• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.4
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• pp.344-359
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• 2016

Due to the increasing occurrence of maritime accidents and high-level requirements and modernization of naval wars, the concept of ship environment adaptability becomes more and more important. Therefore, it is of great importance to carry out an evaluation system for ship environment adaptability, which contributes to both ship design and classification. This paper develops a comprehensive evaluation system for ship environment adaptability based on fuzzy mathematics theory. An evaluation index system for ship environment adaptability is elaborately summarized first. Then the analytic hierarchy process (AHP) and entropy weighting methods are applied to aggregate the evaluations of criteria weights for each criterion and the corresponding subcriteria. Next, the multilevel fuzzy comprehensive evaluation method is applied to assess the ship integrative environment adaptability. Finally, in order to verify the proposed approach, an illustrative example for optimization and evaluation of five ship alternatives is adopted. Moreover, the influence of criteria weights, membership functions and fuzzy operators on the results is also analyzed.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2021.11a
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• pp.76-77
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• 2021

In line with the development of autonomous ships, it is necessary to train professional ship management supervisors to prepare for the transition to the ship's safety management system. Therefore, this study intends to investigate the capabilities required of ship management supervisors in preparation for introduction to autonomously operated ships for ship management supervisors in the field, and to suggest future capability development plans.

• Korean Journal of Remote Sensing
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• v.36 no.4
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• pp.535-544
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• 2020

In synthetic aperture radar (SAR) based ship detection application, false alarms frequently occur due to various noises caused by the radar imaging process. Among them, radio frequency interference (RFI) and azimuth smearing produce substantial false alarms; the latter also yields longer length estimation of ships than the true length. These two noises are prominent at cross-polarization and relatively weak at co-polarization. However, in general, the cross-polarization data are suitable for ship detection, because the radar backscatter from background sea surface is much less in comparison with the co-polarization backscatter, i.e., higher ship-sea image contrast. In order to improve the ship detection accuracy further, the RFI and azimuth smearing need to be mitigated. In the present letter, Sentinel-1 VV- and VH-polarization intensity data are used to show a novel technique of removing these noises. In this method, median image intensities of noises and background sea surface are calculated to yield arithmetic tendency. A band-math formula is then designed to replace the intensities of noise pixels in VH-polarization with adjusted VV-polarization intensity pixels that are less affected by the noises. To verify the proposed method, the adaptive threshold method (ATM) with a sliding window was used for ship detection, and the results showed that the 74.39% of RFI false alarms are removed and 92.27% false alarms of azimuth smearing are removed.

• Journal of Ship and Ocean Technology
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• v.10 no.4
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• pp.12-23
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• 2006

In this paper, a numerical study is carried out to investigate the turbulent flow around a twin-skeg container ship model with rudders including propeller effects. A commercial CFD code, FLUENT is used with body forces distributed on the propeller disk to simulate the ship stem and wake flows with the propeller in operation. A multi-block, matching, structured grid system has been generated for the container ship hull with twin-skegs in consideration of rudders and body-force propeller disks. The RANS equations for incompressible fluid flows are solved numerically by using a finite volume method. For the turbulence closure, a Reynolds stress model is used in conjunction with a wall function. Computations are carried out for the bare hull as well as the hull with appendages of a twin-skeg container ship model. For the bare hull, the computational results are compared with experimental data and show generally a good agreement. For the hull with appendages, the changes of the stem flow by the rudders and the propellers have been analyzed based on the computed result since there is no experimental data available for comparison. It is found the flow incoming to the rudders has an angle of attack due to the influence of the skegs and thereby the hull surface pressure and the limiting streamlines are changed slightly by the rudders. The axial velocity of the propeller disk is found to be accelerated overall by about 35% due to the propeller operation with the rudders. The area and the magnitude of low pressure on the hull surface enlarge with the flow acceleration caused by the propeller. The propellers are found to have an effect on up to the position where the skeg begins. The propeller slipstream is disturbed strongly by the rudders and the flow is accelerated further and the transverse velocity vectors are weakened due to the flow rectifying effect of the rudder.

• Proceedings of the KSRS Conference
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• v.2
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• pp.946-949
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• 2006

With repeated coverage, spaceborne SAR (Synthetic Aperture Radar) instruments provide the most efficient means to monitor and study the changes in important elements of the marine environment. Due to highresolution of SAR data, the coverage of SAR sensor is always limited, especially for a repeat cycle. With more SAR sensors from various satellites, new data products such as ocean surface drift can be derived when two SARs' tracks overlap in a short time over coastal areas. Currently, there are two SAR sensors on different satellites with almost the exactly same path. That is, ERS-2 is following ENVISAT with a 30-minutes delay, which will be a good timing for ocean mesosclae feature tracking. For another application, a mystery ship near a big eddy with strong ship wake has been tracked between ERS-2 and ENVISAT SAR images to estimate its ship speed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.9
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• pp.889-895
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• 2012

A vertical launching system(VLS) is a system for holding and firing missiles on surface ships. When a missile is launched in VLS, relative motion between canister and missile and drag force induced by wind can cause initial unstability of a missile. Thus dynamic analysis of initial behavior of vertically launched missile should be performed to prevent collision with any structure of a ship. In this study, dynamic analyses of initial behavior of vertically launched missile are performed using Monte-Carlo simulation, which relys on random sampling and probabilistic distribution of variables. Each parameter related with dynamic behavior of a missile is modeled with probability variables and Recurdyn, a commercial software for multi body dynamic analysis, is used to perform Monte-Carlo simulation. As a result, initial behavior of a missile is evaluated with respect to various performance indexes in a probabilistic sense and sensitivity of the each parameters is calculated.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.187-193
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• 2011

In this report, We compared the actual test with the result of pow calculation and Resistance/Self-propulsion of the ship using STAR-CCM+ which is the commercial Reynolds Averaged Navier-Strokes(RANs) Solver. The calculation model was the KRISO Container Ship and 205K Bulk Carrier of Sungdong shipbuilding company. For this calculation, We used Realizable K-Epsilon model for flaw analysis, VOF method for the free surface creation, Moving Reference Frame method for reducing the POW calculation time, and Sliding Mesh method for Self-Propulsion analysis. Calculation of Resistance and Self-Propulsion includes the free-surface. And all calculations in this report were based on unstructured grids.

• Bulletin of the Society of Naval Architects of Korea
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• v.14 no.2
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• pp.1-9
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• 1977

Streamlines around a ship's hull can be calculated by using streamline tracing method replacing the ship section with distribution of singularity. The influence of frame lines on the stream surrounding a hull surface, however, can not be found. Jinnaka studied on streamlines for Lewis form by applying the slender body theory. The influence of frame lines on stream surrounding a hull surface is well found in Jinnaka's method. In this paper streamline calculation method for chine type has been developed by using conformal transformation and applying slender body theory as Jinnaka did. Three kinds of model-one of series 62 for chine type, V.L.C.C. and high speed craft built in Korea for Lewis form-were used for streamline calculation;

• Journal of Ship and Ocean Technology
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• v.10 no.4
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• pp.1-11
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• 2006

The finite volume based multi-block RANS code, WAVIS developed at MOERI is applied to the numerical self-propulsion test. WAVIS uses the cell-centered finite volume method for discretization of the governing equations. The realizable $k-{\epsilon}$ turbulence model with a wall function is employed for the turbulence closure. The free surface is captured with the two-phase level set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. The propeller forces are obtained using an unsteady lifting surface method based on potential flow theory. The numerical procedure followed the self-propulsion model experiment based on the 1978 ITTC performance prediction method. The self-propulsion point is obtained iteratively through balancing the propeller thrust, the ship hull resistance and towing force that is correction for Reynolds number difference between the model and full scale. The unsteady lifting surface code is also iterated until the propeller induced velocity is converged in order to obtain the propeller force. The self-propulsion characteristics such as thrust deduction, wake fraction, propeller efficiency, and hull efficiency are compared with the experimental data of the practical container ship. The present paper shows that hybrid RANS and potential flow based numerical method is promising to predict the self-propulsion parameters of practical ships as a useful tool for the hull form and propeller design.

• Journal of Ocean Engineering and Technology
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• v.25 no.4
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• pp.18-22
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• 2011

The Ranking source panel method was used to predict the flow phenomenon of a ship with a goose-neck type bulbous bow penetrating the free surface. The non-linearity of the free surface boundary condition was fully satisfied using an iterative calculation method, and the raised panel method was adopted to obtain a more stable solution at each iteration step. The panel cutting method was applied to generate a hull calculation grid at each iteration step, including the first step. At that time, the nose of the goose-neck type bulbous bow was divided by the free surface and the free surface panel was modified at each iteration step using the variable free surface panel method. Numerical calculations were performed to investigate the validity and efficiency of the applied numerical algorithm using the 3600 TEU container carrier. The computed wave resistance coefficients were compared with the experimentally achieved residual resistance coefficients.