Research On Nonlinear Automatic Berthing Control Of Underactuated Surface Vessels

In navigational practice,most marine surface vessels are underactuated vessels equipped with only propellers and rudders.Underactuated control can design backup controllers for fully-actuated vessels,which is of great significance to improve maritime navigation safety and shipping economy.In addition,the port environment becomes crowded and complex with the increasing vessels,coupled with the external environment disturbance,the risks of vessels berthing and unberthing increased.Therefore,the research of underactuated vessel berthing control algorithm has important practical significance for further improving the berthing efficiency and ensuring berthing safety.The following research works are carried out in this paper.Firstly,a mathematical model of underactuated vessel motion is established,and the mathematical model of three degree-of-freedom(3 DOF)underactuated vessel motion is obtained through analyzing the motion characteristics of vessels and simplifying the motion model.Then,the differential homeomorphism transformation and coordinate transformation are introduced to solve the underactuated problem of the vessel model.Further,the control system is transformed into a chain structure system with general nonlinear characteristics,based on which the subsequent controllers are designed.Secondly,a concise backstepping automatic berthing controller is designed based on the transformed vessel model by utilizing backstepping method and Lyapunov direct method.The designed controller has a simple structure and is easy to implement in engineering.Thirdly,model uncertainties and external disturbances being taken into consideration,an adaptive neural networks automatic berthing controller of underactuated vessel is designed based on radial basis function neural network(RBF NN)and minimum learning parameter(MLP)technology.The designed controller can not only ensure all signals of the closed-loop control system bound,but also reduce the online estimation parameters of the neural network and further improve the performance of the berthing control system.Finally,in the berthing practice,the excessive yaw velocity of the vessel in the restricted water will lead to the problem of berthing insecurity and instability.To solve the above problem,an automatic berthing controller considering the yaw velocity limitation is designed by using the obstacle Lyapunov function(BLF)method and dynamic surface control(DSC)technology.The designed controller can make the yaw velocity of the control system bounded and stable within the constraint boundary.Further,the safety of the vessel berthing is improved.To verify the effectiveness of the above proposed automatic berthing control strategies,simulations are carried out on a vessel model as the simulation object by utilizing the MATLAB.Simulation comparisons show that the proposed automatic berthing controller can solve the automatic berthing control problem of underactuated vessels subject to uncertainties,external disturbances and limited yaw angular velocity.This research has important significance for improving the berthing safety and lays a theoretical foundation for berthing practice.