• Title/Summary/Keyword: Hybrid VOF method

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A Study on a VOF Method for the Improvement of Free Surface Capturing (VOF 법의 자유수면 포착정도 향상을 위한 연구)

  • Park, Il-Ryong;Kim, Wu-Joan;Kim, Jin;Van, Suak-Ho
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.2 s.140
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    • pp.88-97
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    • 2005
  • A new numerical scheme solving two-phase flow, the Hybrid VOF method for improved free surface capturing has been developed by combining a volume capturing VOF method with the Level-Set reinitialization procedure. For validation, the proposed method is applied to 3-D bubble rising problem, dam breaking and the free surface flow around a commercial container ship. The calculated results by using the Hybrid VOF method with the two previously applied VOF formulations are compared with available numerical and experimental data. It is found that the new method provides more reasonable results than the two previous ones.

A Study on a VOF Method for Improved Free Surface Capturing (VOF법의 자유수면 포착정도 향상을 위한 연구)

  • Park Il-Ryong;Kim Wu-Joan;Kim Jin;Van Suak-Ho
    • 한국전산유체공학회:학술대회논문집
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    • 2005.04a
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    • pp.202-206
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    • 2005
  • A new numerical scheme for two-phase flows, the Hybrid VOF method has been developed for improved free surface capturing. The present new method is a volume capturing based VOF method coupled with a reinitialization procedure of a Level-set method. For validation, the proposed method is applied to two test cases: spherical bubble rising and dam breaking. The calculated results by using the Hybrid VOF method with the two previously applied VOF formulations are compared with available numerical and experimental data. It is found that the new method provides more accurate results than the two previous ones.

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Numerical Simulation of Wave Forces acting on Fixed Offshore Structures Using Hybrid Scheme (하이브리드 기법을 이용한 고정된 해양구조물에 작용하는 파랑하중에 관한 수치 시뮬레이션)

  • Nam, Bo-Woo;Hong, Sa-Young;Kim, Yong-Hwan
    • Journal of Ocean Engineering and Technology
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    • v.24 no.6
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    • pp.16-22
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    • 2010
  • In this paper, the diffraction problems for fixed offshore structures are solved using a hybrid scheme. In this hybrid scheme, potential-based solutions and the Navier-Stokes-based finite volume method (FVM) with a volume-of-fluid (VOF) method are combined. We introduce a buffer zone for efficient wave-making and damping. In this buffer zone, the near field solution from FVM-VOF is gradually changed to Stokes' 2nd order wave solutions. Three different models, including the truncated cylinder, sphere, and wigleyIII model, are numerically investigated in regular waves with a wave steepness of 1/30. The efficiency and accuracy of the hybrid scheme are numerically validated from results using different domain sizes and buffer zones. The wave exciting forces from the FVM-VOF simulations are compared with experiments and potential-based solutions from the higher-order boundary element method (HOBEM). This comparison shows good agreement between the hybrid scheme and potential-based solutions.

Study on Improvement in Numerical Method for Two-phase Flows Including Surface Tension Effects (표면장력 효과를 고려한 이상유동 해석법 개선에 관한 연구)

  • Park, Il-Ryong
    • Journal of Ocean Engineering and Technology
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    • v.27 no.5
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    • pp.70-76
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    • 2013
  • The present paper proposes a coupled volume-of-fluid (VOF) and level-set (LS) method for simulating incompressible two-phase flows that include surface tension effects. The interface of two fluids and its motion are represented by a VOF method designed using high-resolution differencing schemes. This hybrid method couples the VOF method with an LS distancing algorithm in an explicit way to improve the calculation of the normal and curvature of the interface. It is developed based on a rather simple algorithm to be efficient for various practical applications. The accuracy and convergence properties of the method are verified in a simulation of a single gas bubble rising in a three-dimensional flow with a large density ratio.

SHIP RESISTANCE AND PROPULSION PERFORMANCE TEST USING HYBRID MESH AND SLIDING MESH (Hybrid mesh 및 sliding mesh를 이용한 선박 저항추진 성능 시험)

  • Park, Bum-Jin;Rhee, Shin-Hyung
    • 한국전산유체공학회:학술대회논문집
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    • 2009.11a
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    • pp.77-83
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    • 2009
  • In this study, we conducted resistance and propulsion performance test of ship composed of the Resistance Test, Propeller Open Water Test and Self Propulsion Test using the CFD(Computational Fluid Dynamics). We used commercial RANS(Reynolds Averaged Navier Stokes equation) solver, as a calculating tool. The unstructured grids were used in a bow and stern of ship, having complex shape, for a convenience of generating grids, and the structured grids were adopted in a central hull and rest of hull having a relatively simple shape which is called hybrid grid method. In addition, The sliding mesh method was adopted to rotate a propeller directly in the Propeller Open Water and Self Propulsion Test. The Resistance Test and Self Propulsion Test were calculated using Volume of Fluid (VOF) model and considering a free surface. And all The three cases were applied realizable k-epsilon model as the turbulence model. The results of calculations were verified for the suitability of calculations by comparing MOERI's EFD results.

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SHIP RESISTANCE AND PROPULSION PERFORMANCE TEST USING HYBRID MESH AND SLIDING MESH (Hybrid mesh 및 sliding mesh를 이용한 선박 저항추진 성능 시험)

  • Lee, Ju-Hyun;Park, Bum-Jin;Rhee, Shin-Hyung
    • Journal of computational fluids engineering
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    • v.15 no.1
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    • pp.81-87
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    • 2010
  • In this study, we conducted resistance and propulsion performance test of ship composed of the Resistance Test, Propeller Open Water Test and Self Propulsion Test using the CFD(Computational Fluid Dynamics). We used commercial RANS(Reynolds Averaged Navier Stokes equation) solver, as a calculating tool. The unstructured grids were used in a bow and stern of ship, having complex shape, for a convenience of generating grids, and the structured grids were adopted in a central hull and rest of hull having a relatively simple shape which is called hybrid grid method. In addition, The sliding mesh method was adopted to rotate a propeller directly in the Propeller Open Water and Self Propulsion Test. The Resistance Test and Self Propulsion Test were calculated using Volume of Fluid (VOF) model and considering a free surface. And all The three cases were applied realizable k-epsilon model as the turbulence model. The results of calculations were verified for the suitability of calculations by comparing MOERI's EFD results.

NUMERICAL SIMULATION OF MULTIPHASE FLOW USING LEVEL CONTOUR RECONSTRUCTION METHOD (Level Contour Reconstruction 방법을 이용한 다상유동 수치해석)

  • Shin, Seung-Won
    • 한국전산유체공학회:학술대회논문집
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    • 2009.11a
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    • pp.193-200
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    • 2009
  • Recently, there have been efforts to construct hybrids among the existing methodologies for multiphase flow such as VOF, Level Set, and Front Tracking with the intention of facilitating simulations of general three-dimensional problems. As one of the hybrid method, we have developed the Level Contour Reconstruction Method (LCRM) for general three-dimensional multiphase flows including phase change. The main idea was focused on simplicity and a robust algorithm especially for the three-dimensional case. It combines characteristics of both Front Tracking and Level Set methods. While retaining an explicitly tracked interface using interfacial elements, the calculation of a vector distance function plays a crucial role in the periodic reconstruction of the interface elements in the LCRM method to maintain excellent mass conservation and interface fidelity. In addition, compact curvature formulation is incorporated for the calculation of the surface tension force thereby reducing parasitic currents to a negligible level.

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A zonal hybrid approach coupling FNPT with OpenFOAM for modelling wave-structure interactions with action of current

  • Li, Qian;Wang, Jinghua;Yan, Shiqiang;Gong, Jiaye;Ma, Qingwei
    • Ocean Systems Engineering
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    • v.8 no.4
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    • pp.381-407
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    • 2018
  • This paper presents a hybrid numerical approach, which combines a two-phase Navier-Stokes model (NS) and the fully nonlinear potential theory (FNPT), for modelling wave-structure interaction. The former governs the computational domain near the structure, where the viscous and turbulent effects are significant, and is solved by OpenFOAM/InterDyMFoam which utilising the finite volume method (FVM) with a Volume of Fluid (VOF) for the phase identification. The latter covers the rest of the domain, where the fluid may be considered as incompressible, inviscid and irrotational, and solved by using the Quasi Arbitrary Lagrangian-Eulerian finite element method (QALE-FEM). These two models are weakly coupled using a zonal (spatially hierarchical) approach. Considering the inconsistence of the solutions at the boundaries between two different sub-domains governed by two fundamentally different models, a relaxation (transitional) zone is introduced, where the velocity, pressure and surface elevations are taken as the weighted summation of the solutions by two models. In order to tackle the challenges associated and maximise the computational efficiency, further developments of the QALE-FEM have been made. These include the derivation of an arbitrary Lagrangian-Eulerian FNPT and application of a robust gradient calculation scheme for estimating the velocity. The present hybrid model is applied to the numerical simulation of a fixed horizontal cylinder subjected to a unidirectional wave with or without following current. The convergence property, the optimisation of the relaxation zone, the accuracy and the computational efficiency are discussed. Although the idea of the weakly coupling using the zonal approach is not new, the present hybrid model is the first one to couple the QALE-FEM with OpenFOAM solver and/or to be applied to numerical simulate the wave-structure interaction with presence of current.

Syudy on the dynamic Stability of Ground Armored Moving Vehicle during cruising river (지상 전투차량의 수상 추진 시 동적 안정성에 대한 연구)

  • Ahn, Tai-Sul;Lee, Kyung-Hoon
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.252-255
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    • 2008
  • In this study, the characteristics of crossing a river of Ground Armored Vehicle (GAV) were evaluated by numerical method and real size tests. 3-D hybrid mesh systems were constructed by 3-D models of the GAV, and a commercial software, FLUENT, was used in numerical analysis. In order to deal with multi-phase problem (air and water), Volume Of Fluid (VOF) method was used, and Moving and Deforming Mesh (MDM) was adapted for unsteady motion of GAV. There were two steps in this research. Firstly, stability of the GAV which cruised a river was evaluated by changing several shapes of water-proof-front-wing of the GAV in steady state, and compared results (free surface shape and drag value in 10km/h) with those of real size tests. Secondly, results of unsteady analysis considering weight and moment of inertia of the GAV were presented. There were showed a maximum velocity with a designed water jet and dynamic stability including pitch, roll, and yaw moment. Based on these results, the optimal shape of water-proof-front-wing of the GAV was determined for a proto-type of the GAV.

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Numerical prediction analysis of propeller bearing force for full-scale hull-propeller-rudder system

  • Wang, Chao;Sun, Shuai;Li, Liang;Ye, Liyu
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.8 no.6
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    • pp.589-601
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    • 2016
  • The hybrid grid was adopted and numerical prediction analysis of propeller unsteady bearing force considering free surface was performed for mode and full-scale KCS hull-propeller-rudder system by employing RANS method and VOF model. In order to obtain the propeller velocity under self-propulsion point, firstly, the numerical simulation for self-propulsion test of full-scale ship is carried out. The results show that the scale effect of velocity at self-propulsion point and wake fraction is obvious. Then, the transient two-phase flow calculations are performed for model and full-scale KCS hull-propeller-rudder systems. According to the monitoring data, it is found that the propeller unsteady bearing force is fluctuating periodically over time and full-scale propeller's time-average value is smaller than model-scale's. The frequency spectrum curves are also provided after fast Fourier transform. By analyzing the frequency spectrum data, it is easy to summarize that each component of the propeller bearing force have the same fluctuation frequency and the peak in BFP is maximum. What's more, each component of full-scale bearing force's fluctuation value is bigger than model-scale's except the bending moment coefficient about the Y-axis.