Integral Line-of-Sight Guidance and Control of Underactuated Marine Vehicles

ii To my parents, Peter and Nadia, and my little sister, Elisabetta, for their support. And to my dear friend Zinajda, for never ever giving up on me. iii iv Summary This dissertation presents an extensive analysis of the integral line-of-sight (ILOS) guidance method for path following tasks of underactuated marine vessels and vehicles, operating on and below the sea surface. It is shown that thanks to the embedded integral action, the guidance law makes the vessels follow straight lines in presence of environmental disturbances such as currents, wind and waves. The analysis develops linearly with a growth of complexity that spans from simple two and three dimensional (2-3D) kinematic models to full kinematic-dynamic models for surface and underwater vehicles including environmental disturbances of different nature. Furthermore, the problem of steering a vehicle against the ocean current or with the ocean current is addressed as well. The ILOS guidance is first applied to a simple kinematic model of surface vessels that neglects the vehicle dynamics. It is shown, using simple and intuitive mathematical tools, that current compensation for underactuated surface vessels reduces to a pure vectorial sum and has one possible solution that identifies the only heading the ship can hold to compensate for the drift. The relative velocity of the vessel is kept constant and compensation is achieved through side-slipping. It is proved that path following of straight lines is obtained. A discussion involving intuitive as well as practical aspects of the ILOS law is also given. A 3D version of the same ILOS is then applied to a kinematic model of underactuated underwater vehicles, thus extending the same concepts and the same analysis to 3D. The following step in complexity consists of including the underactuated dynamics into the Lyapunov analysis of the 2D ILOS guidance law. Disturbances in the form of constant irrotational ocean currents and constant dynamic, attitude dependent, forces are taken into account. The mathematical complexity of the analysis increases significantly compared to the pure kinematic cases, yielding explicit bounds on the guidance law gains to guarantee stability