Numerical and Experimental Study on the Influence of the Set Point on the Operation of a Thruster-Assisted Position Mooring System

Positioning accuracy and power consumption are of great concern in thruster-assisted position mooring systems. Altering the set point (SP) can significantly affect the performance of the positioning system. A model test is conducted with a moored semi-submersible platform exposed to environmental loads in order to determine the vessel’s equilibrium position, where the mean environmental loads are balanced by the mooring forces to avoid conflict between the control action of the thruster assist and the mooring system. Afterward, further numerical and experimental studies are conducted at several relative SPs to investigate the influence on the positioning accuracy and power consumption. Numerical simulations are conducted in both frequency and time domains based on 3-D potential theory and a proportional–integral–derivative (PID) control strategy. The simulation results agree well with the experimental data, which suggest that the proposed SP in the equilibrium position will largely improve the vessel performance while the utilization of the mooring system is maximized.