• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.179-182
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• 2005

We have developed a numerical scheme to reproduce the unsteady flows with cavitation by the finite-difference method. The evolution of cavitation is represented by the source/sink of vapor phase in the incompressible liquid flow. The pressure-velocity coupling is based on the fractional-step method for incompressible fluid flows, in which the compressibility is taken into account through the low Mach number assumption. We applied our method for the cavitating flows in a two-dimensional cascade, which approximates the portion near the tip of inducer in liquid-fuel engine. Particular attention was focused on the influence of turbulence model in this report. Using an eddy viscosity model, although it was not an optimized one for our purpose, the agreement with the experimental observation was improved.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.752-757
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• 2001

The characteristics of heat energy distribution on the fire-proof clay with microwave heating drying are numerically investigated using finite element method. The modelled regular hexahedron chamber$(50cm\times50cm\times50cm)$ filled with air consists of vertical heat source and sink walls, a fire-proof clay model, and adiabatic plates on the top and bottom walls. With different geometrical aspect ratios of the fire-proof clay model, the heat energy distribution is throughly investigated. The model gave a good prediction of the microwave heating characteristics of fire-proof clay. The optimal shape of the fire-proof clay for given chamber geometry and microwave power is analyzed.

• 대한토목학회논문집
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• 제26권3B호
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• pp.311-319
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• 2006

저면경계층에서 부유사와 소류사 flux를 포함하는 실제적인 표사이동에 기초한 지형변화모델(SED-FLUX)이 개발되었다. SED-FLUX는 파랑모듈, 동수역학 모듈 및 부유사농도, 순부상 flux($Q_s$)와 소류사 flux를 계산하는 표사수송 및 확산모듈을 포함하며, 소류사 flux는 파-흐름 공존장에서 검증된 van Rijn의 TRANSPOR 프로그램에 의해 평가되어진다. 저면에서 순부상 flux $Q_s$는 표사확산모듈에서 source/sink 항으로서 평가되어지며, 수심변화모듈은 수심변화량을 계산하고 시간에 따른 bed level의 변화를 계산한다. 모델의 검증을 위하여 소류사이동의 이동한계수심은 방사성 동위원소 추적자를 사용한 현장 실험자료와 파와 흐름에 의한 표사이동한계수심에 대한 몇몇 경험식과 비교되었다. 본 모델을 파에 의한 해빈 단면변화에 적용한 결과 입사파의 특성에 따른 명확한 침식과 퇴적분포를 나타내었다. 끝으로, 이안제 배후에서 파와 해빈류에 의한 수심변화를 계산한 결과 이안제의 배후에서 초기 tombolo의 형성을 보여주었다.

• Journal of Power Electronics
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• 제16권4호
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• pp.1598-1611
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• 2016

In some special occasions with strict size requirements, such as mine hoists, improving the design accuracy of the forced-air cooling systems of NPC three-level inverters is a key technology for improving the power density and decreasing the volume. First, a fast power-loss calculation method was brought. Its calculation principle introduced in detail, and the computation formulas were deduced. Secondly, the average and dynamic power losses of a 1MW mine hoist acting as the research target were analyzed, and a forced-air cooling system model based on a series of theoretical analyses was designed with the average power loss as a heat source. The simulation analyses proves the accuracy and effectiveness of this cooling system during the unit lifting period. Finally, according to an analysis of the periodic working condition, the maximum power-loss range of a NPC three-level inverter under multi cycle operation was obtained and its dynamic power loss was taken into the optimized cooling system model as a heat source to solve the power device damage caused by instantaneous heat accumulation. The effectiveness and feasibility of the optimization design based on the dynamic power loss calculation of the maximum power-loss range was proved by simulation and experimental results.

• 한국해양학회지:바다
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• 제24권2호
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• pp.187-207
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• 2019

고성능 해양모델을 개발하기 위하여 적시 컴파일(Just-In-Time) 언어인 줄리아 언어를 사용하였고, 운동량 방정식의 해를 구하기 위해 연속완화법으로 푸아송 방정식을 푸는 코드를 작성하였다. 다음으로, 줄리아 계산 코드를 시험하기 위하여 두 가지의 모델을 구축하였다. 첫 번째로, 일정한 유량의 생성/소멸(source/sink) 조건을 시험하기 위해 단순한 수로 형태를 모델링하였고, 두 번째로, 조석 외력(tidal forcing) 및 전향력(Coriolis force), 난류확산계수로 인한 효과 등을 시험하기 위해 황해(Yellow Sea)를 단순화하여 모델링하였다. 모델은 두 가지 시나리오 안에서 총 8개의 실험안으로 테스트되었다. 테스트 결과, 시나리오 1에서 3가지 실험안의 수심 평균된 유속은 이론 값에 완벽하게 수렴하였고, 해저마찰로 인한 수직적 유속 구배를 잘 보여주었다. 또한 시나리오 2에서는 황해의 무조점과 우리나라 서해 중부와 남부 연안의 조석 특성을 잘 재현하였고, 전향력과 수직 난류확산계수에 따른 결과의 차이를 잘 보여주었다. 따라서, 줄리아 언어를 이용한 해양모델을 개발하는 데에 성공하였다고 판단되며, 이는 해양모델이 고전적인 컴파일 언어에서 적시 컴파일 언어로 성공적으로 넘어가는 단계에 오게 됐다는 것을 시사한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.202-206
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• 2001

The characteristics of heat transfer on the fire clay with microwave heating are numerically investigated using finite element method. The modelled regular hexahedron chamber($50cm{\times}50cm{\times}50cm$) filled with air consists of vertical heat source and sink walls, a fire clay model, and adiabatic plates at the top and bottom walls. With different geometrical aspect ratios of the fire clay model, the heat energy distribution is throughly investigated. The optimal shape of the fire clay for given chamber geometry and microwave power is analyzed.

• Journal of information and communication convergence engineering
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• 제16권1호
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• pp.38-42
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• 2018

In this paper, we consider measurement allocation problem in a spatially correlated sensor field. Our goal is to determine the probability of each sensor's being measured based on its contribution to the estimation reliability; it is desirable that a sensor improving the estimation reliability is measured more frequently. We consider a spatial correlation model of a sensor field reflecting transmission power limit, noise in measurement and transmission channel, and channel attenuation. Then the estimation reliability is defined distortion error between event source and its estimation at sink. Motivated by the correlation nature, we model the measurement allocation problem into a cooperative game, and then quantify each sensor's contribution using Shapley value. Against the intractability in the computation of exact Shapley value, we deploy a randomized method that enables to compute the approximate Shapley value within a reasonable time. Besides, we envisage a measurement scheduling achieving the balance between network lifetime and estimation reliability.

• 한국전산유체공학회지
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• 제14권1호
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• pp.62-69
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• 2009

The cooling system for electric devices of hybrid vehicles is examined. The present system is composed of coolant paths, inlet diffuser and heat sinks whose shapes are diamond and circular. In this work, inlet duct and fin arrays are combined in proposed models and examined by numerical calculations. Nusselt number and Reynolds number are considered for heat transfer performance. Main focus lies on the looking for optimal model for the cooling system adopted to compact driving module of a hybrid vehicle. The optimal model shows uniform flow patterns in the inlet diffuser and secondary flows after the fins attached to heat source. It is found that the vortical flows around the heat sinks are effective for heat removal mechanism.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.422-425
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• 2009

A sea water source cascade heat pump was designed and tested in this study. The system was designed to perform a single stage operation in summer, as well as a cascade operation in winter to ensure the high temperature lift. A steady-state simulation model was developed to analyze and optimize its performance. The simulation results show that the R717 exhibits best performance among combinations considered in this study. A R410A also exhibits the highest performance among HFCs with the smallest compressor displacement. A 15-RT R410A-R134a pilot system was installed in the 5-story commercial building at Samcheok City by the East Sea. A scroll type R410A compressor, a reciprocating type R134a compressor, plate type condenser/evaporator/ cascade heat exchanger and two electronic expansion valves were used to build a pilot. A titanium plate type heat exchanger is also used for the heat exchanging with a sea water. The heat source/sink water is supplied from the well below the seashore in the depth of 5 m. In the initial test of the system, supply water temperature was rising up to $67^{\circ}C$ using a sea water heat source of $9^{\circ}C$, while an ambient temperature was $4.5^{\circ}C$.

• 한국수산과학회지
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• 제22권6호
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• pp.415-423
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• 1990

In a laboratory model the response of the boundary layer flow over topography is studied in a rotating sliced cylinder by employing the source-sink analogy with Ekman layer dynamics. The boundary layer flow is produced by two different fluid. In the first experiment homogeneous fluid is used both for the source and the working fluid of the container. In the second experiment a denser fluid is used for the source with the same working fluid. For the homogeneous western boundary layer flow both the northward and the southward flow were affected by the topography(ridge) to produce a cyclonic motion near the ridge. When woughward moving heavy boundary flow of slower speed and the northward moving faster flow were present at the same time, the splitting of southward flow and the separating of the northward flow were observed with a cyclonic motion at the ridge. The most important factor that influence production of the cyclonic motion has been turned out to be the presence of the topography in the western boundary layer. In particular the role of the southward moving heavy flow over the interior flow pattern was found to be very significant.