Research On The Control Methods Of Heading And Position When Surface Vessel Rotating Around The Given Position

In this paper, control methods of the surface vessel’s heading and position during theprocess of it performing rotational movements around the given position while the dynamicpositioning system is in automatic positioning mode. The vessel’s rotational movementsaround the given position is an important function of the dynamic positioning system, and hasa wide range of applications in actual engineering practice, such as ships enter the harbor, thesea-bed operation. During the process of the ship’s rotational movements around the givenpoint, the moving center of the vessel was no longer fixed to the default center of the ship,and was given by the operator based on the actual application, the given point was located in afixed position in the ship coordinate system, and control the ship to ensure that it was undercontrol and reached the set heading at the same time.3DOF ship motion mathematical model and environmental interference mathematicalmodel were established, and the coordinate framework involved in the ship motion was given,too. Guidance strategies of the ship’s rotational motion were researched for different givenrotation center. Through comparative analyses of the two existing related guiding methods,which were vector method and polar coordinates method, the complex control problem ofposition, whose control target was the given position, was transformed into a general problemwhose position control target was the ship’s center, apart from this, positioning and beamedmethods were adopted to calculate the expected trajectory of the ship according to the ship’sinitial position, the rotation center the rotation rate given.Nonlinear PID and optimal control, which were more suitable for engineeringapplications, were designed based on the established mathematical model and the designed.First, the control principles of the mass-damper-spring systems’ acceleration feedback andPID feedback was introduced and then they were brought into the nonlinear ship motionmodel. Nonlinear PID control algorithm for the ship’s rotational movement around thefixed-point was designed, and proof of stability was given. The effectiveness and robustnessof this control method was verified by simulating different given rotation points andenvironmental interference.Finally, an optimal control algorithm for ship’s rotational motion around the fixed-pointwas designed, in order to ensure the stability of the control algorithm, the ship parallel to thecoordinate system was adopted during the designing process, the theory of small angle wasapplied to make the ship model linear. Minimizing deviation of the ship’s actual location and heading to the desired values was viewed as the quadratic’s performance index of the optimalcontroller, and the thruster’s saturation limit was also considered, thus the highest accuracy inthe whole control process is ensured. Finally simulation analyses were done.Simulation results showed that both the two control schemes could ensure the ship’srotational motion around the given rotation center, and ultimately positioning at the setheading, but the accuracy is higher while the robustness was better for optimal controls wheninterference changes quickly, and its frequency was high.