Página 12 dos resultados de 1134 itens digitais encontrados em 0.008 segundos

‣ Ocean, platform, and signal processing effects on synthetic aperture sonar performance

Rolt, Kenneth D
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 233 p.; 13450441 bytes; 13450201 bytes; application/pdf; application/pdf
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by Kenneth D. Rolt.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1991.; Includes bibliographical references (p. 226-233).

‣ Acoustic wave scattering from a random ocean bottom

Tang, Dajun
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 130 leaves; 7193559 bytes; 7193318 bytes; application/pdf; application/pdf
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Dajun Tang.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, and Woods Hole Oceanographic Institution, 1991.; Includes bibliographical references (leaves 123-130).

‣ Revenue management for ocean carriers : optimal capacity allocation with multiple nested freight rate classes

Maragos, Spyridon A. (Spyriodon Apostolos)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 134 p.; 6624728 bytes; 6624486 bytes; application/pdf; application/pdf
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by Spyridon A. Maragos.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994.; Includes bibliographical references (p. 131-134).

‣ Freight mode choice : air transport versus ocean transport in the 1990s

Lewis, Dale B. (Dale Brian)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 139 leaves; 12029654 bytes; 12029412 bytes; application/pdf; application/pdf
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by Dale B. Lewis.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995.; Includes bibliographical references (leaves 137-139).

‣ An integrated modal approach to surface and volume scattering in ocean acoustic waveguides

Tracey, Brian Hearne
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 198 p.; 13812695 bytes; 13812452 bytes; application/pdf; application/pdf
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by Brian H. Tracey.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1996.; Includes bibliographical references (p. 192-198).

‣ Spatiotemporal processing and time-reversal for underwater acoustic communications

Wang, Daniel Y
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 67 p.; 2390242 bytes; 2392963 bytes; application/pdf; application/pdf
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High-rate underwater acoustic communication can be achieved using transmitter/receiver arrays. Underwater acoustic channels can be characterized as rapidly time-varying systems that suffer severe Inter Symbol Interferences (ISI) caused by multi-path propagation. Multi-channel combining and equalization, as well as time-reversal techniques, have been used over these channels to reduce the effect of ISI. As an alternative, a spatiotemporal focusing technique had been proposed. This technique is similar to time-reversal but it explicitly takes into account elimination of ISI. To do so, the system relies on the knowledge of channel responses. In practice, however, only channel estimates are available. To assess the system performance for imperfectly estimated time-varying channels, a simulation analysis was conducted. Underwater acoustic channels were modeled using geometrical representations of a 3-path propagation model. Multi-path fading was incorporated using auto regressive models. Simulations were conducted with various estimator delay scenarios for both the spatiotemporal focusing and simple time-reversal. Results demonstrate performance dependence on the non-dimensional product of estimation delay and Doppler spread.; (cont.) In particular...

‣ Multiobjective collaborative optimization of systems of systems; Multi objective collaborative optimization of systems of systems

Wolf, Robert A. (Robert Allen)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 166 p.; 9303014 bytes; 9309978 bytes; application/pdf; application/pdf
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Concept studies for warship designs typically focus on ship performance characteristics by setting design goals for such things as speed, range, and cost. However, warships generally operate as part of a larger battle or strike group. Therefore, the designs should be evaluated as part of a system of multiple ship systems since designing each ship individually may result in underutilized and excess equipment and capability; in other words an inefficient design of the system of systems. This thesis examines the simultaneous design of several ships using the sea base concept as an example application of a network of ships working together. The number and characteristics of these ships determine the mission performance of the sea base. To properly design any of the sea base ships, the interrelationships must be included. A mission simulation is used to combine the performance characteristics of different ship designs into a single performance objective: the time to deliver a brigade size combat force to its assigned objectives.; (cont.) To enable the design of multiple ships, collaborative optimization, a multilevel optimization approach, was used to decompose the problem into individual ship design optimizations with system level interfaces controlled by a system of systems optimization algorithm. This allowed each ship to use techniques and algorithms best suited to reach an optimal design without impacting the design approaches used by the other ships. The classical collaborative optimization approach was relaxed to include multiple objectives such as performance and cost...

‣ Modern fleet planning methods for ocean liner service

Viglundsson, Viglundur Thor
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 194 leaves; 7047692 bytes; 7059657 bytes; application/pdf; application/pdf
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by Viglundur Thor viglundsson.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994.; Includes bibliographical references (leaves 112-113).

‣ Applicability of undermatched welds for high strentgh steel structures

Kafetsis, Nikolas K
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 184 leaves
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by Nikolas K. Kafetsis.; Thesis (Nav.E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.; Includes bibliographical references (leaves 182-184).

‣ Wave theory modeling of three-dimensional seismo-acoustic reverberation in ocean waveguides

Fan, Henry
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 182 leaves
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by Henry Fan.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995.; Includes bibliographical references (leaves 175-182).

‣ A coning motion apparatus for hydrodynamic model testing in a non-planar cross-flow

Johnson, David Craig
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 140 leaves
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by David Craig Johnson.; Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1989 and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1989.; Title as it appears in the M.I.T. Graduate List, June 1989: A cooling motion apparatus for hydrodynamic model testing in a non-planar cross-flow.; Includes bibliographical references (leaves 80-81).

‣ Hydrofoil shape optimization by gradient methods

Tozzi, Gregory Michael
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 125 p.; 4618128 bytes; 4623330 bytes; application/pdf; application/pdf
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A study was carried out to develop and test techniques for the computational optimization of hydrofoil sections and lifting surfaces advancing under a free surface. A mathematical model was developed based on the extension of a two-dimensional potential flow solution to account for three dimensional effects. Prandtl's lifting line theory was used to account for induced drag and downwash at the leading edge of the foil. Strip theory was used to extend the two-dimensional wave drag solutions to three dimensions for high aspect ratio foils. A semi-empirical correction was added to account for viscous drag. The drag-to-lift ratio of foil sections and lifting surfaces were optimized using first order gradient techniques. Optimization studies involving submerged foil sections suggest that trading buoyancy for a reduction in wave drag will lead to optimal geometries. Difficulties encountered resulting from the adoption of a potential flow model were identified and discussed. The lifting surface optimization was carried out using the coefficients of Glauert's circulation series as design variables. At high speeds it was shown that non-elliptical loading can produce reductions in the drag-to-lift ratio of a lifting surface. Induced drag dominated the low-speed optimization...

‣ Force and hydrodynamic efficiency measurements of a three-dimensional flapping foil

McLetchie, Karl-Magnus Weidmann
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 p.; 2374948 bytes; 2377784 bytes; application/pdf; application/pdf
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Investigations into unsteady flapping foil propulsion have shown that it is an efficient and high thrust means of propulsion. Extensive work has been done to optimize the efficiency of two-dimensional flapping foils, varying both the kinematics of the motion and the flexibility of the foil. However, no thorough investigation into the hydrodynamic efficiency of three-dimensional flapping foils has been made. In this thesis, experimental hydrodynamic efficiency measurements and force measurements of a three-dimensional flapping foil are presented. These measurements were made by mounting a small, six-axis dynamometer directly onto the foil shaft of a flapping foil module. The module uses two computer controlled servo motors to actuate a foil in a sinusoidal pitch and roll motion, similar to the motion of a penguin's wing. The measured thrust coefficients compared well to previous experimental results, and the on-shaft dynamometer proved to be a valuable sensor. However, the experimental apparatus must be modified before reliable efficiency results can be made for the entire range of kinematics.; (cont.) Once these improvements are made, a thorough investigation into the effects of foil geometry and flexibility can be done to find the optimum efficiency parameters of a three-dimensional flapping foil. These optimum efficiency parameters will be valuable for the development of flapping foil vehicles.; by Karl-Magnus Weidmann McLetchie.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Identification and resolution of problems with methodology used in selection of technological concepts for R&D support

Hardman, William L
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 183 p.; 7113132 bytes; 7120827 bytes; application/pdf; application/pdf
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How to better evaluate the merits of competing technological concepts. This project is concerned with evaluation of the merits of competing technological concepts and managing the R&D investments needed to bring them to fruition. A weakness of the current R&D process is that arguments regarding who should receive funding come from a concept's proponents, who are usually interested and biased. More objective evaluation methods are needed. As part of this work it is important to understand better how qualified experts evaluate technological concepts. Can a probabilistically formulated method of integrating knowledge of various performance attributes provide better understanding of the likely performance of a technological concept? This is the question of interest. A nuclear power plant example (impetus for the actual study below). The impetus for the study began with The U.S. Department of Energy's Generation IV advanced reactor technology program, the program that will select the next generation of nuclear reactors. Generation IV chose twenty-seven criteria for use in determining which nuclear power plant concepts would be best for a given mission. These criteria came in the form of twenty-seven questions asked of prospective concept designers.; (cont.) The concept designers ranked their own design over a range of seven bins and specified a peak in the most likely bin. The 27 criteria were assumed to be independent and were used in creating three major goals (sustainability...

‣ High speed linear induction motor efficiency optimization

Johnson, Andrew P. (Andrew Peter)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 189 p.; 6915839 bytes; 6923757 bytes; application/pdf; application/pdf
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One of the reasons linear motors, a technology nearly a century old, have not been adopted for a large number of linear motion applications is that they have historically had poor efficiencies. This has restricted the progress of linear motor development. The concept of a linear motor as a rotary motor cut and laid out flat with a conventional rotary motor control scheme as a design basis may not be the best way to design and control a high-speed linear motor. End effects and other geometry subtleties of a linear motor make it unique, and a means of optimizing efficiency with both the motor geometry and the motor control scheme will be analyzed to create a High-Speed Linear Induction Motor (LIM) with a higher efficiency than what is possible with conventional motors and controls. This thesis pursues the modeling of a short secondary type Double-Sided Linear Induction Motor (DSLIM) that is proposed for use as an Electromagnetic Aircraft Launch System (EMALS) aboard the CVN-2 1. Mathematical models for the prediction of effects that are peculiar to DSLIM are formulated, and their overall effects on the performance of the proposed machine are analyzed.; (cont.) These effects are used to generate a transient motor model, which is then driven by a motor controller that is specifically designed to the characteristics of the proposed DSLIM. Due to this DSLIM's role as a linear accelerator...

‣ Lubricant oil consumption effects on diesel exhaust ash emissions using a sulfur dioxide trace technique and thermogravimetry

Plumley, Michael J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 131 p.; 8832895 bytes; 8838361 bytes; application/pdf; application/pdf
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A detailed experimental study was conducted targeting lubricant consumption effects on ,diesel exhaust ash levels using a model year 2002 5.9L diesel engine, high and low Sulfur commercial lubricants, and clean diesel fuels. Regulatory decreases in allowable particulate matter emissions for on road diesel engines are driving industry to develop diesel particulate filters to trap and combust particulate. Remaining ash not combusted in this process clogs filters requiring engine down time and additional cleaning expenses. Recent reductions in fuel Sulfur and ash levels have also made lubricant consumption a significant relative contributor to particulate and ash generation. The goal of this study, a detailed understanding of lubricant contribution to particulate formation and ash transport, is required to enhance future filter design. 'The use of ultra clean fuels enhances accuracy of the Sulfur Dioxide tracer technique for estimating lubricant consumption and increases the relative contribution of lubricant to particulate emission. Results indicate the subject engine lubricant consumption is typical of others reported in literature. Particulate matter emission increases were measured after switching from a relatively low Sulfur, low sulfated ash oil to a high Sulfur...

‣ Shape optimization theory and applications in hydrodynamics

Geçer, Onur
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves; 3800871 bytes; 3804538 bytes; application/pdf; application/pdf
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The Lagrange multiplier theorem and optimal control theory are applied to a continuous shape optimization problem for reducing the wave resistance of a submerged body translating at a steady forward velocity well below a free surface. In the latter approach, when the constraint formed by the boundary conditions and the Laplace's governing equation is adjoined to the objective functional to construct the Lagrangian, the dependence of the state on the control is disconnected and they are treated as independent variables; whereas in the first approach, dependences are preserved for the application of Lagrange multiplier theorem. Both methods are observed to yield identical solutions and adjoint equations. Two alternative ways are considered for determining the variation of the objective functional with respect to the state variable which is required to solve the adjoint equation defined on the body boundary. Comparison of these two ways also revealed identical solutions. Finally, a free surface boundary is included in the optimization problem and its effect on the submerged body shape optimization problem is considered.; (cont.) Noting that the analytical solution to the local optimization problem holds for any initial body geometry, it is therefore concluded that the above study will provide theoretical background for an efficient hydrodynamic shape optimization module to be coupled with up-to-date flow solvers currently available such as SWAN.; by Onur Geçer.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Ultrasonic wave propagation in thick, layered composites containing degraded interfaces

Small, Peter D. (Peter David)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 94 p.; 3589791 bytes; 3593659 bytes; application/pdf; application/pdf
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The ultrasonic wave propagation of thick, layered composites containing degraded bonds is investigated. A theoretical one-dimensional model of three attenuative viscoelastic layers containing two imperfect interfaces is introduced. Elastic material properties and measured 'values of ultrasonic phase velocity and attenuation are used to represent E-glass and vinyl ester resin fiber-reinforced plastic (FRP) laminate, syntactic foam, and resin putty materials in the model. The ultrasonic phase velocity in all three materials is shown to be essentially constant in the range of 1.0 to 5.0 megahertz (MHz). The attenuation in all three materials is constant or slightly increasing in the range 1.0 to 3.0 MHz. Numerical simulation of the model via the mass- spring-dashpot lattice model reveals the importance of the input signal shape, wave speed, and layer thickness on obtaining non-overlapping, distinct return signals in pulse-echo ultrasonic nondestructive evaluation. The effect of the interface contact quality on the reflection and transmission coefficients of degraded interfaces is observed in both the simulated and theoretical results.; by Peter D. Small.; Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and...

‣ A strip theory approximation for wave forces on submerged vehicles in finite depth water

Rybka Jan A. (Jan Andrzej)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 84 leaves; 4176082 bytes; 4179542 bytes; application/pdf; application/pdf
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Autonomous Underwater Vehicles (AUV's) are becoming of increasing use in shallow waters for oceanographic data collection, coastal mapping, and military operations such as mine surveillance along enemy coastlines. Currently the control of AUV's in shallow water is very limited, largely due to a lack of knowledge of vessel forces in shallow water, especially in the presence of surface wave effects. The limitations of current control systems do not afford enough confidence to operate the vehicles in very close proximity to shore or in large waves because the control in the horizontal plane is not adequately reliable enough to prevent bottoming and free surface broaching. Current control system parameters are altered through trial and error to enable reasonable vehicle behavior in shallow water but the control of the vehicle is limited because a thorough understanding of wave forces on these vehicles is non existent. The development of a good analytical tool which adequately models wave forces and moments on an AUV in shallow water waves will enable the development of control systems which will be better able to maneuver the vehicle in shallower water and larger waves than the conditions in which AUV's are currently used.; (cont.) The purpose of this thesis is to further develop...

‣ Structural loading of cross deck connections for trimaran vessels

Rhoads, Jason L
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 176 p.; 1625179 bytes; 2504135 bytes; application/pdf; application/pdf
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This work investigates the fundamental relationships of wave loading on cross deck structures for trimaran vessels. In contrast with a monohull ship, trimaran vessels experience several possible structural loading cases including: longitudinal bending, transverse bending, torsional bending, spreading and squeezing of hulls, inner and outer hull slam pressures, wet deck slam pressures, loading from ship's motions, and whipping of slender hulls. This work investigates wave loading cases that result in transverse and torsional bending of the cross deck structure. The wave loading cases investigated include: side hull troughing and cresting in longitudinal waves, side hull torsion in longitudinal waves, and transverse hogging and sagging. For each of these load cases, a design load using a fully statistical sea state was derived using an analytical model of a trimaran represented by rigidly connected box barges. The design loadings with a reliability index of 5 for almost 500 trimaran configurations were calculated varying main hull length, side hull length, side hull transverse placement, and side hull longitudinal placement. The design loadings were curve fit to a fourth order polynomial in the three independent variables.; (cont.) The load predictions of the analytical box model of a trimaran were applied to a trimaran vessel with a realistic hull form using the finite element ship structural analysis program MAESTRO. Given the number of approximations and assumptions in the analytical model...