Journal of the Kansai Society of Naval Architects, Japan

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For the ultra automatic ship operating system, collision avoidance system is one of the most difficult problems. Usually highly experienced experts such as captains etc. can make a suitable decision considering various environmental conditions. The authors propose an automatic collision avoidance system controlled by an on-board computer. The system contains of the following four parts; data acquisition from radar signal, decision of the collision risk, speed or course change command and course control autopilot. All parts except data acquisition are done by fuzzy reasoning or fuzzy control. Fuzzy control is quite similar to the human control and so flexible even to unexpected environmental changes. First, system design is done and algorithms of each sub-system are described. It is not necessary to apply fuzzy control for course keeping and course changing, but we dare to apply it. Fuzzy control autopilot is very smooth and at the same time very quick for an abrupt course change. Computer simulation is done for the various relative conditions of a target ship and the results are found to be reasonable and reliable as compared with human behaviour carried out at out ship handling simulator. At last, the system is also applied to the collision avoidance very close to the course changing point or with conflicting behaviours of a target ship. For both cases, the system is found to be worked properly.

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The intact stability of a ship travelling in following or quartering seas differs significantly from that in still water, In general, the stability of a ship is reduced when the ship is located at the wave crest, but it is increased when the ship is situated at the wave trough. In this paper, theoretical and experimental analyses have been carried out for the change of stability of a ship in quartering seas. The theoretical explanation of the change of intact stability is described based on the Froude-krylov hypothesis and the predicted righting arm in a quartering sea is compared with the experiments. Agreement between them is satisfactory.

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The behabiour of a ship in the River Tyne near the Western By-pass bridge has been simulated, assuming that the ship has lost control and is under the influence of wind, current and also hydrodynamic forces and moments. The worst possible cases of collision have been considered. It has been found that the ship can hit the pier with its bow, stern or side at any angle from zero to 180 degrees. The kinetic energy lost in the collision and both the impact forces and moments acting on the pier have been calculated for each case to find the maximum values.

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Theoretical and experimental studies were carried out on perfect absorption of regular waves using the terminal device. The device consists of the buoy and the external mechanism. It can give the optimum force acting on the buoy for absorbing regular waves by operating coefficient dials of the force. Theoretical consideration on the mirror image buoy and external mechanism system mentioned above shows that only the symmetrical wave component exists in regular diffraction wave, therefore it is possible to cancel it by the radiation wave generated by heaving motion of the buoy. As the results, perfect absorption of regular waves can realized. Agreement between experimental results and calculated one is fairly good. Wave absorbing coefficient of the device in regular waves is almost 100%.

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