Abstract:
Inspired by the swimming abilities of marine animals, this thesis presents "Finnegan
the RoboTurtle", an autonomous underwater vehicle (AUV) powered entirely by four
flapping foils. Biomimetic actuation is shown to produce dramatic improvements in
AUV maneuvering at cruising speeds, while simultaneously allowing for agility at
low speeds. Using control algorithms linear in the modified Rodrigues parameters to
support large angle maneuvers, the vehicle is successfully controlled in banked and
twisting turns, exceeding the best reported AUV turning performance by more than
a factor of two; a minimum turning radius of 0.7BL, and the ability to avoid walls
detected> 1.8BL ahead, are found for cruising speeds of 0.75BL/S, with a maximum
heading rate of 400
/ S recorded.
Observations of "Myrtle", a 250kg Green sea turtle (Chelonia mydas) at the New
England Aquarium, are detailed; along with steady swimming, Myrtle is observed performing
1800 level turns and rapidly actuating pitch to control depth and speed. Limb
kinematics for the level turning maneuver are replicated by Finnegan, and turning
rates comparable to those of the turtle are achieved. Foil kinematics which produce
approximately sinusoidal nominal angle of attack trace are shown to improve turning
performance by as much as 25%; the effect is achieved despite limited knowledge of
the flow field. Finally, tests with a single foil are used to demonstrate that biomimetically
inspired inline motion can allow oscillating foils utilizing a power/recovery style
stroke to generate as much as 90% of the thrust from a power/power stroke style
motion.
