• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.2
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• pp.104-111
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• 2010

The complete avoidance of cavitation, as a result of gap flow between the fixed and movable portion of a horn type rudder system, is difficult. To reduce gap flow, it is a common practice to attach a half round prismatic bar that protrudes beyond the concave surface of the horn facing the gap and laid along the centerplane of the rudder. However the employment of such a device does not always yield satisfactory results. Previously, the authors have shown that a pair of blocking bars, attached on the convex surface of the movable portion, better enhance the blocking ability of gap flow to that of a single centre bar installed on the concave surface. This also circumvents difficulties that might occur in practical applications. In the present study, a series of numerical computations show that flow injected into the gap of a rudder may also block the flow within, without employment of any physical devices, such as a half circular bar. This study also shows that the combination of flow injection and blocking bars may result in the synergic augmentation of blocking efficiency of gap flow, as demonstrated in computations for a three dimensional rudder system.

• 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.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.228-237
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• 2007

The flow characteristics around a horn-type rudder behind an operating propeller of a high-speed large container carrier are studied through a numerical method in fully wetted and cavitating flow conditions. The computations are carried out in a small scale ratio of 10.00(gap space=5mm) to consider the gap effects. The Reynolds averaged Navier-Stokes equation for a mixed fluid and vapor transport equation applying cavitation model are solved. The axisymmetry body-force distribution technique is utilized to simulate the flow behind an operating propeller. The gap flow, the three-dimensional flow separation, and the cavitation are the flow characteristics of a horn-type rudder. The pattern of three-dimensional flow separation is analyzed utilizing a topological rule. The various cavity positions predicted by CFD were shown to be very similar to rudder erosion positions in real ship rudder. The effect of a preventing cavitation device, a horizontal guide plate, is also investigated.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.578-586
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• 2009

Recently, horn-type rudders are generally being used at high speed container ships and are frequently suffering from the cavitation occurs on the rudder surface in the vicinity of the gap between the horn and rudder plate. In the present study, a fluid supplying device is employed as to decrease the gap cavitation of the horn-type rudder. The device is devised to inject the water against the pressure side through the nozzle installed inside of the gap to control the gap flow. Numerical calculations are performed to investigate the effectiveness of the device and the results show that the device can noticeably reduce the gap cavitation. The rates of water injection for achievement of the maximum retardations of gap flow are also sought.

• 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.39 no.2
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• pp.1-10
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• 2002

Hull-propeller-rudder interactions are studied by the iterative computational procedures. Hull effects on the propeller are reflected through the effective velocities computed by the vortex ring method which used the measured nominal wake as input data. A potential based panel method has been developed to solve the propeller-rudder interactions using the obtained effective velocities. Steady flow characteristics around the rudder surface can be obtained by computing the induced velocities on the rudder by the propeller and vice versa are computed by the iterative manner until the converged solutions are obtained. Flow characteristics around the propeller and the rudder are measured by Laser Doppler Velocimetry(L.D.V.) in large cavitation tunnel at Samsung Heavy industries. The gap flow model is adopted to solve the characteristics of the horn rudder. Numerical results are compared with the experimental values and the computed velocity fields and pressure distributions with rudder angle on the horn rudder surface show good agreement with measured ones in large cavitation tunnel.

• Special Issue of the Society of Naval Architects of Korea
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• 2011.09a
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• pp.1-4
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• 2011

The full spade rudder for the high speed has advantage to prevent gap cavitation of the rudder. DSME has developed the full spade rudder and GL has carried out CFD analysis and FE analysis to confirm strength and fatigue for DSME and Owner. Necessarily, it needs to compare rudder torque & rudder force between CFD, FE analysis and full scale measurement. This report introduces the measurement method and application of strain gauge for measuring the rudder torque and rudder force for the 8,400 TEU container ship.

• Journal of Ship and Ocean Technology
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• v.8 no.4
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• pp.1-9
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• 2004

High lifting devices used for control purposes have received much attention in the marine field. Hydrofoils for supporting the hull, roll stabilizer fins for developing the motion damping performance, rudders for maneuverability are the well-known devices. In the present study, the ability of the rudder with flap to produce high lift was analyzed. The boundary layer control, one of the flow control techniques, was adopted. Especially, to build the blown flap, a typical and representative type of a boundary layer control, a flapped rudder was designed and manufactured so that it could eject the water jet from the gap between the main foil and the flap to the flap surface tangentially. And it was tested in the towing tank. Simultaneously, to know the information about the 2-dimensional flow field, a fin model with similar characteristics as the rudder model applicable for the motion control was made and tested in the cavitation tunnel. In addition, local flow measurements were carried out to obtain physical information, for example, a surface pressure measurement and flow visualization around the flap. And CFD simulation was used to obtain information difficult to collect from the experiment about the 2-dimensional flow.