원형 덕트유동에서의 Graetz 문제에 대한 이중교환 경계요소 해석

최창용,Choi, Chang Yong 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.2

The dual reciprocity boundary element method (DRBEM) is used to solve the Graetz problem of laminar flow inside circular duct. In this method the domain integral tenn of boundary integral equation resulting from source term of governing equation is transformed into equivalent boundary-only integrals by using the radial basis interpolation function, and therefore complicate domain discretization procedure Is completely removed. Velocity profile is obtained by solving the momentum equation first and then, using this velocities as Input data, energy equation Is solved to get the temperature profile by advancing from duct entrance through the axial direction marching scheme. DRBEM solution is tested for the uniform temperature and heat flux boundary condition cases. Local Nusselt number, mixed mean temperature and temperature profile inside duct at each dimensionless axial location are obtained and compared with exact solutions for the accuracy test Solutions arc in good agreement at the entry region as well as fully developed region of circular duct, and their accuracy are verified from error analysis.

G 방정식을 이용한 실린더 챔버 내부 둔각물체 주위의 난류 예 혼합 화염 해석

최창용,박남섭,고상철,Choi Chang-Yong,Park Nam-Seob,Ko Sang-Cheol 한국마린엔지니어링학회 2005 한국마린엔지니어링학회지 Vol.29 No.4

In this investigation, turbulent premixed combustion and flame front propagation in a gas turbine combustion chamber is studied. Direct numerical simulation of turbulent reacting flows demands extremely high computational resources, especially in more complicated geometry. The alternative choice may be left for Large Eddy Simulation (LES) by which only large scales are solved directly. In combustion problems, capturing the large scales' behavior without solving the details of small scales is a difficult task. Using a transport equation for description of the flame front propagation and therefore avoiding the calculation of inner flame structure is the basic idea of this study. For this purpose. the so-called G-equation has been used by which any iso-level of the G variable provides the flame location. A comparison with the experiment indicates that the present method can predict a turbulent velocity field and also capture a instantaneous 3-dimensional flame structure.

SOI-MOSFET의 고온 동작에 관한 연구

최창용,문경숙,구상모,Choi, Chang-Yong,Moon, Kyung-Sook,Koo, Sang-Mo 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.8

The substrate bias effect on the current level of SOI-MOSFETs for high temperature operation has been investigated. In this work, we demonstrate the current level of SOI-MOSFETs can be controlled at different temperatures by applying a control bias to the substrate, showing that all current levels below T=150$^{\circ}C$ can be adjusted to a constant current level. 2D numerical simulation results show that substrate bias effectively controls the current conduction; as the substrate bias effectively lower the potential of the channel, inversion carrier generation is effectively controlled and consequently a constant current conduction level is achieved up to T=150$^{\circ}C$. We also demonstrate that the device simulated in this work has same operation at any temperature below T=150$^{\circ}C$ through mixed mode simulation.

800 V급 4H-SiC DMOSFET 전력 소자 구조 최적화 시뮬레이션

최창용,강민석,방욱,김상철,김남균,구상모,Choi, Chang-Yong,Kang, Min-Seok,Bahng, Wook,Kim, Sang-Cheol,Kim, Nam-Kyun,Koo, Sang-Mo 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.8

In this work, we demonstrate 800 V 4H-SiC power DMOSFETs with several structural alterations to obtain a low threshold voltage ($V_{TH}$) and a high figure of merit ($V_B\;^2/R_{SP,ON}$), To optimize the device performance, we consider four design parameters; (a) the doping concentration ($N_{CSL}$) of current spreading layer (CSL) beneath the p-base region, (b) the thickness of p-base ($t_{BASE}$), (c) the doping concentration ($N_J$) and width ($W_J$) of a JFET region, (d) the doping concentration ($N_{EPI}$) and thickness ($t_{EPI}$) of epi-layer. These parameters are optimized using 2D numerical simulation and the 4H-SiC DMOSFET structure results in a threshold voltage ($V_{TH}$) below $^{\sim}$3.8 V, and high figure of merit ($V_B\;^2/R_{SP,ON}$>$^{\sim}$200 $MW/cm^2$) for a power MOSFET in $V_B\;^{\sim}$800 V range.

후두부에 발생한 유피낭종의 특징

최환준,탁민성,최창용,강상규,이영만,Choi, Hwan-Jun,Tark, Min-Seong,Choi, Chang-Yong,Kang, Sang-Gue,Lee, Young-Man 대한성형외과학회 2010 Archives of Plastic Surgery Vol.37 No.4

Purpose: Congenital dermoid cysts develop during the fusion of the embryo when the ectodermal tissue gets trapped in the line of fusion. Dermoid cysts of the head are rare lesions comprised of epidermal and mesodermal elements. Furthermore, dermoid cysts in the occipital area are extremely rare. Only a few cases of dermoid cysts in the posterior scalp have been reported. Especially, A bilateral, synchronous presentation in this location has not been reported previously in the literature. Methods: All 5 cases had a gradually enlarging mass of the posterior aspect of the scalp. The cysts were mobile, noncompressible, and non-tender, without evidence of an associated sinus tract, skin dimpling, discoloration, or communication with adjacent structures. The CT scan displayed a hypodense cystic lesions about -87 to +24 HU (Housefield units, average +3.2 HU) with hypodense capsule and no postcontrast enhancement. All tumors were found just under the skin, and were well encapsulated, so they were completely removed the mass with adjacent periosteum. Results: On gross findings, all tumors were oval-or round-shaped, and when the cystic tumor was cut open it presented a greasy and caseous substance. Histologically, all specimens contain desquamated squamous epithelium and keratin in the lumen and are encapsulated and lined by keratinized stratified squamous epithelium. And, all cases of posterior mass are the presence of adnexal structures. Conclusion: Appropriate diagnosis requires not only an index of suspicion for this rare tumor a very careful history and search for skin changes. Especially, CT can reveal the exact location of the cyst, its relationship with the adjacent structures. We think that occipital dermoids divide into superficial and deep type. In our cases, because they did not have intra-cranial involvement or fistula formation, they are superficial type. This report describes the clinical and operative aspects of the superficial dermoid cysts and provides a review of the literatures.

태양열 구동 흡수식 냉난방시스템 TRNSYS 모델링

최창용(Choi Chang-Yong),조성환(Cho Sung-Hwan),곽희열(Kwak Hee-Youl),신우철(Shin U-Cheul) 한국태양에너지학회 2006 한국태양에너지학회 학술대회논문집 Vol.- No.-

This paper presents the simulation modeling and its results of the solar thermal driven absorption heating and cooling system for the library reading rooms of a cultural center building located in Gwangju Korea. In this study, single efficiency LiBr-H2O absorption chiller of the rated capacity 10 RT, and 0.7 COP with a evacuated tubular solar collector system is used for the solar cooling facility. A complete system composed of solar collectors, thermal storage tanks, absorption chiller, and auxiliary gas boiler is modelled, and the yearly solar energy supply rate of the system is predicted with the TRNSYS simulation results.

2차원 열전도 문제에 대한 Fast Multipole 경계요소법의 이론과 실행 알고리즘의 분석

최창용(Chang-Yong Choi) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.5

본 논문에서는 조밀한 계수행렬로 인해 경계요소 개수의 증가에 따른 계산 시간의 급격한 증가 때문에 대규모 문제를 쉽게 다룰 수 없는 기존 BEM 문제를 획기적으로 개선하는 새로운 BEM 해법인 FM-BEM을 소개한다. 단순한 2차원 정상상태 열전도문제를 통해서 FM-BEM과 기존 BEM의 계산시간과 정확도에 대한 해석 결과를 제시하였으며, 이로부터 FM-BEM 해법이 기존 BEM과 유사한 정확도를 유지하면서도 계산 속도를 획기적으로 높인다는 결과를 확인하였다. 결과적으로 본 연구에서는 FM-BEM의 적용 이론 및 관련 실행 알고리즘들을 고찰하고 이를 통해서 FM-BEM의 효용성을 검증하였으며, 향후 다양한 공학적 문제로의 적용 범위를 확대하고자 한다. This paper presents the fast multipole boundary element method (FM-BEM) as a new BEM solution methodology that overcomes many disadvantages of conventional BEM. In conventional BEM, large-scale problems cannot be treated easily because the computation time increases rapidly with an increase in the number of boundary elements owing to the dense coefficient matrix. Analysis results are obtained to compare FM-BEM with conventional BEM in terms of computation time and accuracy for a simple two-dimensional steady-state heat conduction problem. It is confirmed that the FM-BEM solution methodology greatly enhances the computation speed while maintaining solution accuracy similar to that of conventional BEM. As a result, the theory and implementation algorithm of FM-BEM are discussed in this study.

디젤탈황 단위공정의 CFD 모델링을 포함한 연료전지 시스템 공정설계 및 최적화

최창용 ( Chang Yong Choi ),임도진 ( Do Jin Im ) 한국화학공학회 2018 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.56 No.3

본 연구에서는 100 kW급 연료전지 시스템의 운영을 위한 공정 및 CFD 모델링을 진행하였다. 공정 모델링을 통해 연료전지 각 단위 공정에 유입되는 유량을 도출하였으며 수소로 전환되지 않는 디젤의 환류량을 도출하였다. 디젤의 환류를 고려한 새로운 유입 유량 조건을 이용해 CFD 해석을 진행한 결과, 환류 디젤이 없는 것으로 가정한 이전 연구 결과에 비해 더 짧은 유입시간과 비슷한 시간의 처리시간을 가지는 이점이 있음을 확인하였다. 6기의 탈황 반응기를 이용해 100 kW급 연료전지를 가동시키는데 필요한 TSA 탈황 시스템 구성을 완료하였으며 전체 TSA 공정 운영을 위한 운용 방안을 도출하였다. 반응기 사이의 열 전달 해석을 통해 저온의 탈황공정과 고온의 재생공정 간의 열 간섭이 크지 않음을 확인하였다. 본 연구결과는 연료전지 시스템의 효율화에 기여할 것이며, 도출된 탈황모듈의 설계는 연료전지 시스템뿐만 아니라 청정 석유화학산업의 기초가 될 것으로 기대된다. We performed process and CFD simulations of a 100 kW fuel cell system. By process simulation, we derived the input flow rate of each unit process and the recycle diesel flow rate. Through CFD simulation considering the recycle diesel flow, more efficient operational condition was found. Using 6 desulfurize reactors, a TSA process for a 100 kW fuel cell system was successfully constructed. Heat interference between reactors was found to be negligible. These results will contribute to increasing the efficiency of fuel cell system and the developed desulfurizing module design will contribute to the clean petrochemical technology as well as fuel cell systems.

유리상 탄소입자의 직접 접촉충전에 의한 전기영동 현상연구

최창용 ( Chang Yong Choi ),임도진 ( Do Jin Im ) 한국화학공학회 2016 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.54 No.4

본 연구에서는 고체 입자인 유리상 탄소입자와 액체인 수용액적을 이용한 접촉충전 비교 실험을 수행하여 액적 접촉충전 현상에 적용했던 완전도체 이론 적용의 적합성 및 고체 도체의 접촉충전 특성을 살펴보았다. 동일한 실험 장치 내에서 비슷한 크기의 수용액적과 유리상 탄소입자를 이용해 가해준 전기장의 세기와 입자의 크기를 변화시키며 충전량을 측정하고 완전도체 이론과의 비교를 통해 충전 특성을 분석하였다. 유리상 탄소입자의 접촉충전 현상은 기본적으로 완전 도체 이론으로 설명이 가능하였으나 실제 충전되는 충전량은 이론치 대비 70~80% 수준으로 측정되었으며 이는 고체 입자가 전극과 접촉하여 전하가 전달되는 과정 중 전극과 오일 사이 오일 필름의 형성으로 주어진 짧은 시간 내에 충분한 전하의 전달이 이루어지지 못해 나타난 것으로 추정된다. 본 연구 결과는 고체 도체의 접촉충전 특성에 대한 이해를 높여 향후 이 분야에 중요한 기초 정보를 제공할 수 있을 것으로 기대된다. We investigated the charging characteristics of a conducting solid sphere (glassy carbon sphere) comparing with that of a water droplet and check the applicability of the perfect conductor theory. For the systematic research, sphere size, applied voltages, viscosity of the medium were changed and the results were compared with that of corresponding water droplets and the perfect conductor theory. Basically, a glassy carbon sphere follows the perfect conductor theory but the charging amount was lower as much as 70~80% of theoretical prediction value due to oil film formed between electrode and a carbon sphere. We hope this result provides basic understandings on the solid sphere contact charging phenomenon and related applications.

대학생 참여 CSR유형에 따른 기업이미지, 기업평판 및 구매의도의 영향력 분석

최창용 ( Chang Yong Choi ),김형재 ( Hyung Jae Kim ) 국제지역학회 2015 국제지역연구 Vol.19 No.1

본 연구의 목적은 대학생 참여 CSR 유형에 따라 해당 변수들에 미치는 영향이 차이가 있는지를 분석하고 해당 사업에 대한 대학생들의 참여의도가 기업이미지, 기업평판 및 구매의도에 어떠한 영향을 주는지를 실증적으로 분석하고자 하는 것이다. 해당 연구의 실증적 연구결과를 도출해내기 위해 서울지역 대학생 468명을 대상으로 설문조사를 실시하였다. 연구결과 대학생 참여 CSR 유형에 따라 해당 변수(참여의도, 기업이미지, 기업평판 및 구매의도)에 미치는 영향은 유의미한 수준에서 차이가 있는 것으로 나타났다. 참여의도와 기업이미지 부분은 외부 타 단체나 기업 등과의 파트너쉽을 통한 외부 사업형태를 기업주도로 했을 경우 보다 긍정적인 반응이 발생되었다. 반면, 기업평판과 구매의도 변수에서는 앞선 참여 의도나 기업이미지와 달리 기업이 직접 CSR 사업을 추진하는 직접사업형태를 기업주도로 추진했을 경우보다 긍정적인 영향을 미친다는 것이 확인되었다. 이는 참여의도, 기업이미지, 기업평판 및 구매의도와 같은 변수들이 서로 상관성이 있는 변수임에도 불구하고 CSR 유형에 따라 반응을 보이는 패턴이 상이하므로 기업들이 대학생 참여 CSR 사업을 구상할 때 사업을 통해 궁극적으로 얻고자 하는 목적에 따라 사업형태를 전략적으로 선택해야 한다는 것을 의미한다. 마지막으로 CSR 유형 및 종속변수 관계에서 참여하는 대학생들의 의도(의지)정도가 높을수록 해당 기업의 CSR 사업 등에 관심도가 상승되고 긍정적인 평가가 형성되었다. In the past, the CSR in Korea used to be a simple type such as donating money to NPO(Non-Profit Organization)s, but the recent CSR for the companies seems to be more active such as forming their own CSR team. The recent trend in CSR which many companies has focused on is the CSR type which university students are involved in. The aim of this study is to analyze whether factors(participant intention, corporate image, corporate reputation and purchase intention) can be affected by the type of CSR involving university students. To get more empirical result from the study, the survey has been carried for 468 university students in Seoul. We found out the fact that there were some differences for the four factors depending on the type of CSR. For participant intention and corporate image, the type of external partnership leading by a corporation can be more positive. On the other hand, the type of direct CSR business leading by a corporation can affect to the factors affirmatively in corporate reputation and purchase intention. It means that we have to consider the different type of CSR as marketing method seriously when we plan the CSR which university students are involved in due to the relationship between the type of CSR and the factors. Lastly, more positive interest and reputation can be, the higher participant intention for university students is getting. Therefore we have to think deeply when choosing the type of CSR for an individual case.