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{Ca,Sr,Ba}$Fe_2As_2$의 전자 및 자성 구조: 동력학적 평균장 이론 접근
이근식,심지훈,Lee, Geun-Sik,Shim, Ji-Hoon 한국초전도학회 2011 Progress in superconductivity Vol.13 No.2
Using the density functional theory and its combination to the dynamical mean field theory (DMFT), we have studied the electronic and magnetic structures of Fe-based superconductors, $AFe_2As_2$ (A=Ca, Sr, Ba). Our results for the electronic structure agree well with existing angle resolved photoemission spectroscopy (ARPES) data. The temperature dependent magnetization has been calculated using DMFT, and the magnetic transition temperatures are reasonably consistent with the experimentally observed trend for three compounds. 제일원리 DFT+DMFT방법을 사용하여 철계열 고온초전도체 122 화합물 $AFe_2As_2$ (A=Ca, Sr, Ba) 에 대한 전자 및 자성 구조를 계산하였다. 계산된 전자구조는 실험에서 보고된 ARPES 결과와 어느 정도 일치함을 확인했다. 또한 계산을 통해 얻은 반자성 전이온도는 실험과 동일한 경향을 보여준다.
이근식,장영수,노승탁,Lee, Geun-Sik,Jang, Yeong-Su,No, Seung-Tak 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.5
In operating the underwater engines such as encountered in exploring submarines, the dumping of the exhaust gas out of the engine requires a large portion of the total power, frequently amounting to 25-30% of the power generated. This unfavorable circumstance can be cured by liquefying the exhaust gas and storing it. In the present study, two liquefaction systems were simulated to enhance the overall efficiency; one is a closed cycle diesel engine and the other is a closed cycle LNG engine. The liquefied natural gas (LNG) is chosen as a fuel, not only because its use is economical but also because its cold energy can be utilized within the liquefaction system. Since a mixture of oxygen and carbon dioxide is used as an oxidizer, liquefying carbon dioxide is of major concern in this study. For further improving this system, the intercooling of the compressor is devised. The necessary power consumed for the liquefying system is examined in terms of the related properties such as pressure and temperature of the carbon dioxide vessel as a function of the amount of the exhaust gas which enters the compressor. The present study was successful to show that much gain in the power and reduction of the vessel pressure could be achieved in the case of the closed cycle LNG engine. The compression power of exhaust gas were observed remarkably lower, typically only 6.3% for the closed cycle diesel engine and 3.4% for the closed cycle LNG engine respectively, out of net engine power. For practicality, a design -purpose map of the operating parameters of the liquefaction systems was also presented.
이근식(Geun Sik Lee),신중하(Jung Ha Shin) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5
반동도에 따른 증기터빈의 설계 및 성능 해석을 컴퓨터 시뮬레이션으로 수행하였다. 깃 각도와 출구면적, 노즐면적과 같은 설계변수들이 반동도에 따라 제시되었다. 터빈동력, 선도효율, 축방향 추력과 같은 성능변수들을 반동도에 따라 제시하였다. 추가적인 설계 및 성능변수에 대한 정보를 제공하기 위하여, 깃 각도와 터빈동력, 선도효율, 축방향 추력과 같은 주된 성능변수들을 유동계수(주속도에 대한 축방향속도)의 함수로 제시하였다. 터빈동력, 선도효율을 최대로 하는 반동도 및 유동계수가 존재함이 밝혀졌으며, 반동도가 증가함에 따라 동익의 깃 형상은 대칭형으로부터 많이 벗어남을 보여주었다. Design and performance analysis of a steam turbine for variations of degree of reaction were performed with aid of computer simulation. Design parameters such as blade angles and exit areas and heights of nozzle and moving blade were represented as a function of degree of reaction. Main performance factors such as turbine power, diagram efficiency, and axial thrust were expressed in terms of degree of reaction. For further information of design and performance, blade angles and main performance factors were investigated as a function of flow coefficient. It was found that there exist maximum values of turbine power and diagram efficiency for both a degree of reaction and a flow coefficient and moving blade has a tendency to deviate from symmetric shape as a degree of reaction is increased.
이근식(Geun Sik Lee),박민영(Min Young Park) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The exact measurement of flow rate is needed in the delivering process of petroleum, city gas, and water, for fair commercial trade or energy saving. The main factors to affect the precision of a positive displacement flowmeter are leakage flows through clearances between housing and inner rotors. In this study, we investigated the inner flow characteristics of an oval-gear flowmeter with higher rotating performance and precision than those of a circular-gear flowmeter, for further improvement of precision. The inner flow field of the housing was examined with aid of ADINA-FSI (Fluid-Structure Interaction) method. The trends were compared with experimental results such as flow visualization and measurements of flowrate, rpm, and pressure drop.
강판 예열용 가스토치의 내외부 형상수정에 의한 출구유동균일도 개선
이근식(Geun Sik Lee),고티엔터(Tu Thien Ngo),웬반합(Hap Van Nguyen),고준호(Jun Ho Go) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
This study focuses on improving the exit flow uniformity of a gas torch with multi-exit holes. Based on the original model, three different models are designed and analysed with aid of CFD software ANSYS FLUENT. The original model has T-shaped configuration with one inlet and multi-exit holes. Model 1 has a long perforated strip with different hole diameters from the center to the right and left ends. Model 2 has a reverse Y-branch(2-symmetric bypass pipes in the inlet region), 2-stage diffuser to the center flow region, and corner cut shape at both ends. Model 3 has an enlarged inlet with triangular shape, a short perforated strip in the center flow region, and corner cut shape at both ends. Flow uniformity(γ) at multi-exit holes(γ=1 means the highest uniform and γ=0 means the lowest uniform) together with velocity distribution was investigated within the Reynolds number ranging from 10,000 to 50,000. Compared with original model to have the flow uniformity ranging from 0.798 to 0.821, the three new models had γ1 = 0.889 - 0.899, γ2 = 0.892 - 0.898 and γ3 = 0.891 - 0.916, respectively. With a pertinent trade-off (between the capital cost to the new design and the operating cost to save the fuel energy and to obtain a good quality for steel preheating), a suitable geometry of gas torch can be drawn.
이근식(Geun-Sik Lee) 한양대학교 수행인문학연구소 2006 수행인문학 Vol.36 No.-
John Stuart Mill was an economic liberalist to oppose any government regulations of trade and prices. But he was a progressive liberalist to insist strongly on institutional reforms to correct unfair economic distribution in capitalism. He wrote that distribution is a matter of human institution solely and it can be changed by institutional reforms. He supported measures to suppress labor population such as population control and foreign colonization, but he opposed such means as minimum wage system and wage allowance system. He defended trade unions, minimum subsistence system and, most of all, partial limitations of the property ownership of land and heritage. Futhermore, he recommended laborers’ cooperative as the ideal form of firms, in which competitions are working and a cooperative is owned collectively by laborers. Like most economists of the times he expected that the stationary state where economy and population stop to grow, would come. But he thought, contrary to others, it would be a desirable state because destructions of nature and conflicts of men would not go on any more. While he supported rational socialism such as Fourierism, he criticized strongly communism which insists on violent revolution, centrally managed national economy by one authority, and perfect equal distribution. He predicted that communistic country would collapse down for the lack of freedom, struggles for power and fall of productivity.