• Journal of the Society of Naval Architects of Korea
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• 제54권2호
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• pp.113-124
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• 2017

Recently, ship owners are requiring an assessment of sailing safety of a ship from an analysis considering maneuverability and environmental loads etc. In this paper, we propose a new approach to assess sailing safety by considering the prescribed parameters. The concept of sailing safety is developed from DP capability analysis and is based on the maneuvering simulations. While the ship is continuously disturbed due to irregular environmental loads during the simulations, it is steered to keep its course along the way points assumed along a straight path. After relative distances between four edges of the ship and allowable safety boundaries are calculated for 3 hours, the minimum values are obtained. The minimum distances are marked on a polar chart and we call this a quantified safe operation judgment chart which indicates quantified sailing safety.

• Journal of the Korean Society of Marine Environment & Safety
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• 제22권1호
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• pp.129-137
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• 2016

In the present study we verified performance of feed-forward control algorithm using short term prediction of ship motion information by taking advantage of developed numerical simulation model of FPSO motion. Up until now, various studies have been conducted about thrust control and allocation for dynamic positioning systems maintaining positions of ships or marine structures in diverse sea environmental conditions. In the existing studies, however, the dynamic positioning systems consist of only feedback control gains using a motion of vessel derived from environmental loads such as current, wind and wave. This study addresses dynamic positioning systems which have feedforward control gain derived from forecasted value of a motion of vessel occurred by current, wind and wave force. In this study, the future motion of vessel is forecasted via Brown's Exponential Smoothing after calculating the vessel motion via a selected mathematical model, and the control force for maintaining the position and heading angle of a vessel is decided by the feedback controller and the feedforward controller using PID theory and forecasted vessel motion respectively. For the allocation of thrusts, the Lagrange Multiplier Method is exploited. By constructing a simulation code for a dynamic positioning system of FPSO, the performance of feedforward control system which has feedback controller and feedforward controller was assessed. According to the result of this study, in case of using feedforward control system, it shows smaller maximum thrust power than using conventional feedback control system.