ABSTRACT Title of thesis: MODELING, ESTIMATION, AND CONTROL OF ACTUATOR DYNAMICS FOR REMOTELY OPERATED UNDERWATER VEHICLES Jordan A. Boehm, Master of Science, 2019 Thesis directed by: Professor Derek A. Paley Department of Aerospace Engineering Institute for Systems Research Modeling and control of remotely operated underwater vehicles is a challenging problem that depends greatly on how the dynamics of their thrusters are compen- sated. In this thesis a novel method for characterizing thruster dynamics using a six-axis load cell is presented. Multiple dynamic models are characterized with this test setup. Model-based control design strategies are used to compensate for nonlin- earities in the dynamics, which include input dead zones and coupling with fluid dy- namics. Multiple estimation methods are presented to construct an estimate of fluid velocity which is handled as an unmeasured state. The different models, controllers, and estimators are comparatively evaluated in closed-loop experiments using the six-axis load cell to measure thrust tracking performance. Full vehicle simulations using the experimentally characterized models provide additional opportunities for comparison of control and estimation strategies. The potential tracking control ben- efits from the variety of presented thruster dynamics compensation strategies are evaluated for a remotely operated underwater vehicle with multiple thrusters. MODELING, ESTIMATION, AND CONTROL OF ACTUATOR DYNAMICS FOR REMOTELY OPERATED UNDERWATER VEHICLES by Jordan A. Boehm Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Master of Science 2019 Advisory Committee: Professor Derek A. Paley, Chair/Advisor Professor David Akin, Co-Advisor Professor Robert M. Sanner c Copyright by Jordan A. Boehm 2019 Dedication To my parents, who encouraged me to always pursue new experiences and learn from my own mistakes. \Research is what I'm doing when I don't know what I'm doing." {Wernher von Braun ii Acknowledgments I owe my gratitude to so many people who made this work possible. While I will try my best to include everyone, there will inevitably be those who are inadver- tently left out. I apologize if anyone is not mentioned, but know that I value your support greatly. Perhaps the most important person to thank is my advisor, Dr. Derek Paley, for granting me the opportunity to work on this project and provid- ing such insightful guidance and feedback during my time working with him. The amount of personal growth I have achieved through his encouragement and instruc- tion has been so much greater than I could have anticipated. For that I will always be grateful. I additionally want to thank my committe, Dr. David Akin and Dr. Robert Sanner, for offering their time and expertise to provide meaningful and valuable feedback to my work. My experiences as an undergraduate in Dr. Paley's, Sanner's, and Akin's courses inspired me to pursue this research and the thought-provoking challenges they have provided me in their graduate courses continue to influence how I investigate and approach engineering problems today. I would not have realized my own love for this field if it were not for the profound knowledge I gained under your instruction. Other faculty I owe thanks to are Dr. Raymond Sedwick and Dr. Mumu Xu who guided me through my undergraduate research projects and encouraged me to stay curious and vigilant in my academic endeavors. I want to give another big thank you to those in the Aerospace Department who helped me in my process through the undergraduate and graduate programs. iii Aileen Hentz, Tom Hurst, Otto Fandino, LaVita Williams, Gabrielle Madison, Matt Sinclair, and all my other friends in the department have been great sources of assis- tance during my time here. I owe special gratitude to Aileen Hentz and Tom Hurst, who offered their time and guidance during my transition from the undergraduate program. When I was uncertain of my post-graduation path, you provided such kind and constructive guidance that led me to where I am today. I cannot be more thankful for that. To my friends and colleagues at National Geographic, thank you for being such fantastic team members. Thank you Eric Berkenpas, Mike Shepard, Kyler Aber- nathy, Brad Henning, Alan Turchik, Arthur Clarke, Mohsen Samak, Cody Gold- hahn, Michelle Rodriguez, and Jessica Elfadl for being great friends and providing amusingly witty conversations during countless hours working on this project. I especially am thankful to Eric Berkenpas and Mike Shepard for their valuable guid- ance and assistance in this project while always remaining upbeat and amusing. I have really come out of my shell during these past two years thanks to all of you. I would be remiss not to acknowledge my CDCL family who I have come to know so well in graduate school more so than any other group. Thank you to Travis Burch, Daniel Gomez, Brian Free, Will Craig, Will Scott, Artur Wolek, Debdipta Goswami, Jinseong Lee, Helene Nguewou, Sheng Cheng, Paul Ghanem, as well as all undergraduates including Jimmy Witkoski who had a part in this work. I owe special thanks to Travis Burch and Daniel Gomez for being great friends and colleagues during countless homeworks, projects, and editing sessions. Thank you also to Girguis Sedky, Jamie King, Kate Melone, Jackson Shannon, Eric Frizzell, iv Mark Moretto, Dominick Montero, Priya Dharmavaram, Angelina Nou, Katherine Smolen, and so many other classmates who offered conversation and companionship over the years. Thank you to my family for being so supportive and patient (when necessary) with me during any and all difficult patches that have been a part of my journey through college. You have had 24 years to get good at it, but I know I still find ways to make offering your help and advice difficult. Thank you, regardless of my behavior, for listening to my issues and rantings, and for still being able to provide support and advice when you could. Thank you, Mom and Dad, for encouraging me to pursue precisely what I want in life, and nothing less. Thank you also for showing me how success can be its own reward, and how mistakes are always learning experiences. The freedom you gave me during my childhood played a huge part in how I have grown into the person I am today, and I always value having been able to learn my values through my own experiences rather than by excessive guidance. Thank you also to my aunts Leah, Jo Anne, and Soupy for being so supportive of my hobbies and musical endeavors, and offering wonderful conversation on those topics. Thank you to my Grandfather for being a constant source of guidance and wisdom in my life, and inspiring me to pursue bold endeavors, and to my Grandmother who did not get to see me grow up and achieve what I have, but who I know is proud of me. Thank you to my friends who have been great sources of joy and support over the years. Thank you Matt and Brett for being the two best friends I could have ever asked for, and for remaining great sources of support, jokes, and activities all v these years and for years to come. Thank you to Emily for always believing in me and supporting me even when we have disagreements. You have been a vital companion in my life for years now and I hope will remain so for countless years to come. Thank you also to the Bertots for being a second family to me over these years. Thank you to my college family: Nick, Jacob, Matt, Steve R., Steve B., Nate, and Steph for being fantastic friends. Thank you also to past friends and teachers who may not have been mentioned here. To Lynda Motiram, Kai Frick, Ruth Goldstraw, Ellen Lehrter, Laura Volkov, Lindsay Reed, Erin Few, Mike Miller, Andrea Linnell, and Lynn Clough for being important influences in my education. You made such an important impact on my life for encouraging me to pursue my interests that I will always be grateful for. Thank you to Elana and Xiaofang for your helpful feedback and guidance through these past few years. Thank you to Donald Fagen for being a constant source of inspiration in my life, as well as his colleague Walter Becker whose untimely passing occurred while this work was being completed. Thank you additionally to all the sources of discouragement I have met in my life for serving to strengthen my resolve and conviction. Perhaps Juan Goytisolo said it best: \To those who inspired it and will not read it." Thank you to all those I have not mentioned but have impacted me in one way or another. Finally, this research would not have been possible without the support of the National Geographic graduate research fellowship that funded it. I gratefully acknowledge that support. vi Table of Contents Dedication ii Acknowledgements iii List of Tables ix List of Figuresx 1 Introduction1 1.1 Motivation.................................1 1.2 Relation to State of the Art.......................2 1.3 Technical Approach............................4 1.4 Contributions of Thesis..........................6 1.5 Outline of Thesis.............................8 2 Background: Underwater Vehicle Modeling and Control9 2.1 Underwater Vehicle Dynamics......................9 2.2 Underwater Vehicle Control....................... 16 3 Simplified Thruster Modeling and Control 18 3.1 Experimental Characterization of Model Parameters.......... 18 3.1.1 Experimental Setup........................ 18 3.1.2 Experimental Procedure..................... 22 3.2 Simplified Thruster Model........................ 23 3.3 Feedback Control Strategy........................ 29 3.3.1 Single-Thruster Control..................... 29 3.3.2 Full Vehicle Control........................ 33 4 Hydrodynamic Thruster Modeling and Control 36 4.1 Experimental Characterization of Model Parameters.........