Remote submersibles -- Design and construction

Underwater vehicles often use acoustics or dead reckoning for global positioning, which is impractical for low cost, high proximity applications. An optical based positional feedback system for a wave tank operated biomimetic station-keeping vehicle was made using an extended Kalman filter and a model of a nearby light source. After physical light model verification, the filter estimated surge, sway, and heading with 6 irradiance sensors and a low cost inertial measurement unit (~$15). Physical testing with video feedback suggests an average error of ~2cm in surge and sway, and ~3deg in yaw, over a 1200 cm2 operational area. This is 2-3 times better, and more consistent, than adaptations of prior art tested alongside the extended Kalman filter feedback system. The physical performance of the biomimetic platform was also tested. It has a repeatable forward velocity response with a max of 0.3 m/s and fair stability in surface testing conditions.

Autonomous Underwater Vehicle (AUV) depth control methods typically use a
pressure sensor to measure the depth, which results in the AUV following the trajectory
of the surface waves. Through simulations, a controller is designed for the Ocean
Explorer AUV with the objective of the AUV holding a constant depth below the still
water line while operating in waves. This objective is accomplished by modeling sensors
and using filtering techniques to provide the AUV with the depth below the still water
line. A wave prediction model is simulated to provide the controller with knowledge of
the wave disturbance before it is encountered. The controller allows for depth keeping
below the still water line with a standard deviation of 0.04 and 0.65 meters for wave
amplitudes of 0.1-0.25 and 0.5-2 meters respectively and wave frequencies of 0.35-1.0
𝑟𝑎𝑑⁄𝑠𝑒𝑐, and the wave prediction improves the depth control on the order of 0.03 meters.

This thesis explores the feasibility of using morphing rudders in autonomous
underwater vehicles (AUVs) to improve their performance in complex current
environments. The modeling vehicle in this work corresponds to the Florida Atlantic
University's Ocean EXplorer (OEX) AUV. The AUV nonlinear dynamic model is
limited to the horizontal plane and includes the effect of ocean current. The main
contribution of this thesis is the use of active rudders to successfully achieve path
keeping and station keeping of an AUV under the influence of unsteady current force.
A constant ocean current superimposed with a sinusoidal component is considered.
The vehicle's response is analyzed for a range of current frequencies.