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Ship Collision Avoidance by Distributed Tabu Search

Kim D., Hirayama K., Okimoto M.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

2015

Vol. 9, no. 1

23--29

More than 90% of world trade is transported by sea. The size and speed of ships is rapidly increasing in order to boost economic efficiency. If ships collide, the damage and cost can be astronomical. It is very difficult for officers to ascertain routes that will avoid collisions, especially when multiple ships travel the same waters. There are several ways to prevent ship collisions, such as lookouts, radar, and VHF radio. More advanced methodologies, such as ship domain, fuzzy theory, and genetic algorithm, have been proposed. These methods work well in one-on-one situations, but are more difficult to apply in multiple-ship situations. Therefore, we proposed the Distributed Local Search Algorithm (DLSA) to avoid ship collisions as a precedent study. DLSA is a distributed algorithm in which multiple ships communicate with each other within a certain area. DLSA computes collision risk based on the information received from neighboring ships. However, DLSA suffers from Quasi-Local Minimum (QLM), which prevents a ship from changing course even when a collision risk arises. In our study, we developed the Distributed Tabu Search Algorithm (DTSA). DTSA uses a tabu list to escape from QLM that also exploits a modified cost function and enlarged domain of next-intended courses to increase its efficiency. We conducted experiments to compare the performance of DLSA and DTSA. The results showed that DTSA outperformed DLSA.

Electrooxidative Conversion of Dibenzoylbenzene Dihydrazones into the Coreesponding Bis-Diazo Compounds and Bis-Dimethyl Acetals

Okimoto M., Numata K., Takahashi Y.

Polish Journal of Chemistry

2005

Vol. 79 / nr 9

1477-1482

Several dibenzoylbenzene dihydrazones were electrochemically oxidized into the corresponding bis-dimethyl acetals in a methanolic solution containing sodium methoxide and catalytic amount of KI. During electrolysis, the anolyte exhibited a characteristic deep purple, which strongly suggested that formation of a diazo compound as an intermediate. Interestingly, some of the diazo compounds could be isolated directly from the anolyte