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김동환(D. H. Kim),권혁무(H. M. Kwon),김택기(T. K. Kim),김희태(H. T. Kim),김윤배(Y. B. Kim) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
The nitrogenation process and magnetic properties of Sm₂Fe_(17)Nx (0 ≤ x ≤ 3) were investigated. During the initial nitrogenation process, the nitrogen content had linear relation with the square root of nitrogenation time, and the activation energy for the process was calculated to be 102.4 kJ/㏖. The magnetic properties of Sm₂Fe_(17)Nx were strongly dependent on the nitrogen content and the composition having Sm₂Fe_(17)N_(2.8) showed optimum magnetic properties with a Curie temperature of 450 oC. The intrinsic magnetic properties of the nitride at room temperature were Ms = 1147 emu/㎤, K₁ = 4.6 × 10^7 erg/㎤, K₂ = 6.0 × 10^7 erg/㎤ and H_A = 290 kOe, respectively.
수직원통형 빙축열조내 외향용융과정시 열전달특성에 관한 연구 -작동유체의 유동방향 및 축열조 형상비에 따른 열성능 비교-
김동환,김동춘,김일경,김영기,임장순,Kim, D.H.,Kim, D.C.,Kim, I.G.,Kim, Y.K.,Yim, C.S. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.2
During the day time in summer, peak of air conditing load, and electric power management system lies under overloaded condition. The reason is the enlarged peak load value of electric power caused by increased air-cooling load in summer. To prevent load concentration during day time and overloaded condition of power management system, some energy storage methods are suggested. One of these methods is ice storage system. Water has some good properties as P.C.M.(Phase Chang Material) : Its melting point is the range of required operation temperature. It has large specific latent heat and is chemically stable compared to other organic or inorganic substances. It is cheap and easy to treat. This study represents experimental results of heat transfer characteristics of P.C.M. under the outward melting process in a vertical cylinder. We experimented with twelve combinations of conditions, i.e., three different inlet temperatures($7^{\circ}C,\;4^{\circ}C\;and\;1^{\circ}C$), two working fluid directions(upward and downward), and two aspect ratios, H/R(4 and 2). At the inlet temperature of $7^{\circ}C$ and $4^{\circ}C$, there was temperature stagnation region where the temperature of P.C.M. remains constant at $4^{\circ}C$ regardless of aspect ratio and direction of working fluid. This temperature stagnation occurs as the water, at its maximum density, flows down to the lower region. The phase change interface formed bell-shaped curve as the melting process continued. With a new set of conditions(4H/R, inlet temperature $4^{\circ}C$ and $1^{\circ}C$, downward/upwerd inlet direction), the movement of phase change interface was faster when the working flued inlet direction was downward. With the same set of conditions, melting rate and total melting energy were larger when the working fluid inlet direction was downward. The results were reversed when the other sets of conditions were applied.
ThMn₁₂ 형 Sm - Fe - Ti 급냉응고리본의 미세구조 및 자기특성
김윤배(Y.B.Kim),유권상(K.S.Ryu),김동환(D.H.Kim),김창석(C.S.Kim) 한국자기학회 1991 韓國磁氣學會誌 Vol.1 No.1
It has been found that the as-quenched ribbons of Sm_xFe_(100-x-y)Ti_y(3.8 ≤ x ≤ 11.5, 3.8 ≤ y ≤ 19.2) are composed of metastable TboCu_7-type structure, α-(Fe, Ti), Fe₂Ti and an unknown phase accompanying strong diffraction line at d=2.l4 Å. The metastable TbCu_7-type phase, which was formed by rapid quenching, did not transform fully to the stable phases after annealing at 850℃ for 45 minutes except the one existed in SmFe₁₁Ti melt-spun ribbon. The SmFe₁₁Ti melt-spun ribbon, annealed at 850℃ for 45 minutes in vacuum, was found to be composed of ThMn₁₂, α-(Fe, Ti) and Fe₂Ti phases. The formation of α-(Fe, Ti) and Fe₂Ti phases in this melt-spun ribbon was due to the evaporation of Sm atoms during the high temperature annealing. The atomic ratios for the surface and the inside of SmFe₁₁Ti melt-spun ribbon annealed in vacuum were SmFe_(25.8)Ti_(2.6) and SmFe_(11.7)Ti_(1.0) respectively. It is thought to be that much of α-(Fe, Ti) and Fe₂Ti phases exist on the surface of ribbon.
피칭운동을 하는 대형 우주발사체 형상의 천음속 비정상 유동해석
김동현(D. H. Kim),김요한(Y. H. Kim),김동환(D. H. Kim),윤세현(S. H. Yoon),김광수(G. S. Kim),장영순(Y. H. Jang),김수현(S. H. Kim) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.11
In this study, steady and unsteady aerodynamic analyses of a huge rocket configuration have been conducted in the transonic flow region. Launch vehicle structural response can couple with transonic flow state transitions at the nose of payload fairing. Before doing fluid-structure coupled transonic aeroealstic simulations for a huge rocket configuration, transonic aerodynamic characteristics are investigated for pitching motions of the rocket with angle-of attack. Unsteady CFD analysis method with moving grid technique based on Reynolds-averaged Navier-Stokes equations with κ-ω SST transition turbulence model is applied to accurately predict the transonic loads of the rocket with pitching motion. It is importantly shown that the fluctuated amplitude of lateral aerodynamic loads imposed on the rocket due to pitching motion can be significantly increased in the transonic region when the rocket has certain angle-of-attack.
피칭운동을 고려한 우주발사체 형상의 천음속 비정상 유동해석
김동현(D.H. Kim),김요한(Y.H. Kim),김동환(D.H. Kim),윤세현(S.H. Yoon),김광수(G.S. Kim),장영순(Y.H. Jang),김수현(S.H. Kim) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.1
In this study, steady and unsteady aerodynamic analyses of a huge rocket configuration have been conducted in a transonic flow region. The launch vehicle structural response are coupled with the transonic flow state transitions at the nose of the payload fairing. Before performing the coupled fluid-structure transonic aeroealstic simulations transonic aerodynamic characteristics are investigated for the pitching motions of the rocket at finite angle-of-attack. An unsteady CFD analysis method with a moving grid technique based on the Reynolds-averaged Navier-Stokes equations with the k-w SST transition turbulence model is applied to accurately predict the transonic loads of the rocket at pitching motion. It is shown that the fluctuating amplitude of the lateral aerodynamic loads imposed on the rocket due to the pitching motion can be significantly increased in the transonic flow region.