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차세대 군용전원용 500W급 마이크로 터빈 발전기 시스템 설계
최상규,최범석,한용식,우병철,송인혁,민성기,임진식,Choi, Sang-Kyu,Choi, Bum-Suk,Han, Yong-Shik,Woo, Byung-Chul,Song, In-Hyuck,Min, Seong-Ki,Lim, Jin-Sik 한국군사과학기술학회 2011 한국군사과학기술학회지 Vol.14 No.6
Recent developments of small-size unmanned or manned mobile systems such as autonomous robots, exoskeleton or armored suits, micro air vehicles, and unmanned armored vehicles require long-lasting independent power sources of high energy and power density to support the systems' operation for up to 72 hours in the fields. Chemical batteries such as Ni-MH, Li-Ion, the current primary power sources for mobile devices, however, are not capable of providing enough power and energy density for the next generation high power mobile machines. For this reason, KIMM along with KERI and KIMS has been carrying out a 500W MTG development project under the DAPA's "Next generation military power source R&D program" since 2009. In this paper, a design process for a 500W MTG system currently being developed at KIMM is briefly described and the technical issues related to its development are addressed.
재활용 산화철 및 알루미늄 분말을 활용한 철도레일 이음용 테르밋 분말 개발
최상규,박성상,백응률,Choi, Sang-Kyu,Park, Sung-Sang,Baek, Eung-Ryul 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.5
Nowadays in Republic of Korea, whole amount of the thermite welding powder for rail joinning is dependent on import. However the demand of the thermite welding powder would be enlarge because some constructing high-speed train and city metro projects are currently in progress. In addition this is the main reason why we should develop the thermite welding powder, domestically. This study is focused on utilizing the recyclable materials like Al powders from cans and iron oxide scales from wire rods as the main components of the thermite welding powder. By minimizing Al content in weld zone by controlling the mixing ratio of the Al powder in the thermite welding powder, the excessive dissolution of the Si and Mn components came from the Al powders could be controled. The tensile strength of welding zone in welded rail was 740 MPa, with that the developed thermite welding powder.
관 유동과 Blasius 유동에서 가장 불안정한 교란에 관하여
최상규,정명균,Choi, Sang-Kyu,Chung, Myung-Kyoon 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.6
The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.
급속열분해를 통하여 생산된 바이오오일 액적의 증발 특성에 관한 수치해석적 연구
최상규 ( Sang Kyu Choi ),최연석 ( Yeon Seok Choi ),김석준 ( Seock Joon Kim ),한소영 ( So Young Han ) 한국공업화학회 2016 공업화학 Vol.27 No.6
바이오매스는 최근 화석연료의 고갈 및 지구온난화 등의 문제에 대응하기 위한 신재생에너지원으로 많은 관심을 받고 있다. 바이오오일은 폐목재, 농업 및 임업 부산물 등의 바이오매스로부터 급속열분해 과정을 통하여 생산되는 액체연료이다. 바이오오일은 일반적인 석유 계통의 연료에 비하여 점도가 매우 높고 고체상의 불순물을 포함하고 있어 버너 적용시 스프레이 분무 특성이 저하된다. 또한, 바이오오일은 셀룰로오스, 헤미셀룰로오스, 리그닌으로부터 유래되는 수백 종류의 화학종들로 이루어져 있어 일반적인 액체연료와는 액적의 증발 특성이 뚜렷하게 구분된다. 본 연구에서는, 바이오오일의 구성 성분을 아세트산, 레보글루코산, 페놀, 수분으로 단순화하여 액적의 증발 특성에 관한 수치해석적 연구를 수행하였다. 다양한 주위공기 온도, 액적의 초기 지름, 에탄올 혼합 비율에 대하여 액적의 증발 특성을 비교하였다. 주위공기 온도가 높아질수록 바이오오일 액적의 증발 시간은 짧아졌으며, 특히 낮은 온도 범위에서는 증발 시간이 공기온도에 매우 민감하였다. 또한 액적의 지름이 감소할수록, 에탄올 혼합 비율이 증가할수록 증발 시간이 단축됨을 알 수 있었다. Biomass is regarded as one of the promising energy sources to deal with the depletion of fossil fuels and the global warming issue. Biocrude-oil can be produced through the fast pyrolysis of biomass feedstocks such as wood, crops, agricultural and forestry residues. It has significantly higher viscosity than that of conventional petroleum fuel and contains solid residues, which can lower the spray and atomization characteristics when applied to the burner. In addition, biocrude-oil consists of hundreds of chemical species derived from cellulose, hemicellulose and lignin, and evaporation characteristics of the bio-crude- oil droplet are distinct from the conventional fuels. In the present study, a numerical study was performed to investigate the evaporation characteristics of biocrude-oil droplet using a simplified composition of the model biocrude-oil which consists of acetic acid, levoglucosan, phenol, and water. The evaporation characteristics of droplets were compared at various surround-ing air temperatures, initial droplet diameters, and ethanol mixing ratios. The evaporation time becomes shorter with increasing air temperature, and it is much sensitive to the air temperature particularly in low temperature ranges. It was also found that the biocrude-oil droplet evaporates faster in cases of the smaller initial droplet diameter and larger ethanol mixing ratio.
최상규(Choi, Sang-Kyu) 한국산학기술학회 2014 한국산학기술학회논문지 Vol.15 No.12
본 연구에서는 GPH(Geweke and Porter-Hudak, 1983) 추정량을 이용하여 KOSPI200지수의 제곱수익률과 절대수익 률을 장기기억속성이 있는지 실증분석을 수행하였다. GPH는 장기기억보전 시계열 모수 d를 직선회귀에 의해서 추정하였으 며 이를 GPH 추정량이라고 하며 이는 대역폭 m에 의존한다. m값에 따른 GPH추정량의 자취를 확인하여 추정 값이 안정적 인 구간을 확인하여 m을 결정한다. 분석 결과 KOSPI200지수의 제곱수익률과 절대수익률은 0< d <0.5를 만족하여 장기기억 속성을 가지고 있는 것으로 나타났다. This study examined the squared returns and absolute returns of KOSPI 200 with GPH (Geweke and Porter-Hudak, 1983) estimators. GPH was estimated by the long-term memory preserving time series parameter d in linear regression. This called the GPH estimator, which depends on a bandwidth m. m was decided by confirming the stable section of the point estimate by validating the track of the GPH estimator according to the value of m. The result suggests that by satisfying 0< d <0.5, the squared returns and absolute returns of KOPI 200 retains long-term memory.
대향류 예혼합화염의 소염 메커니즘에 관한 수치해석적 연구
최상규(Sang-Kyu Choi),조은성(Eun-Seong Cho),정석호(Suk-Ho Chung) 한국연소학회 2009 KOSCOSYMPOSIUM논문집 Vol.- No.39
The extinction mechanisms of premixed flames are investigated numerically. A symmetric double premixed flame in a counterflow configuration is adopted as a model problem, and a local equilibrium temperature is used as a measure of energy loss or gain in order to quantify the extinction mechanism caused by preferential diffusion and incomplete reaction due to the stretch rate for CH₄, H₂, C₃H?, CO, CH₄+H₂, and CO+H₂ premixed flames. The energy loss ratios from preferential diffusion and incomplete reaction were calculated at various equivalence ratios near flame extinction. The Lewis number is responsible for these two distinct modes of flame extinction. Results show that the extinction of lean CH₄, H₂, CH₄+H₂, CO+H₂, and rich C3H? premixed flames results from incomplete reaction due to the insufficient reaction time, implying that the Lewis number is smaller than unity. On the contrary, rich CH₄, H₂, CH₄+H₂, CO+H₂, and lean C₃H? premixed flames are affected by the combined effects of preferential diffusion and incomplete reaction, which indicates that the Lewis number is larger than unity. In CO premixed flames, incomplete reaction was dominant in both lean and rich cases. The extinction mechanisms could be quantified by the local equilibrium temperature, and the effective Lewis numbers were assumed indirectly.