• Ocean and Polar Research
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• 제25권1호
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• pp.63-74
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• 2003

The build-up of the heat field in shallow coastal water due to a point source has been investigated using an analytical solution of a time-integral form derived by extending the solutions by Holley(1969) and also presented in Harleman (1971). The uniform water depth is assumed with non-isotropic turbulent dispersion. The alongshore-flow is assumed to be uni-directional, spatially uniform and oscillatory. Due to the presence of the oscillatory alongshore-flow, the heat build-up occurs in an oscillatory manner, and the excess temperature thereby fluctuates in that course and even in the quasi-steady state. A series of calculations reveal that proper choices of the decay coefficient as well as dispersion coefficients are critical to the reliable prediction of the excess temperature field. The dispersion coefficients determine the absolute values of the excess temperature and characterize the shoreline profile, particularly within the tidal excursion distance, while the decay coefficient determines the absolute value of the excess temperature and the convergence rate to that of the quasi-steady state. Within the e-folding time scale $1/k_d$ (where $k_d$ is the heat decay coefficient), heat build-up occurs more than 90% of the quasi-steady state values in a region within a tidal excursion distance (L), while occurs increasingly less the farther we go to the downstream direction (about 80% at 1.25L, and 70% at 1.5L). Calculations with onshore and offshore discharges indicate that thermal spreading in the direction of the shoreline is reduced as the shoreline constraint which controls the lateral mixing is reduced. The importance of collecting long-term records of in situ meteorological conditions and clarifying the definition of the heat loss coefficient is addressed. Interactive use of analytical and numerical modeling is recommended as a desirable way to obtain a reliable estimate of the far-field excess temperature along with extensive field measurements.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.362-367
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• 2011

The aerodynamic performance of the pantograph of the next generation high sped train is analyzed. The calculation of the flow around pantograph is carried cut by FLUENT; by the steady state flow calculation with ${\kappa}-{\omega}$ SST turbulence model, the lift force of the pantograph is computed. For the verification of the numerical schemes am grid systems, flow calculations are performed with the pantograph shape which was used at the experiments performed at Railway Technical Research Institute (RTRI) in Japan. Then, the difference of lift force between numerical am experimental results is about 10%. Therefore, selected numerical schemes and the current grid system is adequate for the analysis am prediction of the aerodynamic performance of panthograph system. Based on these numerical schemes am grid system, the flow around pantograph of the next generation high sped train is calculated and the lift force of the pantograph is predicted; the lift force of the pantograph is about 146N.

• 대한의용생체공학회:의공학회지
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• 제2권2호
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• pp.89-102
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• 1981

The recirculating flows which occur in the prosthetic heart valve have been known to cause several diseases in the human body. And the recent studies show that the shear stress at the wall of the artery is also very important factor in the formation of thrombus. And many studies knave been devoted in obtaining more information about the blood flow through the prosthetic heart valve. In this Paper, the steady axisymmetric flow through the Disc-Type Heart Valve is studied by using the numerical method. The geometry of the Disc-Type Heart Valve is simplified, and the flow is assumed to be steady axisymmetric flow. The vorticity transport equation derived from the Wavier-Stoke's equation is used as the governing equation, and the explicit finite difference method is used to obtain the steady state solution. The results for several Reynolds numbers show that the recirculating flow becomes large as the Remolds number increases. Furthermore, it can be shown that the magnitudes of the vorticity and the stresses are also increased with the Reynolds number, but there is only a little change in their configurations of distribution and in their positions of maximum values.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.197-200
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• 2015

Understanding the slag flow behavior is important in an entrained coal gasifier for its influence of ash discharge and wall heat transfer rate. This study presents a new model to predict the transient behavior of the liquid and solid slag layers. Unlike the previous steady-state model, the solid slag layer was included in solving the governing equations in order to identify the temporal and spatial transformation between the solid-liquid slag, rather than treating the solid region as a boundary condition of the liquid layer. The performance of the new model was evaluated for changes in the slag deposition rate (${\pm}10%$) and gas temperature (${\pm}50K$) in a simple cylindrical gasifier. The results show that the characteristic times to reach a new steady-state ranged between 80 s to 180s for the changes in the two parameters. Because the characteristic times of the gasifier temperature and slag deposition rate by changes in the coal type and/or operating conditions would be almost instantaneous, the time-scale for the slag thickness at the bottom of the gasifier to stabilize was much larger.

• 대한기계학회논문집B
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• 제24권6호
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• pp.792-801
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• 2000

The problem of phase change from liquid to solid in the inviscid plane-stagnation flow is theoretically investigated. The solution at the initial stage of freezing is obtained by expanding it in powers of time, and the final equilibrium state is determined from the steady-state governing equations. The transient solution is dependent on the three dimensionless parameters, but the equilibrium state is determined by one parameter of (temperature ratio/conductivity ratio). The effect of the fluid flow on the growth rate of the solid in the pure conduction problem can be clearly seen from the solution of the initial stage and the final equilibrium state. The characteristics of the transient heat transfer at the surface of the solid and the liquid side of the solid-liquid interface for all the dimensionless parameters are elucidated.

• 설비공학논문집
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• 제12권1호
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• pp.1-11
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• 2000

This study investigates the problem of phase change from liquid to solid in the inviscid stagnation flow. The solution of dimensionless governing equations is determined by the three dimensionless parameters of (temperature ratio/conductivity ratio), Stefan number, and diffusi-vity ratio. The solution at the initial stage of freezing is obtained by expanding it in powers of time, and the final equilibrium state is determined from the steady-state governing equations. The equilibrium state is dependent on (temperature ratio/conductivity ratio), but is independent of Stefan number and diffusivity ratio. The effect of fluid flow on the pure conduction problem can be clearly seen from the solution of the initial stage and the final equilibrium state, and the characteristics of the solidification process for all the dimensionless parameters are elucidated.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1097-1102
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• 2001

For the purpose of development of high performance gasoline engine, the design technique of the 5-valve(3 intake valves) combustion chamber for a subcompact vehicle has been studied. 3 intake valves cylinder heads were designed by using a 3-dimension CAD program, and steady state flow experiments have been performed with these model. The 5-valve engines, which have larger valve opening areas, have larger intake flow rates and higher flow coefficient than the 4-valve engines. The effects of intake port design parameters of a 5-valve engine on the intake flow rate and bore size were studied, and the design guidelines for the 5-valve engine were established.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.61.2-61.2
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• 2005

• 항공우주기술
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• 제2권1호
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• pp.1-10
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• 2003

항공기용 가스터빈엔진에 대한 경제적인 시험 기법 개발을 위해 천이상태 성능 시험 결과로부터 정상상태 성능을 예측할 수 있는 방안을 모색했다. 천이상태 성능과 정상상태 성능이 서로 달라지는 현상의 원인을 동역학적 천이 효과, 열적 천이 효과, 공기역학적 천이 효과로 구분하고, 각각을 모델링해서 엔진의 천이상태 성능을 통해 정상상태 성능을 계산하는 보정 인자를 정량화했다. 먼저 천이상태 성능시험 시 나타나는 엔진 입ㆍ출구의 온도 변화가 엔진 성능에 미치는 영향을 보정했고, 그 후 도입된 보정 인자를 사용해 정상상태 성능을 예측했다. 이렇게 예측된 결과와 실제 정상상태 성능시험 결과를 비교한 결과, 연료 소모량의 차이 3.68% 이내로 정상상태 성능을 예측할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.995-1000
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• 2001

Distributions of the parameters in proton exchange membrane fuel cell (PEMFC) has been analyzed numerically under steady-state and isothermal conditions. The distributions of the crucial parameters (e.g., temperature and pressure) in a PEMFC have a major impact on its safe and efficient operation. This paper predicts the performance of the model electrode plates by calculating the pressure and temperature distributions of working fluid. The calculated results of pressure and temperature at exit condition shows good agreement to experiments and gives details of flow pattern inside of electrode plates.