Compared to an individual Autonomous Surface Vessel (ASV), greater efficiency and operational capability can be realized by a team of cooperative ASVs for certain operations, such as search and rescue, hydrographic survey and navigation assistance. This paper focuses on cooperative floating object transport, i.e., a group of ASVs coordinate their actions to transport floating objects. We propose a multi-layer distributed control structure for the object transport system. The object transport problem is formulated as the combination of several sub-problems: trajectory tracking of the object, control allocation, and formation tracking of the ASVs. The sub-problems are integrated by a nonlinear towline model that describe the transformation of forces considering the mass and elasticity of the towline. A controller based on Model Predictive Control (MPC) is designed to control the motion of each ASV. A negotiation framework based on the Alternating Direction of Multipliers Method (ADMM) is then proposed to achieve consensus among the ASVs. Numerical simulations of utilizing the proposed cooperative system to move a large vessel sailing inbound the Port of Rotterdam are carried out to show the effectiveness of our method. Besides transporting barges and off-shore platforms, the proposed cooperative object transport system could also be a solution to coordinate non-autonomous vessels and ASVs in future autonomous ports where both human-operated and autonomous vessels exist.
- Cooperative floating object transport
- Cooperative multi-vessel systems
- Distributed model predictive Control
- Formation control