| Summary: | In order to sail safely in a marine environment with neighboring obstacles, a local collision avoidance algorithm based on a steering maneuver considering International Regulations for Preventing Collisions at Sea (COLREGs) is proposed for unmanned surface vehicles (USVs). In this paper, the algorithm consists of three parts: collision risk assessment, steering occasion determination, and navigation waypoint update. The collision risk assessment is used to judge a collision risk based on an analytical feasible angle interval by the closest point of approach method. The steering occasion determination provides a safe distance interval from an obstacle by analyzing a marginal steering angular velocity. The navigation waypoint update generates a temporary waypoint to navigate the USV and considers the overtaking, head-on, and crossing rules of COLREGs. The temporary waypoint is calculated based on a real-time optimal orientation angle, which is determined by an optimization objective function for angle deviation. The three parts for local collision avoidance are determined by a finite state machine. In simulations, a USV with actual dynamic constraints runs successfully in a static and dynamic multiobstacle environment, and the results indicate the feasibility and validity of the proposed algorithm.
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