• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1155-1160
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• 2005

In order to evaluate the safety of navigation at sea and the safety of mooring ship on berthing, it is necessary that the wave and wind induced ship dynamic motion should be measured in real time domain for the validity of theoretical evaluation method such as sea-keeping performance and safety of mooring. In this paper, the basic design of sensors is discussed and some system configurations were shown. The developed system mainly consists of 4 kinds of sensors such as three dimensional accelerator, two dimensional tilt sensor, two displacement sensors and azimuth sensor. Using the this measuring system, it can be obtained the 6 degrees of freedom of ship dynamic motions at sea and on berthing such as rolling, pitching, yawing, sway, heave, surge under the external forces.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.1
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• pp.38-52
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• 2016

This paper describes the nonlinear dynamic motion behavior of a ship equipped with a portable dynamic positioning (DP) control system, under external forces. The waves, current, wind, and drifting forces were considered in the calculations. A self-tuning controller based on a neuro-fuzzy algorithm was used to control the rotation speed of the outboard thrusters for the optimal adjustment of the ship position and heading and for path tracking. Time-domain simulations for ship motion with six degrees of freedom with the DP system were performed using the fourth-order RungeeKutta method. The results showed that the path and heading deviations were within acceptable ranges for the control method used. The portable DP system is a practical alternative for ships lacking professional DP facilities.

• Journal of Navigation and Port Research
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• v.29 no.1 s.97
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• pp.9-15
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• 2005

To design ship channel is one of important factors for planning and developing a port. In most case, the core factors for designing ship channel are the layout and width of channel provided the net underkeel clearance is secured to be safe enough to pass. In this study, Variable Bumper Area(VBA) model is applied to design and assess ship channel. This model reflects ship's particular, ship domain theory, ship speed and mariner's ship handling skill and experience, especially external forces which cause leeway, set and drift and the change of ship maneuvering characteristics. A real time, full mission shiphandling simulator is used to analyze ship dynamic data according to mariner's ship control, external forces, ete. This model defines Domain degree and Domain-index for assessing the efficiency and safety of the channel. The proposed model is applied to Ulsan new port plan which has a channel width of 1.5 times the length of the largest vessel, a radius of 5 times the length of the largest vessel in a curve of 57 degree centerline angle and SBM facility adjacent to the lateral edge of channel. The result of this study shows that the width of the channel and radius of channel curve are suitable for the target ship but the difficulty of ship handling is caused by the large course change and SBM located in the vicinity of channel.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.1
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• pp.37-47
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• 2018

Dynamic simulation is critical for electrical ship studies as it obtains the necessary information to capture and characterize system performance over the range of system operations and dynamic events such as disturbances or contingencies. However, modeling and simulation of the interactive electrical and mechanical dynamics involves setting up and solving system equations in time-domain that is typically time consuming and computationally expensive. Accurate assessment of system dynamic behaviors of interest without excessive computational overhead has become a serious concern and challenge for practical application of electrical ship design, analysis, optimization and control. This paper aims to develop a systematic approach to classify the sophisticated dynamic phenomenon encountered in electrical ship modeling and simulation practices based on the design intention and the time scale of interest. Then a novel, comprehensive, coherent, and end-to-end mathematical modeling and simulation approach has been developed for the latest Medium Voltage Direct Current (MVDC) Shipboard Power System (SPS) with the objective to effectively and efficiently capture the system behavior for ship-wide system-level studies. The accuracy and computation efficiency of the proposed approach has been evaluated and validated within the time frame of interest in the cast studies. The significance and the potential application of the proposed modeling and simulation approach are also discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.718-724
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• 2017

Considerable efforts have been made to expand the boundaries of domestic offshore plant industries, which have focused on the construction of the structures, to the engineering field. On the other hand, time domain analysis, which is one of the most important areas in designing floating offshore plants, relies mainly on the information given by foreign companies. As an early design of the Dynamic Positioning System (DPS) is mostly conducted by several specialized companies, domestic ship builders need to spend time and money to reflect the analysis into the hull shape design. This paper presents the framework required to analyze time domain performance of floating type offshore structures, which are equipped with DPS. To easily perform time domain analysis, framework generates the required input data for the solver, and is modularized to test the control algorithm and performance of a certain DPS. The effectiveness of the developed framework was verified by a simulation with a model ship and the total time for the entire analysis work was reduced by 50% or more.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.36-42
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• 2018

This paper considers the Marine Traffic Risk Assessment for fixed and moving targets, which threaten officers during a voyage. The Collision Risk Assessment Formula was calculated based on a dynamic ship domain considering the length, speed and maneuvering capability of a vessel. In particular, the Navigation Risk Assessment Model that is used to quantitatively index the effect of a ship's size, speed, etc. has been reviewed and improved using a hybrid combination of a vessel's dynamic area and the Collision Risk Assessment Formula. Accordingly, a new type of Marine Traffic Risk Assessment Model has been suggested giving consideration to the Speed Length Ratio, which was not sufficiently reflected in the existing Risk Assessment Model. The larger the Speed Length Ratio (dimensionless speed), the higher the CJ value. That is, the CJ value is presented well by the Speed Length Ratio. When the Speed Length Ratio is large, states ranging from [Caution], [Warning], [Dangerous] or [Very Dangerous] are presented from a greater distance than when the Speed Length Ratio is small. The results of this study, can be used for route and port development, including dangerous route avoidance, optimum route planning, breakwater width, bridge span, etc. as well as the development of costal navigation safety charts. This research is also applicable for the selection of optimum ship routing and the prevention of collisions for smart ships such as autonomous vessels.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.77-81
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• 2009

The radar cross section (RCS) of a warship is one of the most important design features in terms of her survivability in hostile environments. Ocean waves continuously changes the attitude of an objective warship to hostile radar and distorts the RCS as a result. This paper presents a dynamic RCS analysis technique and procedure that considers temporal ship motion. First, data sets are prepared for ship motions in 6 degrees of freedom, which are numerically simulated for an objective warship via frequency to time domain conversion with response amplitude operators and specified ocean wave spectra. Second, a series of RCS analysis models are transformed geometrically by referring to ship motion data sets. Finally, temporal RCS analyses are carried out with the RCS simulation code, SYSCOS. As an example, RCS analysis results are given for a virtual warship, which show that ship motions temporally change RCS values and cause RCS reduction compared with static value in terms of mean values.

• Ocean Systems Engineering
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• v.5 no.3
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• pp.199-220
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• 2015

The paper described the nonlinear dynamic motion behavior of a barge equipped with the portable outboard Dynamic Positioning(DP) control system in short-crested waves. The DP system based on the fuzzy theory is applied to control the thrusters to optimally adjust the ship position and heading in waves. In addition to the short-crested waves, the current, wind and nonlinear drifting force are also included in the calculations. The time domain simulations for the six degrees of freedom motions of the barge with the DP system are solved by the $4^{th}$ order Runge-Kutta method. The results show that the position and heading deviations are limited within acceptable ranges based on the present control method. When the dynamic positioning missions are needed, the technique of the alternative portable DP system developed here can serve as a practical tool to assist those ships without equipping with the DP facility.

• Ocean Systems Engineering
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• v.1 no.3
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• pp.249-261
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• 2011

The stochastic nonlinear dynamic behavior and probability density function of ship rolling are studied using the nonlinear dynamical systems approach and probability theory. The probability density function of the rolling response is evaluated through solving the Fokker Planck Equation using the path integral method based on a Gauss-Legendre interpolation scheme. The time-dependent probability of ship rolling restricted to within the safe domain is provided and capsizing is investigated from the probability point of view. The random differential equation of ships' rolling motion is established considering the nonlinear damping, nonlinear restoring moment, white noise and colored noise wave excitation.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.1 s.145
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• pp.1-14
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• 2006

To improve maritime safety, it is very important not only to make safer design and operation but also to do proper response in case of maritime casualty. The large-scaled casualties will be caused by loss of structural strength and stability due to the progressive flooding and enlargement of damage by the effect of waves and wind. To prevent foundering and structural failure, the prediction of ship motion behavior of damaged ship in wave is necessary. This paper describes the motion behavior of damaged ship in waves through theoretical and experimental studies. A time domain theoretical model of damaged ship motions and accidental flooding, which can be applied to any type of ship or arrangement and considers the effects of flooding of compartments, has been developed. The model tests have been carried out in regular and irregular waves with different wave heights and directions in ship motion basin. Those were performed for three different damaged conditions such as engine room bottom damage, side shell damage and bow visor damage of a Ro-Ro ship. Comparison of theoretical and experimental results was performed.