Trajectory planning for unmanned surface vehicles in multi-ship encounter situations

Abstract

Unmanned surface vehicles (USVs) can encounter traffic ships while navigating toward the target location. For the USVs, collision avoidance (CA) trajectories need to be planned according to the international regulations for preventing collisions at sea (COLREGS). A novel trajectory planning approach is proposed for the collision-free trajectories planning of USVs in the case of multiship encounters. Unlike the existing trajectory planning approaches, the proposed approach uses the holistic thinking to simplify the analysis of encounter situations. Ships approaching from all sides of the USV are treated as one or two equivalent obstacles based on consistent offset velocity direction (COVD) method. Furthermore, planned velocity is designed using the proposed CA strategy and kinematic constraints. This strategy is compliant with COLREGS and includes an emergency CA module to further ensure a safe distance between the USV and traffic ships. The performance of the proposed trajectory planning approach is verified through physical simulations using an existing simulator. The simulation results show that the proposed trajectory planning approach can implement multiple USVs to simultaneously avoid collisions and reach their respective target positions. Moreover, the approach remains effective when other USVs do not follow the COLREGS protocols.