Dynamic Response and Maneuvering

The Odyssey IV autonomous underwater vehicle (AUV) is the next generation of unmanned subsurface robots from the MIT Sea Grant AUV Laboratory. The Odyssey IV AUV has a novel propulsion system, which includes a pair of azimuthing thrusters for maneuvering in surge and heave. An analytical model was developed to describe the complex nonlinear vehicle dynamics, and experiments were performed to refine this model. The fluid dynamics of unsteady azimuthing marine propulsors are largely unstudied, especially for small vehicles like the Odyssey IV AUV. Experiments suggest that thrust developed by an azimuthing propulsor is dependent on the azimuth angle rate of change, and can substantially affect vehicle dynamics. A simple model capturing the effects of azimuthing on the thruster dynamics is developed, and is shown to improve behavior of the model. The use of azimuthing thrusters presents interesting problems and opportunities in maneuvering and control. Nonlinear model predictive control (MPC) is a technique that consists of the real-time optimization of a nonlinear dynamic system model, with the ability to handle constraints and nonlinearities. In this work, several variations of simulated and experimental MPC-based controllers are investigated. The primary challenge in applying nonlinear MPC to the Odyssey IV is solving the time intensive trajectory optimization problem online. Simulations suggest that MPC is able to capitalize on its knowledge of the system, allowing more aggressive trajectories than a traditional PID controller. Thesis Supervisor: Franz S Hover Title: Assistant Professor Acknowledgments First and foremost, I would like to thank my advisor, Professor Franz Hover, for providing me with guidance and encouragement throughout both my undergraduate and graduate careers. The members of the MIT AUV Lab past and present have built an awesome vehicle in the Odyssey IV AUV, and I appreciate all of their support. Justin Eskesen was an amazing source of knowledge regarding all things software. Thank you to the Department of Defense for providing me with a National Defense Science and Engineering Graduate (NDSEG) Fellowship, which has allowed me to dive into my interests. My office mates and the members of the Hover group provided interesting discussions. I want to thank Jordan Stanway for not only keeping me sane, but for also being an incredible source of knowledge and advice. Finally, I thank my family for their constant support and encouragement throughout my entire time at MIT.