Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1992. / Includes bibliographical references (leaves 166-169). / by John Victor Amy Jr. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1998. / Includes bibliographical references (p. 227-244). / by Leonard G. Imas. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2001. / Includes bibliographical references. / In part I of the thesis, a canonical problem of three dimensional surfactant hydrody namics, the three-dimensional laminar interaction between a clean or contaminated free surface and a vortical flow underneath is considered. Initially, the vortical flow is in the form of two modulated finite-core vortex tubes parallel to the free surface. The vortex tubes break down via instability and helical vorticity is generated. The most prominent feature at the surface is that associated with the connection of helical vorticity to the free surface. For clean surface, the helical vorticity would interact fully with the free surface and reconnects to it under the influence of the primary vorticity. The presence of surfactant leads to substantial increase in the generation of free-surface secondary vorticity which results from large gradients in the surface surfactant distribution created by induced velocities at the free surface due to the primary vortex tubes. The secondary structure in the bulk interacts with the he lical vorticity, which totally alters the vortex pattern and connection process. The presence of contamination considerably weakens the connection in terms of strength, location and duration. The degree of secondary vorticity generation by the surfac tant is limited by a closed-loop interaction between the flow field (primary flow and secondary flow) and surfactant transport. / (cont.) The presence of secondary vorticity tends to smooth out the surfactant distribution on the free surface and consequently leads to a reduction in the generation of secondary vorticity itself associated with the sur factant gradient (together with surfactant diffusion). This negative feedback process and the rebounding of the primary vorticity by the secondary vorticity are the key processes underlying effects of insoluble surfactant. For contaminated free surface, the secondary and helical vortical structures interact strongly and new structures are generated. The split of helical vorticity because of the strong secondary vorticity leads to the new structures. When the surfactant is soluble, the effects are generally diminished due to the sorption kinetics between the surface and the bulk phase. Both vorticity isosurfaces and vortex filaments are used to describe vortex structures and their evolution. In Part II of the thesis, we investigated the turbulent flow over a smooth wavy wall undergoing traveling wave motion in the mean flow direction. Results are presented from direct numerical simulation with periodic and non-periodic streamwise boundary conditions. The Reynolds number in terms of mean velocity and motion wavelength is in the range of 3000-6500 and wave phase speed c relative to incoming flow velocity U is in the range of -0.5 and 2.0. The flow pattern is a strong function of c/U.For c = 0, there are features like separated region, attached boundary layer, and free shear layer ... / by Xiang Zhang. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994. / Includes bibliographical references (leaf 66). / by Denis Brnathonne. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1999. / Includes bibliographical references (p. 248-251). / Fluorescence can be a powerful tool for probing biological systems. Prior measurements from Caribbean corals identified five fluorescing pigments in reef corals. In this thesis I study coral fluorescence spectra. I wanted to learn if fluorescence could be useful for large scale mapping and monitoring of the reef as a part of an effort to stop the recently reported global decline in coral reefs condition. 3D excitation I emission spectra, average wavelength locations and shape variability studies of each of the pigments is presented. I also present an in situ corrununity study of the species Montastraea cavernosa and investigate the variability of fluorescence emission among colonies of one species at one location. Coral's fluorescence emission spectrum can result from the excitation of one or more fluorescing pigments. A mathematical algorithm was developed to separate coral fluorescence spectra into individual components. The un-mixing algorithm was combined with a prediction model whose purpose was to predict the response that will be produced by any excitation light source given knowledge of the response produced by a different light source. Energy coupling between two of the pigments was discovered. An empirical coupling efficiency factor was defined and calculated to account for this energy transfer. The energy coupling between these pigments may have important consequences in future investigation of coral's evolution. A new experimental method to separate the reflectance and fluorescence spectral components of fluorescing corals was developed for in vivo and in situ data. Two experimental methods are proposed to measure and calculate a newly defined quantity, "practical fluorescence efficiency". This efficiency factor is essential for correct prediction of coral spectra under different illumination conditions. This part of my work will benefit optical models that calculate light interaction with the bottom of the ocean in shallow waters. Lastly I present a prototype Fluorescence Imaging Laser Line Scanner system and discuss its potential use as a remote sensing system for reef mapping and monitoring. Recommendations are made to better tune the system to the fluorescence characteristics of reef corals. / by Eran Fuchs. / Ph.D.

Massachusetts Institute of Technology. Dept. of Ocean Engineering. Thesis. 1971. M.S. / MICROFICHE COPY ALSO AVAILABLE IN BARKER ENGINEERING LIBRARY. / Several diagrams on transparent sheets. / Includes bibliographical references. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2000. / Includes bibliographical references (leaves 218-224). / Solid Freeform Fabrication (SFF) processes have demonstrated the ability to produce parts with locally controlled composition. To exploit this potential, methods to represent and exchange parts with varying local composition need to be proposed and evaluated. In modeling such parts efficiently, any such method should provide a concise and accurate description of all of the relevant information about the part with minimal cost in terms of storage. To address these issues, several approaches to modeling Functionally Graded Material (FGM) objects are evaluated based on their memory requirements. Through this research, an information pathway for processing FGM objects based on image processing is proposed. This pathway establishes a clear separation between design of FGM objects, their processing, and their fabrication. Similar to how an image is represented by a continuous vector valued function of the intensity of the primary colors over a two-dimensional space, an FGM object is represented by a vector valued function spanning a Material Space, defined over the three dimensional Build Space. Therefore, the Model Space for FGM objects consists of a Build Space and a Material Space. The task of modeling and designing an FGM object, therefore, is simply to accurately represent the function m(x) where x E Build Space. Data structures for representing FGM objects are then described and analyzed, including a voxel based structure, finite element method, and the extension of the Radial-Edge and Cell-Tuple-Graph data structures mains in order to represent spatially varying properties. All of the methods are capable of defining the function m(x) but each does so in a different way. Along with introducing each data structure, the storage cost for each is derived in terms of the number of instances of each of its fundamental classes required to represent an object. In order to determine the optimal data structure to model FGM objects, the storage cost associated with each data structure for representing several hypothetical models is calculated. Although these models are simple in nature, their curved geometries and regions of both piece-wise constant and non-linearly graded compositions reflect the features expected to be found in real applications. In each case, the generalized cellular methods are found to be optimal, accurately representing the intended design. / by Todd Robert Jackson. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2002. / Includes bibliographical references (leaf 61). / by Claudio Cairoli. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2003. / Includes bibliographical references (p. 233-247). / One of the important challenges facing the scientific and engineering community is the development of a reliable computational tool for predicting failure of structures under extreme and/or accidental loads. Considered in the present thesis is the process of formation of ductile cracks, which may be responsible for a catastrophic structural failure. Experimental, numerical and analytical studies are carried out on the prediction of ductile crack formation in uncracked bodies on an example of 2024-T351 aluminum alloy. A methodology for ductile crack formation suitable in industrial applications is developed through the introduction of different weighting functions for different stress triaxiality ranges where different ductile crack formation mechanisms occur ("shear fracture" in negative stress triaxialities, void nucleation, growth, and linkage in high stress triaxialities, a transition mode in intermediate stress triaxialities). A cut off value at the stress triaxiality of -1/3 is discovered. Effects of stress and strain ratios, specimen size and anisotropy are also quantified. It is found that the stress triaxiality and the equivalent strain are the two most important parameters governing ductile crack formation while other parameters are probably of secondary importance. A modification to the criterion is introduced to predict crack formation in a single reversal of straining. A case study of a solid aluminum 2024-T351 beam with a smooth round notch under 3-point bending is conducted. / (cont.) Other cases of component validations on different materials, structures and loadings performed by colleagues in the Impact and Crashworthiness Lab are summarized. It is concluded that the proposed approach of predicting ductile crack formation holds a promise of becoming a reliable and practical calculation tool for industrial applications. / by Yingbin Bao. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1991. / Includes bibliographical references (leaves 140-146). / by Chi-Fang Chen. / Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1991.