• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.182.2-182.2
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• 2016

Hollow cathode discharge(중공 음극)는 음극 표면에서 발생되는 2차 전자를 이용하여 높은 밀도의 플라즈마를 만들 수 있는 장점이 있다. 전원으로 microwave, RF, DC, pulsed dc등을 사용할 수 있으며 박막의 증착, 식각 등에 응용 가능하다. 물리적 현상으로는 중공 음극 재료 표면 물질의 가열 및 이온 스퍼터링, 2차 전자의 가열, 자기장 인가 구조의 경우 전자 거동이 있다. PIC(particle-in-cell)방식의 모델링과 fluid model을 이용한 방법이 있는데 본 연구에서는 상용 fluid model software인 ESI사의 CFD-ACE+를 사용하여 모델링 하였다. 구동 주파수는 13.56 MHz의 상용 고주파 전원과 보다 낮은 1 MHz, 100 kHz의 수치 모델을 이용하여 HF, MF, LF 영역에서의 동작 특성을 해석하였다. 1차적으로는 가스 유동의 특성을 2D, 3D로 조사하였고 플라즈마 거동은 2차원을 주로 진행하였으며 계산 시간이 오래 거리는 3차원 모델을 하나 만들어 그 특성을 조사하였다.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.85-91
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• 2010

In this study, aerodynamic analyses based on unsteady computational fluid dynamics (CFD) have been conducted for a 2-bladed vertical-axis wind turbine (VAWT) configuration. Reynolds-averaged Navier-Stokes equations with standard $k-{\varepsilon}$ and SST $k-{\varepsilon}$ turbulence models are solved for unsteady flow problems. The experiment model of 2-bladed VAWT has been designed and tested in this study. Aerodynamic experiment of the present VAWT model are effectively conducted using the vehicle mounted testing system. The comparison result between the experiment and the computational fluid dynamics (CFD) analysis are presented in order to verify the accuracy of CFD modeling with different turbulent models.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.120-125
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• 2003

Recently, lateral jet has been adopted as an effective control device for high maneuverable tactical missiles in supersonic regime. Aerodynamic interference caused by the lateral jet can be categorized into two phenomena : local interaction redistributing surface pressure near the jet exit region and downstream interaction affecting tail control effectiveness. As part of on-going research, this paper deals with the aerodynamic modeling to predict the variation of force and moment when lateral jet of is activated on the missile body. For this purpose, a series of numerical simulation has been performed and the results are presented. Using the information obtained by CFD, aerodynamic model of preliminary level has been constructed and is reviewed. Some relevant comparison with wind tunnel tests are presented.

• Proceedings of the Membrane Society of Korea Conference
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• 2004.05a
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• pp.15-18
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• 2004

Computational fluid dynamics (CFD) was applied to modeling particle dynamics in microfiltration (MF). The rejection properties of poly methylmethacrylate (PMMA) and polystyrene (PS) were calculated. Calculated rejection (R) of PMMA was independent with the porosity of the membrane, and the R was constant in the range of volume flux between $1\times 1-^{-4}-1\times 10^{-2}$ m/s. These observations were in quantity agreement with our experimental observations. The dependence of PMMA and PS rejection on the ratio of particle diameter and pore diameter were good agreement with the experimental values, which suggesting that the validity of CFD simulation to evaluate rejection of particle in MF membranes. Change of rejection of PMMA as a function of time was molded based on the CFD result which explained well the experimental observation.

• Journal of Korea Water Resources Association
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• v.37 no.5
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• pp.375-386
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• 2004

A water shortage is one of the most important factors for development and management of water resources. For reliable water shortage measurement in a stream, Korea Water Resources Corporation(KOWACO) founded five foot Parshall flume at Yong-dam experimental watershed in 2000. The Parshall flume has a specially designed shape to facilitate flow measurements by eliminating sediment deposition problem that could lead to an incorrect measurement. In this study, computational fluid dynamics(CFD) model was used to analyze flow behavior of Parshall Flume under free discharge of five headwater level cases. The flow rates computed by CFD model are compared with those by ISO's formula, USBR's formula and stage-discharge rating curves. Flow rates computed by ISO's and USBR's formula are mostly same, but flow rate by CFD model is larger than empirical value by 9% and flow rate by stage-discharge rating curves is less than empirical value by 16%.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.29-37
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• 2011

PIV measurements of the velocity field, pressure field, vorticity, and turbulent intensity in the rear of curved section of an oil fence with current speed showed that the flow directions in the rear of flow boundary area were similar to those in the front of it. As the current speed increased, the patterns of pressure distribution were changed, and the turbulent flow became more irregular. CFD simulations under the same conditions as the PIV tests showed that the flow patterns of the wake were similar to those by PIV tests in speed of 0.3 m/s and less, but were distinctively deviated from those in 0.4 m/s due to the flexibility of the oil fence, which was not properly taken care of in CFD modeling.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.847-853
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• 2016

Here has been examined a 3-dimensional computational fluid dynamics (CFD) modeling in order to investigate the performance analysis of proton exchange membrane (PEM) fuel cells with serpentine flow fields. The present CFD model considers the isothermal transport phenomena in a fuel cell involving mass, momentum transport, electrode kinetics, and potential fields. Co-current flow patterns for a PEMFC are considered for various geometries in the single straight cell. Current density distribution from the calculated distribution of oxygen and hydrogen mass fractions has been determined, where the activation overpotential has been also calculated within anode and cathode. CFD results showed that profiles differ from those simulations subjected to each the calculated activation overpotential. It is interesting that the present serpentine flow field shows the specific distribution of current density with respect to the aspect ratio of depth to width and the ratio of reaction area for various serpentine geometries. Simulation results were considered reasonable with the other CFD results reported in literature and global comparisons of the PEMFC model.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.200-205
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• 2003

The Canard rotor/wing (CRW) aircraft concepts offer great potential for application by allowing the use of a common propulsion system for high-speed cruise and low-speed powered lift. Using the rotor for lift in both flight modes increases its utility. In the hovering mode, the exhausted gas from an gas turbine engine is accelerated through the duct system and it provides the tipjet power for rotor system enough to lift the aircraft. In the cruise mode, the rotor is fixed and the exhausted gas is extracted through the main nozzle, such that the aircraft is able to flight with high speed. The duct system was designed using 1-D fanno line flow theory and empirical data. However, the empirical data of the pressure loss coefficient for various bending and dividing ducts were not enough to design our duct system adaptively. Therefore, using 3-D CFD analysis we obtained the pressure loss coefficient for our duct models and chose the appropriate bending or diving duct type. In this paper, we used the CFD-ACE+ software package for the CFD analysis and the modeling of duct system. Through the 3-D CFD analysis, we investigated also the pressure loss and the velocity distributions of the designed whole duct system as well as the blade duct. Comparing the 3-D CFD result with 1-D analysis result, we lessened the uncertainty of the designed duct system and speculated the problem that was not concerned in design state.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.198-205
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• 2015

In this study, numerical studies using a Computational Fluid Dynamics(CFD) method were carried out to estimate the green water load acting on the breakwater plate of bow deck of container carrier, KCS. For the green load water load analysis, a full load condition was considered. The relative motions at bow deck were calculated from the seakeepig analysis. Statistical analysis were carried out to estimate the long term response of the relative motions with the North Atlantic wave scatter diagram. The equivalent design wave was determined from the RAO of the relative motions at bow and the long term responses. CFD geometry modeling with three different locations and simulations for the green water loads were carried out in the equivalent design waves. A commercial CFD program, STAR-CCM+ Ver. 8.04, was used and the green water pressures on the breakwater plate were calculated successfully. The CFD analysis for green water loads can be used as a useful design tool for the evaluation of the breakwater plate of the container vessel.

• Journal of the Korea Society for Simulation
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• v.21 no.1
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• pp.35-43
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• 2012

In this study, underwater behaviors of negative buoyant body and positive buoyant body, which are ejected from a platform, are compared through eject test and simulation. CFD(Computational Fluid Dynamics) method is used to calculate the hydrodynamic derivatives of negative buoyant body with varied hull. Hydrodynamic derivatives that cannot be calculated with CFD are used with the same values of base shape. The pitch angles of test data are much bigger than those of simulated data, and the reason is supposed to be the trailing air effect. A more accurate simulation is possible via modified force modeling which reflects this phenomenon. The underwater behaviors of positive buoyant body and negative buoyant body are somewhat different with each other at the same eject condition, but it may not be a problem in the view of operation.