Robust observers and controllers for marine surface vessels undergoing maneuvering and course-keeping tasks

The dynamic behavior of marine surface vessels is highly nonlinear. Moreover, it is significantly influenced by environmental disturbances induced by winds, random sea waves and currents. The focus of this work is to develop an integrated guidance and control system that enables under-actuated marine surface vessels to operate autonomously and yield robust tracking performance in spite of significant external disturbances and modeling imprecision.;A nonlinear model for a marine surface vessel is developed to serve as a test bed for assessing the performance of the proposed guidance and control systems. The model incorporates recent developments in ship modeling. Its formulation considers the effects of coriolis and centripetal accelerations, wave excitations, retardation forces, nonlinear restoring forces, wind and sea-current loads, linear damping terms, and the control force and moment. Moreover, it captures the dynamics of the rudder and accounts for the physical limitations of both the rudder and the ship propulsion system.;The guidance scheme is based on the concepts of the variable radius line-of-sight (LOS) and the acceptance radius. This scheme has been modified in the current work to vary the LOS radius exponentially with the cross track error. Such a guidance system has been shown herein to yield a faster rate of convergence over existing schemes in guiding the ship toward its desired trajectory.;Two fully integrated guidance and control systems have also been introduced in this work. The first one involves a sliding mode controller and observer. The second system includes an enhanced self-tuning fuzzy-sliding mode controller and a novel design for a self-tuning fuzzy-sliding mode observer. The second guidance and control system is introduced in an attempt to combine the advantages of the variable structure systems (VSS) theory with the self-tuning fuzzy logic controller.;The simulation results demonstrate the capabilities of the proposed robust observers in yielding accurate estimates of the state variables that are needed for the computation of the control signals. Furthermore, they serve to demonstrate that the proposed guidance and control schemes allow under-actuated marine surface vessels to operate autonomously in tracking a desired trajectory. Their performance has been proven to be robust in the presence of modeling imprecision and significant environmental disturbances.