• 한국해양학회지
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• v.16 no.1
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• pp.1-11
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• 1981

The seasonal variations of surface current patterns in the Japan Sea were drawn out from the results of drift bottle experiments, current measurements and hydrographic observations during 1979∼1980. The North Korean Cold Current(NKCC) and the East Korean Warm Current(EKWC) were common features of circulation in the eastern sea of Korea. The intrusion of NKCC along the Korean coast became strong in summer(average velocity of 47.4cm/sec off Jumunjin and 23.4cm/sec near Jugbyeon) when the Tsushima Current was strong. But there was no indication of the NKCC in November 1979. Dynamic topography(August & November 1979) and satellite picture(November 1979) seemed to show the topographic steering of EKWC beginning off Janggigab. Drift bottles arrived at the Japaness coast were affected significantly by the strong Tsushima Current in summer and by the predominant northwesterlies in winter instead of weak current.

• Journal of Ocean Engineering and Technology
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• v.36 no.3
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• pp.143-152
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• 2022

To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water.

• Journal of Navigation and Port Research
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• v.26 no.2
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• pp.221-226
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• 2002

To provide reliable data for drift prediction models, field experiments were carried out in the coastal region off Busan port. Four different size of vessels(10, 30, 50, 90G/T ton) were deployed for the experiment. Among them G/T 50ton class vessel was equipped with instruments measuring the currents, winds, headings and trajectory data. In the rest of vessels only the position data were recorded for the purpose of target divergence study. The trajectories of each vessel were measured by DGPS(Differential Global Positioning System) and collected by APRS(Automatic Position Reporting System). The experiment was done in wind of 2~10m/s and current of 0.5~1.5m/s. The leeway was derived by subtracting surface current velocity from target drifting velocity. The leeway rate of G/T 50ton vessel was found to be about 3.6% and the computed leeway speed equation was $U_L$=0.042 W - 0.034. The processed leeway angle data were deflected by $-30^{\circ}$~$40^{\circ}$ from the direction of ship drift.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.3970-3979
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• 1996

A fluid flow inside a circular cylinder subject to horizontal, circular oscillation is analyzed numerically and experimentally. The steady streaming velocities at the edges of the boundary layers on the bottom and side surfaces of the cylinder obtained in the previous paper are used as the boundary conditions in the governing equations for the steady flow motion in the interior region. The Stokes' drift velocity obtained in the previous paper also constitutes the Lagrangian velocity which is used in the momentum equations. It turns out that the interior steady flow is composed of one cell, ascending at the center and descending near the side surface, at the streaming Reynolds number 2500. However, at the streaming Reynolds number 25, the flow field is divided into two cells resulting in a descending flow at the center. The experimentally visualized flow patterns at the bottom surface agree well with the analytical solutions. The visualization experiment also confirms the flow direction as well as the center position of the cell obtained by the numerical solutions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.61-69
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• 1998

Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.

• 한국기계연구소 소보
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• s.14
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• pp.135-144
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• 1985

A method is described to obtain the first order force and second order steady force on the fixed two dimensional submerged or semisubmerged cylinders at infinite depth of water due to regular waves. The first order diffraction wave velocity potential which describes the flow diffracted by a body is obtained numerically using source distribution method on the mean wetted surface. And a technique to remove the irregular frequency phenomena of the source distribution method is also applied. The second order steady force is calculates by means of direct integration of the pressures on the body as derived from the first order velocity potential and is also computed by means of reflection wave height derives from momentum conservation theory. The results are compared with those of published works, and show good agreement.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.3
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• pp.243-254
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• 1996

The main purpose of this study is to investigate the collection efficiency characteristics of a cylindrical ESP. To do that, it is necessary to analyze the electric field, gas flow field, and mechanism of particle movement by numerical simulation based on EHD model. For a gas flow field, Navier-Stokes equation involving the electric source term was solved by SIMPLE algorithm. In case of the electric field, the current continuity and electric field equations were solved by S.O.R. method. The analysis of particle movement was performed on the basis of PSI-CELL model from the Lagrangian viewpoint. The results showed that the influence on the gas flow field by the electric field is almost negligible in a cylindrical ESP. The particle drift velocity $V_P$ toward the collection surface is increased continuously by the electrostatic force due to the rise of particle charge as the particle is moving to the flow direction and the particle size becomes larger. The collection efficiency is to quitely higher with the increase of applied voltage for the same particle size, while becomes smaller as the inlet velocity is increased.

• Ocean and Polar Research
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• v.35 no.3
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• pp.193-203
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• 2013

A GPS-drifter was newly designed to observe the sea surface skin current and to estimate the direct wind effect on the sea surface. After conducting a test to establish and verify the accuracy of the GPS itself in the laboratory, in-situ experimental campaigns at Saemangeum in Gunsan city and Haeundae in Busan city, Korea, were carried out to ascertain the drifter track and to estimate the velocity data set on Oct. 3, 15, 23, 27 and Nov. 25, 2011. The current meters, RCM9 and ADCP, were moored together to remove the background current field, and the wind data were obtained from several marine stations such as towers and buoys in these areas. The drifter-observed velocity show good agreement with the flow obtained by the HF radar in the Saemangeum area. The direction of the wind-driven current extracted from the drifter-observed velocity was completely deflected to the right, however the degree of the angle was different according to the drift types. The average speed of the wind-driven current matched with 2.19~2.81% of the wind speed and the deflection angle was about $8.0{\sim}10.9^{\circ}$ without adjustment for the land-sea effect, and about 2.19~2.84% and $4.1{\sim}6.0^{\circ}$ with the adjustment for the land-sea effect.

• Journal of the korean society of oceanography
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• v.34 no.2
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• pp.59-72
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• 1999

Cavitating fluid sea ice model of Plato and Hibler (1992) is applied to the Southern Ocean with an idealized, circular Antarctica. Using climatological atmospheric forcing fields averaged in the zonal direction, we show that oceanic heat flux and ice velocity have major effects on the seasonal change of ice edge, as other studies showed. In our model results, there appears a zone of free drift that contains a polynya zone. Thermodynamic forcing functions make dominant contributions to daily increments of ice thickness and compactness, except the zones of ice edge and polynya. The dominant contributions are also shown in distributions of the temperature on ice surface and several to terms in surface heat balance equation, and are also confirmed by those obtained from the thermodynamic-only model with the different locations of ice edge.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.91-99
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• 1997

This paper presents theoretical formulations and numerical computations for predicting first-and second-order hydrodynamic force on a ship advvancing in waves. The theoretical formulation leads to linearized radiation and diffration problems solving the three-dimensional Green function integral equations over the mean wetted body surface. Green function representing a translating and pulsating source potantial for infinite water depth is used. In order to solve integral equations for three dimentional flows using Green function efficiently, the Hoff's method is adopted for numerical calculation of the Green function. Based on the first-order solution, the mean seconder-order forces and moments are obtained by directly integrating second-order pressure over the mean wetted body surface. The calculated items are carried out for analyzing the seakeeping characteristics of Series 60. The calculated items are hydrodynamic coefficients, wave exciting forces, frequency response functions and addd resistance in waves.