Violent Free Surface Flows Research Articles

A low diffusive Lagrange-remap scheme for the simulation of violent air-water free-surface flows

In 2002, Despres and Lagoutiere [17] proposed a low-diffusive advection scheme for pure transport equation problems, which is particularly accurate for step-shaped solutions, and thus suited for in...

A numerical investigation into the correction algorithms for SPH method in modeling violent free surface flows

A quantitative comparison of the usual and recent numerical treatments which are applied to the Smoothed Particle Hydrodynamics (SPH) method are presented together with a new free-surface treatment. A series of numerical treatments are studied to refine the numerical procedures of the SPH method particularly for violent flows with a free surface. Two dimensional dam-break and sway-sloshing problems in a tank are modeled by solving Euler's equation of motion utilizing weakly compressible SPH method (WCSPH). Initially, the dam-break benchmark problem is studied by adopting only conventional basic equations of SPH without any numerical remedy and then by considering numerical treatments of interest one after another. In the WCSPH method, the precise calculation of the densities of the particles is vital for the solution, accordingly a density correction algorithm is presented as a basic numerical treatment. Subsequently, Monaghan's (1994) [1] XSPH velocity variant algorithm, artificial particle displacement (APD) algorithm (Shaldoo et al., 2011) [2], and a hybrid combination of velocity updated XSPH (VXSPH) and APD algorithms are implemented separately, but all with the density correction algorithm as a default treatment. The effects of each of these treatments on the pressure and on the free surface profiles are analyzed by comparing our numerical findings with experimental and numerical results in the literature. After the detailed scrutiny on the dam-break problem, sway-sloshing problem is handled with the VXSPH+APD algorithm which has been noted to provide the most reliable and accurate results in the dam-break problem. For the sway-sloshing problem, the time histories of free surface elevations on the left side wall of the rectangular tank are compared with experimental and numerical results available in the literature. It was shown that the VXSPH+APD treatment significantly improves the accuracy of the numerical simulations for violent flows with a free surface and lead to the results which are in very good agreement with experimental and numerical findings of literature in terms of both the kinematic and the dynamic point of view.

Numerical simulation of hydro-elastic problems with smoothed particle hydrodynamics method

Violent free surface flows with strong fluid-solid interactions can produce a tremendous pressure load on structures, resulting in elastic and even plastic deformations. Modeling hydro-elastic problems with structure deformations and a free surface breakup is difficult by using routine numerical methods. This paper presents an improved Smoothed Particle Hydrodynamics (SPH) method for modeling hydro-elastic problems. The fluid particles are used to model the free surface flows governed by Navier-Stokes equations, and the solid particles are used to model the dynamic movement and deformation of the elastic solid objects. The improved SPH method employs a Kernel Gradient Correction (KGC) technique to improve the computational accuracy and a Fluid-Solid Interface Treatment (FSIT) algorithm with the interface fluid and solid particles being treated as the virtual particles against their counterparts and a soft repulsive force to prevent the penetration and a corrective density approximation scheme to remove the numerical oscillations. Three typical numerical examples are simulated, including a head-on collision of two rubber rings, the dam break with an elastic gate and the water impact onto a forefront elastic plate. The obtained SPH results agree well with experimental observations and numerical results from other sources.

A new adaptive Cartesian-grid CIP method for computation of violent free-surface flows

A new adaptive Cartesian-grid for the CIP (constrained interpolation profile) method is proposed and applied to two-dimensional numerical simulations of violent free-surface flows. The CCUP (CIP combined and unified procedure) method is employed and combined with this adaptive Cartesian-grid for robust and efficient computation. This adaptive grid is capable of tracking regions where flows vary violently, and a much finer grid is then concentrated automatically on these regions to adapt to the violent changing of the flow. Unlike the abacus-like Soroban grid which is an adaptive meshless grid with complicated algorithms and inefficiency of evaluation of frequently computed spatial derivatives, the present approach not only simplifies computational algorithm but also enhances efficiency of frequently-computed spatial derivatives. It is also different from most of the remeshing schemes that no additional CPU-time for the value-mapping from the old grid to the new grid is taken in this adaptive grid system provided that the advection velocity is interpolated, since the value-mapping process is accomplished simultaneously within the advection process. To validate the accuracy and efficiency of this newly-proposed CFD model, several two-dimensional benchmark problems are performed, and the results are compared with experimental measurements and other published numerical results. Numerical simulations show that the proposed numerical model is robust, accurate, and efficient for strongly nonlinear free-surface flows.

Hybrid boundary condition combined with data assimilation for simulations of free surface flows using lattice Boltzmann method

In this paper, we combine the single-phase lattice Boltzmann method (LBM) including the hybrid boundary condition with the assimilation of experimental data into a simulation. This combination improves the accuracy of numerical simulations of violent free surface flows performed using the LBM. An unknown wall effect parameter used in the hybrid boundary condition is determined through iterative calculations to minimize the objective function that measures the discrepancy between the simulation and measurement. The present method is applied to a dam failure problem involving a very large deformation of a free surface. We confirm that the method proposed in this study can optimally incorporate the hybrid boundary condition into the LBM without ad hoc specification of the wall effect parameter.

Numerical and Experimental Investigation of Nonlinear Shallow Water Sloshing

Abstract A numerical and experimental analysis of sloshing phenomena (i.e. violent fluid motions inside a tank) has been conducted in shallow water regimes. A narrow tank has been used to limit three-dimensional effects and allow for an extensive study of two-dimensional waves. A large range of experimental data from small to large amplitude sway motions has been considered for five different filling heights. The numerical simulations have been performed to cover the configurations where no experiments were available and provide an exhaustive description of the shallow-water sloshing motion. Specifically, the numerical simulations have been performed through a δ-SPH model since such a scheme proved to be robust and reliable in studying violent free-surface flows.

Incompressible SPH for free surface flows

Violent free surface flows exist in a number of physical processes related to marine engineering. Traditionally, these are simulated using mesh-based methods formulated in an Eulerian frame of reference. Lagrangian meshless and particle-based methods, like Smoothed Particle Hydrodynamics (SPH), represent an interesting alternative as they circumvent several common problems related to the free surface. This work is devoted to the properties and implementation of an SPH method based on pressure projection for incompressible inviscid flows with free surfaces. Novel features include a time integration scheme designed to improve stability, and a new treatment of the free surface pressure boundary condition. The mechanisms and performance of the algorithm are addressed with a study of the evolution of an elliptical drop, and the more practical problems of rigid body water entry and internal tank sloshing. The results are compared to those of competing methods.

Validation of a CIP-based tank for numerical simulation of free surface flows

A constrained interpolation profile CIP-based numerical tank is developed to simulate violent free surface flows. The numerical simulation is performed by the CIP-based Cartesian grid method, which is described in the present paper. The tangent of hyperbola for interface capturing (THINC) scheme is applied for capturing complex free surfaces. The new model is capable of simulating a flow with violently varied free surface. A series of computations are conducted to assess the developed algorithm and its versatility. These tests include the collapse of water column with and without an obstacle, sloshing in a fixed tank, the generation of regular waves in a tank, the generation of extreme waves in a tank. Excellent agreements are obtained when numerical results are compared with available analytical, experimental, and other numerical results.

CFD as a seakeeping tool for ship design

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.

CFD as a seakeeping tool for ship design

Seakeeping analysis has progressed from the linear frequency-domain 2D strip method to the nonlinear time-domain 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.

Implementation of the moving particle semi-implicit method on GPU

The Moving Particle Semi-implicit (MPS) method performs well in simulating violent free surface flow and hence becomes popular in the area of fluid flow simulation. However, the implementations of searching neighbouring particles and solving the large sparse matrix equations (Poisson-type equation) are very time-consuming. In order to utilize the tremendous power of parallel computation of Graphics Processing Units (GPU), this study has developed a GPU-based MPS model employing the Compute Unified Device Architecture (CUDA) on NVIDIA GTX 280. The efficient neighbourhood particle searching is done through an indirect method and the Poisson-type pressure equation is solved by the Bi-Conjugate Gradient (BiCG) method. Four different optimization levels for the present general parallel GPU-based MPS model are demonstrated. In addition, the elaborate optimization of GPU code is also discussed. A benchmark problem of dam-breaking flow is simulated using both codes of the present GPU-based MPS and the original CPU-based MPS. The comparisons between them show that the GPU-based MPS model outperforms 26 times the traditional CPU model.

Numerical simulation of dam breaking using smoothed particle hydrodynamics and viscosity behavior

Smoothed particle hydrodynamics (SPH) is a Lagrangian meshless particle method. It is one of the best method for simulating violent free surface flows in fluids and solving large fluid deformations. Dam breaking is a typical example of these problems. The basis of SPH was reviewed, including some techniques for governing equation resolution, such as the stepping method and the boundary handling method. Then numerical results of a dam breaking simulation were discussed, and the benefits of concepts like artificial viscosity and position correction were analyzed in detail. When compared with dam breaking simulated by the volume of fluid (VOF) method, the wave profile generated by SPH had good agreement, but the pressure had only reasonable agreement. Improving pressure results is clearly an important next step for research.

CFD simulations of wave–current-body interactions including greenwater and wet deck slamming

A numerical method for the solution of unsteady Navier–Stokes equations has been employed in conjunction with an interface-preserving level-set method for the simulation of greenwater effect on offshore structures and ships. In this method, the free surface flows are modeled as immiscible air–water two-phase flows and the free surface itself is represented by the zero level-set function. The Navier–Stokes equations for both the water and air flows are formulated in moving curvilinear coordinate system and discretized using the finite-analytic method on a non-staggered multi-block grid system. Large eddy simulation (LES) approach is used with Smagorinsky model to account for the effects of turbulence induced by violent free surface motions. A chimera domain decomposition approach is implemented using overlapping, embedding, or matching grids to facilitate the simulation of complex flow around practical configurations. The overset grid system also greatly simplified the simulation of arbitrary translational and rotational motions among various computational blocks. Calculations were performed first for dam-breaking flow and free jet problems involving violent free surface motions. The level-set Navier–Stokes method was then employed for the simulation of slamming of a hemisphere, greenwater on offshore structure and ships, and wet deck slamming of an X-Craft in pitch and heave motions. The numerical results clearly demonstrated the capability of the level-set method to deal with violent free surface flows involving breaking waves, water droplets, trapped air bubbles, and wave–current-body interactions.

APPLICABILITY OF MPS METHOD TO BREAKING AND POST-BREAKING OF SOLITARY WAVES

As a meshfree particlemethod, the MPS (Moving Particle Semi-implicit) method is an efficient numerical tool for simulating flowswith complicated behavior of water surface, such aswave breaking. In this paper, the MPS method hasbeen applied to solve the Navier-Stokes equation for simulating the breaking and post-breaking of solitary waves on a uniform slope. The high precision of MPS method in the simulation of violent free surface flows, likethebreaking waves, isconfirmed through both quantitative and qualitative comparisons to other numerical results by the BEM or the VOF and experimental data. The process of splashup which ishard to be simulated by conventionalgrid-based methods is alsowell reproduced by the MPS method.

Simulation of flows with violent free surface motion and moving objects using unstructured grids

AbstractA volume of fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier–Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three‐dimensional structures. The present implementation follows the classic VOF implementation for the liquid–gas system, considering only the liquid phase. Extrapolation algorithms are used to obtain velocities and pressure in the gas region near the free surface. The VOF technique is validated against the classic dam‐break problem, as well as series of 2D sloshing experiments and results from SPH calculations. These and a series of other examples demonstrate that the ability of the present approach to simulate violent free surface flows with strong nonlinear behaviour. Copyright © 2006 John Wiley & Sons, Ltd.

On the simulation of flows with violent free surface motion

A volume of fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier–Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures. The present implementation follows the classic VOF implementation for the liquid–gas system, considering only the liquid phase. Extrapolation algorithms to obtain velocities and pressure in the gas region near the free surface have been implemented. The VOF technique is validated against the classic dam-break problem, as well as series of 2D sloshing experiments and results from smoothed particle hydrodynamics (SPH) calculations. These and a series of other examples demonstrate that the present CFD method is capable of simulating violent free surface flows with strong nonlinear behavior.

A CIP-based method for numerical simulations of violent free-surface flows

A CFD model is proposed for numerical simulations of extremely nonlinear free-surface flows such as wave impact phenomena and violent wave–body interactions. The constrained interpolation profile (CIP) method is adopted as the base scheme for the model. The wave–body interaction is treated as a multiphase problem, which has liquid (water), gas (air), and solid (wave-maker and floating body) phases. The flow is represented by one set of governing equations, which are solved numerically on a nonuniform, staggered Cartesian grid by a finite-difference method. The free surface as well as the body boundary are immersed in the computation domain and captured by different methods. In this article, the proposed numerical model is first described. Then to validate the accuracy and demonstrate the capability, several two-dimensional numerical simulations are presented, and compared with experiments and with computations by other numerical methods. The numerical results show that the present computation model is both robust and accurate for violent free-surface flows.