Thrust Distribution Method And Dynamic Positioning Capability Analysis Of Semi-submersible Ship

The thrust distribution module and the controller module have significant effects in the dynamic positioning system.The main principle is to calculate the required thrust and thrust torque according to the expected position of the ship and the interference of the external environment.The thrust distribution module will distribute it to Each thruster to realize the positioning function finally.The reasonable design of the thrust distribution module and the controller module plays an important role in the positioning ability of the dynamic positioning system.In this paper,a semi-submersible ship is the research object and a simulation model of the semi-submersible dynamic positioning system is constructed.The dynamic positioning capability of the semi-submersible ship is analyzed,and a DPS simulator of the semi-submersible ship is created.The specific contents are as follows:First,the dynamics and kinematics models of the semi-submersible ship are established,according to the environmental load model carried out by the previous experiments.The simulation model of motion of the semi-submersible ship is established combined with the parameters of the semi-submersible ship.The analysis of lateral movement,longitudinal movement and slewing movement of the simulation model show that the built model meets the requirements of the expected dynamic positioning system.This paper studies the control function of the semi-submersible ship and combined with the built simulation model of the semi-submersible ship,the hybrid control mode of the semi-submersible ship has been designed.Based on the LOS guidance algorithm and PID control method,derives six hybrid controls Guidance laws of the model are derived and six mixed control model controllers are designed to establish a complete control simulation model of the semi-submersible ship.Finally,the simulation of controlling of the position and attitude of the ship under wind,wave and current conditions shows that the six mixed control mode controllers designed in this paper can accurately complete the positioning and motion control of the ship,which meets the requirements of the DP manual.The optimization and constraint conditions of the objective function of thrust distribution of the ship are introduced.,The total thrust of the 12 thrusters in the three axis directions of the semi-submersible hull coordinate system and the combined thrust moments are obtained to calculate the vector layout matrix of the semi-submersible propulsion system finally.Then,a mathematical model of thrust distribution of the semi-submersible ship is built.The analysis results of the three thrust distribution methods show that the function set method can consider the maximum thrust of the propeller,the actual response and other constraints completely,and has strong real-time performance.Besides,it can also meet the requirements of the principle of optimal power.So the function set method is selected to analyze the failure mode of the semi-submersible vessel,and finally the dynamic positioning capability curve of the semi-submersible vessel under different failure modes is obtained.It can be found that in the event of a failure,the propulsion configuration of the semi-submersible vessel can still maintain positioning and heading in the required operating marine environment and meet the requirements of the ship’s positioning and orientation capabilities in various directions under the operating environment even for the failure conditions.C/C++ languages are used to build the dynamic link library,and finally a semi-submersible DPS simulator is created based on the QT creator.The basic idea is to write each module as a function,and call the function,then the ship status will be displayed on the control interface as a result.For the design of the simulator’s automatic control mode,manual control mode,mixed control mode switching operation,the switching operation between Auto Surge mode and Joystick mode with or without environmental force,The simulation model of LOS linear path tracking is carried out.The results show that the simulator designed in this paper can meet the relevant requirements of the semi-submersible vessel dynamic positioning system and can be used to train operators and plan previews to provide a research basis for the overall design of the semi-submersible vessel.