COLREGS-Compliant collision avoidance for physically coupled multi-vessel systems with distributed MPC

This paper proposes a distributed control scheme for autonomous tugboats to tow a ship in a restricted water traffic environment ensuring collision avoidance while being compliant with maritime regulation called COLREGS. The complex problem is cooperatively solved by addressing three sub-optimization problems. The first is to optimize the towing forces and angles for solving ship waypoint following and collision avoidance problems. The second is to optimize the tug thruster forces and moment for solving the tug online trajectory tracking and collision avoidance problems. The third is to optimize the Lagrange Multipliers for solving the consensus problem between the ship and tugs. The distributed control architecture follows the Model Predictive Control (MPC) strategy using the Altering Direction Method of Multipliers (ADMM). Simulation experiments indicate that the proposed control scheme can deal with static and dynamic obstacles in restricted waterways for a physically interconnected multi-vessel system executing the towing process, and the collision avoidance complies with COLREGS rules.