• Journal of the Korean Institute of Navigation
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• v.13 no.2
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• pp.37-55
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• 1989

When a ship is sailing on the sea, she has the six-degrees of freedom of motion. It means that she meets a lot of dangerous situations. Especially, when the VLCC is travelling in irregular sea, the slamming, the deck-wetness and the propeller racing are occured with the sea state she is on. These are the representative steps that a heave-to and a scudding are used for a ship building , but for a predominance in both. The author intends to clarify this problem theoretically. The methods of statistical calculation are based with the ITTC spectral formulation and with the assumption that the wave height histogram follows the Rayleigh distribution. In this study, the author gives an attention on the relative bow motion to a wave in the irregular sea. It is verified that the relative diplacement at the bow to sea level in the following sea is less than that in the head sea. It is confirmed that, therefore, one have to sail with scudding when he is threatened to heave-to at a rough sea. But he must bear the propeller racing in mind in the cases.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.3
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• pp.740-753
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• 2023

Text recognition in natural scene images is a challenging problem in computer vision. The accurate identification of ship number characters can effectively improve the level of ship traffic management. However, due to the blurring caused by motion and text occlusion, the accuracy of ship number recognition is difficult to meet the actual requirements. To solve these problems, this paper proposes a dual-branch network based on the CRNN identification network. The network couples image restoration and character recognition. The CycleGAN module is used for blur restoration branch, and the Pix2pix module is used for character occlusion branch. The two are coupled to reduce the impact of image blur and occlusion. Input the recovered image into the text recognition branch to improve the recognition accuracy. After a lot of experiments, the model is robust and easy to train. Experiments on CTW datasets and real ship maps illustrate that our method can get more accurate results.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1404-1409
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• 2003

The sway control problem of the pendulum motion of the container crane hanging on the trolley, which transports containers from the container ship to the truck, is considered in this paper. In the container crane control problem, the main issue is to suppress the residual swing motion of the container at the end of the acceleration, deceleration or the case of that the unexpected disturbance input exists. For this problem, in general, the trolley motion control strategy is introduced and applied to real plants. In this paper, we suggest a new type of swing motion control system for a crane system in which a small auxiliary mass is installed on the spreader. The actuator reacting against the auxiliary mass applies inertial control forces to the spreader of the container crane to reduce the swing motion in the desired manner. In this paper, we consider that the length of the rope varies is we design the anti-sway control system based on LMI(linear matrix inequality) approach. And, it will be shown that the proposed control strategy is useful and it can be easily applicable to the real world. So, in this study, we investigate usefulness of the proposed anti-sway system and evaluate system performance from simulation and experimental studies.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.152-172
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• 1992

The ship sailing among waves are suffered the various wave loads that comes from its motion throughout its life. Because there are dynamic, the analysis of ship structure must be considered as the dynamic problem precisely. In the rationally-based design, the dynamic structural analysis is carried out using dynamic wave loads provided from the results of the ship mouton calculation as the rigid body. This method is based on the linear theory assumed low wave height and small amplitude of motion. But at the rough sea condition, high wave height, relatively ship's depth, is induced the large ship motion, so the ship section configulation below water line is rapidly changed at each time. This results in non-linear problem. Considering above situation in this paper, the strength analysis method is introduced for the hull glider among waves considering non-linear hydrodynamic forces. This paper considers that the overall or primary level of the ship structural dynamic loading and dynamic response provided from the non-linear wave forces, and bottom and bow flare impact forces estimated by momentum slamming theory, in which the ship is idealized as a hollow thin-walled box beam using thin-walled beam theory and the finite element method. This method is applied to 40,000 Ton Double-Skin Tanker and attention is paid to the influence of the response of ship speed, wave length and wave height compared with linear strip theory.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.38-47
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• 1992

The motion response of a ship moored in a rectangular harbor excited by long waves has been studied theoretically and experimentally. Within the framework of potential theory, matched asymptotic expansion techniques are exployed to analyze the problem. The fluid domain is divided into the ocean and the harbor regions for the analysis of wave response in a harbor without ship. The wave responses in both the ocean and the harbor sides are solved first independently in terms of Green's functions, which are the solutions of the Helmholtz equation satisfying appropriate boundary conditions. Slender body approximations are used to obtain the velocity jumps across the ship, which are associated with the symmetric motion modes of the ship. Unknowns contained in each solution are finally determined by matching at an intermediate zone between two neighboring regions. Theoretical results predict the ship motion qualitatively well. The main source of quantitative discrepancies is presumably due to real fluid effects such as separation at the harbor entrance and friction on harbor boundaries.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.3
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• pp.271-277
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• 2013

A novel approach to solve signal variation due to ship rocking in maritime wireless communication is introduced. We assume a ship-to-shore based communication scenario, where the transmitter is on shore and the receiver on the ship. Due to the ocean conditions, such as the presence of waves and wind etc. the ship is not stable and constantly experiences some form of rocking motion. This rocking motion causes the antenna on the ship to sway, creating instability in the signal reception. We envisage that the signal is offset at the receiver incurring high Bit Error Rate. This paper is to investigate and counter this problem by using Multiple-input Multiple-output (MIMO) technique. We propose to implement beamforming technique with multiple transmit antennas. The implementation of this proposed method crafts a robust maritime communication network.

• Journal of Ship and Ocean Technology
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• v.3 no.1
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• pp.1-11
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• 1999

Numerical simulation for the axisymmetric body with contractive and dilative periodic motion is carried out. The present analysis shows that a propulsive force can be obtained in highly viscous fluid by the contractive and dilative motion of axisymmetric body. An axisymmetric code is developed with unstructured grid system for the simulation of complicated motion and geometry. It is validated by comparing with the results of Stokes approximation with the problem of uniform flow past a sphere in low Reynolds number($R_n$ = 1). The validated code is applied to the simulation of contractive and dilative periodic motion of body whose results are quantitatively compared with the two dimensional case. The simulation is extended to the analysis of waving surface with projecting part for finding out the difference of hydrodynamics performance according to variation of waving surface configuration. The present study will be the basic research for the development of the propulsor of an axisymmetric micro-hydro-machine.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.191-192
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• 2003

A numerical method for a wave diffraction problem in three-dimensional channels is developed. The physical models are various shapes of channel connected to the open sea. When a ship or an offshore structure is moored in various configurations of channel connected to an open sea, the prediction of the hydrodynamic force exerting on the moored ship could be important for the prediction of its motion. It is assumed that the fluid is inviscid and incompressible and its motion is irrotational. From the continuity equation, the Laplace equation can be obtained as the governing equation. The surface tension at free surface is neglected, and wave amplitude is assumed to be small compared to the wave length. Then the free surface condition can be linearized. The numerical method used here is the localized finite element method based on a variational formulation

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.606-623
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• 2019

The path following problem of a ship sailing in restricted waters under wind effect is investigated based on Robust $H_{\infty}$ Guaranteed Cost Control (RHGCC). To design the controller, the ship maneuvering motion is modeled as a linear uncertain system with norm-bounded time-varying parametric uncertainty. To counteract the bank and wind effects, the integral of path error is augmented to the original system. Based on the extended linear uncertain system, sufficient conditions for existence of the RHGCC are given. To obtain an optimal robust $H_{\infty}$ guaranteed cost control law, a convex optimization problem with Linear Matrix Inequality (LMI) constraints is formulated, which minimizes the guaranteed cost of the close-loop system and mitigates the effect of external disturbance on the performance output. Numerical simulations have confirmed the effectiveness and robustness of the proposed control strategy for the path following goal of a ship sailing in restricted waters under wind effect.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.57-64
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• 2021

Maneuvering motions of a ship in calm water are studied through the concept of MMG model. Governing forces are defined by the use of available empirical formulae that require only main ship particulars as input variables. In order to validate the calculation tool, a full-scale sea experiment was carried out in Osaka Bay using a 17-m twin-screw passenger ferry. Test execution and data measurement were performed through the utilization of an autopilot control unit and satellite compass. The result of a straight running test confirms the acceptable accuracy in addressing the surge motion problem. Reasonable agreement between simulation and experiment is also confirmed for 5°/5° and 10°/10° zig-zag tests despite the strong environmental disturbance. The current model can generally represent the subject ship maneuvering motions and is promising for the application to other ship hulls.