Distributed Control of a Drifting Formation of Autonomous Underwater Vehicles

Abstract

Cooperative underwater missions grow larger and larger. For survey mission such as seismic acquisition, such missions would involve hundreds of independent nodes in formation. But batteries limit the endurance. To make longer survey missions possible, currents can be used to drive the formation through the area of interest.The current is involved in a double way. On one hand, large scale currents need to be predictable for operational purposes, on the other hand, spatial current variations will disturb the formation. This thesis aims at providing a review of small scale current modeling and a formation control scheme for a drifting swarm.In current modeling, it focuses on the submesoscale, and in particular a tool is developed to build a current field from the extrapolated SSH spectral current.Specific formation control schemes are also needed to obey the drifting philosophy. A short review of formation control theory is made and their application to a drifting swarm is discussed. This thesis attempts to develop distributed formation control with limited communications in agreement with the drifting philosophy.Two types of designs are retained and developed. A first design applies virtual structure fitting locally and a local controllers track the desired position. A second design uses passivity techniques and potential functions to achieve formation without fighting the average current.Simulations with the MiT-developed MOOS suite are conducted to test the designs.