Abstract
This work develops an energy-efficient robust control for arctic position mooring systems subject to discontinuous ice loads and system uncertainties. To provide a safe and energy-efficient reference position for moored offshore structures, an improved structural reliability-based setpoint chasing algorithm is proposed. An ice-load disturbance observer is constructed to handle the arctic environmental disturbances, relaxes the continuity, differentiability, and boundedness requirements of disturbances. The system uncertainties are addressed by an adaptive fuzzy estimator. With the reference position and disturbance estimation, an improved dynamic surface control law is derived by introducing a novel filter to improve the convergence rate of the filter error, it enhances also the control performance of the arctic position mooring with fast response. Theoretical analysis proves the stability of the resulting closed-loop system and the boundedness of all its signals with the invariant set mechanism and Lyapunov theory. Comparative numerical simulations are carried out on a turret-moored floating production storage and offloading (FPSO) vessel to demonstrate the performance and effectiveness of the proposed control scheme.