Finite-time adaptive anti-disturbance constrained control design for dynamic positioning of marine vessels with simulation and model-scale tests

Abstract

For practical and complex offshore operations, preventing violations of system constraints can ensure safety and avoid potential marine accidents in harsh environments. This paper addresses a finite-time constrained control for dynamic positioning (DP) of vessels in the presence of inherent uncertainties, ocean disturbances, full-state and input constraints. For operational safety assurance, the core logic of the proposed constrained control strategy is to constrain the state variables including position output, velocity state, input control command within the designed safe region by employing barrier function and auxiliary system, respectively. To attenuate the adverse effects of unknown disturbances on safety and stability, an adaptive neural disturbance observer (ANDO) is constructed to compensate for lumped disturbances caused by inherent uncertainties, unmodeled dynamics, and sea loads. Then, the composite finite-time anti-disturbance constrained control strategy is formally proposed, which can guarantee semi-global practical finite-time stable (SGPFS) of the closed-loop systems. In offshore engineering, control schemes are not only theoretically feasible, but also need to be accurately verified to provide practical guidance value. For this purpose, the simulation and model-scale test are carried out to realistically reproduce the time-domain motion response of the vessels under ocean disturbances. The verification results further elucidate the applicability and feasibility of the proposed control design in practical offshore engineering.