Research On Ship Dynamic Positioning With The Unknown Upper Bound Of Ocean Environment Disturbances

With the development and exploration of ocean resources,people started to focus on the resourceful ocean more and more passionately,the pace is getting faster and faster,to make the marine equipment and marine engineering technology develop rapidly.Therefore,Dynamic Positioning System,as a high-tech marine equipment,plays an importantrole in accelerating the development of deep-sea equipment.This papertakesa dynamic positioning ship with known Mathematical model parameters as the object of study.Inthe presence of known and unkown disturbances,a series ofstate feedback studies inDynamic positioning control are carried outsystematically by dynamic surface control technology,adaptive control approaches.The research work includes the following points:First of all,in order to describe the state of a ship’s motion,we employa6-DOFmodel,which is divided intoa 3-DOF kinematics model of ship and a 3-DOF dynamics model of ship.According to the effect of marine environmental forces on ship motion,models of sea wind,sea wave and sea current are established separately.The parameters of the ship model used in the method validation are given,and the basic maneuverability simulation of the ship model is established.Secondly,according to the time-varying disturbance and known bounds of marine environmental forces,a control law for dynamic ship positioning wasdevelopedbyconstructing two steps of Lyapunov function based on the Backstepping method,and the global stability control is achieved.Meanwhilein the presence of unknown bounds,the control law is described through the introduction of the evaluation signal,and meets the standard gain of L₂ norm with all signals uniformly ultimately bounded.In the end,the simulation studies are carried out respectively byutilizing Matlab/Simulink toolboxso as to verify the effectiveness of the robust designs,which are mentioned above.Finally,adaptive robust control laws are proposed for a dynamic position shipwith known shipparameters,combining dynamic surface control with Backstepping methodwith the time-varying disturbance and known bounds of marine environmental forces.Owing to theintroduction of afirst-order low-pass filter,the nonlinear control law,which is proposed by derivation,turns the differentiation of virtual control vector into a simple algebraic calculation.Therefore the state feedback control of dynamic positioning ship is designed based on the dynamic surface method,and the control law is easier to be realized in practical engineering.Meanwhilein the presence of unknown bounds,the design of dynamic surface control law is carried on by introducing a parameter adaptive law with a modified leakage term,andall the signals in the closed-loop system are uniformly ultimately bounded by the Lyapunov function.Finally,the simulation studies are carried out respectively byutilizing Matlab/Simulink toolboxso as to verify the effectiveness of the robust designs,which are mentioned above.