• 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.

• 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.34 no.5
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• pp.325-330
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• 2010

An open water rudder test was carried out to figure out the flow characteristics around a twin rudder at $Re=1.5{\times}10^4$. In the analysis, the unique characteristics of a twin rudder, which affects rudder forces, were explained. The analysis includes varying angles of attack from 10 to 30 degrees. In this paper, the measured results have been compared with each other to predict the performance characteristics of a twin rudder's 2-dimensional section by 2-frame grey level cross correlation PIV method. The length L=0.75C between upper and lower rudders could be defined as the critical length.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.419-426
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• 2018

Recently, in an effort to reduce the energy efficiency design index (EEDI), studies on energy saving devices (ESDs) have been conducted. In this study, we designed a post-device suitable for a KRISO container ship (KCS) using computational fluid dynamics (CFD). In order to increase the efficiency of the post-device, a twisted rudder was used, which has a proven performance (showing a 1.34% reduction in DHP compared to the bare hull at 24 knots) in previous research at Pusan National University. In addition, an increase in efficiency was expected by the use of a rudder bulb, including the discontinuous section of the twisted rudder and a divergent propeller cap to prevent the contraction of the wake. The optimization criterion was the case where the delivery power was the least compared with the bare hull. We analyzed the cause of the efficiency increase through an analysis of the self-propulsion factor. The case study for optimization was divided into 4 types (1. clearance of the bulb and cap, 2. shape of the bulb, 3. size of the bulb and cap, and 4. asymmetric bulb). Finally, with a clearance of 50 mm from the ship, a spherical bulb with the cap having an angle of $5^{\circ}$, and an asymmetric rudder bulb with a bulb diameter of 1.2HH/1.4H (horizontal/vertical) showed a 2.05% reduction in DHP compared to the bare hull at 24 knots. We will fabricate a post-device that will be optimized in the future and verify the performance of the post-device through model tests.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.3
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• pp.167-174
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• 2021

In this study, the amount and frequency characteristics of cloud cavitation formed on a navy ship rudder were investigated through cavitation image processing technique and cavitation noise analysis. A high-speed camera with high time resolution was used to observe the cavitation on a full-spade rudder. The deflection angle range of the full-spade rudder was set to 8 to 15 degrees so that cloud cavitation was generated on the rudder surface. For images taken at 10⁴ fps (frame per second), reference values for detecting cavitation were defined and detected in Red, Green, Blue and Hue, Saturation, Lightness color spaces to quantitatively analyze the amount of cavitation. Intrinsic frequency characteristics of cloud cavitation were detected from the time series data of the amount of cavitation. The frequency characteristics of cloud cavitation obtained by using the image processing technique were found to be the same through the analysis of the noise signal measured by the hydrophone installed on the hull above the rudder, and its peak value was in the frequency band of 30~60Hz.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.306-306
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• 2011

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.1
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• pp.21-26
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• 1992

Generally a navigator evaluated the maneuverability of his ship by the scale of turning circle which was described only by the largest rudder angle of the port and starboard sides. But to have the sufficient knowledge of his ship's maneuvering characteristics he should consider the data about the new course keeping test, the spiral test, and the turning circle tests in accordance with the rudder angles together. In this paper the author performed the above tests to study the maneuverability of the stern trawler M.S. Pusan 404 which is a training ship of the National Fisheries University of Pusan. The obtained results are summarized as follows: 1. When the rudder angles being 5。, 10。, 20。, 30。, 35。 the advances of the starboard side turning circles were 12.8, 8.2, 4.8, 2.9, 2.7 times as large as the length of the ship, and of the port side turning circles were 13.3, 8.7, 5.4, 3.5, 2.9, time as large as the large as it. Under the same conditions the tactical diameters were 15.1, 9.7, 5.2, 3.1, 2.8 times as large as the length of the ship, for starboard side, and 17.2, 12.4, 6.4, 3.7, 3.2 times as large as it for port side. 2. As the rudder angle being increased the ratio of the advance to the tactical diameter was nearly 1 and her obeying ability was better than that of the small angle. 3. The mean values of the rates of speed reduction during the steady turning motion were 0.96, 0.92, 0.82, 0.71, 0.65 in accordance with the rudder angles. 4. The relative formulas between the distance to the new course y and the altering course x were as follows: When rudder angles being 10。, 20。, 30。, y=52.2222+1.6133x, y=48.750+0.9383x, y=39.250+0.655x respectively. 5. There was little difference of the distance to the new course between rudder angle 20。and 30。, and so it is desirable for a navigator to a navigator to use the small rudder angles unless sudden emergencies. 6. Though her rudder angle being small her course stability was good according to the spiral tests.

• Corrosion Science and Technology
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• v.10 no.3
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• pp.101-107
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• 2011

Marine ships have played an important role as a carrier, transporting much more than 80% of all international trading, and marine transportation is an internationally competitive, strategic, and great national important industry. However, those marine ships have the characteristics such as voyage of long distance, large-volume and lower speed than the other carry system. Therefore, it is important to manufacture a larger and faster ship, however, the steel plates which are consisted with most of those ships has brought about many corrosion problems in sea water such as general corrosion, localized corrosion, cavitation and erosion corrosion etc.. Most hulls of the ships have been protected with paintings, sacrificial anode, marine growth prevention system, and impressed current cathodic protection methods against numerious corrosion problems mentioned above. However, these conventional methods are not very effective because the rudder of ships stern are exposed to very severe corrosive environment such as tides, speeds of ships, cavitations and erosion corrosion, etc.. In this study, electrochemical and cavitation characteristics was investigated for the rudder material of ship which is exposed to serious corrosive environment. As a result, it is considered that the optimum cathodic protection potentials of rudder material is the range of -0.6 V ~ -0.8 V(Ag/AgCl) in static seawater.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.5
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• pp.460-470
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• 2009

In recent practice a half round prismatic bar has fillet welded or formed through foundry work along the centerline on rear concave surface of the horn to mitigate gap flow between fixed and movable part of the rudder system. When the gap clearance has been blocked with this practice, numerical simulations indicate that the practices are not only effective in reducing the gap flow but also in mitigating the cavitation. The blocking effects are remarkably improved when a pair of blocking bar is bisymmetrically attached with respect to centerline on the opposite convex surface of the movable part. The blocking bar could be placed on the exposed surface under maximum rudder angle. This implies that the blocking bar could be easily adopted not only in a design stage but also in a maintenance stage for mitigating rudder cavitation. In addition, the numerical simulations imply that more improvements could be anticipated through the selection of section shape of prismatic bar for gap flow blocking.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.5 s.149
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• pp.578-585
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• 2006

Cavitation related erosion damages on semi-spade rudder generally occur at around leading edge of lower-face and behind gap of lower pintle. To get the idea of gap entrance profile for the latter case, a series of tests with large models has been carried out at MOERI. In the tests, the flow pattern around lower pintle have been investigated and visualized by high speed camera. Additionally, cavitation inception tests and pressure measurements have also been conducted for better comparison. As a result a new model (F rudder) has been developed. The new model turned out to have stable pressure distribution along the surface and so the cavitation inception speeds within ${\pm}5^{\circ}$ of rudder angle were delayed approx. 4 knots in average.