Study On Environmental Loads Feed-forward Of Dynamic Positioning System

As the exploration and exploitation of ocean is extending to the deep water, thepositioning technology of ocean structures has been one of the key research fields inocean engineering. Dynamic positioning (DP) system can keep ocean structures at thedesired position and heading angle by using active thrusters. Since the application ofDP system cannot be constrained by water depth, DP system has been widely used invarious applications of ocean engineering especially in deep water. Due to thedisadvantages of feedback control strategy in DP system dealing with rapid-changingenvironmental loads, the main topic in the thesis is the integration of feed-forwardcontrol strategy into DP system. In the first part of the thesis, the theories and methodsof constructing time-domain simulation program of DP system have been studied anda time-domain simulation program has been completed and tested as a tool for furtherresearch. The second part is mainly concerned with the thrust system in DP system,where a novel idea of dynamic forbidden sectors for azimuth thrusters has beenproposed and so has an effective thrust allocation strategy dealing with the layout ofvarious kinds of thruster including main thruster and rudder in DP system. Finally,after studying the theory and research progress in feed-forward control in DP system,a new kind of real-time estimate method of second-order wave loads is put forwardand integrated into the time-domain simulation program of DP system. The results ofsimulations show that feed-forward control of environmental loads is able to improvethe performance of DP system exposed to rapid-changing disturbances.