• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.331-334
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• 2010

The supersonic speeds slowing down by shock waves is a common problem during the transonic region. So how to study the status of shock on the surface of airplane and wings is crucial adjective during transonic region. However, the theoretical and computational transonic flow problems were very hard. This paper introduced using Navier-Stokes Schemes to study characteristics of AGARD Wing 445.6 by ANSYS CFX in transonic region. From simulations results, as the Mach number increases, shock waves appear in the flowfield, getting stronger as the speed increases, these shock waves will lead to a rapid increase in drag.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.174-180
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• 2002

A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D-Numerical Wave Tank. The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation, and the Marker-Density function technique is adopted to implement the fully-nonlinear free-surface kinematic condition. The marine environmental situations, i.e. waves, currents, wind, etc., are reproduced by use of multi-segmented wavemaker on the basis of the so-called "snake-principle". In this paper, some numerical reproduction techniques for regular and irregular waves, multi-directional waves, Bull's-eye wave, wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.

• Journal of Korean Port Research
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• v.9 no.1
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• pp.57-63
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• 1995

In this paper we examine the mass transport within the boundary layer near the sea bottom. The fluid domain is seperated into inner and outer region of boundary layers. In outer region, the wave field is assumed to be inviscid and irrotational. When the incident waves enter the arrays of circular cylinders, the scattering of water waves by an array of N bottom mounted vertical circular cylinders is solved using the method proposed by Linton & Evans under the potential theory. In inner region, the Navier-Stokes equation must be satisfied with boundary conditions at the boundary later and bottom is to be represented by the sum of the Eulerian mean drift and the Stokes' drift.

• Journal of Ocean Engineering and Technology
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• v.21 no.2 s.75
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• pp.12-21
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• 2007

As the economy grows and the population increases, we need to develop our coastal area and make use of it for various purposes. Specifically, investigation of the wave interactions on and around the vertical cylinders is very important in the design of the offshore or coastal structures. The nonlinear potential analysis developed so far, although very useful, has been found to be limited in application, as strong nonlinear waves generated by the interference between multilayered cylinders and wave impact forces by breaking waves can hardly be estimated. In this study, using a 3-Dimensional volume tracking method VOF(Volume of Fluid), based on Namer-Stokes equations, was developed to simulate highly nonlinear effects, such as breaking waves at the interface or complicated interference waves among structures. A numerical method for nonlinear interaction wave and vertical cylinders is newly proposed. The wave forces and wave transformations computed by the newly proposed numerical simulation method were compared to the other researcher's experimental results, and the results agree well. Based on the validation of this study, this numerical method is applied to the two vertical cylinders to discuss their nonlinear wave forces and wave transformations, according to the variations of separate distance of vertical cylinders.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.4
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• pp.329-339
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• 1995

To clarify the surface drift velocity in gravity waves. experimental data measured in a two-dimensional wave flume were compared with theoretical values predicted by the Stokes 2nd- and 5th- order theories as well as by the conduction solution or Longuet-Hinggins (1953). Relative water depth and wave height ranged 0.040.13. For a closed flume condition, Stokes 2nd-order theory gives lower values than the experimental data, and the differences increase as both relative water depth and wave height increase. Based on the observed data of the surface drift velocities, a modified Parabolic model of the return current velocity Profile has been suggested, which is Proved to fit better to the existing experimental data of mass transport velocity profiles in a closed wave flume than the models of Longuet-Hinggins (1953) and Stokes wave theories do.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.53-59
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• 1991

By employing multiple-scale expansion techniques, the diffraction of sinusoidally-modulated nonlinear Stokes waves by a stationary thin wedge has been studied within the framework of potential theory. It is found that the evolution of diffracted waves can be described by the Zakharov equation to the leading order and it can be replaced by the cubic $Schr\ddot{o}dinger$ equation with an additional linear term for stable modulations. Computations are made for the cubic $Schr\ddot{o}dinger$ equation with different values of nonlinear and dispersion parameters. Numerical results well reflect the experimental findings in the amplitude and width of generated stem waves. It is numerically confirmed that the nonlinearity dominates the wave field, while the dispersion hardly affects the wave evolution, and stem waves are likely to be formed for steep incident waves in the case of stable sinusoidal modulations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.202-216
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• 2015

In the narrow water channel, which has been frequently deployed in the artificial canal in the South Korea due to the lack of available land, solitary wave type ship induced waves can occur. In order to test this hypothetical view, we carried out the numerical simulation. Numerical model consists of Navier-Stokes Equations and VOF, and the verification is implemented using the data by PIANC (1987) and the analytical model derived in this study. It was shown that numerically simulated front wave height are much larger than the one by PIANC (1987), and the fluctuation of free surface near the channel bank persists much longer (around 20s). For the case of stern waves, numerically simulated wave height are somewhat smaller than the data by PIANC (1987). These results seriously deviates from the general characteristics of ship induced waves observed in the wide water channels, and leads us to conclude that ship induced waves is severely affected by the width of water channel. It was also shown that the currents from the channel banks toward a ship, and currents from the ship toward the channel banks are alternatively occurring due to reflection at the channel banks. The velocity of currents reaches its maximum at 0.90 m/s, and these values are sustained through the entire depth. which implies that severe scourings at the channel bottom can be underway.

• Journal of Ocean Engineering and Technology
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• v.10 no.3
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• pp.62-73
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• 1996

Numerical simulation is made of the three-dimensional wave breaking motion about a part of a floating offshore structure containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity wave generated by a numerical wave maker. TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of density-function technique the three-dimensional wave breaking motion is approximately implenented in the framework of rectangular grid system. A porosity technique is devised for the implementation of the no-slip bydy boundary conditions. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with containing degree of quantitative and qualitative accuracy.

• 한국전산유체공학회:학술대회논문집
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• 1996.05a
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• pp.93-98
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• 1996

Numerical computations are carried out to analyze characteristics of flow fields around an Wigley hull form which is advacing in the incoming waves. Navier-Stokes equations are solved by a finite difference method and a MAC method is used for coupling of pressure and velocity fields, and O-H grid topology is used.

• International Journal of Ocean System Engineering
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• v.1 no.1
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• pp.37-45
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• 2011

The nonlinear free-surface motions interacting with a floating body were investigated using the Moving Particle Semi-implicit (MPS) method proposed by Koshizuka and Oka [6] for incompressible flow. In the numerical method, more realistic Lagrangian moving particles were used for solving the flow field instead of the Eulerian approach with a grid system. Therefore, the convection terms and time derivatives in the Navier-Stokes equation can be calculated more directly, without any numerical diffusion, instabilities, or topological failure. The MPS method was applied to a numerical simulation of predicting the efficiency of floating-type breakwater interacting with waves.