A Cartesian cut cell free surface capturing method for 3D water impact problems

2012 ◽  
Vol 71 (10) ◽  
pp. 1238-1259 ◽  
Author(s):  
Z. Z. Hu ◽  
D. M. Causon ◽  
C. G. Mingham ◽  
L. Qian
Keyword(s):  
Free Surface ◽  
Water Impact ◽  
Cut Cell ◽  
Free Surface Capturing ◽  
Impact Problems ◽  
Cartesian Cut

scholarly journals NUMERICAL SIMULATION OF WATER IMPACT INVOLVING THREE DIMENSIONAL RIGID BODIES OF ARBITRARY SHAPE

2011 ◽  
Vol 1 (32) ◽  
pp. 14
Author(s):  
Zheng Zheng Hu Hu ◽  
Derek Causon ◽  
Clive Mingham ◽  
Ling Qian
Keyword(s):  
Free Surface ◽  
Rigid Bodies ◽  
The Body ◽  
Green Water ◽  
Water Impact ◽  
Cut Cell ◽  
Impact Phenomena ◽  
Local Impact ◽  
Cartesian Cut ◽  
Solid Bodies

As is well known, the design of coastal or offshore structures whether a ship, wave energy device or other fixed or floating structure, needs to consider its operation in a very hostile environment, including heavy storms. For example, an extremely high or steep wave impact on the bow or stern of a moored FPSO may result in a large amount of water on deck. Known as green water, this may cause severe damage to the deck house or other deckside equipment. Thus, there is great need for simulation tools to predict impact loadings and to provide more insight into the physics of local impact phenomena. Published research or prediction work on the water impact problem has mostly related to studies in 2D. For example, Greehow& Lin (1983), Greenhow (1987), Zhao & Faltinsen (1993), Mei et al.(1999) have studied the hydrodynamics of rigid bodies entering water both theoretically and experimentally. More recently, a laboratory investigation of the pressure distribution on a free-falling wedge entering water by Yettou et al.(2006 has been compared a numerical and experimental study carried out by Campbell and Weynberg (1980). Water impact and green water loading in 3D has been simulated by Kleefsman et al. (2005) using a VOF method, which for dam break and water entry problems. In this study, we have developed the AMAZON-3D code for studies of water impact problems involving various 3D rigid solid bodies. The in-house Cartesian cut cell approach has been used to simulate 3D water impact involving both moving rigid solid bodies and the free surface. The Cartesian cut cell method in the AMAZON-3D code is unrestricted in terms of boundary complexity or range of boundary movement. Solid objects are carved out of a background mesh, leaving a set of irregularly shaped cells aligned with the surface boundary. The advantages of the cut cell approach have been outlined previously by Causon et al. (2000, 2001) and Hu et al.(2009) including its flexibility for dealing with arbitrarily complex geometries and moving bodies. There is no requirement to re-mesh globally or even locally for the case of a moving body. All that is required is to update the cut cell data at the body contour for as long as the body motion continues. The AMAZON-3D finite volume code solves the incompressible Navier-Stokes equations in both air and water regions simultaneously treating the free surface as a contact surface in the density field that is captured automatically in a manner analogous to shock capturing in compressible flow. A time-accurate artificial compressibility method and high Godunov-type scheme replaces the pressure correction solver used in other methods (see Qian et al. 2006). We believe that the success of a study of water impact depends ultimately on the problem under consideration and the computer resources available and for each method there is a class of problem for which one method may perform better another. Each method has its own advantages and disadvantages and it is not possible to assert conclusively that one method is uniformly superior. However, we believe we can demonstrate that our method can be used successfully to study real local impact phenomena including the egress of an arbitrary rigid body from air to water or vice versa, the splash zone and entrapment of one fluid into the other. The code has been validated by recourse to a number of test cases including a cone undergoing forced oscillations and water impact of a rigid wedge with constant entry velocity where data and/or analytical results are available for comparison purposes. A range of results including the free surface elevation and force calculations will be presented for the water impact of various 3D rigid bodies.

An improved free surface capturing method based on Cartesian cut cell mesh for water-entry and -exit problems

2009 ◽  
Vol 465 (2106) ◽  
pp. 1843-1868 ◽  
Author(s):  
Wenhua Wang ◽  
Yanying Wang
Keyword(s):  
Free Surface ◽  
Variable Density ◽  
Water Entry ◽  
Solid Boundary ◽  
Entry And Exit ◽  
Cut Cell ◽  
Free Surface Capturing ◽  
Cartesian Cut ◽  
Volume Method ◽  
Exit Problems

The free surface capturing method based on Cartesian cut cell mesh is extended to the water-entry and -exit fields with body–fluid interaction. The governing equations are the incompressible Euler equations for a variable density fluid system with a free surface, which is treated as a contact discontinuity. The solver is based on the artificial compressibility method with a dual time-stepping technique for time advancing and the finite-volume method with a high-resolution Godunov-type upwind scheme on spatial discretization. For solving the numerical problem caused by the extension, the acceleration term of body is introduced for the new pressure condition of moving solid boundary, and the exact Riemann solution is used to calculate the flux of the solid boundary. In addition, a new solution of gradients based on the least-squares idea is presented for simply calculating the gradients. Finally, test cases show that the present method is available and can be successfully applied in various water-entry and -exit phenomena.

Cartesian Cut Cell Free Surface Capturing Solver for Wave Floating Body Interactions

2007 ◽  
Author(s):  
Ling Qian ◽  
Derek Causon ◽  
Clive Mingham
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Green Water ◽  
Floating Body ◽  
Upwind Schemes ◽  
Body Interaction ◽  
Cut Cell ◽  
Free Surface Capturing ◽  
Cartesian Cut ◽  
Cell Data

A newly developed free surface capturing code based on a two fluid formulation of Navier-Stokes equations and Cartesian cut cell grid system has been applied to study wave/floating body interaction problems. The basic flow solver uses an efficient dual time-stepping artificial compressibility algorithm and modern Riemann solver based upwind schemes of the Godunov-type which capture the moving free surface accurately as part of the numerical solution. Mesh generation in the conventional sense is eliminated in favour of defining local cut cell data on a stationary background Cartesian grid. For wave/floating body interaction problems where bodies can undergo arbitrary movement in response to the incoming waves, the only required changes to the meshing procedures consist of local updates to the cut cell data at the boundaries that are in motion. A test case has been simulated and the results are in a good agreement with available experimental data. The numerical model is generic and can be applied to a number of engineering flow problems such as green water overtopping of vessels and offshore floating structures.

scholarly journals Comments on ‘An improved free surface capturing method based on Cartesian cut cell mesh for water-entry and -exit problems’

2011 ◽  
Vol 468 (2138) ◽  
pp. 305-309 ◽  
Author(s):  
Ling Qian ◽  
Derek Causon ◽  
Clive Mingham
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Water Entry ◽  
Moving Boundaries ◽  
Entry And Exit ◽  
Cut Cell ◽  
Pressure Boundary Condition ◽  
Free Surface Capturing ◽  
Cartesian Cut ◽  
Exit Problems

In the paper entitled ‘An improved free surface capturing method based on Cartesian cut cell mesh for water-entry and -exit problems’ ( Wang & Wang 2009 Proc. R. Soc. A 465 , 1843–1868 ( doi:10.1098/rspa.2008.0410 )), the present authors' earlier work ( Qian et al . 2006 , Proc. R. Soc. A 462 , 21–42 ( doi:10.1098/rspa.2005.1528 )) has been specifically applied to the study of water-entry and -exit of solid objects. An extended boundary condition, retaining the term owing to acceleration of moving boundaries in the momentum equation, has been implemented for calculating the pressure gradient at solid surfaces and, based on their numerical experiments, it was concluded by Wang and Wang that without this term the calculation will substantially under-predict the impact forces and may even break down. Therefore, a more complex procedure based on the exact solution of a Riemann problem for moving boundaries was implemented. In this short comment, by applying the authors' free surface capturing code to the same flow problem of water-entry of a wedge, it can, however, be demonstrated that the results from implementing the new pressure boundary condition are nearly identical to that of employing the original boundary condition without the acceleration term, indicating that its effects on the simulation results are minimal. A further examination of the implementation details on the pressure boundary condition also supports this conclusion.

scholarly journals Cloud Cavitating Flow That Surrounds a Vertical Hydrofoil Near the Free Surface

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Chang Xu ◽  
Yiwei Wang ◽  
Chenguang Huang ◽  
Chao Yu ◽  
Jian Huang
Keyword(s):  
Free Surface ◽  
Cfd Simulation ◽  
Cavity Growth ◽  
Cavitating Flow ◽  
Water Tank ◽  
Eddy Simulation ◽  
Cut Cell ◽  
High Froude Number ◽  
Cavity Evolution ◽  
Cartesian Cut

Unstable cavitation presents an important speed barrier for underwater vehicles such as hydrofoil craft. In this paper, the authors concern about the physical problem about the cloud cavitating flow that surrounds an underwater-launched hydrofoil near the free surface at relatively high-Froude number, which has not been discussed in the previous research. A water tank experiment and computational fluid dynamics (CFD) simulation are conducted in this paper. The results agree well with each other. The cavity evolution process in the experiment involves three stages, namely, cavity growth, shedding, and collapse. Numerical methods adopt large eddy simulation (LES) with Cartesian cut-cell mesh. Given that the speed of the model changes during the experiment, this paper examines cases with varying constant speeds. The free surface effects on the cavity, re-entry jet location, and vortex structures are analyzed based on the numerical results.

NUMERICAL SIMULATION OF WAVE POWER DEVICES USING A TWO-FLUID FREE SURFACE SOLVER

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1479-1482 ◽  
Author(s):  
LING QIAN ◽  
CLIVE MINGHAM ◽  
DEREK CAUSON ◽  
DAVID INGRAM ◽  
MATT FOLLEY ◽  
...  
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Variable Density ◽  
Surface Flow ◽  
Flow Problems ◽  
Cut Cell ◽  
Wide Range ◽  
Complex Fluid ◽  
Cartesian Cut ◽  
Two Fluid

A generic two-fluid (water/air) numerical model has been developed and applied for the simulation of the complex fluid flow around a wave driven rotating vane near a shoreline in the context of a novel wave energy device OWSC (Oscillating wave surge converter). The underlying scheme is based on the solution of the incompressible Euler equations for a variable density fluid system for automatically capturing the interface between water and air and the Cartesian cut cell method for tracking moving solid boundaries on a background stationary Cartesian grid. The results from the present study indicate that the method is an effective tool for modeling a wide range of free surface flow problems.

Sign in / Sign up

Export Citation Format

Share Document