• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.3
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• pp.240-249
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• 1993

The suspended sediment mechanism was systematically investigated by analyzing existing data together with new data obtained under several wave folds. A simple empirical formula has been developed to predict the time-averaged suspended sediment concentration above movable bed by the effect of wave and current interaction. The present study shows linear dependency of the diffusion coefficient of suspended sediment on the eddy viscosity coefficient obtained by considering the ripple geometry. Furthermore, it is proved that reference sediment concentration is reduced by the effect of ripple asymmetry.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.355-365
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• 1994

An analytical model of return flow is presented outside the surf zone. The governing equation is derived from the Navier-Stokes equation and the continuity. Each term of the governing equation is evaluated by the ordering analysis. Then the infinitesimal terms, i.e. the turbulent normal stress, the squared vertical velocity of water particle and the streaming velocity, are neglected. The driving forces of return flow are calculated using the linear wave theory for the shallow water approximation. Especially, the space derivative of local wave heights is described considering a shoaling coefficient. The vertical distribution of eddy viscosity is discussed to the customary types which are the constant, the linear function and the exponential function. Each coefficient of the eddy viscosities which sensitively affect the precision of solutions is uniquely decided from the additional boundary condition which the velocity becomes zero at the wave trough level. Also the boundary conditions at the bottom and the continuity relation are used in the integration of the governing equation. The theoretical solutions of present model are compared with the various experimental results. The solutions show a good agreement with the experimental results in the case of constant or exponential function type eddy viscosity.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.1
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• pp.101-112
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• 2007

This study has used RMA2 model and RMA4 model, which are depth-averaged two-dimensional flow and water-quality prediction models, to analyze the variation of the water-quality by the gates operation in the Seonakdong River. Sensitivity analysis is performed to get the Manning coefficient and the coefficient of eddy viscosity for RMA2 model, and to get the diffusion coefficient for RMA4 model. Since the numerical simulation using RMA2 and RMA4 models did not consider tributary pollutant load except for that of Joman River, it could make a little difference from the natural phenomenon. Nevertheless, the numerical simulation shows that the discharge of $30m^3/s$, which is the continuous inflow from the Daedong-gate, can make it possible to achieve the target water-quality (BOD 4.3mg/L) of Nakbon-N watershed about 10 days later if the Daejeo-gate could remain opened in connection with the Noksan-gate operation.

• Journal of computational fluids engineering
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• v.10 no.4 s.31
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• pp.39-50
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• 2005

An application of the KFLOW3D code which has been developed at KAIST is presented. This paper briefly describes the underlying methodology and summarizes the results for the DLR-F6 transport configuration recently presented in the second AIAA CFD Drag Prediction Workshop held in Orlando, FL, June 2003. KFLOW3D is a parallelized Reynolds averaged Navier-Stokes solver for multi-block structured grids. For the present computations, 2-equation k-$\omega$ WD+ nonlinear eddy viscosity model is used. The emphasis of the paper is placed on the implementation of the k-$\omega$ WD+ model in the multigrid framework and practicality of KFLOW3D for accurately predicting not only the integrated aerodynamic property such as the drag coefficient but pressure distributions.

• Journal of Energy Engineering
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• v.24 no.2
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• pp.110-114
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• 2015

A numerical investigation has been carried out on recirculation zone formed downstream of a compressible flow over a backward facing step. The study has been performed by solving Two-Dimensional Navier-Stokes equations. The system of governing equations has been solved, using an explicit Harten-Yee Non- MUSCL Modified flux type TVD scheme and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The recirculation region dimensions are characterized over a range of Mach numbers of fixed step height 5mmThe detail of recirculation zone such as pressure, temperature, recirculation length, strength etc are reported. The variations of these characteristics due to change of Mach number are also presented.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.97.1-97.1
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• 2010

본 연구에서는 천수방정식의 매개변수인 조도계수와 난류점성계수에 따른 사행수로에서의 유속분포를 수치모의하였다. 벽면조도계수와 텐서형 난류점성계수를 변화시켜 8가지 수치모의 조건을 구성하였으며, 만곡부 정점에서의 횡방향 유속분포를 수리실험에 의한 측정값과 비교하였다. 벽면조도계수가 커질수록 벽면에서의 유속이 감소하여 실측값과 가까워지지만 벽면 이외의 영역에서는 오히려 유속이 증가하여 실측값보다 커졌다. 난류점성계수가 커질수록 만곡부 내외측의 유속차는 작게 나타났으며 xx와 yy방향으로 가중된 난류점성계수를 가지는 경우가 xy방향으로 가중된 난류점성계수를 가지는 경우에 비해 내외측 유속차가 약간 작게 나타났다.

• Nuclear Engineering and Technology
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• v.43 no.2
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• pp.175-186
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• 2011

Previous evaluations of the safety of the Ulchin Nuclear Power Plant in the event of a tsunami have the shortcoming of uncertainty of the tsunami sources. To address this uncertainty, maximum and minimum wave heights at the intake of Ulchin NPP have been estimated through a parametric study, and then assessment of the safety margin for the intake has been carried out. From the simulation results for the Ulchin NPP site, it can be seen that the coefficient of eddy viscosity considerably affects wave height at the inside of the breakwater. In addition, assessment of the safety margin shows that almost all of the intake water pumps have a safety margin over 2 m, and Ulchin NPP site seems to be safe in the event of a tsunami according to this parametric study, although parts of the CWPs rarely have a margin for the minimum wave height.

• Journal of Korea Water Resources Association
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• v.56 no.spc1
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• pp.1007-1014
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• 2023

Two-dimensional flow analysis, a fundamental component of hydrodynamics, plays a pivotal role in numerically simulating fluid behavior in rivers and waterways. This modeling approach heavily relies on parameters such as eddy viscosity and roughness coefficient to accurately represent flow characteristics. Therefore, combination of appropriate parameters is very important to accurately simulate flow characteristics. In this study, an automation algorithm was developed and applied to find the optimal combination of parameters. Previously, when applying a two-dimensional flow analysis model, former researchers usually depend on the empirical approach, which causes many difficulties in finding optimal variable values. Using the experimental data, we tracked errors according to the combination of various parameters and applied the algorithm that can determine the optimal combination of parameters with the Python language. The automation algorithm can easily determine the most accurate combination by comparing the flow velocity error values among the two-dimensional flow analysis results among the combinations of 121 (11×11) parameters. In the perspective of utilizing automation algorithm, there is an expected high utility in promptly and straightforwardly determining the optimal combination of parameters with the smallest error.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.772-778
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• 2002

A numerical analysis of turbulent gas-particle two-phase flow is performed in conjunction with the experiments of Fackrell ＆ Robins and Raupach & Legg that considered ground-level source and/or elevated source flat plate flow. K-$\omega$ turbulence model is used in order to analyze fully turbulent flow field and the concentration equation with settling velocity is adopted for the concentration field. The model of Einstein and Chien is applied that couples the velocity field and the concentration field. Turbulent eddy viscosity is re-evaluated in this model. The present numerical results have good agreement between the simulation and the experimental data for the mean flow velocities and particle concentrations. While the previous study shows about 27% error in the vicinity of the source of particle concentration, the .present study allows about 14% error. A new turbulent gas-particle flow model developed by this study is able to cut down error by 13% at a near source.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.59.2-59.2
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• 2011

Although there are many activities on the construction of wind farm to produce amount of power from the wind, in practice power productions are not as much as its expected capabilities. This is because a lack of both the prediction of wind resources and the aerodynamic analysis on turbines with far wake effects. In far wake region, there are velocity deficits and increases of the turbulence intensity which lead to the power losses of the next turbine and the increases of dynamic loadings which could reduce system's life. The analysis on power losses and the increases of fatigue loadings in the wind farm is needed to prevent these unwanted consequences. Therefore, in this study velocity deficits have been predicted and aerodynamic analysis on turbines in the far wake is carried out from these velocity profiles. Ainslie's eddy viscosity wake model is adopted to determine a wake velocity and aerodynamic analysis on wind turbines is predicted by the numerical methods such as blade element momentum theory(BEMT) and vortex lattice method(VLM). The results show that velocity recovery is more rapid in the wake region with higher turbulence intensity. Since the velocity deficit is larger when the turbine has higher thrust coefficient, there is a huge aerodynamic power loss at the downstream turbine.