Research On Thrust Allocation And Path Following Control Of Variable Rotation Center Of Dynamic Positioning Pipelaying Vessel

For the laying of marine pipelines,especially in deep-water areas and areas with severe sea conditions,requirements for path planning,guidance,position control,attitude maintenance,and path following control capabilities of dynamic positioning(DP)pipelaying vessels are higher.At the same time,in order to meet the laying requirements of various marine pipelines,the position of the motion control point(also known as the variable rotation center)of the DP pipelaying vessel is mobile,which can be located at the moon pool,at the stern of the ship,or at the pipe releasing point.When that position changes,the propulsion system layout matrix and the thrust distribution constraint matrix of the vessel will also change.Therefore,it is necessary to develop an integrated DP control system that can achieve autonomous analysis,planning,guidance,and motion control of the expected pipe-laying path according to the requirements of marine pipe-laying operations.Meanwhile,it is of great engineering value and theoretical significance to study the thrust allocation algorithm adapted to the variable rotation center.First,a three-degree-of-freedom(3-DOF)maneuvering model for conventional surface ships and the marine environmental force model including wind,wave and current are established.And a catenary theory is used to approximately calculate the pipeline tension.Then based on the general 3-DOF maneuvering model for vessel,a 3-DOF motion model of the vessel with variable rotation center is derived,which is verified to be accurate through simulation.Second,a thrust allocation method suitable for motion control with variable rotation center is designed.For that purpose,mathematical models of the resultant force and torque of the thrusts generated by the thrusters at the selected rotation center is established according to the thruster layout characteristics of the vessel.Then according to the arrangement of the thrusters and the interference rule among thrusters,the thrust-restricted area of each thruster is determined.In order to adapt to the solution of the quadratic programming algorithm,the thrust feasible region of each azimuth thruster is linearized.Finally,a mathematical model of thrust allocation for optimal power and minimum distribution error is established,which is solved using the method of active set.In order to facilitate the construction of the convex constraint equation for the local feasible region of the azimuth thruster,a practical constraint equation construction method is designed.Simulation results show that the designed thrust allocation method can meet the motion control requirements of the DP system with variable rotation center.Then,according to the characteristics of pipe-laying path,a path planning and guidance system for the vessel is designed.A path following control method based on path coding and sliding matrix is proposed.The sliding matrix is a matrix containing local path and control information of the ship,which can slide down along the waypoint table as the vessel moves.In order to adapt to the guidance control of the arc path of a full-drive vessel,a LOS guidance algorithm suitable for the arc path is proposed.Finally,a motion controller for vessel speed and heading angle is designed.For speed control,the speed distribution method is used to decompose the combined speed into the local coordinate system.Relevant simulation is carried out to verify the availability of the system designed for path planning,guidance and motion control.Finally,a DP pipelaying operation simulator is develop using the Qt Creator.Considering the formation of the DP system and the related thrust allocation algorithms and path planning guidance algorithms studied in this paper,a function corresponding to each functional module is established first.The corresponding input and output structure is created as the input and output parameter types of the function based on the input and output information of each module.In addition,the user interface design function,the interface information acquisition and dynamic information display function of the simulator are also programmed.Different functions are also created for different functional modes of the DP system.Finally,a comprehensive simulation and analysis of the pipe-laying vessel motion is performed using the developed DP pipe-laying operation simulator.