Research On The Control Algorithms For Dynamic Positioning System Of Watercrafts

As the requirements of watercrafts in offshore operations continue to be increased, thetraditional control algorithms have been unable to meet the work requirements of watercraftdynamic positioning system in complicated sea state. In order to extend the working rangeof watercraft’s dynamic positioning system and improve its efficiency in complicated seaconditions. In this paper, the dynamic positioning system of watercrafts is the researchobject. The main idea of the paper is to design a more general algorithm so that it can beapplied in a variety of sea state conditions. This paper is relied on the high-tech researchproject of Technology Department of Jiangsu Province—“The research and application ofmarine engineering ship dynamic positioning system’s key techniques”. Combined with thework requirements of a large trailing suction hopper dredger, the paper have tested thealgorithms and achieved relatively good results. The paper studies with a clear direction andvalue in use, which mainly includes the following aspects:In view of the dynamic positioning system of water surface vessels and other floatingstructures have similar models. The paper has built the mathematical models of dynamicpositioning system about watercrafts from the macro perspective. Its low frequency andhigh frequency motion models are both analyzed. The three main factors of environmentaldisturbance effects—wind, wave, flow are also being constructed with model equations. Thepaper also shows how to calculate their disturbance forces and moments.For the observer part, it has designed three filtering algorithms based on three typicalsea state conditions. Second-order low-pass filter is used to filter out the high frequencydisturbance and noise of a ship under calm sea state. The Kalman filter is able to estimatethe speed of the ship effectively so that the problem of frequent oscillating signals can beavoided. It also provides a reference for the calculation of other unknown parameters. Thenonlinear observer is able to estimate the position of the three degrees of freedom for theship accurately.For the controller part, three control algorithms also have been designed respectivelyaccording to three typical environmental conditions. Integral Separation PID controller canbe used to achieve low-speed tracks maintaining function of a ship. Fuzzy self-tuning PIDcontroller can be used to control the rudder angle of the autopilot system well. Accelerationfeedback controller is used to solve the precise positioning problem under severeenvironmental conditions.Finally, the hybrid control of dynamic positioning system is designed and simulated.The result is that the ship can maintain normal operating state in three typical sea states. Firstly, the paper establishes the structured flowchart of hybrid control system. Then thepaper shows the switching methods based on both the observers and the controllers. Usingtime-delay switch logic algorithm can not only ensure the stability of the switching systembut also prevent the prediction error from being increased. At the end of this paper, anengineering ship is used to test the efficiency of algorithms. The result shows that ship’s DTtrajectory tracking function can be achieved under several sea state conditions. The paperhas certain reference value to future research about the dynamic positioning system of oceanengineering vessels.