Study On Simulation Technology Of Ship Dynamic Positioning System

The positioning of floating structures is a problem of great concern with the rapid development of exploitation and production in deep seas. Dynamic Positioning system is different to traditional anchor system. Dynamic positioning system is a closed-loop control system to let the marine vessel maintain a fixed position and heading in the horizontal plane, or to follow a predetermined track. Now the DP system is widely applied to floating offshore structures and ships. The objective of this thesis is to establish the simulation program for the DP system by studying on the control method and thrust allocation method. . The major work of the thesis includes:(1) Firstly, two mathematical models were established, one is the control plant model and another is the progress plant model. The process plant model is a model describing the real world as accurate as possible. This model is most often used in numerical simulation as an imitation of the real world. Contrarily, the control plant model is a simplified ship model to be used in controller design. It is the basis when designing controllers and observers, or when doing stability analysis.(2) Secondly, Kalman Filter and LQG controller is designed with the control plant model.(3) The thesis proposed a new thrust allocation method. Thrust allocation problem is formulated as an optimization problem, which objective is to minimize the energy consumption, including fuel consumption, tear and wear of thrusters and thrust error. The boundary conditions include thrust limitation, maximum thrust change rate of thrust, maximum slew rate of thrusts, forbidden sector for the thrust direction angle.(4) The numerical simulation results were compared with those form model test and the consistence was analyzed.The following innovations were obtained:1) A new thrust allocation method which was used in both numerical simulation and model test was established, and good results were obtained.2) The simulation program of DP was developed and was applied to a deep water pipe-laying crane vessel with seven azimuthing Model test results were compared with numerical results and good agreement was obtained.