Research On Dynamic Positioning Control Of Single Point Mooring Ship

Nowadays, the need of the development of the sea rose more and more higher. There aremore and more engineering ship in the sea, including the reviewing ship, aquatic productcatching ship, oil exploring ship, mine laying ship and so on. It is an important way ofpositioning for ship working at sea through the single point mooring which has simplestructure and which is reliable and economical. But while working in deep sea or under harshsea state, ship is hard to position accurately using single point mooring singly and it would doharm to mooring lines, thus dynamic positioning is needed. The dynamic position system ofsingle point mooring ship can improve position accuracy and system safety.In this paper, single point mooring ship with dynamic position system is studied.Mathematic model of kinematics and dynamics of a single point mooring ship is build underthe NED reference frame and body-fixed reference frame. Because the wind, waves andcurrent have effect on the ship in the sea, the model of environmental force is build, the forceand moment of the environment is estimated. According to the situation that single pointmooring ship affected by forces, model of single point mooring system is build and at thesame time mooring force is calculated.Motion of single point mooring ship under the effect of environmental disturbance isstudied. There are two forms of motion of single point mooring ship: maintaining at stableequilibrium position and fishtail swing. Impact of environmental force, the length andmaterial of mooring line on ship motion is researched through simulation. The researchshowed that pulse tension produced while ship is experiencing fishtail swing is the mainreason that led the mooring line broken. These influences are very important of the safe of thesingle point mooring ship.According to the study of the characteristics of single point mooring ship motion andlinear quadratic optimal control theory, ship model is linearised and state transformation isdone. A linear quadratic optimal state feedback controller was designed to ensure tension ofmooring line change within the load range. A positioning point was determined throughenvironmental disturbance, thus dynamic positioning of single point mooring ship isachieved.Feasibility of the designed optimal state feedback controller is tested through simulation.The result showed that the designed controller could carry out dynamic positioning of singlepoint mooring ship and mooring line tension is ensured to change within load range. The performance of optimal controller and PID controller is compared and the result showed thatoptimal controller could minimize error and output of the controller.