Guidance System for Autonomous Surface Vehicles

There has been a rapid growth in autonomous technology in several fields the past decade. One of these is autonomous navigation, where the DARPA Grand Challenges has been a major research catalyst. Today, the Centre of Excellence “Centre for Autonomous Marine Operations and Systems (AMOS)” in cooperation with the maritime industry seeks to develop autonomous technology for marine applications. A robust collision avoidance system is crucial for an Autonomous Surface Vessel (ASV). In order to operate at sea, near other traffic, it also needs to adhere to the “rules of the road”, the International Regulations for Avoiding Collisions at Sea (COLREGs). In this thesis, a COLREGs compliant guidance, navigation and control (GNC) system has been developed with the Velocity Obstacle (VO) method as the basis for collision avoidance. To validate the performance of the GNC system, a general nonlinear 3-DOF surface vessel simulator has been implemented. It features simple models for slow and fast-varying disturbances (e.g. waves, wind and current). The system has been implemented in the Robotic Operating System (ROS) framework. Three main scenarios has been designed to test the guidance system in all main COLREGs scenarios: overtaking, head-on and crossing. Each scenario requires multiple COLREGs compliant maneuvers. Several special cases are also examined and discussed. The VO method performs very well in the simulated scenarios and its avoidance maneuvers complies with all main COLREGs requirements. A thorough discussion highlights both advantages and disadvantages with method and suggests actions to mitigate less ideal behavior experienced in some special cases. The thesis also features a rich discussion on further development and improvements to the system. Samandrag Det siste århundret har vi sett ein enorm vekst innan autonom teknologi i ulike felt. Eit av desse felta er autonom navigasjon, der DARPAs «Grand Challenge»-ar har vore ein viktig forskingskatalysator. I dag ynskjer senter for framifrå forsking, «Senter for Autonome Marine Operasjonar og System (AMOS)» i samarbeid med den maritime industrien å utvikle autonom teknologi for marine applikasjonar. Eit robust kollisjonsomgåingssystem er ein svært viktig del av eit autonomt overflateskip. For å nyttast til sjøs, nær anna trafikk, må systemet òg lyde dei internasjonale reglane for kollisjonsomgåing til sjøs (COLREGs). I denne avhandlinga er eit styrings-, navigasjonsog kontrollsystem som lyder COLREGs utvikla, med «Velocity Obstacle (VO)»-algoritmen som basis for kollisjonsomgåing. For å kunne validere funksjonaliteten til systemet har ein generell simulator for fartøy med tre fridomsgradar òg vorte utvikla. Denne inneheld enkle modellar for sakteog hurtigvarierande forstyrringar (t.d. bølgjer, vind og straum). Systemet er implementert i «Robot Operating System (ROS)»-rammeverket. Tre hovudscenario har vorte designa for å teste styringssystemet i dei viktigaste COLREGs-situasjonane: overtaking, front-mot-front og kryssing. Kvart scenario krev fleire COLREGs-samsvarande manøvrar. I tillegg, er fleire spesialtilfelle undersøkt og diskutert. VO-metoden yter særs bra i dei simulerte scenaria og alle omgåingsmanøvra samsvarar med COLREGs-reglementet. Ein djuptgåande diskusjon belyser både fordelar og ulemper med metoden og foreslår tiltak for å minske mindre ideell oppførsel erfart i einskilde tilfelle. Avhandlinga inneheld òg ein rik diskusjon kring vidare utvikling og forbetringar av systemet. Preface This thesis is written as a compulsory part of the Master’s degree in Engineering Cybernetics at the Department of Engineering Cybernetics at the Norwegian University of Science and Technology (NTNU). The thesis has been written in cooperation with DNV GL. Acknowledgements I would like to thank my supervisors Kristin Y. Pettersen (NTNU) and Øystein Engelhardtsen (DNV GL). I would also like to thank Bjørn-Olav, Stine and Sveinung whom I shared office space with the past year. A special thanks goes out to Bjørn-Olav for all the interesting discussions regarding collision avoidance strategies. Thomas Stenersen, Trondheim, June 2015