• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.131-142
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• 2019

In this paper, a Wavy Twisted Rudder (WTR) is proposed to address the discontinuity of the twisted section and increase the stalling angle in comparison to a conventional full-spade Twisted Rudder (TR). The wave configuration was applied to a KRISO Container Ship (KCS) to confirm the characteristics of the rudder under the influence of the propeller wake. The resistance, self-propulsion performance, and rudder force at high angles of the wavy twisted rudder and twisted rudder were compared using Computational Fluid Dynamics (CFD). The numerical results were compared with the experimental results. The WTR differed from the TR in the degree of separation flow at large rudder angles. This was verified by visualizing the streamline around the rudder. The results confirmed the superiority of the WTR in terms of its delayed stall and high lift-drag ratio.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.715-722
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• 2014

Three twisted rudders fit for large container ships have been developed; 1) the Z-twisted rudder that is an asymmetry type taking into consideration incoming flow angles of the propeller slipstream, 2) the ZB-twisted rudder with a rudder bulb added onto the Z-twisted rudder, and 3) the ZB-F twisted rudder with a rudder fin attached to the ZB-twisted rudder. The twisted rudders have been designed computationally with the hydrodynamic characteristics in a self-propulsion condition in mind. The governing equation is the Navier-Stokes equations in an unsteady turbulent flow. The turbulence model applied is the Reynolds stress. The calculation was carried out in towing and self-propulsion conditions. The sliding mesh technique was employed to simulate the flow around the propeller. The speed performances of the ship with the twisted rudders were verified through model tests in a towing tank. The twisted versions showed greater performance driven by increased hull efficiency from less thrust deduction fraction and more effective wake fraction and decreased propeller rotating speed.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.1
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• pp.18-25
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• 2017

This study deals with numerically comparing performance according to rudder shape called 'Twisted rudder and Wavy twisted rudder'. In comparison with conventional rudder, rudder with wavy shape has showed a better performance at high angles of attack($30^{\circ}{\sim}40^{\circ}$) due to delaying stall. But most of study concerned with wavy shape had been performed in uniform flow condition. In order to identify the characteristics behind a rotating propeller, the present study numerically carries out an analysis of resistance and self-propulsion for KCS with twisted rudder and wavy twisted rudder. The turbulence closure model, Realizable $k-{\epsilon}$, is employed to simulate three-dimensional unsteady incompressible viscous turbulent and separation flow around the rudder. The simulation of self-propulsion analysis is performed in two step, because of finding optimization case of wavy shape. The first step presents there are little difference between twisted rudder and case of H_0.65 wavy twisted rudder in delivered power. So two kind of rudders are employed from first step to compare lift-to-drag ratio and torque at high angles of attack. Consequently, the wavy twisted rudder is presented as a possible way of delaying stall, allowing a rudder to have a better performance containing superior lift-to-drag ratio and torque than twisted rudder at high angles of attack. Also, as we indicate the flow visualization, check the quantity of separation flow around the rudder.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.169-177
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• 2018

Twisted rudder, twisted rudder with bulb, and twisted rudder with bulb and fin have been developed computationally for 3,000 TEU container ship through parametric study. The objective function is to minimize delivered power in model scale. Design variables are twisted angle, rudder bulb diameter and fin angle. The governing equation is Reynolds averaged Navier-Stokes equations in an unsteady turbulent flow and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. The calculation was carried out in towing and self-propulsion conditions at design speed. The sliding mesh technique was employed to simulate the flow around the propeller. Form factor is obtained from the towing computation. Self-propulsion point is obtained from the self-propelled computations at two propeller rotating speeds. The delivered power due to the designed twisted rudder, twisted rudder with bulb, and twisted rudder with bulb and fin are reduced by 1.1%, 1.6%, and 2.0%, respectively.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.6
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• pp.391-399
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• 2021

In order to investigate force and cavitation characteristics for the flat & twisted rudders in the Large Cavitation Tunnel (LCT), the rudder dynamometer was designed and manufactured. The measuring capacities of lift, drag and moment are ±1000 N, ±2000 N, and ±150 N-m, respectively. The present dynamometer uses the actuator with a harmonic drive to control the rudder angle without backlash. As the target ship is a military ship with twin shaft, each dynamometer was installed above the port & starboard rudders. After the installation of the model ship with all appendages, the model test composed of rudder force measurement and cavitation observation was conducted for the existing flat rudder & the designed twisted rudder. While the flat rudder showed the big difference of lift & moment between port & starboard, the twisted rudder presented a similar trend. The cavitation of the twisted rudder showed better characteristics than that of the flat rudder. Another set of model tests were conducted to investigate rudder performance by the change of the design propeller. There was little difference in rudder performance for the design propellers with slight geometric change. Through the model test, the characteristics of the flat & twisted rudders were grasped. On the basis of the present study, it is thought that the rudder with better performance would be developed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.322-334
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• 2012

This paper shows the numerical and experimental results about the hydrodynamic characteristics of X-Twisted rudders having continuous twist of the leading edge along the span. All the results were compared with those of the semi-balanced rudder. Calculation through the Reynolds-Averaged Navier-Stokes Equation (RANSE) code with propeller sliding meshes shows large inflow angle and fast inflow velocity in the vicinity of ${\pm}0.7$ R from the shaft center, so it may cause cavitation. Also, X-Twisted rudder has relatively small inflow angles along the rudder span compared with semi-balanced rudder. For the performance validation, rudders for two large container carriers were designed and tested. Cavitation tests at the medium sized cavitation tunnel with respect to the rudder types and twisted angles showed the effectiveness of twist on cavitation and the tendency according to the twist. And the resistance, self-propulsion and manoeuvring tests were also carried out at the towing tank. As a result, in the case of X-Twisted rudder, ship speed was improved with good manoeuvring performance. Especially, it was found out that manoeuvring performance between port and starboard was well balanced compared with semi-balanced rudders.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.5
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• pp.479-487
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• 2009

This paper describes the design of a full-spade twisted rudder section by using the genetic algorithm based on VLM(Vortex Lattice Method) and panel method. The developed propeller- rudder analysis program has been validated by comparing with experimental data. The developed code has been used for the design of a twisted full-spade rudder especially for finding out optimum section. The optimization has been firstly carried out by the genetic algorithm. The more detail variation of a rudder section has been also conducted by changing section profile in more detail to confirm the most optimum section profile. The developed new twisted rudder has been compared with existing twisted rudder by cavitation testing in the cavitation tunnel at MOERI. It is concluded that the developed twisted rudder has a lower cavity in comparison with existing twisted rudder. The verification of efficiency gain is expected to be carried out through self-propulsion tests in the near future.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.163-177
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• 2010

This article examines hydrodynamic characteristics and speed performances of a ship attached with a full spade and a twisted rudder based on a computational method. For this study, a 13,100 TEU container carrier is selected. The turbulent flows around a ship are analyzed by solving the Reynolds-averaged Navier-Stokes equation together with the application of Reynolds stress turbulence model. The computations are carried out at the conditions of rudder, bare hull, hull-rudder and hull-propeller-rudder. An asymmetric body-force propeller is applied. The speed performance is predicted by the model-ship performance analysis method of the revised ITTC'78 method. The hydrodynamic forces are compared in both rudder-open-water and self-propulsion conditions. The flow characteristics, the speed performance including propulsion factors and the rudder-cavitation performance are also compared. The model tests are conducted at a deep-water towing tank to validate the computational predictions. The computational predictions show that the twisted rudder is superior to the full spade rudder in the respect of the speed and the cavitation performances.

• 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.57 no.6
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• pp.381-387
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• 2020

According to the increase of concern for environmental problems, the energy saving becomes an important issue because it is one of the most effective methods of decreasing CO2 which is major environmental problem. In the present study, the post device after propeller related with rudder has been focussed. Recently the full-spade twisted rudder has been frequently used not only to increase the efficiency but also to remove the cavitation risk on leading edge. In addition to that the rudder bulb is also applied to the rudder to increase the propulsion efficiency as well as to minimize the cavitation erosion risk around twisting part. The parametric study has been conducted for investigating the optimum configuration of twisting rudder with bulb by CFD. The present optimization has been applied to the KVLCC2 full-body ship. The verification of the computed results is also expected to be conducted by the comparison with experimental results in the near future.