• Title/Summary/Keyword: Free-Surface Flows

### Numerical Calculation of the free-Surface Flows around a Submerged Body (잠수체 주위 자유표면 유동의 수치계산)

• 김용직;하영록;홍사영
• Journal of the Society of Naval Architects of Korea
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• v.40 no.2
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• pp.11-20
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• 2003
• In this paper, the high-order spectral/boundary-element method is developed to calculate the 3-dimensional water waves generated by a submerged body. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated Tn time-domain. Three-dimensional free-surface flows generated by a submerged sphere which is moving under the free-surface are calculated. Through example calculations, nonlinear effects on free-surface profiles and hydrodynamic forces are shown. Comparisons with others' results show good agreements.

### Computation of Two-Fluid Flows with Submerged hydrofoil by Interface Capturing Method (접면포착법에 의한 수중익 주위의 이층류 유동계산)

• 곽승현
• Journal of Korean Port Research
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• v.13 no.1
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• pp.167-174
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• 1999
• Numerical analysis of two-fluid flows for both water and air is carried out. Free-Surface flows with an arbitrary deformation have been simulated around two dimensional submerged hydrofoil. The computation is performed using a finite volume method with unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell-wise local mesh refinement. the integration in space is of second order based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels The linear equation systems are solved by conjugate gradient type solvers and the non-linearity of equations is accounted for through picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations the continuity equation the conservation equation of one species and the equations or two turbulence quantities.

### Numerical Study on Sub-Breaking of Free Surface Viscous Flow (자유표면 점성 유동의 준쇄파 수치연구)

• Kwag, Seung-Hyun
• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• pp.226-231
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• 2003
• The viscous interaction of stern wave is studied by simulating the free-surface flows, including sub-breaking phenomena around a high speed catamaran hull advancing on calm water. The Navier-Stokes equation is solved by a finite difference method where the body-fitted coordinate system, the wall function and the triple-grid system are invoked. The numerical appearance of the sub-breaking waves is qualitatively supported by the experimental observation They are also applied to study precisely on the stern flow of S-103 as to which extensive experimental data are available. For the catamaran, computations are carried out for the mono ana twin hulls.

### Nonlinear Free Surface Flows for an Axisymmetric Submerged Body (축대칭 몰수체에 대한 비선형 자유표면 유동)

• Chang-Gu Kang
• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.27-37
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• 1991
• In this paper the nonlinear free surface flows for an axisymmetric submerged body oscillating beneath the free surface are solved and the forces acting on the body are calculated. A boundary integral method is applied to solve the axisymmetric boundary value problem and the Runge-Kutta 4-th order method is used for the time stepping of the free surface location. The nonlinear forces acting on the axisymmetric body are computed and compared with published results.

### CFD as a seakeeping tool for ship design

• Kim, Sun-Geun Peter
• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.1
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• pp.65-71
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• 2011
• Seakeeping analysis has progressed from the linear frequency-domain 2D strip method to the nonlinear timedomain 3D panel method. Nevertheless, the violent free surface flows such as slamming and green water on deck are beyond the scope of traditional panel methods based on potential theory. Recently, Computational Fluid Dynamics (CFD) has become an attractive numerical tool that can effectively deal with the violent free surface flows. ABS, as a classification society, is putting forth a significant amount of effort to implement the CFD technology to the advanced strength assessment of modern commercial ships and high-speed naval craft. The main objective of this study is to validate the CFD technology as a seakeeping tool for ship design considering fully nonlinear three-dimensional slamming and green water on deck. The structural loads on a large container carrier were successfully calculated from the CFD analysis and validated with segmented model test measurements.

### Parallel finite element simulation of free surface flows using Taylor-Galerkin/level-set method (Taylor-Galerkin/level-set 방법을 이용한 자유 표면의 병렬 유한 요소 해석)

• Ahn, Young-Kyoo;Choi, Hyoung-Gwon;Cho, Myung-Hwan;Yoo, Jung-Yul
• Proceedings of the KSME Conference
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• pp.2558-2561
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• 2008
• In the present study, a parallel Taylor-Galerkin/level set based two-phase flow code was developed using finite element discretization and domain decomposition method based on MPI (Message Passing Interface). The proposed method can be utilized for the analysis of a large scale free surface problem in a complex geometry due to the feature of FEM and domain decomposition method. Four-step fractional step method was used for the solution of the incompressible Navier-Stokes equations and Taylor-Galerkin method was adopted for the discretization of hyperbolic type redistancing and advection equations. A Parallel ILU(0) type preconditioner was chosen to accelerate the convergence of a conjugate gradient type iterative solvers. From the present parallel numerical experiments, it has been shown that the proposed method is applicable to the simulation of large scale free surface flows.

### Critical Free Surface Flows in a Sloshing Tank

• Scolan, Y.M
• Journal of Advanced Research in Ocean Engineering
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• v.4 no.4
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• pp.163-173
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• 2018
• There are many issues in fluid structure interactions when dealing with the free surface flows in a sloshing tank. For example the problem of how yielding a highly nonlinear wave with a simple forced motion over a short duration is of concern here. Nonlinear waves are generated in a rectangular tank which is forced horizontally; its motion consists of a single cycle of oscillation. One of the objectives is to end up with a shape of the free surface yielding a wide range of critical flows by tuning few parameters. The configuration that is studied here concerns a plunging breaker accompanied with a critical jet where great kinematics are simulated. The numerical simulations are performed with a twodimensional code which solves the fully nonlinear free surface boundary conditions in Potential Theory.

### A VOLUME OF FLUID METHOD FOR FREE SURFACE FLOWS AROUND SHIP HULLS (선체주위 자유수면 유동 해석을 위한 VOF법 연구)

• Park, I.R.
• Journal of computational fluids engineering
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• v.20 no.1
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• pp.57-64
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• 2015
• This paper describes a volume of fluid(VOF) method, mRHRIC for the simulation of free surface flows around ship hulls and provides its validation against benchmark test cases. The VOF method is developed on the basis of RHRIC method developed by Park et al. that uses high resolution differencing schemes to algebraically preserve both the sharpness of interface and the boundedness of volume fraction. A finite volume method is used to solve the governing equations, while the realizable ${\kappa}-{\varepsilon}$ model is used for turbulence closure. The present numerical results of the resistance performance tests for DTMB5415 and KCS hull forms show a good agreement with available experimental data and those of other free surface methods.

### Bow Wave Breaking and Viscous Interaction of Stern Wave

• Kwag, Seung-Hyun
• Journal of Mechanical Science and Technology
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• v.14 no.4
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• pp.448-455
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• 2000
• The bow wave breaking and the viscous interaction of stern wave are studied by simulating the free-surface flows. The Navier-Stokes equation is solved by a finite difference method in which the body-fitted coordinate system, the wall function and the triple-grid system are invoked. After validation, the calculations are extended to turbulent flows. The wave elevation at the Reynolds number of $10^4$ is much less than that at $10^6$ although the Froude number is the same. The numerical appearance of the sub-breaking waves is qualitatively supported by experimental observation. They are also applied to study the stern flow of S-103 for which extensive experimental data are available. Although the interaction between separation and the stern wave generation are not yet clear, the effects of the bow wave on the development of the boundary layer flows are concluded to be significant.

### Direct imposition of the wall boundary condition for simulating free surface flows in SPH

• Park, Hyung-Jun;Seo, Hyun-Duk;Lee, Phill-Seung
• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.497-518
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• 2021
• In this study, a new method for treating the wall boundary in smoothed particle hydrodynamics (SPH) is proposed to simulate free surface flows effectively. Unlike conventional methods of wall boundary treatment through boundary particles, in the proposed method, the wall boundary condition is directly imposed by adding boundary truncation terms to the mass and momentum conservation equations. Thus, boundary particles are not used in boundary modeling. Doing so, the wall boundary condition is accurately imposed, boundary modeling is simplified, and computation is made efficient without losing stability in SPH. Performance of the proposed method is demonstrated through several numerical examples: dam break, dam break with a wedge, sloshing, inclined bed, cross-lever rotation, pulsating tank and sloshing with a flexible baffle. These results are compared with available experimental results, analytical solutions, and results obtained using the boundary particle method.