Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): Anthony J. Healey. Includes bibliographical references (p. 41-42). Also available online.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): Anthony J. Healey. Includes bibliographical references (p.65-66). Also available online.

Rapid and high resolution motion and tension measurements were made of a typical vertically tethered system, a caged deep-sea ROV, while it operated at sea. The system is essentially one-dimensional because only the vertical motions of the underwater platform and the ship were coherent, while horizontal motions of the platform were weak and incoherent with any component of motion of the ship. The natural frequency of the system is found to be within the frequency band of ship motion for most of its operating range and the platform response is weakly non-linear. This results in a vertical acceleration of the platform that is up to 2.2 times larger than that of the ship. Large vertical excursions of the ship produce momentary slack in the tether near the platform. At the instant prior to re-tensioning, the tether and platform are moving apart and upon re-tensioning, the inertia of the platform imparts a large strain—a snap load—in the tether. The resulting strain wave propagates to the surface with the characteristic speed (3870 ms⁻¹) of tensile waves in the tether. An extremely repeatable pattern of echoes is detectable at each end. Two models, a continuous (closed form) non-dimensional frequency domain model and a discrete finite-element time domain model are developed to represent vertically tethered systems subject to surface excitation. Both models accurately predicts the measured response, with slightly better accuracy in the discrete version. The continuous model shows that the response is governed by only two non-dimensional parameters. The continuous model is invalid for slack tether and inherently unable to predict snap loads. By slightly increasing the ship motion, the discrete model accurately reproduces the observed snap loads and their characteristics. Discrepancies between the predicted and measured response of the platform bring into question the concepts of a constant drag coefficient and a constant added mass for oscillatory flow around the platform. By adding a simple wake model to account for flow history, the error in the calculated platform motion and tension in the tether were reduced by almost a factor of 2. Passive ship-mounted and cage-mounted heave compensation systems were investigated with a view to reducing the cage motion and tension in the tether. Both systems were found to be effective and for reasonable parameters, they can reduce the motion of the cage and the tension in the tether by a factor of 2. Addition of either compensation system reduced the natural frequency of the system and extended the operating sea state of a cage ROV system. However, the characteristics of the compensation systems must be carefully chosen or the operational problems will be exacerbated. In particular, the natural frequency of higher modes may enter the waveband for deeper operating depths. During extreme sea states, the cage compensated system eliminated all snap loads. / Graduate

This project proposes the development of an autonomous underwater vehicle that can be used to perform underwater research missions..The vehicle can be pre-programmed to complete a specified mission. Missions may include underwater pipe inspection, a survey of the sea floor or just the transport of given sensors to a certain depth or position and take measurements of underwater conditions. The Mechatronics and Micro Manufacturing group at the CSIR is engaged in developing a portfolio of autonomous vehicles as well as fur- ther research into the development and implementation of such vehicles. Underwater vehicles will form part of the portfolio of autonomous vehicle research. Autonomous underwater vehicles (AUVs) are mostly used for research purposes in oceanographic studies as well as climate studies. These scientists use AUVs to carry a payload of sensors to specified depths and take measurements of underwater conditions, such as water temperature, water salinity or carbon levels as carbon is being released by plankton or other ocean organisms. Very little information is available about what is happening below the surface of the oceans and AUVs are being used to investigate this relatively unknown environment. The area covered by the world's ocean is 361 million km2 with an average depth of 3790 m. The deepest surveyed depth point in the ocean is at a depth of about 11 000 m at the southern end of the Mariana Trench in the Pacific Ocean. This just shows the need for research into this mostly unexplored world. Research and exploration in the oceans can be achieved through the use of autonomous underwater vehicles. A big problem to overcome is the fact that GPS is not available for navigation in an underwater environment. Other sensors need to be found to be used for navigational purposes. The particular vehicle developed for this study will be used to facili- tate further research into underwater vehicle navigation and underwater robotics. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.S. in Mathematics) Naval Postgraduate School, December 1995. / "December 1995." Thesis advisor(s): Carlos Borges, Bard K. Mansager. Includes bibliographical references. Also available online.

An open source, MATLAB (trademarked)-based propeller design code MPVL was improved to include rapid prototyping capabilities as well as other upgrades as part of this effort. The resulting code, OpenPVL is described in this thesis. In addition, results from the development code BasicPVL are presented. An intermediate code, BasicPVL, was created by the author while OpenPVL was under development, and it provides guidance for initial propeller designs and propeller efficiency analysis. OpenPVL is part of the open source software suite of propeller design codes, Openprop. OpenPVL is in the form of a Graphical User Interface (GUI) which features both a parametric design technique and a single propeller geometry generator. This code combines a user-friendly interface with a highly modifiable platform for advanced users. This tool offers graphical propeller design feedback while recording propeller input, output, geometry, and performance. OpenPVL features the ability to translate the propeller design geometry into a file readable by a Computer Aided Design (CAD) program and converted into a 3D-printable file. Efficient propellers reduce the overall power requirements for Autonomous Underwater Vehicles (AUVs), and other propulsion-powered vehicles. The focus of this study is based on the need of propeller users to have an open source computer-based engineering tool for the rapid design of propellers suited to a wide range of underwater vehicles. Propeller vortex lattice lifting line (PVL) code in combination with 2D foil theory optimizes propeller design for AUVs. Several case studies demonstrate the functionality of OpenPVL, and serve as guides for future propeller designs. The first study analyzes propeller thruster performance characteristics for an off-the-shelf propeller, while the second study demonstrates the process for propeller optimization-from the initial design to the final file that can be read by a 3D printer. / Contract number: N62771-97-G-0026 / US Naval Academy (USNA) author.

Thesis (Ocean E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 150-151. / M.S.

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Alan R. Washburn, Samuel E. Buttrey. Includes bibliographical references (p. 39). Also available online.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, March 1992. / Thesis Advisor(s): Kanayama, Yutaka ; Zyda, Michael J. "March 1992." Appendix G videotape located at VHS 5000043. Includes bibliographical references (p. 240-247). Also available in print.