• International Journal of Ocean System Engineering
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• 제1권1호
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• pp.28-31
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• 2011

An attempt was made to compute the free surface deformation due to the impact of a water droplet. The Cauchy Poisson, i.e. the initial value problem, was solved with the kinematic and dynamic free surface boundary conditions linearized. The zero order Hankel transformation and Laplace transform were applied to the related equations. The initial condition for the free surface profile was derived from a captured video image. The effect of the surface tension was not significant with the water mass used in this investigation. The computed and observed free surface deformations were compared.

• 대한조선학회논문집
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• 제51권5호
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• pp.419-428
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• 2014

This paper presents a numerical simulation method for the flow around advancing ships in regular waves by using a rectilinear grid system. Because the grid lines do not consist with body surface in the rectilinear grid system, the body geometries are defined by the interaction points of those grid lines and the body surface. For the satisfaction of body boundary conditions, no-slip and divergence free conditions are imposed on the body surface and body boundary cells, respectively. Meanwhile, free surface is defined with the modified marker density method. The pressure on the free surface is determined to make the pressure gradient terms of the governing equations continuous, and the velocity around the free surface is calculated with the pressure on the free surface. To validate the present numerical method, a vortex induced vibration (VIV) phenomenon and flows around an advancing Wigley III ship model in various regular waves are simulated, and the results are compared with existing and corresponding research data. Also, to check the applicability to practical ship model, flows around KRISO Container Ship (KCS) model advancing in calm water are numerically simulated. On the simulations, the trim and the sinkage are set free to compare the running attitude with some other experimental data. Moreover, flows around the KCS model in regular waves are also simulated.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.36-39
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• 2004

In this study, we present the theoretical, numerical and experimental results of the sink flow from a rotating, circular tank Strikingly enough, when the upper free surface was set with no-slip boundary conditions, the Ekman boundary-layer develops not only above the bottom surface but under the free surface. The sink fluid is coming from the two Ekman layers, and the mass transfer from the bulk, inviscid region is dependent on the rotational speed. It is also remarkable to see that all the fluid gathered along the axis flows through a rapidly rotating fluid column with almost the same size as the hole.

• 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.

• 대한기계학회논문집
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• 제11권6호
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• pp.1026-1035
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• 1987

본 연구에서는 두께방향에 따른 유동을 해석하는데 "fountain effect" 및 열 전달 현상을 동시에 고려하면서 진전하는 자유표면의 형상을 정확히 구하기 위한 유한 요소법을 이용한 수치해석법을 제안하고 그 방법을 적용하여 금형벽의 온도를 변화시 켜가면서 구체적인 유동특성을 해석하였다.특성을 해석하였다.

• 한국해안·해양공학회논문집
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• 제36권2호
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• pp.70-79
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• 2024

본 연구에서는 3차원 공간에서 바닥의 움직임에 따른 선형파의 생성을 모의할 수 있는 스펙트럼 법을 소개한다. 지배방정식은 선형의 동역학적 및 운동학적 자유수면 경계조건이며, 두 식은 Fourier 공간에서 해석된다. 해석된 속도포텐셜 및 자유수면변위는 연속방정식과 운동학적 바닥경계조건을 항상 만족해야 한다. 수치해석에서 시간 적분은 4차 Runge-Kutta 법을 이용하여 해석하였다. Fourier 공간에서 해석한 결과는 Fourier 역변환을 통해 실제 공간에서의 속도포텐셜과 자유수면변위로 표현된다. 본 수치모델을 이용하여 다양한 형상의 바닥이 규칙적으로 움직이는 경우 생성되는 규칙파에 대해 모의하였다. 또한 바닥의 움직임을 이용하여 비스듬히 전파하는 규칙파의 생성도 모의하였다. 수치모델의 결과는 해석해와 비교하였으며, 거의 일치하는 결과를 보였다.

• Ocean Systems Engineering
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• 제4권2호
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• pp.83-97
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• 2014

Wave propagation in a three-dimensional (3D) fully nonlinear numerical wave tank (NWT) is studied based on velocity potential theory. The governing Laplace equation with fully nonlinear boundary conditions on the moving free surface is solved using the indirect desingularized boundary integral equation method (DBIEM). The fourth-order predictor-corrector Adams-Bashforth-Moulton scheme (ABM4) and mixed Eulerian-Lagrangian (MEL) method are used for the time-stepping integration of the free surface boundary conditions. A smoothing algorithm, B-spline, is applied to eliminate the possible saw-tooth instabilities. The artificial wave speed employed in MTF (multi-transmitting formula) approach is investigated for fully nonlinear wave problem. The numerical results from incorporating the damping zone (DZ), MTF and MTF coupled DZ (MTF+DZ) methods as radiation condition are compared with analytical solution. An effective MTF+DZ method is finally adopted to simulate the 3D linear wave, second-order wave and irregular wave propagation. It is shown that the MTF+DZ method can be used for simulating fully nonlinear wave propagation very efficiently.

• 한국항해항만학회지
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• 제30권8호
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• pp.631-636
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• 2006

본 연구에서는 자유수면 위를 고속으로 항주하는 트랜섬 선미를 채택한 선박에 의하여 발생되는 선박주위 및 트랜섬 선미 끝단에서의 비선형 자유수면 경계조건식을 만족하는 자유 수면에서의 파형을 해석하는 수치해석 기법에 대하여 연구, 선체주위 유동해석프로그램을 개발하였다. 개발된 수치해석 프로그램의 타당성을 검증하기 위하여 고속선인 Athena선형, KCS(KRISO container ship)선형에 대하여 수치해석을 실시하였으며, 그 결과를 모형시험에 의하여 계측된 실험결과와 서로 비교하였다.

• 대한조선학회논문집
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• 제48권2호
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• pp.107-112
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• 2011

The aim of this study is to analyze the hydrodynamic properties of a 2D floating body with moon pool using a 2D fully nonlinear Numerical Wave Tank(NWT). This NWT was developed based on the Boundary Element Method(BEM) with potential theory and fully nonlinear free surface boundary conditions. Free surface elevations in the moon pool were calculated in the time domain for various frequencies of forced body motions. The added-mass and damping coefficients of the heaving body were also obtained. The present numerical results were compared with the analytic and experimental results and their accuracy was verified.

• 한국해양공학회지
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• 제21권6호
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• pp.53-58
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• 2007

A particle method, recognized as one of gridless methods, has been developed to investigate non-linear free-surface motions interacting with structures. This method is more feasible and effective than conventional grid methods for solving flow fieldswith complicated boundary shapes. The method consists of particle interaction models representing pressure gradient, diffusion, incompressibility, and the free-surface boundary conditions without grids. In the present study, broken dam problems with various viscosity values are simulated to validate the developed method.