Nonlinear Model Predictive Control for Structural Reliable Position-Mooring of FPSO based on Nonlinear Extended State Observer

This paper proposes a structural reliability-based position mooring control scheme subject to unknown environment disturbance, system uncertainties and control input constraints. Structural reliability of mooring cables is proposed as a breaking strength evaluating index to derive the mathematical model of position mooring system. A nonlinear extended state observer is constructed to estimate position, velocity and total system uncertainties, it is independent of an accurate system model and prior knowledge. Considering the constraints of structural reliability, control input and control increment, a structural reliability-based nonlinear model predictive controller is proposed to solve control input saturation. It is proved that the proposed controller can maintain the structural reliability and heading at the desired value. It is able to fully use the mooring system for positioning while keeping the cable safe, so that the vessel can realize the safe and energy-efficient area keeping. Comparative simulations are performed to demonstrate the effectiveness of the proposed position mooring control scheme.