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Mechanical Engineering - Master's degree
Mostrando recursos 1 - 20 de 2.373
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Design and characterization of tunable stiffness flexural bearings - Ramirez, Aaron Eduardo
Compressed flexures have a downwards-tunable stiffness in their compliant directions; their stiffness can theoretically be reduced by up to four orders of magnitude. The compression-stiffiness relation is linear for most of the loading, and this behavior can be taken advantage of to use the flexure as a tunable spring, opening up new design possibilities. Compressed flexures present the possibility of developing more sensitive flexure-based instruments such as accelerometers. The purpose of this research was to characterize the behavior of compressed flexures and develop guidelines for their design. Tradeoffs were assessed when substituting compressed flexures for conventional flexures and their suitability...
2.
Exploring the value proposition of integrating back-up saline storage into anthropogenic CO₂ supplied EOR operations - Toukan, Ibrahim (Ibrahim Khaled)
Enhanced oil recovery (EOR) through carbon dioxide (CO₂) sequestration from anthropogenic sources has been gaining attention in policy circles. In particular, it is viewed as a potential way to help accelerate the deployment of carbon capture and sequestration (CCS) technologies. The interest in the EOR-CCS model stems from the economic, geologic and regulatory benefits this model offers when compared to the waste-driven CCS model that utilizes saline aquifers for CO₂ storage. However, there are still some major challenges impeding the deployment of the EOR-CCS model; chief among these challenges is the mismatch between CO₂ supplies from anthropogenic sources and CO₂...
3.
New product development methods : a study of open design - Smith, Ariadne G. (Ariadne Geneviève)
This thesis explores the application of open design to the process of developing physical products. Open design is a type of decentralized innovation that is derived from applying principles of open source software and crowdsourcing to product development. Crowdsourcing has gained popularity in the last decade, ranging from translation services, to marketing concepts, and new product funding. However, it is only in the past few years that open design has been considered as a method to create more innovative products in less time and for less money. While truly open design requires participants to collaborate and make contributions at each...
4.
Large grain Ge growth on amorphous substrates for CMOS back-end-of-line integration of active optoelectronic devices - Pearson, Brian (Brian Sung-Il)
The electronic-photonic integrated circuit (EPIC) has emerged as a leading technology to surpass the interconnect bottlenecks that threaten to limit the progress of Moore's Law in microprocessors. Compared to conventional metal interconnects, photonic interconnects have the potential to increase bandwidth density while simultaneously reducing power consumption. However, photonic devices are orders of magnitude larger than electronic devices and therefore consume valuable substrate real estate. The ideal solution, in order to take advantage of optical interconnects without decreasing transistor counts, is to monolithically implement dense threedimensional integration of electronics and photonics. This involves moving the photonic devices off the substrate, and...
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Practical electron cloaking in solids - Liao, Bolin, S.M. Massachusetts Institute of Technology
The design and experimental realization of "metamaterials" in the past decade has opened up new venues to obtain artificial materials with exotic properties that are desirable but not commonly encountered in the nature. Optical metamaterials have shown great potentials in applications such as optoelectronics, subwavelength imaging, and optical information processing etc. The invisibility effect, or "cloaking effect", is one of the most striking demonstrations of the unprecedented ability of manipulating light provided by optical metamaterials. As a natural extension, the cloaking effect of acoustic waves and quantum matter waves has also been discussed recently. Currently the main strategy of designing...
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Origins and implications of intrinsic stress in hydrogenated amorphous silicon thin films - Johlin, Eric (Eric Carl)
Despite decades of research on hydrogenated amorphous silicon (a-Si:H), there remains much to be understood about the relationship between deposition conditions and the resulting structural, optical, and bulk properties of the material. In this work we investigate these correlations for a-Si:H films created using plasma enhanced chemical vapor deposition (PECVD), focusing on the creation of intrinsic stresses within the films. Through experimental examination of the deposition process pressure, we model the plasma ion momentum using a combination of theoretical models and empirical trends. We find that compressive stress is controlled by ion bombardment causing of peening the film, and leading...
7.
Path planning in time dependent flows using level set methods - Lolla, Sri Venkata Tapovan
Autonomous underwater vehicles such as gliders have emerged as valuable scientific platforms due to their increasing uses in several oceanic applications, ranging from security, acoustic surveillance and military reconnaissance to collection of ocean data at specific locations for ocean prediction, monitoring and dynamics investigation. Gliders exhibit high levels of autonomy and are ideal for long range missions. As these gliders become more reliable and affordable, multi-vehicle coordination and sampling missions are expected to become very common in the near future. This endurance of gliders however, comes at an expense of being susceptible to typical coastal ocean currents. Due to the...
8.
Composite force sensing foot utilizing volumetric displacement of a hyperelastic polymer - Chuah, Meng Yee (Meng Yee Michael)
In this thesis, I will describe the fabrication and characterization of a footpad based on an original principle of volumetric displacement sensing. It is intended for use in detecting ground contact forces in a running quadrupedal robot. The footpad is man- ufactured as a monolithic, composite structure composed of multi-graded polymers which are reinforced by glass fiber to increase durability and traction. The volumetric displacement sensing principle utilizes a hyperelastic gel-like pad with embedded magnets that are tracked with Hall-effect sensors. Normal and shear forces can be detected as contact with the ground which causes the gel-like pad to deform...
9.
Direct and quantitative absorptive spectroscopy of nanowires - Tong, Jonathan Kien-Kwok
Photonic nanostructures exhibit unique optical properties that are attractive in many different applications. However, measuring the optical properties of individual nanostructures, in particular the absorptive properties, remains a significant challenge. Conventional methods typically provide either an indirect or qualitative measure of absorption. The objective of this thesis is to therefore demonstrate a method capable of directly and quantitatively measuring the absorptive properties of individual nanostructures. This method is based on atomic force microscope (AFM) cantilever thermometry where a bimorph cantilever is used as a heat flux sensor. These sensors operate on the principle of a thermomechanical bending response and by...
10.
Flow separation control with rotating cylinders - Schulmeister, James Crandall
The hydrodynamic forces on ocean vehicles increase dramatically during sharp maneuvers as compared to forward motion due to large areas of separated flow. These large forces severely limit maneuverability and reduce efficiency. Applying active flow separation control to ocean vehicles would reduce resistance during maneuvers and thereby improve maneuvering performance. In this thesis I discuss experiments in active separation control in a simpler, but still relevant, two-dimensional flow past a circular cylinder at moderate sub-critical Reynolds numbers (37,000 and 52,000 in experiment and 100 and 10,000 in simulation). The active control injects momentum into the boundary layer via the moving...
11.
Cold side thermal energy storage system for improved operation of air cooled power plants - Williams, Daniel David
Air cooled power plants experience significant performance fluctuations as plant cooling capacity reduces due to higher daytime temperature than nighttime temperature. The purpose of this thesis is to simulate the detailed operation of a cold side thermal energy storage system in order to evaluate its potential. An organic Rankine cycle geothermal power station is used as an example application. Detailed sizing and operation considerations are discussed. Several representative case studies compare the performance of candidate configurations. Operation of the selected configuration is then simulated for a full year and a proposed integration of the system with existing plant hardware is...
12.
Bridging adaptive estimation and control with modern machine learning : a quorum sensing inspired algorithm for dynamic clustering - Tan, Feng, S.M. Massachusetts Institute of Technology
Quorum sensing is a decentralized biological process, by which a community of bacterial cells with no global awareness can coordinate their functional behaviors based only on local decision and cell-medium interaction. This thesis draws inspiration from quorum sensing to study the data clustering problem, in both the time-invariant and the time-varying cases. Borrowing ideas from both adaptive estimation and control, and modern machine learning, we propose an algorithm to estimate an "influence radius" for each cell that represents a single data, which is similar to a kernel tuning process in classical machine learning. Then we utilize the knowledge of local...
13.
Global vorticity shedding for a vanishing foil - Steele, Stephanie Chin
We explore several aspects of the phenomenon we call global vorticity shedding. Global vorticity shedding occurs when an object in viscous fluid suddenly vanishes, shedding the entire boundary layer vorticity into the wake at once. In our experiments we approximate the disappearance of a towed foil by rapidly retracting the foil in the span-wise direction. Global vorticity shedding is in distinct contrast with conventional shedding, in which vorticity is shed from a body from only a few separation points into the fluid. In this work, we show that for a square-tipped vanishing foil at an angle of attack, the globally...
14.
A controllably adhesive climbing robot using magnetorheological fluid - Wiltsie, Nicholas Eric
In this thesis, the novel adhesive effects of magnetorheological fluid for use in climbing robotics were experimentally measured and compared to existing cohesive failure fluid models of yield stress adhesion. These models were found to correlate with experimental results at yield stresses below 1.12 kPa. MR fluid samples activated to have yield stresses above 1.12 kPa were limited to an adhesive stress of approximately 25-30 kPa regardless of inital fluid thickness or yield stress. A climbing robot capable of utilizing MR fluid adhesion was constructed and shown to be capable of adhering to surfaces of any orientation and climbing rough...
15.
Directional impedance of geared transmissions - Wang, Albert Duan
The purpose of this research is to develop a design tool for geared actuation systems that experience bidirectional exchange of energy with the environment. Despite the asymmetry of efficiency depending on the direction of power transfer in geared systems, typical dynamic models consider a fixed transmission efficiency for all conditions which can result in significant error depending on specific gear selection and the number of stages. This error can cause issues especially in dynamic legged robots and haptic devices when accurate force control is desired. In this paper we present directional impedance, a characteristic of geared transmissions in which the...
16.
Hybrid solar-fossil fuel power generation - Sheu, Elysia J. (Elysia Ja-Zeng)
In this thesis, a literature review of hybrid solar-fossil fuel power generation is first given with an emphasis on system integration and evaluation. Hybrid systems are defined as those which use solar energy and fuel simultaneously, thus excluding the viable alternative of solar thermal plants which use fossil fuels as backup. The review is divided into three main sections: performance metrics, the different concentrated solar receiver technologies and their operating conditions, and the different hybridization schemes. In addition, a new linear combination metric for analysis of hybrid systems, which considers trade-off of different metrics at the fleet level, is presented....
17.
Analysis of multiphase fluid flows via high speed and synthetic aperture three dimensional imaging - Scharfman, Barry Ethan
Spray flows are a difficult problem within the realm of fluid mechanics because of the complicated interfacial physics involved. Complete models of sprays having even the simplest geometries continue to elude researchers and practitioners. From an experimental viewpoint, measurement of dynamic spray characteristics is made difficult by the optically dense nature of many sprays. Flow features like ligaments and droplets break off the bulk liquid volume during the atomization process and often occlude each other in images of sprays. In this thesis, two important types of sprays are analyzed. The first is a round liquid jet in a cross flow...
19.
Robust acoustic signal detection and synchronization in a time varying ocean environment - Gieleghem, Ryan Thomas
Signal detection and synchronization in the time varying ocean environment is a difficult endeavor. The current common methods include using a linear frequency modulated chirped pulse or maximal length sequence as a detection pulse, then match filtering to that signal. In higher signal to noise ratio (SNR) environments (- 0 dB and higher) this has been a suitable solution. As the SNR drops lower however, this solution no longer provides an acceptable probability of detection for a given tolerable probability of false alarm. The issue derives from the inherent coherence issues in the ocean environment which limit the useful matched...
20.
Monofilament MgB₂ wires for MRI magnets - Ling, Jiayin
MRI magnets are useful medical devices in early detection and efficient treatment of disease or injury. Because of the significant better performance, MRI magnets are made of superconductors rather than made of copper. Nowadays, there are over 20,000 superconducting MRI magnets installed worldwide. Most of them are made of NbTi or Nb₃Sn, but they are usually very expensive to purchase or operate. So, my colleagues chose MgB₂ wires to develop low-cost and easy-to-operate MRI units which serve to the majority of the humanity. Because we have a reliable technology to fabricate superconducting joints with monofilament MgB₂ wire, we decided to...
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