• 대한조선학회논문집
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• 제43권6호
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• pp.638-646
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• 2006

In this paper a new hull-panel generation algorithm named 'Panel Cutting Method' was developed to solve the flow phenomena around a ship advancing on the free surface with a constant speed. In this algorithm the non-linearity of the free surface boundary conditions was taken into account using the iterative method and the raised panel was used at each iteration step. Numerical calculations were performed to investigate the validity of the developed algorithm using the series $60(C_B=0.60)$ hull The wave resistance coefficients, the wave patterns and the wave heights were compared between the computed and the experimental results at Fn=0.25 and 0.316. The comparison showed good agreement between computation and experiment.

• 대한조선학회논문집
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• 제45권2호
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• pp.132-143
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• 2008

The sloshing phenomena in a two-dimensional rectangular tank are investigated using a level set method based on finite volume method. The code validations are performed by comparing between the present results and previous numerical results, which gives a good agreement. We present the streamlines pattern, free surface shape, maximum free surface elevation and pressure fluctuation patterns in the tank under the pitch and surge motions with various frequencies. These two different motions cause the different flow structures in the tank. The time variations of surface elevation and pressure at the different locations in the tank strongly depend on the exciting frequency of tank moving.

• 한국수자원학회논문집
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• 제45권4호
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• pp.349-360
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• 2012

본 연구에서는 3차원 점성 흐름에 적용될 수 있는 비정수압 자유수면 모형을 수평방향 직교 곡선좌표계에서 개발하였다. 개발된 수치모형은 엇갈린 격자를 사용함으로써 발생되는 자유수면에서의 경계조건 종결 문제를 수면층 방정식을 도입하여 해결하였으며, 난류의 유동 해석을 위한 폐합식으로 등방성의 k-${\varepsilon}$ 난류모형을 이용하였다. 본 연구에서 운동량방정식은 이송-확산항만으로 중간단계의 유속을 예측하고, 압력 및 중력을 포함하는 생성항과 연속방정식을 결합하여 다음 시간단계의 유동장을 결정하는 계산 단계 분리법을 이용하였다. 수치모형의 적용성 평가를 위하여 폐쇄된 2차원 수조에서의 취송류, 급경사를 가지는 2차원 수로에서의 흐름, 원심력에 의한 이차류 흐름특성 분석을 위한 3차원 급변 만곡류에 대한 모의를 실시하였다. 수치모의 예측치는 수리모형 실험값과 수위, 유속, 난류특성 등에서 일치하는 양상을 보이는 것이 확인되었다.

• 대한조선학회논문집
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• 제31권3호
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• pp.80-86
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• 1994

자유수면을 항주하는 선박에 의하여 발생되는 비선형 조파현상을 해석하기 위한 수치해석법을 개발하였다. 유동은 비점성, 비압축성으로 가정하고 선체 및 자유수면 형상과 일치하는 좌표계의 생성을 위하여 타원형 편미분방정식을 수치해석하여 물체적합 좌표계를 생성하였으며 변환된 정규격자 물체적합 좌표계에 대한 Euler방정식을 유한차분법(Finite Difference Method)을 이용하여 계산하였다. 수치해석을 위하여 시간에 대한 미분항은 전진차분, 공간에 대한 미분항은 중심차분법으로 이산화하였고 대류항에는 수치계산의 안정을 위해 인위적인 소산(dissipation)항을 첨가하였다. 자유수면의 형상은 매 시간 단계마다 자유수면 경계조건들을 만족하도록 다시 계산되었고 격자점들은 자유수면형상의 변화에 적합하게 다시 생성되도록 하였으며 압력에 대한 Poisson방정식은 반복연산법에 의하여 풀고 그 결과를 이용하여 속도를 외삽하였다. 개발된 수치해석법의 검증을 위해 수식선형인 Wigley 모형에 대한 계산을 Fn=0.250-0.408에 대하여 수행하고, 그 결과를 실험 결과와 비교하여 잘 일치함을 보였다.

• 대한조선학회논문집
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• 제42권6호
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• pp.593-600
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• 2005

The finite volume based multi-block RANS code, WAVIS developed at KRISO, is used to simulate the turbulent flow field around the KRISO container ship (KCS) and the modified KRISO tanker (KVLCC2M). The realizable k-$\varepsilon$ turbulence model with a wall function is employed for the turbulence closure. The free surface flow with and without propeller is mainly investigated for the KCS and the double model flow is concerned for the KVLCC2M which is obliquely towed in still water. The computed results are compared with the experimental data provided by CFD Tokyo Workshop 2005 in terms of wave profiles, hull surface pressure and wake distribution with and without propeller for the HCS and wake distribution and hydrodynamic forces and moments with various drift angles for the KVLCC2M.

• 대한조선학회논문집
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• 제49권2호
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• pp.151-157
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• 2012

The present study explored the possibilities of the applications of open source libraries to shipbuilding and marine engineering industries. A computational fluid dynamics (CFD) code, termed SNUFOAM, was developed and tested for turbulent flow around a ship, free surface flow around a hull, cavitating flow, and vortex shedding dynamics around a cylinder. The results using the developed CFD codes were compared against existing experimental data and solution of commercial CFD codes. SNUFOAM showed the nearly same results as commercial CFD codes and proved to be an alternative to commercial CFD codes for shipbuilding and marine engineering industries.

• 한국가시화정보학회지
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• 제8권3호
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• pp.41-48
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• 2010

A visualization study to evaluate bubble motion in a tab water filled cylindrical tank with a varying flow rate of compressed air is conducted. The flow rate of compressed air varies from 1 to 5 L/min. Time resolved images are acquired by a high speed camera in 10 bit gray level at 100 fps and the measurement volume is irradiated by a 230 W halogen lamp. It is observed that there are three different regions; the bubble formation region, the rising bubble region and the free surface region. During the rise of bubble, the shape is changed as if an elastic body. Based on the binarized bubble image, the mean diameters of rising bubbles are estimated at beneath of the free surface. As the gas flow rate increases, the mean diameter is increased and the rising velocity also increases with buoyancy force.

• 대한수학회논문집
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• 제12권2호
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• pp.479-490
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• 1997

We consider long nonlinear waves in the two-layer flow of an inviscid and incompressible fluid bounded above by a free surface and below by a rigid boundary. The flow is forced by a bump on the bottom. The derivation of the forced KdV equation fails when the density ratio h and the depth ratio $\rho$ yields a condition $1 + h\rho = (2-h)((1-h)^2 + 4\rho h)^{1/2}$. To overcome this difficulty we derive a forced modified KdV equation by a refined asymptotic method. Numerical solutions are given and hydraulic fall solution of a two layer fluid is expressed analytically in the case that derivation of the forced KdV (FKdV) equation fails.

• 대한조선학회지
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• 제24권3호
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• pp.9-16
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• 1987

In this paper, the fluid flow in the two-dimensional tank is analyzed by the Finite Difference Method. The Navier-Stokes equation is modified for the tank fixed coordinate system. For the treatment of the free surface, the Volume of Fluid Method by Hirt and Nichols is adopted. The continuity equation and the Poisson equation which is derived from the Navier-Stokes equation to find the pressure are solved by the Successive-Line-Overrelaxation Method. The comparison of the calculated results with experimental data show a favorable agreement. The fluid flow in the two-dimensional tank can be predicted reasonably before the free surface reaches breaking by this numerical method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.448-450
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• 2010

Free surface liquid jet impingement, which is applicable to cooling of hot plates in a steel-making process, is investigated numerically by solving the conservation equations of mass, momentum and energy in the liquid and gas phases. The free-surface of liquid-gas interface is tracked by an improved level-set method incorporating a sharp-interface technique for accurate imposition of stress and heat flux conditions on the liquid-gas interface. The level-set approach is combined with a non-equilibrium $k-{\omega}$ turbulence model. The computations are made for slit nozzle jets to investigate their flow and cooling characteristics. Also, the effects of jetting angle, velocity and moving velocity of plate on the interfacial motion and the associated flow and temperature fields are quantified.