• 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.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.241-255
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• 2012

Three types of 100 kW-class tidal stream turbines are proposed and their performance is studied both numerically and experimentally. Following a wind turbine design procedure, a base blade is derived and two additional blades are newly designed focusing more on efficiency and cavitation. For the three designed turbines, a CFD is performed by using FLUENT. The calculations predict that the newly designed turbines perform better than the base turbine and the tip vortex can be reduced with additional efficiency increase by adopting a tip rake. The performance of the turbines is tested in a towing tank with 700 mm models. The scale problem is carefully investigated and the measurements are compared with the CFD results. All the prediction from the CFD is supported by the model experiment with some quantitative discrepancy. The maximum efficiencies are 0.49 (CFD) and 0.45 (experiment) at TSR 5.17 for the turbine with a tip rake.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.6
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• pp.782-793
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• 2018

A small-scale horizontal axis hydrokinetic turbine is designed, manufactured and studied both experimentally and numerically in this study. The turbine is expected to work in most of China's sea areas where the ocean current velocity is low and to supply electricity for remote islands. To improve the efficiency of the turbine at low flow velocities, a magnetic coupling is used for the non-contacting transmission of the rotor torque. A prototype is manufactured and tested in a towing tank. The experimental results show that the turbine is characterized by a cut-in velocity of 0.25 m/s and a maximum power coefficient of 0.33, proving the feasibility of using magnetic couplings to reduce the resistive torque in the transmission parts. Three dimensional Computational Fluid Dynamics (CFD) simulations, which are based on the Reynolds Averaged Navier-Stokes (RANS) equations, are then performed to evaluate the performance of the rotor both at transient and steady state.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.191-196
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• 2002

The paper presents a numerical and experimental investigation on dynamic behaviors of a towed low tension cable. In the numerical study, an implicit finite difference algorithm is employed for three-dimensional cable equations. Fluid and geometric non-linearity and bending stiffness are considered and solved by Newton-Raphson iteration. Block tri-diagonal matrix method is applied for the fast calculation of the huge size of matrices. In order to verify the numerical results and to see real physical phenomena, an experiment is carried out for a 6m cable in a deep and long towing tank. The cable is towed in two different ways; one is towed at a constant speed and the other is towed at a constant speed with top end horizontal oscillations. Cable tension and shear forces are measured at the top end. Numerical and experimental results are compared with good agreements in most cases but with some differences in a few cases. The differences are due to drag coefficients caused by vortex shedding. In the numerical modeling, non-uniform element length needs to be employed to cope with the sharp variation of tension and shear forces at near top end.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.83-87
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• 2002

종강도 위주의 일반 상선의 LMC 의 경우는 단지 선박을 l 차원 Beam Model 로 단순화하여 선미로부터 선수까지의 Weight Distribution 과 Buoyancy Distribution 을 계산하여 두 값의 차이를 Shear Force 로 계산하고 Shear Force 적분값을 Bending Moment 로 계산한다. 횡강도가 중요시되는 Barge 선의 경우 Global Transverse Strength 같은 경우에는 위의 식을 적용할 수 있으나 복수의 바지선을 Hinge Type 이 아닌 Fixed Type 으로 고정시켜 사용할 경우 각각의 Connector 에 작용하는 Strength 값이 횡강도의 큰 비중을 차지한다. 일반적인 Load Master Computer 의 경우 이와 같은 계산이 불가능하며 NAPA 와 같은 전용 계산 프로그램의 경우 하나의 Condition 을 계산하는데 소요되는 시간이 많아 실질적인 Monitoring 은 불가능하다. 이에 특수목적의 Load Master Computer(ShipManager-88) 를 제작하게 되었고 이 Program 을 이용하여 Loadout 과 Floatoff 의 Simulation 을 수행하고 Monitoring 하였다. ShipManager-88 은 Barge 선의 종강도 횡강도, Stability, Trim & Draft 등을 계산하며 Sequence 기능으로 실제 LOADOUT 과 FLOATOFF 시의 모의시뮬레이션을 수행해 볼 수 있으며 Online Interlace 제공으로 Tank 에 설치된 센서에서 Level 값을 받아 실시간으로 현재 선박의 상태를 정확하게 계산할 수 있다. 실제 LOADOUT and FLOATOFF 를 수행하면서 Check 한 부분은 종강도, 횡강모 Stability, Deform, Connector Strength, Level 등을 Check 하였고 종방향의 LOADOUT 이 불가능한 Project 를 위해 Transverse LOADOUT 을 이용할 계획이다.

• Journal of Ocean Engineering and Technology
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• v.28 no.3
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• pp.199-208
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• 2014

In this study, propeller open water characteristics ($K_P$, $K_T$ and ${\eta}_o$) were compared for three different ducted propellers using a Computational Fluid Dynamics (CFD) analysis, as well as an experimental test at a basin. The best shape of the duct was selected from the three types of specially designed ducts based on the CFD analysis results. The same propeller model (Kaplan type propeller) was used inside all three duct models, and the propeller open water characteristics were compared, predominantly at the design speed for an underwater vehicle. Finally, the results of the CFD test simulations for the selected duct case were verified by experimental open water tests in a towing tank.

• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.386-392
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• 2018

It is necessary to predict hydrodynamic derivatives when assessing the maneuverability of a submarine. The force and moment acting on the vehicle may affect its motion in various modes. Conventionally, the derivatives are determined by performing captive model tests in a towing tank or applying a system identification method to the free running model test. However, a computational fluid dynamics (CFD) method has also become a possible tool to predict the hydrodynamics. In this study, virtual captive model tests for a full-scale submarine were conducted by utilizing a Reynolds-averaged Navier-Stokes solver in ANSYS FLUENT version 18.2. The simulations were carried out at design speed for various modes of motion such as straight forward, drift, angle of attack, deflection of the rudder, circular, and combined motion. The hydrodynamic force and moment acting on the submarine appended rudders and stern stabilizers were then obtained. Finally, hydrodynamic derivatives were determined, and these could be used for evaluating the maneuvering characteristics of the submarine in a further study.

• Journal of Korean Port Research
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• v.7 no.1
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• pp.89-114
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• 1993

ICLL 66 is the most widely ratified instrument of the IMO and is, along with the International Convention on Safety of life at Sea (SOLAS), the primary document setting forth internationally agreed ship safety standards. ICLL 66 set freeboard requirement based on experience gained from the first Load Line Convention in 1930 and on contemporary developments in ship design. Reexamination of ICLL 66 is indicated by the proliferation of novel ship designs for which it lacks adequate regulations and by significant advancements in analytical seakeeping and deck wetness prediction techniques now available to the designer. In this paper, the Freeboard Advisory Group reviews these issues against the changing climate of the marine industry and maritime administrations, discusses the state of the art in analytical seakeeping programs, and outlines a series of recommendations for the establishment of a new international load line convention for the next century. The steps needs for an international program at IMO are discussed and a new convention is proposed.

• Journal of Ship and Ocean Technology
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• v.9 no.3
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• pp.1-13
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• 2005

A design procedure for a ship with minimum total resistance has been developed using a numerical optimization method called SQP (Sequential Quadratic Programming) to search for optimized hull form and CFD(Computational Fluid Dynamics) technique. The friction resistance is estimated using the ITTC 1957 model-ship correlation line formula and the wave making resistance is evaluated using a potential-flow panel method based on Rankine sources with nonlinear free surface boundary conditions. The geometry of hull surface is represented and modified using B-spline surface patches during the optimization process. Using the Series 60 hull ($C_B$ =0.60) as a base hull, the optimization procedure is applied to obtain an optimal hull that produces the minimum total resistance for the given constraints. To verify the validity of the result, the original model and the optimized model obtained by the optimization process have been built and tested in a towing tank. It is shown that the optimal hull obtained around $13\%$ reduction in the total resistance and around $40\%$ reduction in the residual resistance at a speed tested compared with that of the original one, demonstrating that the present optimization tool can be effectively used for efficient hull form designs.

• Journal of Ship and Ocean Technology
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• v.9 no.4
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• pp.23-34
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• 2005

Increased usage of AUVs has led to the development of alternative navigational methods that use the acoustic beacons and dead reckoning. This paper describes a concurrent mapping and localization (CML) scheme that uses range sonars mounted on SNUUV­I, which is a small test AUV developed by Seoul National University. The CML is one of such alternative navigation methods for measuring the environment that the vehicle is passing through. In addition, it is intended to provide relative position of AUV by processing the data from sonar measurements. A technique for CML algorithm which uses several ranging sonars is presented. This technique utilizes an extended Kalman filter to estimate the location of the AUV. In order for the algorithm to work efficiently, the nearest neighbor standard filter is introduced as the algorithm of data association in the CML for associating the stored targets the sonar returns at each time step. The proposed CML algorithm is tested by simulations under various conditions. Experiments in a towing tank for one dimensional navigation are conducted and the results are presented. The results of the simulation and experiment show that the proposed CML algorithm is capable of estimating the position of the vehicle and the object and demonstrates that the algorithm will perform well in the real environment.