6. Adaptive Control of Thruster-Assisted Single-Point Mooring Systems

Chapter 6 is dedicated to the control problem of a thruster-assisted single-point mooring system in the presence of uncertainties and unknown backlash-like hysteresis nonlinearities. Using the backstepping technique and Lyapunov synthesis and employing neural networks (NNs) to approximate the unknown nonlinear functions, robust adaptive backstepping control is developed for the full-state feedback case. Subsequently, in order to overcome the measure difficulty in the vessel velocity vector, a high-order NN-based observer is constructed to estimate the unmeasurable state vector. It is shown that the proposed observer has an excellent estimation performance in spite of the existence of uncertainties and unknown backlash-like hysteresis nonlinearities. Based on this observer, robust adaptive output feedback control is developed via backstepping design. Under the proposed control, the semiglobal uniform boundedness of all the signals in the closed-loop systems is guaranteed for both full-state and output feedback cases.