• Journal of the Korean Society of Marine Environment & Safety
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• v.14 no.1
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• pp.21-27
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• 2008

Triangular structure is used as basic shape of artificial structures for generating the upwelling current in order to make rich fishing ground at sea. Artificial upwelling current could bring the deep sea water containing a lot of nutrients from the bottom up to the surface. The purpose of this study is to examine the flow characteristics around underwater triangular structure with various stratification parameter. An experimental study was carried out for the triangular structure model in the circulating water channel to investigate flow characteristics by flow visualization method. A velocity fields around the underwater structure were measured by particle image velocimetry(PIV). The experimental results showed that the upwelling effect at the back and upper region of the structure could be best when the water depth was 2 times of the structure height and the stratification parameter was approximately 3.0. These quantitative data will be useful to determine the functional efficiency cf artificial upwelling structures.

• Proceedings of KOSOMES biannual meeting
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• 2007.11a
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• pp.177-183
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• 2007

Flow characteristics of the cylinder wake controlled with a small control cylinder were experimentally investigated by the PN (Particle Image Velocimetry) technique. Flow visualization of the flow around a circular cylinder was conducted in the Circulating Water Channel. The control cylinder having diameter of d=5mm, 10mm and 20mm was installed behind a circular cylinder of D=50mm. And the Reynolds number were $Re=4.9{\times}10^3,\;Re=9.9{times}10^3$ and $Re=1.9{\times}10^4$. In this study, the frequency characteristics of the controlled wake were analyzed by using spectral analysis of the measured wake velocity signals. As a result, the controlled wake had smaller vortex shedding frequency than that of circular cylinder wake by the effect of the control cylinder. Governing parameters of the flow control were d/D, and Reynolds number and they largely influenced the frequency characteristics of the cylinder wake. And vortex shedding frequency appeared most lowly at d=0.2D

• Journal of the Korean Institute of Navigation
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• v.25 no.1
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• pp.1-9
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• 2001

It is well known that, especially in the case of full-bodied ship, the course stability may become the severest among 4 items of requirement in Interim Standards for Ship Manoeuvrability adopted by IMO in 1993. The purpose of this study is to find some ideas for characteristics of fluid flow pattern around ship's stern in manoeuvring motion with parameter of changes in rudder size. We carried out two kinds of model experiment in obliquely running condition at circulating water channel. One is measurement on straightening effect of incoming flow to rudder and the other is experiment on flow visualization around the gap between rudder and stern-bottom. We discuss the correlation between the flow characteristics around ship's stem and flow straightening effect at rudder from the viewpoint of course stability. As a result, it is clarified that the gap between rudder and stern-bottom plays an important role in course stability of full-bodied ship. It is pointed out that there is quite a possibility of bad course stability as the gap between rudder and stern-bottom decreases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.567-575
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• 2013

A POD analysis based on time-resolved PIV measurements in a circulating water channel has been conducted to identify the skin friction reduction mechanism of outer-layer vertical blades. A recent PIV measurement indicated 2.73% and 7.95% drag reduction in the blade plane and the blade-in-between plane, respectively. In the present study, the influence of vertical blades array upon the characteristics of the turbulent coherent structures was analyzed by the POD method. It is observed that the vortical structures are cut and deformed by the blades array and that their temporal evolution is strongly associated with the skin-friction drag reduction mechanism in the turbulent boundary layer flow.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.6
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• pp.484-488
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• 1987

The model experiments were performed in tile circular water tank on the simple cambered and the super-V otter boards attached with the slotted fowler flap at the trailing edge in order to develop more efficient shearing characteristics. The dimension of the model otter boards was varied slightly in the flap chord ratio $0.20\~0.22$ and in the area $432\~426cm^2$ in accordance with the flap angle $30\~50^{\circ}$. The maximum shearing coefficient $C_L=1.78$ and hydrodynamic efficiency $C_L/C_D=4.0$ in the superV type were higher than their efficiencies $C_L=1.75$ and $C_L/C_D=3.7$ in the simple cambered type. As the shearing forces of the otter boards with flap were increased $20\~30\%$ mere than these without flap in spite of increasing the drag and the instability. The effect of flap should be fully investigated for the application.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.1-8
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• 1996

A potential-based panel method has been developed for numerical computation of wave resistance on a hybrid hydrofoil. Hybrid hydrofoil is composed of a main body, two struts and two hydrofoils. The main body, which is assumed to be an axisymmetric body for the present analysis, is normally used to support displacement of a body with its buoyancy. Normal dipoles and the sources are distributed on the body(main body, struts, hydrofoils) and the sources are distributed on the free surface. Linearized free surface and the radiation conditions are satisfied using the fourth order finite difference operator and the semi-linear pressure Kutta condition is used for the numerical computation of the hydrofoils. Poisson type free surface condition has been used for the numerical computation and hyperboloidal panel method has been used for better numerical accuracy. To verify this numeric method, model tests are performed in circulation water channel. From the comparison of experimental results with numeric ones, the present method can be used as a useful tool for the design of high speed vessels.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.200-207
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• 2017

The purpose in having a control surface on ships is to control the motion of the ship. The control surface may be composed entirely of a single movable surface or of a combination of fixed and movable portions. A control surface has one sole function to perform in meeting its purpose, and that is to develop a control force in consequence of its orientation and movement relative to the water. The forces and moments generated as a result of this rotation and angle of attack then determine the manoeuvring characteristics of the ship. In this paper, two-dimensional flow characteristics of a flapped rudder and a water-blowing control rudder were accomplished respectively by PIV method in a circulating water channel. Model test has been carried out with different angles of attack of main foil (NACA 0012) and flap's deflection angles to predict the performance of the flapped rudder and the water-blowing control rudder. The 2-frame particle tracking method has been used to obtain the velocity distribution in the flow field. $Re{\fallingdotseq}3.0{\times}10^4$ has been used during the whole experiments and measured results have been compared with each other.

• Journal of Navigation and Port Research
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• v.30 no.5 s.111
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• pp.375-379
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• 2006

The keel attached on bottom of hull part prevents yacht from flowing sideway by sailing posture. The keel remove a heel moment and make the force of stability. The selection of suitable keel is important bemuse it has an influence on the safety. Also the appendage attached on bottom of keel part lower ballast weight center and have influence on hull stability. The optimum shape about the keel is very important. So this study has compared with characteristics of resistance depending on the shape of the lower part of fin keel in the same surface of water submersion, we have attached three different types of models of lower part of fin keels to the model ships using circulating water channel and analyzed resistance characteristics per shape to arrive at the optimum shape of reduction of resistance.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.235-239
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• 2006

The keel attached on bottom of hull part prevents yacht from flowing sideway by sailing posture. So this study has compared with characteristics of resistance depending on the shape af the lower part of fin keel in the same surface af water submersion, we have attached three different types of models of lower part of fin keels to the model ships using circulating water channel and analyzed resistance characteristics per shape to arrive at the optimum shape of reduction of resistance.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.65-79
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• 1994

In the present paper, An emphasis is laid upon effects of stern bulb on hydrodynamic property and manoeuvring performance. We carried out captive model tests in circulating water channel with two ship models of which the frame lines of aft bodies are different. such as normal stern form and stern form with bulb, but of which the other parts are exactly same. The tests conducted consist of hull resistance test, effective thrust measurement, oblique tow test, and measurements of factors related to rudder force. From the results of model tests, we discussed effects of stern bulb on hull forces and on hull-propeller-rudder interactions, comparing with normal stern form. Furthermore, we also discussed effects of stern bulb on course stability. turning ability. spiral characteristics and zig-zag manoeuvre by computer simulation. As a result, it is clarified that the adoption of stern bulb makes course stability the worse and turning ability the better. The difference of the hydrodynamic derivatives of naked hull between two ship forms cause the worse course stability of the ship with stern bulb. The differences of the effective inflow velocity to rudder and hull forces induced by steered rudder cause the better turning ability of the ship with stern bulb.