• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.352-359
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• 2010

In recent years, the market has shown increasing interest in pump-turbines. The prompt availability of pumped storage plants and the benefits to the power system achieved by peak lopping, providing reserve capacity, and rapid response in frequency control are providing a growing advantage. In this context, there is a need to develop pumpturbines that can reliably withstand dynamic operation modes, fast changes of discharge rate by adjusting the variable diffuser vanes, as well as fast changes from pumping to turbine operation. In the first part of the present study, various flow patterns linked to operation of a pump-turbine system are discussed. In this context, pump and turbine modes are presented separately and different load cases are shown in each operating mode. In order to create modern, competitive pump-turbine designs, this study further explains what design challenges should be considered in defining the geometry of a pump-turbine impeller. The second part of the paper describes an innovative, staggered approach to impeller development, applied to a low head pump-turbine project. The first level of the process consists of optimization strategies based on evolutionary algorithms together with 3D in-viscid flow analysis. In the next stage, the hydraulic behavior of both pump mode and turbine mode is evaluated by solving the full 3D Navier-Stokes equations in combination with a robust turbulence model. Finally, the progress in hydraulic design is demonstrated by model test results that show a significant improvement in hydraulic performance compared to an existing reference design.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제37권10호
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• pp.947-954
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• 2009

Starting from the Eu's GH(Generalized Hydrodynamic) theory, the multi-species GH numerical solver is developed in this research and its computatyional behaviors are examined for the hypersonic rarefied flow over an axisymmetric body. To improve the accuracy of the developed multi-species GH solver, various slip-wall boundary conditions are tested and the computed results are compared. Additionally, in order to validate the entropy characteristics of the GH equation, the entropy production and entropy generation rates of the GH equation are investigated in the 1-dimensional normal shock structure test at a high Knudsen number.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제65권8호
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• pp.1376-1382
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• 2016

The discharge characteristics of inductively coupled $Ar/CH_4$ plasma were investigated by fluid simulation. The inductively coupled plasma source driven by 13.56 Mhz was prepared. Properties of $Ar/CH_4$ plasma source are investigated by fluid simulation including Navier-Stokes equations. The schematics diagram of inductively coupled plasma was designed as the two dimensional axial symmetry structure. Sixty six kinds of chemical reactions were used in plasma simulation. And the Lennard Jones parameter and the ion mobility for each ion were used in the calculations. Velocity magnitude, dynamic viscosity and kinetic viscosity were investigated by using the fluid equations. $Ar/CH_4$ plasma simulation results showed that the number of hydrocarbon radical is lowest at the vicinity of gas feeding line due to high flow velocity. When the input power density was supplied as $0.07W/cm^3$, CH radical density qualitatively follows the electron density distribution. On the other hand, central region of the chamber become deficient in CH3 radical due to high dissociation rate accompanied with high electron density.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제65권7호
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• pp.1211-1217
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• 2016

Discharge characteristics of inductively coupled plasma were investigated by using electrostatic probe and fluid simulation. The Inductively Coupled Plasma source driven by 13.56 Mhz was prepared. The signal attenuation ratios of the electrostatic probe at first and second harmonic frequency was tuned in 13.56Mhz and 27.12Mhz respectively. Electron temperature, electron density, plasma potential, electron energy distribution function and electron energy probability function were investigated by using the electrostatic probe. Experiment results were compared with the fluid simulation results. Ar plasma fluid simulations including Navier-Stokes equations were calculated under the same experiment conditions, and the dependencies of plasma parameters on process parameters were well agreed with simulation results. Because of the reason that the more collision happens in high pressure condition, plasma potential and electron temperature got lower as the pressure was higher and the input power was higher, but Electron density was higher under the same condition. Due to the same reason, the electron energy distribution was widening as the pressure was lower. And the electron density was higher, as close to the gas inlet place. It was found that gas flow field significantly affect to spatial distribution of electron density and temperature.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2012년도 학술발표회
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• pp.108-111
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• 2012

최근에 태풍 매미 등 이상 기후로 인한 기상이변이 빈번히 발생함에 따라 그에 대한 대처방안을 모색하기 위해 2005년 해양수산부에서는 지역 및 해역별 특성을 분석하여 종전 설계기준을 강화하였다. 하지만, 기존에 설계된 항만 구조물의 마루높이 및 피복재 중량 등이 새로 개정된 설계기준에 미치지 못하는 등 안전성에 대한 문제가 발생하고 있으며, 이러한 문제점을 개선하기 위해 기존 방파제를 보강하는 여러 방식이 제안되고 있다. 그 중 부유식방파제는 해수의 소통을 방해하지 않는 친환경적인 구조물로써, 연약지반에 시공이 가능하고 시공 시 오탁이 적게 발생하여 시공이 편하다는 장점을 가지고 있다. 또한 구조물의 해체 및 보강시 건설폐기물을 발생시키지 않는 친환경적인 구조물이기 때문에 새로운 방식의 대체 외곽항만구조물로 관심을 받고 있다. 이에, 본 연구에서는 사석경사제 전면에 부유식구조물을 설치하여 방파제 보강하는 방안을 제시하고자, 부유식구조물을 통과한 파랑이 사석경사제와 만나 발생하는 처오름높이를 분석하였다. 본 수치모의에서는 유체의 점성 및 난류특성을 포함하고 있는 Navier-Stokes 방정식을 그대로 해석하는 2차원 수치파동수조(CADMAS-SURF)를 이용하여 수치 모의을 수행하였다. 부유식구조물은 불투수성구조물로 수면에 고정시키는 방식을 적용하여 사석경사제의 전면에 설치하였으며, 고정된 부유식구조물의 흘수심을 변화시켜 사석경사제에서의 처오름높이를 산정하였다.

• Proceedings of the Korean Information Science Society Conference
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• 한국정보과학회 2006년도 가을 학술발표논문집 Vol.33 No.2 (A)
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• pp.143-147
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• 2006

자연 현상에서 나타나는 연기나 난류의 움직임을 사실적으로 시뮬레이션을 할 때 Navier-Stokes 방정식을 이용한다. 이 방정식을 이용한 구현은 방대한 연산량과 계산의 복잡성으로 인하여 실시간 시뮬레이션이 어렵다. 이 때문에 실시간 처리를 위하여 복잡한 수식을 근사화한다. 유체 시뮬레이션의 이류(advect) 과정에서 근사화를 위해 Semi-Lagrangian 방법을 이용할 때, 연기 시뮬레이션은 시간이 지남에 따라 밀도가 현저히 줄어들고 소규모의 소용돌이(small-scale vorticity) 현상이 급격히 감소하는 등의 수치적 소실이 발생한다. 본 논문에서는 이 문제를 해결하기 위해 이류항(advection term)을 계산할 때 새로운 수치적 방법을 제안한다. 본 논문에서는 이류항의 값을 구할 때, 현재 격자 주변의 값 중에서 다음 단계에 현재 격자의 위치로 오는 속도를 가진 격자를 찾아, 그 격자의 속도를 이류 속도 벡터로 활용한다. 이는 밀도와 소용돌이 현상의 수치적 소실을 줄여서 사실성을 높이고 실시간 처리도 가능하게 한다. 또한 본 논문에서는 GPU 구현을 통해 벡터 연산 등의 효율성을 높이며 시뮬레이션의 속도를 향상시킨다.

• Journal of Hydrogen and New Energy
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• 제32권4호
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• pp.277-284
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• 2021

This paper deals with multi-objective optimization using response surface method to improve the hydraulic performances of a 2 vane pump for wastewater treatment. For analyzing the internal flow field in the pump, steady Reynolds-averaged Navier-Stokes equations were solved with the shear stress transport turbulence model as a turbulence closure model. The impeller and volute variables were defined in the shape of the 2 vane pump. The objective functions were set to satisfy the total head at the design flow rate as well as to improve the efficiency. The hydraulic performance of the optimally designed shape was verified by numerical analysis results.

• Journal of Wind Energy
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• 제5권1호
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• pp.22-32
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• 2014

The structural design of a wind turbine must show the verification of the structural integrity of all load-carrying components. Also, design load calculations shall be performed using appropriate and accurate methods. In this study, advanced numerical approach for the calculation of design loads based on unsteady computational fluid dynamics (CFD) is presented considering extreme design load conditions such as the extreme coherent gust (ECG) and the 50 year extreme operating gust (EOG). Unsteady aerodynamic loads are calculated based on Reynolds average Navier-Stokes (RANS) equations with shear-stress transport k-ω(SST k-ω) turbulent model. A full three-dimensional 5 MW offshore wind-turbine model with rotating blades, hub, nacelle, and tower configuration is practically considered and its aerodynamic interference effect among blades, nacelle, and tower is also accurately considered herein. Calculated blade loads based on unsteady CFD method with respect to blade azimuth angle are compared with those by NREL FAST code and physically investigated in detail.

• Journal of Wind Energy
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• 제13권3호
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• pp.5-12
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• 2022

A methodology of wind turbine blade design has been established with PROPID code, which is an aerodynamic blade design tool developed by UIUC. PROPID code can design and analyze a wind turbine blade in a steady state flow. The methodology of wind turbine blade design includes an initial blade concept design, airfoil selection, basic design, and detailed design steps. Inverse design and performance analysis of the 2.3 MW U113 wind turbine blade was performed to verify the wind turbine blade design methodology. The differences in calculated power between PROPID code and GH Bladed code are under 1.0% in all wind conditions. Both blade shape design and performance analysis results using PROPID code are accurate. The aerodynamic characteristics of a U113 blade were investigated by computational fluid dynamics. Separation flow was captured by a Reynolds-averaged Navier-Stokes steady flow simulation using ANSYS CFX code. The numerical aerodynamic analysis methodology was verified by comparing the analysis results through CFD with BEMT-based program GH Bladed code results. Therefore, the blade design methodology will be applied to develop a super-capacity 20 MW wind turbine blade in the future.

• The Journal of the Acoustical Society of Korea
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• 제36권6호
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• pp.371-377
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• 2017

The performance of an air conditioner is closely related to the cooling performance of a split-type outdoor unit so that, in most of the relevant preceding studies, the independent performance of an axial fan in an outdoor unit has been studied. However, there is a lack of research on the effects of other components in an outdoor units was rarely investigated. Therefore, in this paper, the effects of the fan orifice among other parts on the flow performance of the outdoor unit was numerically investigated. A virtual fan tester consisting of 18 million grids was developed for highly resolved flow simulation. The unsteady RANS (Reynolds-averaged Navier-Stokes) equations are numerically solved by using finite-volume CFD (Computational Fluid Dynamics) techniques. In order to verify the validity of the numerical methods, the predicted P-Q curve of the cooling fan in a full outdoor unit is compared with the measured one. Optimization of orifice shape was carried out for maximum flow performance of the outdoor unit using the validated numerical method.