Study On Ship Collision Risk Assessment And Anti-Collision Decision Making Methodology

Maritime transportation plays a significant role in international trade system. The safety of ships during navigation and operation is one of the most important preconditions. Many types of accident like ship collisions and groundings often result in great economic loss, fatalities and the environmental contamination. Consequently, maritime risk assessment is one of the most important focus areas for waterway transportation. A lot of attentions have been paid to the risky areas where traffic density is high for a long time. The areas include gulfs, straits, ports, busy waterways and so on. In a lot of maritime risk assessment, the subjective opinions from experts in relevant domains can be an effective complement in the scarcity of historic data. How to make assessment by combining historic data with expert opinions has been one of the most concerns for researchers. What’s.more, as one of the most common types of accident, collision risk assessment and intelligent anti-collision decision-making are also important topics in maritime transportation. The research of this thesis mainly focuses on the above topics, and the results are as follows:(1) A novel method called Generalized Belief Rule Base (G-BRB) was proposed by making differential treatment for subjective knowledge from different experts, which the traditional method treats them equally. G-BRB can get the final result by combining expert opinions with historical data. The proposed method was further used into collision risk assessment. The indicators were first divided into two parts, namely safety situation and emerging resource cost. Safety was evaluated by accident/incident, distress and death/missing toll while emerging resourcecost was evaluated by salvage and other vessels’assistance. The proposed G-BRB was used to make inference to get the final result. The proposed method was then compared with traditional BRB and Bayes Belief Network (BBN) as well as sensitivity analysis. The results show that the proposed method has higher precision and reliability.(2) A quantitative anti-collision decision making evaluation model called spatial-temporal forensic in collision situation was proposed. The model makes evaluation both in the dimension of space and time. The spatial gain was measured by the distance and DCPA between two ships and the temporal gain was measured by the TCPA between two ships. The D-S theory was then used to combine spatial and temporal gain to get the final evaluation at each time point. Furthermore, the sensitivity and reliability analysis were carried out by changing relevant curves used in the model.(3) Ship anti-collision under the COLREGs based on the maneuverability model was discussed and further studied. The study took all encounter situations into account and obtained the minimum distance required for two encountering ships to maintain clearance of each other under normal situations and critical situations respectively. The results obtained in this paper are also used to compare the proposed model with the traditional anti-collision parameters such as the TCPA and the DCPA. The results show that assessing the collision risk by only the TCPA and the DCPA is quite likely to mislead navigators to take action too late to avoid collision. Therefore, the minimum distances required under both normal situations and critical situations obtained in this paper are necessary for navigators to make wise decisions. At last, three typical encounter situations were used to do case studies. The results show that the two ships can avoid collision successfully within required distance by taking right actions(4) Multi-ship anti-collision problem is studied in a distributed and real time way in this paper. The decision making procedure is carried in a distribute way under the requirements of COLREGs and all the involved ships make decision by their own judgments by treating itself as "Own Ship (OS)" and all the other ships as "Target Ships (TSs)". Both course and speed changing are considered according to the encounter situations. In the model, not only the situation that all the involved ships are complied with requirements from COLREGs is considered, but also the decision making for stand-on ship given that the give-way ship violates the rules is studied. The simulation results show that the proposed procedure can avoided successfully even when some ships did not undertake their responsibilities. The study also draws the following conclusions:(i) Most of the anti-collision operations are carried out by single operation, even in multi-ship encounter situations. What’s more, it is not possible that a ship changes course and speed simultaneously,(ii) Some conflicts between ships’ operations may happen sometimes when they make decisions in a distributive mode. Real-time communication and cooperation among them is very important for collision avoidance,(iii) Turning port side is not advisable for ships to avoid collision according to COLREGs, unless in extreme situations.