Página 13 dos resultados de 1134 itens digitais encontrados em 0.008 segundos

‣ System identification from ship manoeuvres in currents.

Szeto, Feut Feat
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (xxiv, 912 [i.e. 916] leaves); 58911603 bytes; 58911358 bytes; application/pdf; application/pdf
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Thesis. 1977. Ocean E.--Massachusetts Institute of Technology. Dept. of Ocean Engineering.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Includes bibliographical references.

‣ Evaluation of transport relative to the tidal mixing front on Southern Georges Bank

Katrein, Jody M. (Jody Marie), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 119 p.; 6995254 bytes; 6995007 bytes; application/pdf; application/pdf
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by Jody M. Katerin.; Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), September 2001.; Includes bibliographical references (leaves 65-67).

‣ Experimental visualization of the near-boundary hydrodynamics about fish-like swimming bodies

Techet, Alexandra Hughes
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 155 leaves; 12787005 bytes; 12786764 bytes; application/pdf; application/pdf
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This thesis takes a look at the near boundary flow about fish-like swimming bodies. Experiments were performed up to Reynolds number 106 using laser Doppler velocimetry and particle imaging techniques. The turbulence in the boundary layer of a waving mat and swimming robotic fish were investigated. How the undulating motion of the boundary controls both the turbulence production and the boundary layer development is of great interest. Unsteady motions have been shown effective in controlling flow. Tokumaru and Dimotakis (1991) demonstrated the control of vortex shedding, and thus the drag on a bluff body, through rotary oscillation of the body at certain frequencies. Similar results of flow control have been seen in fish-like swimming motions. Taneda and Tomonari (1974) illustrated that, for phase speeds greater than free stream velocity, traveling wave motion of a boundary tends to retard separation and reduce near-wall turbulence. In order to perform experiments on a two-dimensional waving plate, an apparatus was designed to be used in the MIT Propeller tunnel, a recirculating water tunnel. It is an eight-link piston driven mechanism that is attached to a neoprene mat in order to create a traveling wave motion down the mat. A correlation between this problem and that of a swimming fish is addressed herein...

‣ Geoacoustic inversion in laterally varying shallow-water experiments using high-resolution wavenumber estimation

Becker, Kyle M
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 170 leaves; 11937415 bytes; 11937169 bytes; application/pdf; application/pdf
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Sound propagation in shallow water is highly dependent on the interaction of the sound field with the bottom. In order to fully understand this problem, it is necessary to obtain reliable estimates of bottom geoacoustic properties that can be used in acoustic propagation codes. In this thesis, perturbative inversion methods and exact inverse methods are discussed as a means for inferring geoacoustic properties of the bottom. For each of these methods, the input data to the inversion is the horizontal wavenumber spectrum of a point-source acoustic field. The main thrust of the thesis work concerns extracting horizontal wavenumber content for fully three-dimensionally varying waveguide environments. In this context, a high-resolution autoregressive (AR) spectral estimator was applied to determine wavenumber content for short aperture data. As part of this work, the AR estimator was examined for its ability to detect discrete wavenumbers in the presence of noise and also to resolve closely spaced wavenumbers for short aperture data. As part of a geoacoustic inversion workshop, the estimator was applied to extract horizontal wavenumber content for synthetic pressure field data with range-varying geoacoustic properties in the sediment. The resulting wavenumber content was used as input data to a perturbative inverse algorithm to determine the sound speed profile in the sediment. It was shown using the high-resolution wavenumber estimator that both the shape and location of the range-variability in the sediment could be determined.; (cont.) The estimator was also applied to determine wavenumbers for synthetic data where the water column sound speed contained temporal variations due to the presence of internal waves. It was shown that reliable estimates of horizontal wavenumbers could be obtained that are consistent with the boundary conditions of the waveguide. The Modal Mapping Experiment (MOMAX)...

‣ Horizontal linear array sensor localization and preliminary coherence measurements from the 2001 ASIAEX South China Sea experiment; Horizontal linear array sensor localization and preliminary coherence measurements from the 2001 Asian Seas International Acoustic Expreiment SCS experiment

Schroeder, Theodore Herbert, 1967-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 105 p.; 7152011 bytes; 7151768 bytes; application/pdf; application/pdf
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by Theodore Herbert Schroeder.; Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), 2002.; Includes bibliographical references (p. 105).

‣ Acoustic scattering by axisymmertic finite-length bodies with application to fish : measurement and modeling

Reeder, D. Benjamin (Davis Benjamin), 1966-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 148 leaves; 5018894 bytes; 5018703 bytes; application/pdf; application/pdf
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This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically efficient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. The model presented is an extension of a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies of revolution. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped, linearly swept, frequency modulated signal was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles of orientation in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation...

‣ Attitude control of an underwater vehicle subjected to waves

Willy, Christopher John
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 152 leaves
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by Christopher John Willy.; Thesis (Ocean. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994.; GRSN 707473; Vita.; Includes bibliographical references (leaves 137-139).

‣ Estimating Gulf of Maine zooplankton distributions using multiple frequency acoustic, video and environmental data

Warren, Joseph David
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 219 p.
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by Joseph David Warren.; Thesis (Ph.D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), February 2001.; Includes bibliographical references (p. 211-219).

‣ Numerical and experimental analysis of initial water impact of an air-dropped REMUS AUV

Roe, Stephen Michael
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 79 leaves
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The initial water impact of a free-falling object is primarily related to the fluid forces on the wetted surface of the object. The shape-dependent added-mass coefficients express the fluid forces integrated over the body, and thus physically represent the additional inertia of water accelerated with the body. The field of hydrodynamic impact has been primarily concerned with estimating the added-mass coefficients of various types of bodies for different water impact types, such as seaplane landings, torpedo drops, and ship slamming. In this study, a numerical model has been constructed to estimate the hydrodynamic impact loads of a REMUS dropped in free-fall from a helicopter in a low hover. Developed by von Alt and associates at Woods Hole Oceanographic Institution, the REMUS (Remote Environmental Monitoring UnitS) is a small, man-portable, torpedo shaped Autonomous Underwater Vehicle (AUV) that is normally operated from small boats for a variety of scientific, industrial, and military applications. Finite-element method software and computer aided drafting tools were used to create a simplified model of REMUS without fins, propeller, or transducers.; (cont.) This axisymmetric REMUS model was cut by a flat free surface at various pitch angles and submergence values...

‣ Verification of numerical models for hydrothermal plume water through field measurements at TAG

Wichers, Sacha
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 65 p.
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Hydrothermal vents discharge superheated, mineral rich water into our oceans, thereby providing a habitat for exotic chemosynthetic biological communities. Hydrothermal fluids are convected upwards until they cool and reach density equilibrium, at which point they advect laterally with the current. The neutrally buoyant plume layer can have length scales on the order of several kilometers, and it therefore provides the best means to detect the presence of vent fields on the seafloor, which typically have length scales on the order of a few meters. This thesis uses field measurements of the velocity, temperature and particulate anomalies associated with the TAG hydrothermal plume to demonstrate that tidal currents exert a strong impact on the plume shape, and to provide new constraints on the thermal power of the TAG hydrothermal system. The results show that the power output of the TAG system is on the order of 6000 MW, which is up to two orders of magnitude greater than previous estimates, and that there is considerably more entrainment than had previously been assumed.; by Sacha Wichers.; Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution)...

‣ Large scale structure from motion for autonomous underwater vehicle surveys

Pizarro, Oscar
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 190 p.
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Our ability to image extended underwater scenes is severely limited by attenuation and backscatter. Generating a composite view from multiple overlapping images is usually the most practical and flexible way around this limitation. In this thesis we look at the general constraints associated with imaging from underwater vehicles for scientific applications - low overlap, non-uniform lighting and unstructured motion - and present a methodology for dealing with these constraints toward a solution of the problem of large area 3D reconstruction. Our approach assumes navigation data is available to constrain the structure from motion problem. We take a hierarchical approach where the temporal image sequence is broken into subsequences that are processed into 3D reconstructions independently. These submaps are then registered to infer their overall layout in a global frame. From this point a bundle adjustment refines camera and structure estimates. We demonstrate the utility of our techniques using real data obtained during a SeaBED AUV coral reef survey. Test tank results with ground truth are also presented to validate the methodology.; by Oscar Pizarro.; Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology...

‣ Emulating the fast-start swimming performance of the Chain Pickerel (Esox niger) using a mechanical fish design

Watts, Matthew Nicholas
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75 p.
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Mean maximum start-up accelerations and velocities achieved by the fast-start specialist, northern pike, are reported at 120 ms-2 and 4 ms-1, respectively (Harper and Blake, 1990). In this thesis, a simple mechanical system was created to closely mimic the startle response that produces these extreme acceleration events. The system consisted of a thin metal beam covered by a urethane rubber fish body. The mechanical fish was held in curvature by a restraining line and released by a pneumatic cutting mechanism. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish. The fish motion was recorded and the kinematics analyzed while using a number of different tail shapes and materials. Performance of the mechanical fish was determined by maximum acceleration, peak and averaged maximum velocity, and hydrodynamic efficiency. Maximum start-up acceleration was calculated at 48 ms-2. Peak and averaged maximum velocity was calculated at 0.96 ms-1 and 0.8 ms-1, respectively. The hydrodynamic efficiency of the fish, calculated by the transfer of energy, was 11%. Flow visualization of the mechanical fast-start wake was also analyzed. The visualization uncovered two specific vortex-shedding patterns; a single and a double-vortex pattern are described.; by Matthew Nicholas Watts.; Thesis (S.M. in Oceanographic Engineering)--Joint Program in Ocean Engineering/Applied Ocean Physics and Engineering (Massachusetts Institute of Technology...

‣ Large-area visually augmented navigation for autonomous underwater vehicles

Eustice, Ryan M
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 187 p.
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This thesis describes a vision-based, large-area, simultaneous localization and mapping (SLAM) algorithm that respects the low-overlap imagery constraints typical of autonomous underwater vehicles (AUVs) while exploiting the inertial sensor information that is routinely available on such platforms. We adopt a systems-level approach exploiting the complementary aspects of inertial sensing and visual perception from a calibrated pose-instrumented platform. This systems-level strategy yields a robust solution to underwater imaging that overcomes many of the unique challenges of a marine environment (e.g., unstructured terrain, low-overlap imagery, moving light source). Our large-area SLAM algorithm recursively incorporates relative-pose constraints using a view-based representation that exploits exact sparsity in the Gaussian canonical form. This sparsity allows for efficient O(n) update complexity in the number of images composing the view-based map by utilizing recent multilevel relaxation techniques. We show that our algorithmic formulation is inherently sparse unlike other feature-based canonical SLAM algorithms, which impose sparseness via pruning approximations. In particular, we investigate the sparsication methodology employed by sparse extended information filters (SEIFs) and offer new insight as to why...

‣ Performance analysis of subaperture processing using a large aperture planar towed array

Watson, Jennifer Anne, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (215 leaves)
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In recent years the focus of passive detection and localization of submarines has moved from the deep ocean into the littoral regions. the problem of passive detection in these regions is complicated by strong multipath propagation with high transmission loss. Large aperture planar arrays have the potential to improve detection performance due to their high resolution and high gain, but are suceptible to two main performance degradation mechanisms: limited spatial coherence of signals and nonstationarity of high bearing rate interference sources common in littoral regions of strategic importance. This thesis presents subarray processing as a method of improving passive detection performance using such large arrays. This thesis develops statistical models for the detection of performance of three adaptive, sample-covariance-based subarray processing algorithms which incorporate the effects of limited spatial coherence as well as finite snapshot support. The performance of the optimum processor conditioned on known data coveriances is derived as well for comparison. These models are then used to compare subarray algorithms and partitioning schemes in a variety of interference environments using plane wave and matched-field propagation models.; (cont.) The analysis shows a tradeoff between the required adaptive degrees of freedom...

‣ Vortex Induced Vibrations of cylinders : experiments in reducing drag force and amplitude of motion; VIV of cylinders : experiments in reducing drag force and amplitude of motion

Farrell, David Emmanuel
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 92 p.
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Reducing the deleterious effect of Vortex Induced Vibrations (VIV) in marine risers is an important task for ocean engineers; and many competing factors exist in the design of VIV suppression devices. This thesis explores the experimental minimization of the drag force and the disruption of vortex formation by utilizing VIV suppression devices. Two series of tests are conducted-both utilizing separate testing designs. The first tests are the flexible cylinder experiments, detailed in Chapter 2, which determine the drag force and vibration amplitude of numerous, original testing configurations. The second series of tests are the rigid cylinder, PIV experiments, detailed in Chapter 3. These tests measure both the drag force on the cylinder and the oscillating component of the lift force, the latter of which is a good indication of vortex formation. The Chapter 3 tests also image the test section wake-providing helpful insight into the physical process of vortex formation. In brief, this thesis presents a detailed description and results of the two series of original VIV suppression tests. Many original configurations are tested, and the results are contained herein.; by David Emmanuel Farrell.; Thesis (S.M. in Mechanical Engineering)--Joint Program in Ocean Engineering/Applied Ocean Physics and Engineering (Massachusetts Institute of Technology...

‣ Advances in the visualization and analysis of boundary layer flow in swimming fish

Anderson, Erik J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 245 p.
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In biology, the importance of fluid drag, diffusion, and heat transfer both internally and externally, suggest the boundary layer as an important subject of investigation, however, the complexities of biological systems present significant and unique challenges to analysis by experimental fluid dynamics. In this investigation, a system for automatically profiling the boundary layer over free-swimming, deforming bodies was developed and the boundary layer over rigid and live mackerel, bluefish, scup and eel was profiled. The profiling system combined robotics, particle imaging velocimetry, a custom particle tracking code, and an automatic boundary layer analysis code. Over 100,000 image pairs of flow in the boundary layer were acquired in swimming fish alone, making spatial and temporal ensemble averaging possible. A flat plate boundary layer was profiled and compared to known laminar and turbulent boundary layer theory. In general, profiles resembled those of Blasius for sub-critical length Reynolds numbers, Rex. Transition to a turbulent boundary layer was observed near the expected critical Rex and subsequent profiles agreed well with the law of the wall. The flat plate analysis demonstrated that the particle tracking and boundary layer analysis algorithms were highly accurate.; (cont.) In rigid fish...

‣ Integrated optimization and simulation model for resource acquisition and utilization : an application to ocean/river articulated tug/barge system

Ji, Ming
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 203 leaves
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by Ming Qi.; Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1997.; Includes bibliographical references (leaves 199-203).

‣ Approximation with interval B-splines for robust reverse engineering

Shen, Guoling, 1967-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 136 leaves
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by Guoling Shen.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1997.; Includes bibliographical references (leaves 132-136).

‣ Seismo-acoustic rough interface scattering of surface-generated ambient noise in a stratified ocean

Liu, Jin-Yuan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: xxiii, 194 p.
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by Jin-Yuan Liu.; Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1993.; Includes bibliographical references (p. 187-194).

‣ Investigations of scalar transfer coefficients in fog during the Coupled Boundary Layers and Air Sea Transfer experiment : a case study; Investigations of scalar transfer coefficients in fog during the CBLAST experiment : a case study

Crofoot, Robert Farrington
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 72 leaves
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The uncertainty in the determination of the momentum and scalar fluxes remains one of the main obstacles to accurate numerical forecasts in low to moderate wind conditions. For example, latent heat fluxes computed from data using direct covariance and bulk aerodynamic methods show that there is good agreement in unstable conditions when the latent heat flux values are generally positive. However, the agreement is relatively poor in stable conditions, particularly when the moisture flux is directed downward. If the direct covariance measurements are indeed accurate, then they clearly indicate that the bulk aerodynamic formula overestimate the downward moisture flux in stable conditions. As a result, comparisons of the Dalton number for unstable and stable conditions indicate a marked difference in value between the two stability regimes. Investigations done for this thesis used data taken primarily at the Air-Sea Interaction Tower (ASIT) during the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Experiment 2003 from the 20-27 August 2003. Other data from the shore based Martha's Vineyard Coastal Observatory (MVCO) and moored buoys in the vicinity of the ASIT were also incorporated.; (cont.) During this eight day period, the boundary layer was often characterized by light winds...