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Bernard Parent,최정열(Jeong-Yeol Choi) 한국추진공학회 2008 한국추진공학회 학술대회논문집 Vol.2008 No.11
스크램젯 비행체에서 극초음속 순항미사일의 추진 특성을 향상시키고 항력을 적게 발생하면서 전력을 생산하는 장치로써 MHD 장치가 최근 들어 큰 관심을 받아왔다. 이전에 보였던 것보다 보다 완전한 물리적 모델을 바탕으로 하면, 경계층 박리 억제나 파워 바이패스를 통해 극초음속 추진 시스템의 성능 향상을 하는 MHD의 쓰임새를 논의하는 것은 불필요한 일이 된다. MHD 유동 제어를 하게 되면 엔진 성능에 상당한 역효과를 미치는 불가피한 Joule 가열이 크게 발생한다. 하지만, 예비조사에 따르면 MHD는 약간의 항력만을 더 발생하면서 스크램젯 엔진을 장착한 무기에 메가와트 단위의 큰 전력을 생산해 낼 수 있을 것으로 여겨진다. Magnetohydrodynamics (MHD) devices have received considerable attention in recent years as a means to either improve the propulsive characteristics of hypersonic cruise missiles or as a means to generate power at low cost in drag and weight aboard scramjet powered vehicles. Based on more complete physical models than previously used, it is here argued that the use of MHD is not valuable in improving the performance of hypersonic propulsion systems through prevention of boundary layer separation or power bypass. This is due to the inevitable high amount of Joule heating accompanying MHD flow control having considerable undesired adverse effects on the engine performance. On the other hand, preliminary estimates indicate that MHD is likely to succeed in generating high amounts of power with little additional drag to feed megawatt-class energy weapons on-board scramjet engines.
배철오,신명철,김윤식,길경석 한국정보통신학회 1999 한국정보통신학회논문지 Vol.3 No.2
In MHD power generation system, enthalpy of the working gas is convened to electric power directly through expansion in generator channel. It means that electric power can be generated without a moving mechanical linkage such as turbine blades. The principle of MHD generation is based on Faraday'law of induction that eletromotive force(u$\times$B) is generated when the working gas of velocity u flows a channel in which magnetic field of strength(B) exists. In this paper, helium gas seeded with cesium is used as working gas. There are two types of generator in MHD generation; linear type faraday and disk type hall generator. Rogowski coils having the bandwidth of the 100(Hz) ~ 20(kHz) were used for measuring current flowing MHD disk channel. Optimum load resistor value of the MHD generator studied was 2.5[$\Omega$]. Disk type hall generator's generation performance is the main target of this paper, which superiors to linear type Faraday generator in many points. Isentropic efficiency and enthalpy extraction rate of disk type shock tube driven hall generator is discussed here.
노창주,김윤식,공영경,이성근 한국마린엔지니어링학회 1993 한국마린엔지니어링학회지 Vol.17 No.3
Usually ship is propelled by the conventional propeller. When the conventional propeller is used for ship's propulsion, reduction of propeller noise is big issue in some special vessel. In order to reduce the acoustic noise of the propeller, novel propulsion system named as MHD propulsion system has been studied among researchers. In this paper, thruster characteristic analysis and system analysis of MHD propulsion system have been carried out. Firstly basic experimental apparatus is designed, fabricated and installed and test is carried out. Test results are compared with numerical analysis. It is confirmed that test results agreed with numerical results satisfactorily.
Mucha-Habermann disease successfully treated with methotrexate
( Seung-ju Lee ),( Jong Hoon Kim ),( Soo-chan Kim ) 대한피부과학회 2019 대한피부과학회 학술발표대회집 Vol.71 No.1
Mucha-Habermann disease (MHD) is a rare variant of pityriasis lichenoides et varioliformis acuta (PLEVA) characterized by generalized erythematous coalescing papules with necrotic ulcerations and crusts with fever or systemic manifestations. Histopathologic findings show vacuolar change of the basal layer, lymphohistiocytic infiltrate in the dermis, and numerous erythrocytes into the epidermis. Early diagnosis and management are crucial, since MHD is a potentially fatal disease. To date, several treatment options have been suggested for MHD, such as systemic steroids, cyclosporine, or methotrexate. Herein, we report a case of MHD successfully treated with methotrexate. A 24-year-old female presented with generalized erythematous papules and necrotic ulcerative crusted lesions on the whole body with flexural accentuation since she was eight years old. Skin biopsy showed serocrust and ulceration on the epidermis, perivascular inflammatory cellular infiltration, necrotic keratinocytes, and extravasation of erythrocytes. The laboratory test did not show any significant abnormal finding. From these clinical and histopathological findings, the patient was diagnosed with MHD. The treatment of methotrexate (7.5~15mg/week) was started. The patient showed remarkable improvement within two months without any complication.
MHD발전용 작동 플라즈마를 고온가열하기 위한 효율적 방안에 관한 연구
김윤식,노창주,김영길,공영경,최춘성 대한기계학회 1993 대한기계학회논문집 Vol.17 No.1
본 연구에서는 각 운전모드별 열특성을 전체적으로 고려하여 양질의 MHD발전 용 작동플라즈마를 얻기 위하여 필요한 효과적인 방책에 관하여 집중적으로 고찰하고 자 한다. Heat transfer processes in the combustion chamber of a pebble bed regenerative heat exchanger for MHD power generation has been analyzed numerically for heating, evacuation argon heating periods individually. The calculated result well explain the measured temperature change at the top of the pebble bed. The analytical result point out that the length of evacution period and the geometry optimization both for the combustion chamber and the heat storage bed are very important factors for the improvement of thermal performance in MHD power generation.
전자기 전항을 이용한 압전 구동방식 마이크로 펌프의 유동 및 성능 특성에 관한 수치해석적 연구
안용준(Yong Jun An),최청렬(Chung Ryul Choi),김창녕(Chang Nyung Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
A numerical analysis has been conducted for flow characteristics and performance of a micropump with piezodisk and MHD(Magnetohydrodynamics) fluid. Various micro systems which could not be considered in the past have been recently growing with the development of MEMS(Micro Electro Mechanical System) and micro machining technology. Especially, micropumps, essential part of micro fluidic devices, are being lively studied by many researchers. In the present study, the piezo electric micropump with electromagnetic resistance for electrically conducting fluids is considered. The prescribed grid deformation method is used for the displacement of the membrane. The change of the performance of the micropump and flow characteristics of the electrically conducting fluid with the magnitude of the magnetic fields, duct size, the position of the inlet and outlet duct are investigated in the present study.
Unique continuation type theorem for the self-similar Euler equations
Academic Press ; Elsevier Science B.V. Amsterdam 2015 Advances in Mathematics Vol.283 No.-
We prove a unique continuation type theorem for the self-similar Euler equations in R<SUP>3</SUP>, assuming the time periodicity. Namely, if a time periodic solution V(y,s) of the time dependent self-similar Euler equations has the property that V(0,s)=0 for all s@?[0,S<SUB>0</SUB>], where S<SUB>0</SUB> is the time period, and y=0 is a local extremal point of V(y,s) near the origin, then, V(y,s)=0 for all (y,s)@?R<SUP>3</SUP>x[0,S<SUB>0</SUB>]. A similar result holds for more general system with arbitrary coefficients, and also for the inviscid incompressible magnetohydrodynamic (MHD) system. As a consequence we obtain new criteria for the absence of the discretely self-similar singularities for the 3D Euler equations and the inviscid 3D MHD.
ASYMPTOTIC BEHAVIOR OF SOLUTIONS FOR THE GENERALIZED MHD AND HALL-MHD SYSTEMS IN ℝ<sup>n</sup>
Zhu, Mingxuan Korean Mathematical Society 2018 대한수학회보 Vol.55 No.3
This paper deals with the asymptotic behavior of solutions to the generalized MHD and Hall-MHD systems. Firstly, the upper bound for the generalized MHD and Hall-MHD systems is investigated in $L^2$ space. Then, the effect of the Hall term is analyzed. Finally, we optimize the upper bound of decay and obtain their algebraic lower bound for the generalized MHD system by using Fourier splitting method.