• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.87-99
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• 1994

Reynolds Averaged Navier-Stokes equations are solved numerically for the computation of turbulent flow around a Wigley double model. A second order finite difference method is applied for the spatial discretization on the nonstaggered grid system and 4-stage Runge-Kutta scheme for the numerical integration in time. In order to increase the time step, residual averaging scheme of Jameson is adopted. Pressure field is obtained by solving the pressure-Poisson equation with the appropriate Neumann boundary condition. For the turbulence closure, 0-equation turbulence model of Baldwin-Lomax is used. Numerical computation is carried out for the Reynolds number of 4.5 million. Comparisons of the computed results with the available experimental data show good agreements for the velocity and pressure distributions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.526-534
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• 2004

A new second-moment closure model for turbulent heat fluxes is proposed on the basis of the elliptic equation. The new model satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. The predictions of turbulent heat transfer in a channel flow have been carried out with constant wall heat flux and constant wall temperature difference boundary conditions respectively. The velocity field variables are supplied from the DNS data and the differential equations only fur the mean temperature and the scalar flux are solved by the present calculations. The present model is tested by direct comparisons with the DNS to validate the performance of the model predictions. The prediction results show that the behavior of the turbulent heat fluxes in the whole region is well captured by the present model.

• Journal of Korea Water Resources Association
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• v.47 no.8
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• pp.703-715
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• 2014

This study aims to investigating the effect of Schmidt number (${\sigma}_c$) on sediment suspension and hydrodynamics calculation. The range of ${\sigma}_c$ is also studied based on the flux Richardson number ($Ri_f$) and gradient Richardson number ($Ri_g$). Numerical experiments are carried out by 1 dimensional vertical model. Both cohesive and non-cohesive sediments are tested under the conditions of pure current and oscillatory flow. The turbulence damping effect due to sediment suspension is examined considering ${\sigma}_c$ as a constant for the damping effect. The results of this study show the consistent effect of ${\sigma}_c$ on sediment suspension regardless of hydrodynamic condition. It is also found that the model overestimates the flow velocity and turbulent kinetic energy when the damping effect is not considered. Under the conditions of $Ri_f$ and $Ri_g$ causing density stratification, it is known that the vertical mixing of sediment is reasonably calculated in the range of ${\sigma}_c$ from 0.3 to 0.5.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.1
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• pp.1-8
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• 2001

The computations of the turbulent flow around the ship models with the free-surface effects were carried out. Incompressible Reynolds-Averaged Navier-Stokes equations were solved by using an explicit finite-difference method with the nonstaggered grid system. The method employed second-order finite differences for the spatial discretization and a four-stage Runge-Kutta scheme for the temporal integration. For the turbulence closure, a modified Baldwin-Lomax model was exploited. The location of the free surface was determined by solving the equation of the kinematic free-surface condition using the Lax-Wendroff scheme and a free-surface conforming grid was generated at each time step so that one of the grid boundary surfaces always coincides with the free surface. An inviscid approximation of the dynamic free-surface boundary condition was applied as the boundary conditions for the velocity and pressure on the free surface. To validate the computational method developed in the present study, the computations were carried out for beth Wigley and Series 60 $C_B=0.6$ ship model and the computational results showed good agreements with the experimental data.

• Journal of Korean Port Research
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• v.11 no.1
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• pp.121-128
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• 1997

To analyze the ocean wave more efficiently, more fine grids are used with relatively less computer memory. Each element of free surface is discretized into more fine grids because the ocean waves are much influenced by the mesh used in the finite difference scheme. According to the flow analysis, remarkable improvements could be seen in the free surface generation. The multi grid is applied to confirm the validity of scheme. The Baldwin Lomax turbulence model is used for the analysis of S103 Inuid ship. Finally some discussion on experiments was made for the physical phenomena of the viscous

• Journal of Korea Water Resources Association
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• v.57 no.5
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• pp.347-357
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• 2024

Numerous prior studies have delineated the size distribution of noncohesive sediment in suspension, focusing on mean size and standard deviation. However, suspensions comprise a heterogeneous mixture of sediment particles of varying sizes. The transport dynamics of suspended sediment in turbulent flow are intimately tied to settling velocities calculated based on size and density. Consequently, understanding the grain size distribution becomes paramount in comprehending sediment transport phenomena for noncohesive sediment. This study aims to introduce a straightforward modeling approach for simulating the grain size distribution of suspended sediment amidst turbulence. Leveraging insights into the contrast between cohesive and noncohesive sediment, we have meticulously revised a stochastic flocculation model originally designed for cohesive sediment to aptly simulate the grain size distribution of noncohesive sediment in suspension. The efficacy of our approach is corroborated through a meticulous comparison between experimental data and the grain size distribution simulated by our newly proposed model. Through numerical simulations, we unveil that the modulation of grain size distribution of suspended sediment is contingent upon the sediment transport capacity of the carrier fluid. Hence, we deduce that our simplified approach to simulating the grain size distribution of suspended sediment, integrated with a sediment transport model, serves as a robust framework for elucidating the pivotal bulk properties of sediment transport.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.142-150
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• 2003

Turbulent flows and related heat transfer in a square heated duct is investigated by a turbulence model and a large eddy simulation. The cooling channel of calorimeter is modeled to the square duct. The nonlinear k-ε-fμ model of Park et al. [3] is slightly modified and their explicit heat flux model is employed. The Reynolds number is varied in the range 4000≤Reｂ≤20000. The heat transfer is closely linked to the secondary flows which driven by the turbulent motion. Its magnitude is 1~3% of the mean streamwise velocity. The relation of Nu~Re0.8Pr0.34 is validated by comparing with the predicted Nu of k-ε-fμ model. Finally, the coherent structures and thermal fluctuations are scrutinized.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.469-473
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• 2009

저수지에서 잠재적 대규모 조류발생을 감소시키기 위하여 인공적 성층파괴 장치가 2006년 용담댐에 설치되었다. 본 연구는 저수지에서 여름철 발생하는 성층파괴에 대한 대류순환식 폭기장치의 효과를 검토하기 위해 수행되었다. 성층파괴 장치의 성능을 분석하기 위하여 반경 25m, 높이 45m의 실린더 용기에 34.6만개의 격자로 구성된 CFD모형을 적용하였다. 적용결과, 사면체 격자는 온도와 유속에서 실측자료와 밀접하게 일치하였다. 이와 같은 결과는 난류확산항이 제거되었을때 보다 태양광 열전도를 고려한 경우가 보다 좋은 결과를 보였다. 결과적으로 성층파괴 장치의 지속적인 운영은 인공적 외부력을 통하여 성층화된 수체를 혼합시키는데 유용할 것으로 나타났으나 현재 설치되어 있는 장비로는 크기나 숫자에서 충분하지 못해 원래 목적을 달성하기에는 부족한 것으로 나타났다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.4
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• pp.189-197
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• 2017

The development and application of accurate numerical models is essential to promptly respond to early stage of oil spill incidents occurring in nearshore area. In this study, the coupled modelling system was developed by integrating the advection-diffusion-transformation model for oil slick with the Boussinesq model, which incorporates non-linear, discrete, turbulent and rotational effects of wavy flows for accurate representation of nearshore hydrodynamics. The developed model examined its applicability through the application into real coastal region with topographical complexity and characteristics of the resulting flow originated from it. The highly-resolved, coupled model developed in this study is believed to assist in establishing the disaster prevention system that can prepare effectively for oil disasters under extreme ocean climate conditions and thus minimize industrial, economical, and environmental damages.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.1-10
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• 1997

Viscous flow around actual ship is calculated by an use of RANS equations. The propriety of this computing method, usefulness to hull form design and the scale effect which is the effect of viscous flow depending on the scale of ship model are investigated. Reynolds stress is modelled by using k-${\varepsilon}$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the arbitrary 3-dimensional shape of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM. In the calculation of pressure, SIMPLE method is adopted and the solution of the discretized equation is obtained by the line-by-line method with the use of TDMA The calculations of two ships, 4410 TEU container carrier and 50,000 DWT class bulk carrier, are performed at model and actual ship scale. The results are compared and discussed with the model test results which are viscous resistance, nominal wake distribution at propeller plane and limiting streamline on the hull surface. They describe the effect of stem form and the scale effect very well. In particular, the calculated nominal wake distribution and limiting streamline are agreed qualitatively with the experiments and the viscous resistance values are estimated within ${\pm}5%$ difference from the resistance tests.