Ocean engineering.

This dissertation concerns the dynamics and control of an autonomous underwater
vehicle (AUV) which uses internal actuators to stabilize its horizontalplane
motion. The demand for high-performance AUVs are growing in the field of
ocean engineering due to increasing activities in ocean exploration and research.
New generations of AUVs are expected to operate in harsh and complex ocean environments.
We propose a hybrid design of an underwater vehicle which uses internal
actuators instead of control surfaces to steer. When operating at low speeds or in
relatively strong ocean currents, the performances of control surfaces will degrade.
Internal actuators work independent of the relative
ows, thus improving the maneuvering
performance of the vehicle.
We develop the mathematical model which describes the motion of an underwater
vehicle in ocean currents from first principles. The equations of motion of a
body-fluid dynamical system in an ideal fluid are derived using both Newton-Euler
and Lagrangian formulations. The viscous effects of a real fluid are considered separately.
We use a REMUS 100 AUV as the research model, and conduct CFD simulations to compute the viscous hydrodynamic coe cients with ANSYS Fluent. The
simulation results show that the horizontal-plane motion of the vehicle is inherently
unstable. The yaw moment exerted by the relative flow is destabilizing.
The open-loop stabilities of the horizontal-plane motion of the vehicle in
both ideal and real fluid are analyzed. In particular, the effects of a roll torque and
a moving mass on the horizontal-plane motion are studied. The results illustrate
that both the position and number of equilibrium points of the dynamical system
are prone to the magnitude of the roll torque and the lateral position of the moving
mass.
We propose the design of using an internal moving mass to stabilize the
horizontal-plane motion of the REMUS 100 AUV. A linear quadratic regulator
(LQR) is designed to take advantage of both the linear momentum and lateral position
of the internal moving mass to stabilize the heading angle of the vehicle. Alternatively,
we introduce a tunnel thruster to the design, and use backstepping
and Lyapunov redesign techniques to derive a nonlinear feedback control law to
achieve autopilot. The coupling e ects between the closed-loop horizontal-plane
and vertical-plane motions are also analyzed.

As humans explore greater depths of Earth’s oceans, there is a growing need for the installation of subsea structures. 71% of the earth’s surface is ocean but there are limitations inherent in current detection instruments for marine applications leading to the need for the development of underwater platforms that allow research of deeper subsea areas. Several underwater platforms including Autonomous Underwater Vehicles (AUVs), Remote Operated Vehicles (ROVs), and wave gliders enable more efficient deployment of marine structures.
Deployable structures are able to be compacted and transported via AUV to their destination then morph into their final form upon arrival. They are a lightweight, compact solution. The wrapped package includes the deployable structure, underwater pump, and other necessary instruments, and the entire package is able to meet the payload capability requirements. Upon inflation, these structures can morph into final shapes that are a hundred times larger than their original volume, which extends the detection range and also provides long-term observation capabilities.
This dissertation reviews underwater platforms, underwater acoustics, imaging sensors, and inflatable structure applications then proposes potential applications for the inflatable structures. Based on the proposed applications, a conceptual design of an underwater tubular structure is developed and initial prototypes are built for the study of the mechanics of inflatable tubes. Numerical approaches for the inflation process and bending loading are developed to predict the inflatable tubular behavior during the structure’s morphing process and under different loading conditions. The material properties are defined based on tensile tests. The numerical results are compared with and verified by experimental data. The methods used in this research provide a solution for underwater inflatable structure design and analysis. Several ocean morphing structures are proposed based on the inflatable tube analysis.