Research On Nonlinear Model Predictive Control For Dynamic Positioning Ship

With the gradual extension of Marine engineering to the deep sea,the application of dynamic positioning system in Marine engineering is becoming more and more extensive,and it is very urgent and necessary to research Dynamic Positioning technology.Focus on ship Dynamic Positioning system,the dissertation research the problem of Dynamic Positioning ship six-DOF manoeuvring motion mathematical model and Dynamic Positioning control algorithm by the method of MMG separate modeling idea and nonlinear model predictive control.This research work includes the following 4 key aspects:Firstly,the characteristics of multi-propellers multi-rudders Dynamic Positioning ship with low speed and large drift angle motion is considered,which is easily affected by the marine environmental disturbance.A six-DOF motion maneuvering mathematical model of DP ship is proposed based on the separate modeling idea.The model takes full account of the multi quadrant working conditions of the variable pitch propeller,the irregular wind disturbance and the short peak irregular wave disturbance in the marine environment.Circle turning test,stopping test and lateral thruster test are carried out on a deep DP tug vessel.Simulation results show that the model satisfies the precision requirement of DP system testing simulation platform and ship DP simulator.Secondly,the nonlinear control problem of Dynamic Positioning ship subject to input and input rate saturation under time-varying disturbances is considered.The linearized ship motion mathermatic model is used as predictive control.Model predictive control algorithm for dynamic positioning ship is proposed with an integrator.Furthermore,to solve the control problem that the dynamic positioning ship is a complex nonlinear system,and the linear model predictive control algorithm is easily divergent,ship Dynamic Positioning nonlinear model predictive control algorithm based on exact feedback linearization is proposed.A new linear system is transformed from the old nonlinear system by the exact feedback linearization method.And the nonlinear constraint problem is solved by sequential quadratic programming.Simulation results on a DP supply vessel show that the proposed control algorithm can overcome the marine environment unknown time-varying disturbance and force the vessel reach and keep the desired position and heading under the input and input rate saturation.Thirdly,to solve the real time control problem of that nonlinear large amount of computation online of the original model predictive control algorithm,a novel and fast nonlinear model predictive control algorithm for Dynamic Positioning ship is improved based on Laguerre function.The proposed nonlinear control algorithm is low time-cost by introducing the Laguerre function to describe the feedback linearization system input increments,to reduce the matrix dimension of nonlinear optimization problem.Simulation results on a DP supply vessel shows that the novel algorithm keep the good control performance of the origin nonlinear model predictive control algorithm,and its compute load is reduced to satisfy the requirement of real time running.Finally,as for the needs of the different stages the system testing before the application of the dynamic positioning system,and the shortcomings of ship Dynamic Positioning system tests on sea trials or model trial which features high risk,long debugging period and high expense,two testing simulation system is developed.A testing simulation platform for Dynamic Positioning control algorithm testing,which adopts multi-thread technology,3D graphics technology and computer network technology.The platform software is easy to use whose user interface is friendly.Moreover,based on the marine simulator and six-DOF motion maneuvering mathematical model of DP ship,A Hardware-in-closed-loop testing simulation system for Dynamic Positioning control system is developed.The system is connected to the real Dynamic Positioning control system from Nederland,which verifies the validation of the simulation system.In this thesis,mathematic model of Dynamic Positioning ship and ship Dynamic Positioning control algorithm are studied,which has the practical significance of improve control accuracy of Dynamic Positioning system,and promoting the development of marine engineering equipment.That would provide the theoretical basis for developing Green marine economy.