Dynamic positioning of a turret moored FPSO using sliding mode control

This paper presents the application of a sliding mode control technique to the dynamic positioning of a turret moored FPSO. The proposed controller is robust with respect to modelling errors and variations in the intensity and direction of environmental forces. Since the system is strongly non‐linear, the sliding mode methodology is appropriate because it does not require linearization and uses the complete model for the controller design. Furthermore, the design of the controller term that guarantees robustness is very simple, and can be generalized to any adopted model of dynamic and environmental forces. The main drawback of the sliding controller, related to the high oscillatory control action, is avoided by the definition of a “boundary layer” near the sliding surface. The controller was tested through numerical simulations of a moored VLCC under several environmental conditions, confirming the stability and performance robustness.