• Journal of Fisheries and Marine Sciences Education
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• v.11 no.2
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• pp.184-202
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• 1999

The roll damping characteristics of the three models of a small fishing(3 ton class fishing vessel), such as the bare hull, hull with bilge keels, and hull with bilge keels and a central wing are investigated by the free roll and head waves tests in calm water in a towing tank with the various forward speeds, initial angles and OG's. The experimental results are compared with the numerical results of mathematical modelings by the energy method for these three models and the energy dissipation patterns are also compared. And the wave length variations are also included. The experimental results are compared with the numerical results of mathematical modelings by the energy method for these three models and the energy dissipation patterns are also compared. The roll damping moment of the models is increased for zero speed cases, but as the speed increases, the effect of the waves on the roll damping of the models with the additional devices is negligible due to the much increased damping caused by the lift increase.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.414-430
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• 2013

This paper shows the study of preswirl duct as an effective energy saving devices that have been devised and reviewed to support the propeller performance, especially for the ship of VLCC with large block coefficients. From the bare hull wake measurements, typical upper/lower asymmetry of hull wake at the propeller disk was found. The 2 kinds of pre-swirl duct, Unconventional half circular duct and Conventional circular pre-swirl duct have been designed and reviewed to recover the loss of propeller running in that condition. The general function of the pre-swirl duct was set to work against this asymmetry of wake and generate pre-swirled flow into the propeller against the propeller rotating direction. The optimum self propulsion tests with various angle configurations were carried out and the best configuration was decided. Accordingly, cavitation test was carried out with best configuration of unconventional half circular duct. The blade surface and tip vortex cavitation behaved smoother when the duct was mounted. The hull pressure amplitudes reflected this difference, so the hull pressure amplitude with duct was smaller than that of without duct.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.688-696
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• 2023

In the present study, free roll decay and resistance performances of fishing vessels were evaluated with the combinations and variations of in the parameters of appendages which are attached to improve motion performance of fishing vessels. Computational Ffluid Ddynamics was used to perform free roll decay and resistance analysis. The roll period and decay coefficient were derived by the variations in the combination and dimensions of the primary appendages of the bilge keel and the under keel. It was observed thatThe variations of in the length of the under keel did not significantly impact to the roll damping coefficient. Conversely, for the bilge keel, an increase in the length and angle resulted in an increase in the roll damping coefficient. Comparison of resistance performance was additionally assessed among the selected hulls with the appendages and bare hull. The resistance of the hull with the appendages was higher than that of the bare hull due owing to the changes of in the pressure on the surface of the hull and trim angle. Throughout the present study, the impact of appendage parameter and arrangement on the free roll decay and resistance performance of fishing vessels were was assessed,. which This will be beneficial for the application of appendages to fishing vessels.

• Journal of Navigation and Port Research
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• v.38 no.6
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• pp.585-591
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• 2014

The primary objective of the current work is to predict speed performance of the medium patrol boat over $F_N=0.5$ employing experimental materials based on the CFD before model tests. In other words, the predicted brake powers according to ship speeds are assessed satisfying the main engine capacity. The subject ships are selected the two different stern hull forms. The flow computation are conducted considering free surface and dynamic trim using a commercial CFD code(STAR-CCM+). The resistances of the bare-hull are obtained from CFD. Wave patterns, pressures and limiting streamlines on the hull and velocity distribution in the propeller plane for the two hull forms are compared using CFD. The effective powers of the object ships are assessed based on CFD. Resistance increase according to the attached appendages and quasi-propulsive efficiency are employed the experimental datas. Speed performance prediction method concerning high speed vessels like a medium patrol boat is developed employing CFD and experimental data.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.5
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• pp.523-529
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• 2008

The course stability performance for tankers is evaluated by computational fluid dynamics. In the present work, a Reynolds averaged Navier-Stokes (RANS) code is applied to a maneuvering problem covering the pure drift and yaw motions. The purposes of this study are to evaluate the hydrodynamic force in the bare hull (AFRAMAX) in pure drift and yaw motion and to provide information about the trends in the forces and moments when the rudder angles are varied. The flow simulation is performed by FLUENT. The CFD code is examined to find the optimistic computational condition such as size of grid, turbulence model and initial condition. The hydrodynamic derivatives in drift and pure yaw motion are estimated by the numerical simulation, and then the stability levers are calculated. It is confirmed that the computations show the superiority and inferiority of course stability performance according to the hull forms. Finally, the CFD code is applied to the estimation of the rudder forces when the rudder angles are varied. The propeller effect expressed by the body force distribution is also included.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.4
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• pp.397-402
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• 2013

In this study, numerical hull form development of a platform supply vessel, a full scale with the overall length of 26.75m, was performed to predict a bare-hull resistance and a large scale of model tests with a 1/10 scaled model were conducted to verify the success of numerical results. Numerical analysis on heave and pitch motion as a function of encounter frequency and ship's speed for the prediction of seakeeping characteristics are also presented. The experiment results of resistance agreed well with numerical analysis. As a result in the motion response characteristics, the heave RAO indicates high values with the range of encounter frequency 1.8~2.0. The Pitch RAO indicates high motion response characteristics at Beaufort scale No. 3 and 4 in rough seas.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.3
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• pp.145-152
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• 2013

Recently, with oil price jumping and environmental issues, Green ship is paid deep attention to by ship owner, operator, builder, class and government. Fuel efficiency and reduction of $CO_2$ emissions are expected to have a strong influence on the design and operation of merchant ships. Many ship owners and operators are seeking the more economic method by the best operating route and the application of reliable and effective energy saving devices. With the Energy Efficiency Design Index (EEDI) in 2013 attention will more than ever be focused at achieving maximum fuel economy in the hydrodynamic design of hull forms, their appendages and propellers. IMO requirements for $CO_2$ emission for ships will now be implemented for vessels ordered from 1st January 2013. So far, a lot of new idea and patents have been proposed, tested, claimed and applied for various kinds of ship type. This paper shows numerical and experimental work related to a study on a energy saving devices particularly for fuller ship such as merchant vessel of Tanker and Bulker. From the bare hull wake measurements, typical upper/lower asymmetry of hull wake at the propeller disk was found. The pre-swirl duct have been designed and reviewed to recover the loss of propeller running in that condition. The general function of the pre-swirl duct was set to work against this asymmetry of wake and generate pre-swirled flow into the propeller against the propeller rotating direction.

• 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.26 no.5
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• pp.1-4
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• 2012

A energy saving device "Crown duct" has been developed and its efficiency gain has been verified experimentally in the towing tank of SSPA. The preswirl stator is well known as one of energy saving devices, which recovering the rotational energy of propeller slipstream. Crown duct has two functions of recovers the rotational energy by three blades on top of duct and of flow concentration by semi-duct. The model tests showed 4.4% efficiency gain with Crown Duct at full load condition and 6.9% at ballast condition compared with the bare hull ones for the middle class tanker.

• International Journal of Ocean System Engineering
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• v.3 no.2
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• pp.77-89
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• 2013

The propeller performance has been investigated using a benchmark Duisburg Test Case ship with RANSE. First, the hydrodynamic characteristics of propeller in case of open water have been analyzed by a commercial CFD program and the results are compared with those of experimental data. Later, the flow around the bare hull has been solved and the frictional resistance value and form factor of the ship have been obtained and compared with those of ITTC57 formulation and experimental results for validation. The free surface effect has been ignored. A good agreement has been obtained between the results of RANSE and experiments at both stages. Then the ship - propeller interaction problem was solved by RANSE and the differences in thrust, torque and efficiency of propeller as compared with the open-water numerical results have been discussed.