transfer resistance reached a maximum of 1.0104 times of the initial value. This research indicate that performance of fuel cell is affected by vibration and this study is expected to contribute to the safety of fuel cell for unmanned aircraft.

• 대한기계학회논문집A
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• 제40권10호
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• pp.857-864
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• 2016

항공산업의 발달로 하늘에는 많은 비행기, UAV, 드론이 비행하고 있다. 비행기와 UAV는 빠른 속도로 비행하며 드론의 프로펠러는 빠른 속도로 회전하고 있다. 이렇게 빠른 속도의 비행체간의 충돌은 비행기 운항과 승객의 안전성을 위협하고, 지상에 있는 인명과 재산에 피해를 줄 수 있다. 비행체의 운항속도는 음속(340m/s) 내외이며, 프로펠러의 회전 속도는 그 보다 작은 속도 영역이다. 현재까지의 충돌 실험은 공기의 힘을 이용한 방식으로 충돌 속도를 얻었고, 공기 팽창에 따른 넓은 공간을 필요로 한다. 하지만 전자기력 발사장치는 그보다 작은 공간에서 충분한 속도를 얻을 수 있다.(~500m/s) 본 논문에서는 전자기력 발사장치의 설계와 이에 따른 제작에 관한 방법을 제시하고자 한다.

• Nuclear Engineering and Technology
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• 제12권3호
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• pp.163-170
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• 1980

4KJ의 에너지 뱅크(16.5KV, 35nH)를 사용하여 Mather형의 플라즈마총을 1 torr이하의 낮은 기체압력에서 동작시키면서 플라즈마의 효율적인 집속조건을 구하였다. 중수소기체의 충전압력이 0.18torr, 저장에너지가 3.8KJ일때 방전전류의 최고치는 180KA이었고 플라즈마의 축방향 평균속도는 약 $7cm/\mu\textrm{s}$이었다. 이것은 snowplow모델에 의해 계산된 속도보다 작은 값인데 이는 절연재 표면을 통한 전류의 손실에 기인하는 것으로 생각된다. H. Bruzzone의 플라즈마 집속장치(1KJ, 16KV, $4.2\mu\textrm{s}$)에 비해 본 실험에서는 기체압력이 낮은 역역에서 플라즈마 접속이 일어났다. 이는 이 실험에서 사용한 플라즈마총의 크기가 저장에너지에 비해 크고 또 잔여기체의 함량이 비교적 높기 때문이다. 집속된 플라즈마로 부터 방출되는 중성자는 Long counter를 사용해서 계측했다.

• Journal of Advanced Marine Engineering and Technology
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• 제29권1호
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• pp.116-123
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• 2005

The PID controllers have been widely accepted in many industrial systems due to their robust performance in a wide range of operating conditions and their functional simplicity To implement a PID controller, its three parameters must be determined for the given plant. Conventional tuning methods are mainly based on experience and experiment and are lack of systematic procedure Recently. to overcome drawbacks of conventional tuning methods, genetic algorithms have been used, In this paper a real-coded genetic algorithm is employed to search for the optimal parameters of the PID controller for speed control of marine gas turbine engines. Simulation results show the effectiveness of the proposed scheme.

• 한국분무공학회지
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• 제16권1호
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• pp.37-43
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• 2011

The present study conducted computational simulation for multiphase flow in the flame spray coating process with commercially available Ni-Cr powders. The flows in a flame spray gun is characterized by very complex phenomena including combustion, turbulent flows, and convective and radiative heat transfer. In this study, we used a commercial computational fluid dynamics (CFD) code of Fluent (ver. 6.3.26) to predict gas dynamics involving combustion, gas and particle temperature distributions, and multi-dimensional particle trajectories with the use of the discrete phase model (DPM). We also examined the effect of particle size on the flame spray process. It was found that particle velocity and gas temperature decreased rapidly in the radial direction, and they were substantially affected by the particle size.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2000년도 전력전자학술대회 논문집
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• pp.581-586
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• 2000

Gas metal arc welding(GMAW) uses a continuously fed electrode as a filler metal. The arc is shielded from atmospheric contamination by an inert gas active or inert/active gas mixture delivered through the welding gun and cable assembly. The recent research topics on $CO_2$ are welding machines are focused mainly on the reduction method of generated spatter by using new type consumable electrode metal or inverter control method. The various current waveform control methods have been researched for welding performance improvement. Until now current waveform control methods reduce to spatter occurred by instantaneous short circuiting,. but these methods is drawback that no reduce spatter occurred by arc reignition. In this paper the previous arc reignition current control method for welding performance improvement of inverter arc welding machine is studied and compared the various current control methods with the previous arc reignition current control method.

• Transactions on Electrical and Electronic Materials
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• 제6권4호
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• pp.173-176
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• 2005

A new $MoO_3$ based microsensor with low power consumption was presented. Typical size of sensor was 5mm in width and 8mm in length. As a sensitive electrode, $MoO_3$ was successfully fabricated by IC technology on pyrex glass of $250{\mu}m$ in thickness. After annealing at $550^{\circ}C$ for 3hrs, the film was fully crystallized and demonstrated as pure $MoO_3$ structure. The grain size of $MoO_3$ was plat like and typical size was about $1{\mu}m$. Based on the results of sensitivity measurement, $MoO_3$ microsensor shows especially high selectivity to $H_2$ reducing gas atmosphere. The applied heater power was lower than 0.5 Watt.