• Journal of computational fluids engineering
• /
• v.11 no.4 s.35
• /
• pp.9-13
• /
• 2006

In the present study, a numerical analysis of transient mixer flow is performed considering free surface formation. The flow patterns and free surface shape in a mixers formed by flat paddle and pitched paddle impellers are predicted. In a flat paddle mixer, two flow circulation regions are formed due to strong radial flow, whereas one large circulation is formed in a pitched paddle mixer due to axial downward flow. These differences affect the free surface evolution and shape. It is seen from the results that a flat paddle mixer gives deeper free surface at center region than a pitched paddle mixer. The free surface of 8-blades-flat-paddle mixer is also simulated to compare with the available experimental and simulation results. The present computational results agree reasonably well with the experimental data.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.09b
• /
• pp.842-845
• /
• 2005

A method for the numerical simulation of two-dimensional free-surface flow resulting from the propagation of regular gravity waves over topography with arbitrary bottom shape is presented. The method is based on the numerical solution of the Euler equations subject to the fully nonlinear free-surface boundary conditions and the appropriate bottom, inflow and outflow conditions using a hybrid finite-differences and spectral-method scheme. The formulation includes a boundary-fitted transformation, and is suitable for extension to incorporate large-eddy simulation (LES) and large-wave simulation (LWS) terms for turbulence and breaking wave modeling, respectively. Results are presented for the simulation of the free-surface flow over two different bottom topographies, with constant slope values of 1:10 and 1:20, two different inflow wave lengths and two different inflow wave heights. An absorption outflow zone is utilized and the results indicate minimum wave reflection from the outflow boundary. Over the bottom slope, lengths of waves in the linear regime are modified according to linear theory dispersion, while wave heights remain more or less unchanged. For waves in the nonlinear regime, wave lengths are becoming shorter, while the free surface elevation deviates from its initial sinusoidal shape.

• 한국전산유체공학회:학술대회논문집
• /
• 1999.05a
• /
• pp.48-57
• /
• 1999

This paper deals with the numerical simulation of the behavior of single bubble rising near the free surface. Volume fraction of fluid (VOF) method with continuum surface force (CSF) model, the well known method for two phase flow simulation is adopted. A bubble of spherical shape positioned beneath the free surface is assumed at the initial stage. The difference according to the fluid properties of surrounding medium is examined. Simulation results are depicted and explained with the time history of bubble shape, velocity field and vorticity distribution.

• Journal of computational fluids engineering
• /
• v.11 no.4 s.35
• /
• pp.90-100
• /
• 2006

A digital wave tank (DWT) simulation technique has been developed by authors to investigate the interactions of fully nonlinear waves with 3D marine structures. A finite-difference/volume method and a modified marker-and-cell (MAC) algorithm have been used, which are based on the Navier-Stokes (NS) and continuity equations. The fully nonlinear kinematic free-surface condition is implemented by the marker-density function (MDF) technique or the Level-Set (LS) technique developed for one or two fluid layers. In this paper, some applications for various engineering problems with free-surface are introduced and discussed. It includes numerical simulation of marine environments by simulation equipments, fully nonlinear wave motions around offshore structures, nonlinear ship waves, ship motions in waves and marine flow simulation with free-surface. From the presented simulations, it seems that the developed DWT simulation technique can handle various engineering problems with free-surface and reliably predict hydrodynamic features due to the fully-nonlinear wave motions interacting with such marine structures.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2004.11a
• /
• pp.154-159
• /
• 2004

A new finite difference scheme is studied fur the simulation of free surface, surface the third derivative tenn for the wave elevation is artificially added in the the free-surface boundary condition. This study presents a comparative analysis with simulations performed by using the classical MAC method. More systematic computations are carried out by changing the submergence depth and angle of attack. Through the numerical simulation, it is found that a new numerical method becomes more efficient for the reason that the free surface elevation is reasonably developed at tire rear of trailing edge.

• Journal of Ocean Engineering and Technology
• /
• v.4 no.1
• /
• pp.55-61
• /
• 1990

For the tracking of three dimensional free surface motions, a method referred to as the Volume of Fluid(VOF) algorithm is extended. In order to calculate the slope of three dimensional free surface which is the most important for the advection algorithm that decides the amount of fluid from cell to cell and for the application of free surface boundary condition, a simple method utilizing two dimensional slope informations is introduced. The extended algroithm is tested by demonstrating the simulation of a propagating sinusoidal wave through the channel whose width changes abruptly.

• Journal of the Society of Naval Architects of Korea
• /
• v.54 no.1
• /
• pp.26-33
• /
• 2017

In this study, the surface marker method, one of the particle tracking methods, used to track the free surface is extended to cover the more general cases easily including the collision and separation of the free surface. In surface particle method to redistribute particles effectively using the grid system, the free surface is composed of the sum of quadrilaterals having four curves where fixed markers are placed at ends of each curve. Fixed markers are used to know how curves are connected to each other. The position of fixed markers can move as the free surface deforms but all fixed markers cannot be deleted during all time of simulation to keep informations of curve connection. In the case of the collision or separtion of the free surface where several curves can be intersected disorderly, severe difficulties can occur to define newly states of curve connection. In this study, the adaptable surface parTicle method without fixed markers is introduced. Intersection markers instead of the fixed markers are used to define quadrilaterals. The position of the intersection markers is defined to be the intersection point between the free surface and the edge of the grid and it can be added or deleted during the time of simulation to allow more flexibilities. To verify numerical schemes, two flow cases are simulated and the numerical results are compared with other's one and shown to be valid.

• Journal of Ship and Ocean Technology
• /
• v.5 no.4
• /
• pp.29-43
• /
• 2001

In this paper, free surface flows around an advancing two-dimensional rectangular cylinder piercing the free surface are studied using numerical and experimental methods. Especially, wave breaking phenomenon around the cylinder is treated in detail. A series of numerical simulations and experiments were performed for the purpose of comparison. For the numerical simulations, a finite difference method was adopted with a rectangular grid system, and the variation of the free surface was computed by the marker density method. The computational results are compared with the experiments. It is confirmed that the present numerical method is useful for the numerical simulation of nonlinear free surface waves around a piercing body.

• Korean Journal of Materials Research
• /
• v.10 no.8
• /
• pp.581-588
• /
• 2000

Phase transition of the Lennard-Jonesian binary system with a free surface was studied by employing molecular dynamics simulation. The main focus of this study was to investigate the effect of size misfit and solute concentration on phase transition during heating and quenching. For a binary system with a free surface, the melting point and the critical quenching rate decrease as size misfit and solute concentration increase.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.6
• /
• pp.422-432
• /
• 2013

A System Identification method to develop parametric models linking free surface elevation and wave pressure is presented and two models are built allowing for either wave pressure or free surface elevation simulation. Linear, time invariant model structures with static nonlinearities are assumed and solutions are sought in a form of autoregressive model with extra input (ARX). An arbitrary chosen free-surface elevation and wave pressure dataset is used for estimation of the models, which are subsequently verified against datasets with similar pressure gauge depth but different free-surface elevation spectra due to different meteorological conditions. It is shown that free-surface simulation using System Identification methods can perform better than traditional linear transfer function derived from linear wave theory (LTF), while wave pressure simulation quality using presented methods is generally similar to that obtained with corrected LTF.