Research On The Nonlinear Estimate Filter Of Ship Dynamic Positioning System

Dynamic positioning system can make the vessel keep certain position and direction on the sea, have advantages that are not restricted by the depth of water and enter or retreat rapidly, and achieve the precise flexibility of ships. To many vessels which carry on the operation on the sea, it is necessary to use the dynamic positioning system.The movement of vessels on the sea usually divide for low frequency movement that composes of wind, current, second-order wave drift and high frequency movement that composes of first-order wave-induced distrubances. As the performance of high frequency movement is cycliccal shocks and will not lead to the influence of average position, in order to avoid unnecessary energy waste and the thruster system wear, it usually isolates the low frequency signal to control from comprehensive position signal of vessels. So, filter plays a very important role in the dynamic positioning system. This paper is based on DP ship, a simple motion mathematical model of the vessel is established and educed according to some reasonable supposition. A environment disturbance estimate model is established for the slowly varying environmental forces and moments, such as second-order wave drift, sea current, and integrate this model into DP system model, we design a nonlinear estimate filter. The proposed estimate filter produces noise-free estimates of the low-frequency position, the velocity and the slowly varying environmental disturbances.Finally, the nonlinear estimate filter has been simulated on a computer model of a supply vessel. A series of experiments, by means of without controller, with controller but no estimate filter, with controller and estimate filter and so on, the simulation results show the excellent performance.This dissertation has concentrated on estimate filter for ship DP system. The emphasis is the research on the application of nonlinear systems theory on DP control system. And the system stability is analyzed particular. A great number of simulations are conducted. The effectivenes of designed system is proven by simulation results.