Adaptive interval type-2 fuzzy logic observer for dynamic positioning

Observer also known as wave filter is an essential element of a dynamic positioning system. This paper presents an adaptive interval type-2 fuzzy logic observer for dynamic positioning of floating vessels under time-varying hydrodynamic disturbances. The combination of approximation-based adaptive technique and interval type-2 fuzzy logic system allows the time-varying disturbances to be handled without exact information on them. The stability of the observer error dynamics is explored through Lyapunov analysis where sufficient condition for guaranteeing global asymptotical convergence of the estimation errors is proposed. The adaptive observer includes features like estimations of both the low frequency displacements and velocities of the vessel from noisy displacement measurements and wave filtering. Simulation study with a container ship demonstrates the satisfactory performance of the proposed observer.