Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Ocean Engineering
Department
Ocean Engineering
First Advisor
Stephen Licht
Abstract
This dissertation explores overactuated depth control of autonomous underwater vehicles (AUVs). The depth actuators that are explored include the traditional aft thruster and maneuvering fins, as well as an actively controlled ballast/buoyancy system and some form of vertical thruster system. Our ultimate goal is to combine the mobility of an AUV with the hovering capability of a controllable float. We aim to assess control systems that can strategically allocate control effort between actuators in a manner informed by the strengths and weaknesses of these actuators. The ultimate objective is to allow an AUV to operate through the full range of speeds from hovering operation (zero forward speed) to full design speed, but in this research, the exploration of control using these actuator types was split into two distinct investigations: frequency-based allocation between “fast” (such as fins and thrusters) versus “slow” (buoyancy system) actuators, and the second investigation involves examining vehicle-speed-dependent actuators (fins and thrusters). Chapter 1 focuses on investigating hovering operation and frequency based allocation. Chapter 2 investigates the properties of the high-frequency actuators across a range of vehicle speeds and introduces a method that can be used to determine speed-based allocation for any type of AUV.
The first investigation, which explores frequency-based control allocation, uses a hovering (zero surge speed) AUV which utilizes a water-filled buoyancy bladder and vertical thrusters to follow varying depth trajectories. This investigation included both an assessment of two strategies (PID-only and PID combined with a complementary filter) for splitting the high and low frequency components, as well as an analysis of the effect of depth and controller tuning on the vehicle’s energy consumption. While this specific set of experiments uses a stationary AUV, these control allocation methods can also be used for allocating between fins and buoyancy systems.
The second investigation, which explores surge-speed-dependent actuators, focuses on using dynamometry to determine the quantitative relationship between speed ratio (between vehicle forward speed and thruster exit speed) and thrust ratio (between thrust at forward speed and thrust at zero speed). This was conducted with three vertical thruster structures: a traditional through-hull tunnel thruster, a “wing thruster” where two thrusters are cantilevered off of the sides of the vehicle, and a “bare thruster” which tests the two-thruster configuration of the wing thruster trials except without the presence of the vehicle body. In addition to the quantitative trials, we also used particle image velocimetry (PIV) to directly visualize the flow fields near the thrusters and identify flow patterns that correspond with features noted in the dynamometry data.
From the dynamometry data that we collected, we demonstrated a method determine the envelope of possible vertical heave force at varying vehicle speeds if the vehicle is equipped with both vertical thruster(s) and a set of traditional fins with an axial propulsion thruster. This demonstration also includes a method of determining the energy consumption of the combination of fins and thrusters for varying speeds. In this way, this information can be used to determine the control and energy requirements of the high-frequency actuators and can be combined with the frequency-dependent actuator analysis methods from the first chapter in order to determine control design for an operational vehicle.
Recommended Citation
Sondergeld, Alexei, "EXPLORATION OF OVERACTUATED AUV CONTROL: INVESTIGATION OF FREQUENCY BASED CONTROL ALLOCATION FOR HOVERING OPERATION AND CROSS BODY THRUSTER DYNAMICS FOR VARIABLE FORWARD SPEED OPERATION" (2024). Open Access Dissertations. Paper 1724.
https://digitalcommons.uri.edu/oa_diss/1724
Terms of Use
All rights reserved under copyright.
