Dynamic Modeling and Control of Biologically Inspired Vortex Ring Thrusters for Underwater Robot Locomotion

A new type of underwater thruster was designed to provide high-accuracy, low-speed maneuvering to underwater robots. Located internal to the vehicle surface, these thrusters have a minimal effect on the forward-drag profile of the vehicle. These thrusters, whose inspiration comes from the natural propulsion of cephalopods and jellyfish, generate control forces by successive ingestion and expulsion of jets of water from a cavity mounted in the hull of the vehicle. The jetting process has no net mass flux but results in a positive momentum flux. A time-dependent thrust model was developed, which predicted the thruster dynamics as a function of time, actuation frequency, and thruster-driving parameters. A linear transfer-function model was developed to approximate both the thruster and vehicle dynamics, which led to maneuver categorization into three regimes: Cruising, Docking, and Transition. The predicted frequency response was verified through hybrid simulation to be accurate for predicting general trends and cutoff frequency.