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Formation Control Method for Multiple Tugboats Assisting Large Ship Operations

At present, due to the poor rudder efficiency of the underactuated large ships during low-speed maneuvering, tugboats assistance has become an integral part of their operations. However, it is difficult to control multiple tugboats manually, applying formation control technology to multiple tugboats control is a desirable solution. In this paper, we first constructed a mathematical model of the interaction between the ship and the tugboats, thrust allocation problem was solved by using a sequential quadratic programming algorithm (SQP) to determining the thrust and direction of each tugboat. We considered the formation control problem of tugboats moving in a leader-follower formation, In the presence of uncertain tugboat model parameters, an adaptive backstepping terminal sliding mode controller was designed using the radial basis function neural network (RBFNN) to fit their uncertain parameters, the allocated thrusts and directions as the inputs to be tracked by each tugboat. We also conduct a Lyapunov stability analysis to show that the errors are globally asymptotically stable. The simulation results reveal that the proposed method of tugboats formation to assist large boat operations is effective.