Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1997. / Includes bibliographical references (leaves 184-196). / by Andrew Arnold Bennett. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2003. / Includes bibliographical references (leaves 117-126). / This thesis addresses problems of free-form object matching for the point vs. NURBS surface and the NURBS surface vs. NURBS surface cases, and its application to copyright protection. Two new methods are developed to solve a global and partial matching problem with no a priori information on correspondence or initial transformation and no scaling effects, namely the KH and the umbilic method. The KH method establishes a correspondence between two objects by utilizing the Gaussian and mean curvatures. The umbilic method uses the qualitative properties of umbilical points to find correspondence information between two objects. These two methods are extended to deal with uniform scaling effects. The umbilic method is enhanced with an algorithm for scaling factor estimation using the quantitative properties of umbilical points. The KH method is used as a building block of an optimization scheme based on the golden section search which recovers iteratively an optimum scaling factor. Since the golden section search only requires an initial interval for the scaling factor, the solution process is simplified compared to iterative optimization algorithms, which require good initial estimates of the scaling factor and the rigid body transformation. The matching algorithms are applied to problems of copyright protection. / (cont.) A suspect model is aligned to an original model through matching methods so that similarity between two geometric models can be assessed to determine if the suspect model contains part(s) of the original model. Three types of tests, the weak, intermediate and strong tests, are proposed for similarity assessment between two objects. The weak and intermediate tests are performed at node points obtained through shape intrinsic wireframing. The strong test relies on isolated umbilical points which can be used as fingerprints of an object for supporting an ownership claim to the original model. The three tests are organized in two decision algorithms so that they produce systematic and statistical measures for a similarity decision between two objects in a hierarchical manner. Based on the systematic statistical evaluation of similarity, a decision can be reached whether the suspect model is a copy of the original model. / by Kwang Hee Ko. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2002. / Includes bibliographical references (p. 347-354). / The long range imaging of submerged objects, seafloor and sub-seafloor geomorphology in continental shelf waters using an active sonar system is explored experimentally and theoretically. A unified model for 3-D object scattering and reverberation that takes into account the coupling between propagation and scattering in a stratified medium is developed from wave theory. The conditions necessary for scattering in a waveguide to become diffuse is derived directly from Green's Theorem. Simulations with the unified model indicate that the detection of submerged target echoes above diffuse seafloor reverberation is highly dependent upon waveguide properties, bandwidth, array aperture, measurement geometry, and the scattering properties of the target. Analysis with the unified model shows that it is theoretically plausible for coherent returns from the scattering of evanescent waves by extended but discrete sub-bottom geologic features to stand significantly above diffuse or incoherent returns arising from small-scale roughness of the waveguide boundaries. A long-range bistatic sonar system was deployed in a field experiment and used to image extensive networks of buried river channels and inclined sub-seafloor strata over tens of kilometers in nearreal time. Such a capability is of great advantage in geophysical applications. Since buried river channels are expected to be ubiquitous in continental shelf environments, sub-seafloor geomorphology will play a major role in producing "false alarms" or cluster in long-range sonar systems that search for submerged objects such as underwater vehicles. / (cont.) A generalized extinction theorem for object scattering in a stratified medium is derived that can be applied to detect and classify objects from the total field in the forward scatter direction in a waveguide. Analytic expressions are derived for the attenuation and dispersion in the forward propagated field due to scattering from random surface and volume inhomogeneities in a waveguide. The unified model is applied to show that the active sonar equation is not in general valid for scattering in a waveguide. It is shown that the sonar equation may be made approximately valid in a waveguide by lowering the active frequency of operation sufficiently for the given measurement scenario to simplify analysis for target classification and localization. / by Purnima Ratilal. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995. / Includes bibliographical references (p. 241-245). / by Matthew Conti. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1993. / Includes bibliographical references (leaves 164-165). / by Manoj B. Keshavan. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995. / Includes bibliographical references (leaves 124-132). / by Hanumant Singh. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1996. / Includes bibliographical references (leaves 80-83). / by Scott Nielsen Miller. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2005. / Includes bibliographical references (p. 137-140). / The dynamics of breaking waves significantly affect air-sea fluxes of heat, momentum, mass and energy across the ocean interface. Breaking waves also contribute considerable loading to offshore and coastal structures, and furthermore, the quasi-steady bow wave on a ship increases drag and ease of detection by the bubbly wake. However, the complexity of the phenomenon has severely limited our ability to describe it and predict its occurrence. Research has typically involved field observations, controlled laboratory studies, and numerical simulations. A recent simulation presented new information about local energy dissipation and the coupled air-water effects of small breaking waves. In light of these findings, the objective of this thesis is to experimentally study small-scale breaking waves and examine the combined air-water flow fields using advanced visualization techniques. This research was performed in a narrow wavetank which was 2.5m long. Waves were generated with a hinged paddle and breaking occurred as the train propagated up a 15 degree slope to a level plateau. Waves were studied using surface piercing wave probes, high speed video, and Particle Image Velocimetry (PIV). / (cont.) Surface tension was found to have a significant effect on the breaking dynamics at this scale. After a thorough exploration of its effect on surface tension, isopropyl alcohol was added to distilled water in a 10% solution by volume, which reduced the surface tension to approximately 43 dynes/cm. A wave breaking database was created which included 26 different wave trains over a frequency band of 1.5-4Hz. The corresponding Weber numbers ranged from 400 through 14,600 with Reynolds numbers from 38,200 through 280,000. The wave probes measured significant potential energy losses to breaking which are expected. The air- water flow fields are studied by seeding the air and water with reflective particle and processing the video results with PIV software. Qualitative results from PIV including vector and vorticity maps agree well with previous theory and recent numerical results. / by Angus Kai McDonald. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2004. / Includes bibliographical references (leaves 167-169). / Light Emitting Diode (LED) technology has advanced dramatically in a few short years. An expensive and difficult to manufacture LED array containing nearly 100 individual LEDs and measuring at least 5 cm² can now be replaced by a single 5 Watt LED smaller than a quarter. As the light output for a given package size continues to increase, doubling every two years, it is possible to consider using these new LEDs to improve existing lighting systems and to explore non-traditional methods of underwater photographic illumination. So, can these high-output LEDs be used for underwater illumination, under what circumstances are they a good choice, and what is the optimal way to deploy them for a given set of conditions? In this thesis I attempt to answer these questions. In this thesis, I tested these 5W LEDs in a number of conditions and orientations in order to simulate the lighting conditions experienced by autonomous underwater vehicles (AUVs) illuminating and imaging targets on the ocean floor. These LEDs were characterized and compared to existing lighting systems and methods. Their suitability for use both as vehicle-carried illumination and off-the-vehicle lighting packages was examined. / (cont.) Finally, conclusions were drawn as to the effectiveness of the 5W LEDs for underwater illumination and a guideline for LED illumination is presented to help AUV researchers determine the optimal lighting package for use on their missions. / by Joseph R. Curran. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995. / Includes bibliographical references. / by Raymond K. Joe. / M.S.