ABSTRACT

The authors propose algorithm for the automatic track keeping algorithm using fuzzy inference to realize a realistic operation in this paper. Cross track error, heading angle and yaw rate were considered for rudder control. An appropriate timing or point for using rudder was derived from an angle of course change. Numerical simulations with wind and current were carried out to verify the effectiveness of the proposed system. The results show that the algorithm has a good performance for ship track keeping.

INTRODUCTION

The purposes of automatic navigation are to ensure safe navigation and to implement economical operation. Accurately following the desired track, it makes possible to minimize energy loss during operation and reach a destination in a short time. It also contributes to reduce maritime accidents such as collisions or groundings at sea. Therefore, an automatic track keeping system has been considered as one of important functions comprised in an automatic navigation system. The work of determining a desired track and guiding a ship to follow the desired track has been carried out depending on the experience and knowledge of ship operators. Generally, ship operators set up waypoints consisting of a path to be taken for safe navigation in consideration of environmental condition and other ships or obstacles surrounding own ship. When a ship changes her course near the waypoints, the ship deviates from the desired track if the ship does not use a rudder at proper timing or point.

Therefore, researches related to track keeping system including a rudder control have been conducted in order to follow the desired track consisting of waypoints precisely. LOS (Line-of-Sight) guidance algorithm has been widely applied to decrease cross track error (Fossen et al., 2003; Velasco et al., 2008; Lekkas and Fossen, 2013; Guo et al., 2015) and there are studies on a waypoint switching system to determine a timing to use rudder so as to change course appropriately (Mcgookin et al., 2000; Velagic et al., 2003). However, LOS guidance algorithm needs to create LOS set points additionally, which are two intersection points between a circle with certain radius around the ship and a straight track defined by two waypoints. Even though operators of ships generally use rudder angle less than 10 degrees to prevent accidents during changing course due to large roll motion induced by taking large rudder angle, most of past researches have not taken the maximum rudder angle into account when they design automatic track keeping systems.

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