• Title/Summary/Keyword: 자유표면효과

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Numeric Analysis of 2-Dimensional Nonlinear Viscous Free-Surface Wave Problems (점성을 고려한 2차원 비선형 자유표면파 문제의 수치해석)

  • Y.H. Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.30 no.2
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    • pp.98-111
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    • 1993
  • Two-dimensional nonlinear free-surface wave problems are analyzed with consideration of viscosity. Navier-Stokes equation and continuity equation are solved by the application of Finite Analytic Method, and MAC scheme is used far the treatment of free surface. Surface tension effect is also considered and laminar flow is assumed. The free-surface waves in shallow water, the flows around a vortex-pair with free surface and the wave ahead of a rectangular body are simulated to test the present numerical scheme. In the shallow water problem, viscous effect due to the friction on the bottom is observed. In the second problem, the approach of a vortex-pair to the free surface is simulated to examine the interaction of vortex-pair with the free surface. In the third problem, the wave ahead of a semi-infinite floating body is simulated.

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Effects of Non-hydrostatic Pressure on Free Surface Environmental Flows (자유표면 환경유동에 대한 비정수압 효과)

  • Yoon, B.S.;Park, C.W.
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.8 no.3
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    • pp.116-121
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    • 2005
  • In the present paper, a new calculation algorithm far solving large scale environmental or geophysical flows with free surface is proposed where the non-hydrostatic pressure component is taken into consideration. Predictor-corrector fractional step approach with explicit, forward time marching scheme in the sigma coordinate system is employed. In order to validate the present calculation algorithm and to estimate the effects of non-hydrostatic pressure on resultant flow and free surface movements, example calculations are carried out for typical steady and unsteady flow problems. Present method can be applied to the meso-scale free surface flows with complex bottom topography where MAC-like 3-d hydrodynamic calculations are quite ineffective and uneconomic.

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Effect of grif size on the compututation of free-surface waves (자유표면파 계산에서의 격자크기영향)

  • 곽승현
    • Journal of Ocean Engineering and Technology
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    • v.11 no.2
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    • pp.70-76
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    • 1997
  • 수치격자의 크기제한에 의한 자유표면 유동해석 문제를 효율적으로 다루기 위하여 자유표면의 모든 격자를 x 방향으로 4,8,12개로 등분할 하고, y 방향으로는 4개로 잘라서 계산하였다. 이중격자 또는 삼중격자로 Navier-Stokes 방정식의 각항에 크기가 다른 격자를 사용해 효율을 향상시키는 계산방법의 연장으로, 본 논문에서는 자유표면 방정식에 보다 세분화된 격자를 적용해, Marker Particle 이동 및 자유수면 형성에 효율향상을 줄수 있는 수치방법을 도입하였다. 계산결과에 의하면 초기사용 격자가 coarse한 경우가 본방법의 효과가 커짐을 알 수 있고 대상물로는 층류유동에서 Wigley모형과 낭류유동의 S103 모형이다.

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Adaptive Air-Particle Method for Vortex Effects of Water in Free Surface (자유표면내 물의 와류효과를 위한 적응적 공기 입자 기법)

  • Kim, Jong-Hyun;Lee, Jung
    • Journal of the Korea Computer Graphics Society
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    • v.23 no.1
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    • pp.17-24
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    • 2017
  • We propose an efficient method to express water spray effects by adaptively modeling air particles in particle-based water simulation. In real world, water and air continuously interacts with each other around free surfaces and this phenomenon is commonly observed in waterfall or sea with rough waves. Due to thin spray water, the interfaces between water and air become vague and the interactions between them lead to heavy vortex phenomenon. To express this phenomenon, we propose methods of 1) generating adaptive air cell in particle-based water simulation, 2) expressing water spray effects by creating and evolving air particles in the adaptive air cells, and 3) guaranteeing robustness of simulation by solving drifting problem occurred when adjacent air particles are insufficient. Experiments convincingly demonstrate that the proposed approach is efficient and easy to use while delivering high-quality results.

Time-Domain Simulation of Nonlinear Free-Surface Flows around a Two-Dimensional Hydrofoil (2차원 수중익주위 비선형 자유표면유동의 시간영역 시뮬레이션)

  • Yong-J. Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.31 no.2
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    • pp.45-56
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    • 1994
  • A computationally efficient numerical method based on potential flow is developed for time-domain simulation of the nonlinear free-surface flows around a 2-dimensional hydrofoil. This numerical method, namely, spectral/boundary-element method, is a mixed one of the high-order spectral method and the boundary-element method in time-domain. The high-order spectral method is used to calculate the nonlinear evolution of free-surface, and the boundary-element method is used to calculate the effects of the hydrofoil and the shed vortex. As application examples, nonlinear free-surface flows around a 2-dimensional hydrofoil which starts from the rest and translates near the free-surface with or without harmonic oscillations are calculated. Nonlinear/unsteady results of free-surface waves and hydrodynamic farces are shown and discussed. Particularly, the results of steady-state which are obtained as a special case of the present unsteady solution are compared with others' calculated and experimental results, and good agreements are observed.

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3차원 표면효과익의 자유표면 효과에 관한 수치연구

  • Gwak, Seung-Hyeon
    • Journal of Ocean Engineering and Technology
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    • v.12 no.2 s.28
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    • pp.79-86
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    • 1998
  • A three-dimensional WIG (Wing In Ground effect) moving above free surface is numerically studied by means of finite difference techniques. The air flow field around the WIG is analyzed by MAC (Marker & Cell) method, and interactions between WIG and the free surface are appeared as the variation of pressure distribution acting on the free surface. To analyze the wavemaking phenomena by those pressure distributions, the NS (Navier-Stokes) solver is employed in which nonlinearities of the free surface conditions can be included. Through the numerical simulation, Cp values and lift/drag ratio are carefully reviewed by changing the height/chord ratio. The section shape of model is NACA0012 with the span/chord ratio of 3.0. Through computational results, it is confirmed that the effect of free surface is small enough to treat it as a rigid wavy wall.

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On Two-Dimensional Large-Amplitude Motions in Regular Wave (규칙파중에서의 주상체의 대진폭 운동에 관한 연구)

  • Yong-Jig,Kim
    • Bulletin of the Society of Naval Architects of Korea
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    • v.26 no.2
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    • pp.25-31
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    • 1989
  • Two-dimensional large-amplitude motions in regular harmonic wave are treated in time domain, by satisfying the exact body boundary condition and the linear free surface condition. For the present numerical calculation, the method of free-surface spectral representation with simple source distribution on the instantaneous body surface has been extended to include the effect of the incident wave. Calculations of the wave exciting force are performed for a submerged circular cylinder fixed or oscillating with large amplitude. Especially, nonlinear effects on the time-mean forces are studied in detail. It is shown that relative motion between the body and the fluid particle gives a significant effect on the lift and drift forces. Also, large-amplitude motion of a submerged circular cylinder and that of a floating Lewis-form cylinder are directly simulated in time domain. In the calculation results, some nonlinear effects are shown.

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Wave Generation with a Hydrofoil by More Efficient Free-Surface Boundary Condition (고효율 자유표면 경계조건에 의한 수중익 주위의 파도생성)

  • Kwag, S.H.
    • Journal of Korean Port Research
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    • v.12 no.1
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    • pp.87-93
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    • 1998
  • For the calculation of the free-surface elevation, a new finite difference scheme is studied where the third derivative term for the wave elevation is artificially added in the Eulerian expression of the free-surface boundary condition. The paper presents a comparative analysis with simulations performed by the classical MAC method. More schematic computations are carried out by changing the submergence-depth and angle-of-attack. The present study shows that this new method is very efficient for the simulation of free-surface elevation around the trailing edge.

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Computation of Two-Fluid Flows by Finite Volume Method and Discussion on Wave Breaking (유한체적법에 의한 이층류 계산 및 쇄파에 관한 토의)

  • Milovan Peric
    • Journal of Ocean Engineering and Technology
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    • v.14 no.1
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    • pp.11-16
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    • 2000
  • 수중날개를 대상으로 임의로 변형하는 이층류의 수직계산을 수행하였다. 계산은 비구조격자와 접면포착법을 이용하여 자유표면의 형상을 결정하였다 본 연구에 의하면 낮은 물속 깊이와 높은 프루드수에서 쇄파현상이 발생하였다 수중날개에 대하여 쇄파형상의 효과를 연구하였고 실험값과 계산값을 상호비교함으로서 격자의 민감성을 수직적으로 확인하였다.

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