• 대한기계학회논문집
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• 제14권3호
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• pp.702-715
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• 1990

본 연구에서는 개수로 후래시 증발기 내부를 단순화된 형태로 가정하여 앞서 언급된 운전조건 및 유입되는 기포의 갯수유량(혹은 기공률)에 따라 증발기 내부의 속 도 및 온도분포를 수치적으로 계산해 보고자 한다. 이를 위해 유동을 정상상태의 난 류유동으로 가정하였으며, 구형의 기포에 대해 평균적인 운동 및 성장을 지배하는 방 정식을 세우고 상변화에 의한 증발량을 구하였다. 즉 입구에서 유입된 기포들이 성 장하면서 자유표면을 통해서 빠져나가는 운동 궤적을 추적함으로써 증발기 내부 유동 의 속도 및 온도분포를 구하고 이를 바탕으로 총 증발량 및 증발성능을 예측해 보고자 하는 것이다. 그리고 이렇게 계산된 결과들을 기존의 실험값과 비교하였다.

• 대한기계학회논문집
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• 제16권1호
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• pp.142-155
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• 1992

본 연구에서는 실제 빙축열 시스템의 해석을 위한 기초 모델로서 수직원관 주 위의 응고과정에 대하여 밀도차와 자연대류 효과 및 최대 밀도점을 나타내는 밀도-온 도 관계식을 도입한 수치해석과 실험을 통하여 여러가지 매개변수들이 상변화에 미치 는 영향을 알아 보았다.

• 한국항공우주학회지
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• 제38권7호
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• pp.637-646
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• 2010

포텐셜 기저 패널법과 시간전진법을 통합한 시간영역 패널법을 이용하여 융합익기 형상 초소형 무인기 FM07에 대한 정상/비정상 공력해석을 수행하였다. 융합익기 형상 무인기인 FM07의 공력해석에는 초기 설계형상(Case I)과 가로세로비를 증가시키고 무게중심을 후방으로 이동시킨 개선형상(Case II)이 사용되었다. 정상 공력해석을 통해 FM07 무인기의 개선형상이 초기형상에 비하여 보다 큰 양항비와 높은 피칭 안정성을 나타냄을 확인하였다. FM07의 비정상 급가속(발사체 이륙단계)을 나타낸 공력해석에서는 초기 급격한 증가를 보이는 공력계수들이 수초 후에 안정화되어 정상상태에 근사한 값을 나타내었다. FM07의 순항시 발생할 수 있는 피치진동운동에 대한 해석을 수행하여 진동에 따른 공력계수의 이력 현상을 확인하였으며, 개선형상이 보다 큰 민감도를 갖는 것을 확인하였다.

• 대한기계학회논문집B
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• 제23권6호
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• pp.778-787
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• 1999

In this study, the autoignition process of liquid fuel, injected into hot and stagnant air in a 2-D axisymmetric confined cylindrical combustor, has been investigated. Eulerian-Lagrangian scheme was adopted to analyze the two-phase flow and combustion. The unsteady conservation equations were used to solve the transition of the gas field. Interactions between two phases were accounted by using the particle source in cell (PSI-Cell) model, which was used for detailed consideration of the finite rates of transports between phases. And infinite conduction model was adopted for the vaporization of droplets. The results have shown that the process of the autoignition consists of heating up of droplets, vaporization, mixing and ignition. The ignition criteria could be determined by the temporal variations of temperature, reaction rate and species mass fraction. And the effects of various parameters on ignition phenomena are examined. These have shown that the increasing the reaction rate and/or the vaporization rate can reduce the ignition delay time.

• Wind and Structures
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• 제32권5호
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• pp.487-499
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• 2021

The wind-blown sand effect on the high-speed train is investigated. Unsteady RANS equation and the SST k-ω turbulent model coupled with the discrete phase model (DPM) are utilized to simulate the two-phase of air-sand. Sand impact force is calculated based on the Hertzian impact theory. The different cases, including various wind velocity, train speed, sand particle diameter, were simulated. The train's flow field characteristics and the sand impact force were analyzed. The results show that the sand environment makes the pressure increase under different wind velocity and train speed situations. Sand impact force increases with the increasing train speed and sand particle diameter under the same particle mass flow rate. The train aerodynamic force connected with sand impact force when the train running in the wind-sand environment were compared with the aerodynamic force when the train running in the pure wind environment. The results show that the head car longitudinal force increase with wind speed increasing. When the crosswind speed is larger than 35m/s, the effect of the wind- sand environment on the train increases obviously. The longitudinal force of head car increases 23% and lateral force of tail increases 12% comparing to the pure wind environment. The sand concentration in air is the most important factor which influences the sand impact force on the train.

• 대한토목학회논문집
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• 제3권1호
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• pp.13-24
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• 1983

장주기파(長週期波)에 의한 항내(港內)의 반응(反應)을 예측(豫測)하기 위하여 비선형(非線型) 편미분방정식(偏微分方程式)으로 표현(表現)되는 2차원(二次元) 부정류(不定流)의 운동방정식(運動方程式)과 연속방정식(連續方程式)을 확정(確定)하고, 이 식(式)들에 Abbott의 Implicit 형(型) 차분형(差分型)을 적용(適用)하여 유한(有限) 차분방정식(差分方程式)의 형태(形態)로 유도(誘導)한 후(後), double sweep 알고리즘에 의하여 해석(解析)하는 수학적(數學的) 모형(模型)을 개발(開發)하였다. 본(本) 모형(模型)은 임의(任意)의 파형(波形), 풍속(風速)과 수심(水深), 위도(緯度) 등(等)을 입력자료(入力資料)로 하여 임의(任意)의 지형(地形)을 가진 항내(港內)에서의 반응(反應)을 해석(解析)할 수 있도록 설계(設計)되었다. 특(特)히 파향(波向), 이송항(移送項), 항입구(港入口)로 되돌아 나오는 에너지의 방사현상(放射現象) 등(等)을 수치해석적(數値解析的)으로 처리(處理)하는 수법(手法)의 개발(開發)에 관(關)하여 연구(硏究)하였다. 본(本) 모형(模型)에 의한 해석결과치(解析結果値)는 1차원(次元) 및 2 차원(次元) 정진동(靜振動)(seiche) 수치실험(數値實驗)을 통(通)하여 검정(檢定)하였으며, Ippen과 Goda의 이론해석치(理論解析値) 및 실험결과치(實驗結果値)와 비교(比較)하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권6호
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• pp.589-601
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• 2016

The hybrid grid was adopted and numerical prediction analysis of propeller unsteady bearing force considering free surface was performed for mode and full-scale KCS hull-propeller-rudder system by employing RANS method and VOF model. In order to obtain the propeller velocity under self-propulsion point, firstly, the numerical simulation for self-propulsion test of full-scale ship is carried out. The results show that the scale effect of velocity at self-propulsion point and wake fraction is obvious. Then, the transient two-phase flow calculations are performed for model and full-scale KCS hull-propeller-rudder systems. According to the monitoring data, it is found that the propeller unsteady bearing force is fluctuating periodically over time and full-scale propeller's time-average value is smaller than model-scale's. The frequency spectrum curves are also provided after fast Fourier transform. By analyzing the frequency spectrum data, it is easy to summarize that each component of the propeller bearing force have the same fluctuation frequency and the peak in BFP is maximum. What's more, each component of full-scale bearing force's fluctuation value is bigger than model-scale's except the bending moment coefficient about the Y-axis.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.291-293
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• 2003

This paper deals with a thrust generation of flapping-airfoil by dynamic stall. From many other previous research results, phase angle $ between pitching and plunging mode of flapping motion must be 90 deg. to satisfy maximum propulsive efficiency. In this case, leading edge vortex is relatively small. This phenomenon is related dynamic stall. So preventing leading edge vortex induced by dynamic stall guarantees maximum propulsive efficiency. But, in this paper we insist the leading edge vortex yields quite a positive influence on thrust generation and propulsive efficiency. In order to certify our opinion, pitching and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.1-6
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• 2002

How is the flow in a rotating impeller. About 35 years have passed since one experimentalist rotating with the impeller. of a huge centrifugal blower made the flow measurements using a hot-wire anemometer (Fowler 1968). Optical measurement methods have great advantages over the intrusive methods especially for the flow measurement in a rotating impeller. One is the optical flow visualization (FV) technique (Senoo, et al., 1968) and the other is the application of laser velocimetry (LV) (Hah and Krain, 1990). Particle image velocimetries (PIVs) combine major features of both FV and LV, and are very attractive due to the feasibility of simultaneous and multi-points measurements (Hayami and Aramaki, 1999). A high-pressure-ratio transonic centrifugal compressor with a low-solidity cascade diffuser was tested in a closed loop with HFC134a gas at 18,000rpm (Hayami, 2000). Two kinds of measurement techniques by image processing were applied to visualize a flow in the compressor. One is a velocity field measurement at the inducer of the impeller using a PIV and the other is a pressure field measurement on the side wall of the cascade diffuser using a pressure sensitive paint (PSP) measurement technique. The PIV was successfully applied for visualization of an unsteady behavior of a shock wave based on the instantaneous velocity field measurement (Hayami, et al., 2002b) as well as a phase-averaged velocity vector field with a shock wave over one blade pitch (Hayami, et al., 2002a. b). A violent change in pressure was successfully visualized using a PSP measurement during a surge condition even though there are still some problems to be overcome (Hayami, et al., 2002c). Both PIV and PSP results are discussed in comparison with those of laser-2-focus (L2F) velocimetry and those of semiconductor pressure sensors. Experimental fluid dynamics (EFDs) are still growing up more and more both in hardware and in software. On the other hand, computational fluid dynamics (CFDs) are very attractive to understand the details of flow. A secondary flow on the side wall of the cascade diffuser was visualized based either steady or unsteady CFD calculations (Bonaiuti, et al.,2002). EFD and CFD methods will be combined to a hybrid method being complementary to each other. Measurement techniques by image processing as well as CFD calculations give a huge amount of data. Then, data mining technique will become more important to understand the flow mechanism both for EFD and CFD.

• 대한기계학회논문집B
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• 제30권11호
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• pp.1131-1138
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• 2006

Aerodynamic shape design of a partial admission turbine using CFD has been performed. Two step approaches are adopted in this study. Firstly, two-dimensional blade shape is optimized using CFD and genetic algorithm. Initially, the turbine cascade shape is represented by four design parameters. By controlling the design parameters as variables, the non-gradient search is analyzed for obtaining the maximum efficiency. The final two-dimensional blade proved to have a more blade power than the initial blade. Secondly, the three-dimensional CFD analysis including the nozzle, rotor and stator has been conducted. To avoid a heavy computational load due to an unsteady calculation, the frozen rotor method is implemented in steady calculation. The frozen rotor method can detect a variation of the flow-field dependent upon the blade's circumferential position relative to the nozzle. It gives a better idea of wake loss mechanism starting from the lip of the nozzle than the mixing plane concept. Finally, the combination of two and three dimensional design method of the partial admission turbine in this study has proven to be a robust tool in development phase.