Synchronized tracking control for dynamic positioning vessel

Abstract

This article addresses the time‐synchronized control problem for a floating liquefied natural gas (FLNG) vessel and a liquefied natural gas carrier (LNGC) in side‐by‐side offloading operation. For such a problem, the existing finite‐time control approaches available are essentially only designed to ensure that the system state‐variables converge within a certain time. Specifically how each state‐variable converges is typically not considered in the design process. Along this line, the approach of time‐synchronized design in this paper attains the more comprehensive and desirable outcome of having the marine vessels' state‐variables arrive at the sliding mode surface in a fixed time. Also additionally, the state‐variables converge at the same moment. This approach thus can attain synchronous tracking of the LNGC to the FLNG vessel. All these desirable properties and outcomes of control system convergence are rigorously proved in the work here via the methods of Lyapunov‐type theorems and associated stability analysis. Furthermore, in order to ensure that the approaches developed here are suitably applicable in real‐world engineering conditions (with system uncertainties and external disturbances), robustness extensions are also incorporated. In the presented work, the analytical issues and the methodologies in the designed control system solution under the conditions of the disturbed systems are discussed in detail. The numerical simulations conducted verify the merits of the proposed algorithm. Comparative numerical simulations on the developed scheme, and on traditional control, are carried out to demonstrate the important and improved outcomes attained with the time‐synchronized features.