Coordinated Motion Control of Multiple Autonomous Underwater Vehicles

Spawned by recent advances in technology, widespread attention has been focused on the coordination of multiple autonomous vehicles. In numerous mission scenarios, the concept of a group of agents cooperating to achieve a determined goal is very attractive when compared with the solution of one single, heavily equipped vehicle, as it exhibits better performance in terms of efficiency, flexibility and robustness, and can more effectively react and adapt itself to the environment in which it operates. Applications of coordinated control of multiple vehicles include microsatellite clusters, formation flying of unmanned aerial vehicles and automated highway systems. In the field of ocean exploration there has been a surge of interest worldwide in the development of autonomous robots equipped with systems to steer them accurately and reliably in the harsh marine environment and allow them to collect data at the surface and underwater. The cooperation of multiple autonomous underwater vehicles (AUVs) yields several advantages and leads to safer, faster, and far more efficient ways of exploring the ocean frontier, especially in hazardous conditions. The dynamics of underwater vehicles however are characterized by hydrodynamic effects that must necessarily be taken into account during the control design. Moreover, it is common for underwater vehicles to be underactuated, that is, to have fewer actuators than degrees-of-freedom. Motion control for this class of vehicles is especially challenging because most of these systems exhibit nonholonomic constraints. As there are strong practical limitations to the flow of information among vehicles, which is severely restricted by the nature of the supporting communications network, one of the aims of formation control must be to reduce the frequency at which information is exchanged among the systems involved. This is especially true in the case of AUVs, since underwater communications and positioning rely heavily on acoustic systems, which are plagued with intermittent failures, latency, and multipath effects. It is in this framework that this thesis proposes a decentralized control structure, based on Lyapunov techniques and graph theory, that explicitly takes into account both the complex nonlinear dynamics of the cooperating vehicles and the constraints imposed by the topology of the inter-vehicle communications network. For a single vehicle, the solution