Autonomous ships or Unmanned Surface Vehicles (USV) collision avoidance and path planning problems among multi-vessels are investigated in this paper. Firstly, a modified fuzzy dynamic risk of collision model based on time and space collision risk index is proposed, which is much closer to real ship applications. Then, the fitness functions based on the risk of collision, navigational economy, International Regulations for Preventing Collisions at Sea 1972 (COLREGs) and collision avoidance timing are established respectively to ensure the rationality of ship collision avoidance decisions. Moreover, path planning with global search capability is realized by the multi-objective decision theory combined with a genetic algorithm. The practicability and rationality of the recommended trajectory are guaranteed. Meanwhile, the problem of the non-inferior solution can be addressed by adapting the weight method and the constraint method and the optimized solution of the decision-making system can be achieved finally. Simulation results are further presented to validate the effectiveness of the proposed path planning and collision avoidance methods.
In order to solve the problem of ship's curve trajectory-tracking control, the Norrbin nonlinear response model which can accurately describe the ship's motion state is selected in this paper. The hyperbolic tangent function is used to design the expected hemispheric angle equation, then the complex track control is transformed into a heading control problem. The fast terminal sliding mode (FTSM) is introduced together with the Backstepping control technique to reduce the system adjustment time, eliminate the chattering. Bying combined with extended states observer (ESO) and dynamic surface control (DSC) technique, the internal and external disturbances in real-time can be estimated and compensated, and the "explosion of complexity" caused by backstepping technique is solved. The state of the control system is bounded and stable, and the system error converges to zero. Matlab simulation proves that the controller can realize the trajectory-tracking control quickly and accurately, and has strong robustness to external disturbances. INDEX TERMSFast terminal sliding mode; Extended states observer; Ship trajectory-tracking control; Robustness I.INTRODUCTION
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