Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
collision risk. It can not, however, propose an optimal trajectory to avoid collison (Lazarowska, 2014: 1013).
Planning a safe trajectory at sea comprises a complex process which should include precision and optimality (Lazarowska, 2017: 469). Controlling a ship safely depends on a number of factors such as the speed and course of the ships, the distance between them, maneuverabilty, their size, and the feature of the trajectory (Grinyak, 2016: 249).
Although many methods have been proposed, the problem has not been so far completely solved. Because of the complexity of the problem, it is difficult to form a definite solution regarding all of the constraints and demands, illustrated in Figure 1, such as weather condition, maneuveribility of ships, static obstacle, multi-ship encounter, dynamic particulars of ships, etc (Lazarowska, 2016: 1024).
Figure 2. Diagram for encounter situation at sea
Figure 1. Restrictions regarding a ship’s safe trajectory process. Source: Lazarowska, 2016: 1024
In case of an encounter situation at sea, ships are obliged to obey COLREGs defined by the International Maritime Organization (IMO). The situations are classified by COLREGs as head-on, crossing and overtaking which is illustrated in Figure 2. The role of ships to avoid collison for each situation is determined by COLREGs through Rule 13 to Rule 17. Rule 13 (Overtaking) states that any vessel overtaking any other shall keep out of the way of the vessel being overtaken. Rule 14 (Head-on) defines that when two power-driven vessels are meeting on reciprocal or nearly reiprocal courses so as to involve risk of collision each shall alter her course to starboard so that each shall pass on the port side of the other. Rule 15 (Crossing) makes it clear that when two power driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel. Rule 16 (Give-way vessel) orders that every vessel which is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to avoid collison. Rule 17 (Stand-on vessel) demands that where one of two vessels is to keep out of the way the other shall keep her course and speed.
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In this study, unlike the studies in related literature, a Web- Based Deterministic Algorithm (WBDA) to solve encounter situation at sea has been introduced in compliance with the general requirements of COLREGs. The proposed system allows the own ship (OS) to change her course in a deterministic manner to avoid collision optimally. It guarantees that the global optimum is revealed. The study is restricted to one-to-one ship encounter situation because of the nature of COLREGs. The developed system is a guidance system, which contributes to navigator decision-making capability. It can be integrated into any autonomous system like an Unmanned Surface Vehicle (USV). It is believed that the presented approach provides guidance to navigators on the decision-making process and constitutes a valuable contribution to intelligent marine systems.
The remaining sections of the paper are organized as follows: section II introduces and discusses related studies in the literature, section III gives information about the methodology and model description of the developed system including the framework and terminology, and section IV provides experimental test results and findings which indicate the efficiency of the method. The conclusion is also presented at the end of the paper.
2. LITERATURE REVIEW
The ship collision avoidance problem has attracted quite interest of researchers by means of the technological development (Tam and Bucknall, 2013: 25). On the other hand, the increase of marine traffic density has led to research to find out the new solutions to the problem (Szlapczynska and Szlapczynski, 2017: 591).
Many studies have been proposed through the years to solve collision avoidance trajectory planning. These studies have been reviewed and discussed with different frameworks by Tam et al. (2009), Statheros et al. (2008) and Fışkın et al. (2018). On the other hand, some studies recently introduced are as follows:
©2019: The Royal Institution of Naval Architects
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