http://hdl.handle.net/1721.1/7850 Mon, 20 May 2013 03:21:12 GMT 2013-05-20T03:21:12Z http://hdl.handle.net/1721.1/78544 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 for use in a precision system. An experimental setup was designed and built to test a stage guided by four compressed flexure bearings. Compression was applied to the test flexures via a displacement input that was deamplified by a wedge pair to increase preload resolution. The motion in each of the stage's six degrees of freedom in response to flexure compression and in response to a voice coil actuator acting in the flexure's compliant direction was measured by seven capacitance probes arranged around the test stage, and a seventh capacitance probe measured the input displacement. With the experimental setup it was found that a stiffness reduction of a factor of 7 was possible. The magnitude of parasitic motions in the test stage were found to increase linearly with flexure compression. When being actuated in the compliant direction, parasitic motions were evident with magnitudes of the same order of magnitude as the sensor noise. Compressed flexures are highly sensitive to thermal variations; a 0.5 C temperature increase resulted in an 11% increase in stiffness. A model developed in this thesis predicts that deviations from column straightness of 2% of the flexure thickness limit the stiffness reduction to a factor of 1.2, while a deviation of 0.2% allows for a stiffness reduction of 10,000. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 139-140). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/78544 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/78540 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 demand from EOR operations. One potential way to address this challenge is through a CO₂ stacked storage system. A CO₂ stacked storage system utilizes brine formations adjacent to EOR oilfields for the purpose of storing any additional quantities of CO₂ the EOR operation cannot handle. The concept of a stacked storage system with focus on CO₂ supplies from coal-fired power plants was analyzed using a case study. A U.S. coal-fired power plant and a U.S. EOR oilfield were used to model a stacked storage system in order to determine the economic and technical viability of such a model. More specifically, this thesis has three main objectives. The first is to determine the overall cost of implementing the stacked storage system. The overall cost of the system came to approximately $90 per ton of CO₂ avoided. Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 83-85). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/78540 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/78500 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 stage of the product development process, applications of open design to physical product development have been limited to accepting external contributions at only certain, less technical phases of design, such as planning, idea generation, or obtaining idea feedback. This thesis seeks to explore two questions related to creating a tool for open design in physical product development: what kind of tool can be developed to support crowdsourcing the full development of a physical product, and what types of design environments can benefit from this tool? Through a collaboration with GE Global Research for DARPA's Adaptive Vehicle Make (AVM) program, this thesis presents an early prototype of an online tool that allows for the open design of an entire product development process, in application to the development of a vehicle. Then, a framework is developed in order to identify the tool's applicability to other product development industries. Interviews with potential lead users in a number of different industrial sectors were conducted to better understand how this open design environment might be used and adapted for applications outside of a DARPA-driven vehicle design domain. Though the sensitive nature of projects in the defense and medical device industries prohibits this tool from used for its intended crowdsourcing purposes, there is promise for further development of the tool for uses in academic and education environments, and as an internal project management tool in other product development industries, such as aviation and consumer product design. Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 70-75). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/78500 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/78240 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 into the metal interconnect stack. Moving photonic devices into the interconnect stack imposes two fabrication limitations. First, the available thermal budget allowed for photonic device processing is limited to 450 °C. Second, the metal interconnects are embedded within amorphous dielectrics and therefore there is no crystalline seed to initiate epitaxial growth. This thesis addresses two major barriers for integration of photonics in the back end: (1) how to fabricate high quality Ge for active regions of optoelectronic devices while adhering to back-end processing constraints, and (2) how to couple optical power to these devices. First, an approach was developed to fabricate the active region of Ge-based optoelectronic devices. A new technique, known as two-dimensional geometrically confined lateral growth (2D GCLG), has demonstrated single crystalline Ge on an amorphous substrate. This thesis presents the first application of the 2D GCLG technique to fill a lithographically defined Si0 2 trench with large grain Ge, while adhering to back-end processing constraints. A modified design is then proposed to increases the yield of 2D GCLG structures. This trench filling technique is an integral step towards fabricating Ge-based optoelectronic devices that are capable of being integrated into the back-end of a microprocessor. Once it was established that high quality Ge trenches could be fabricated in the back-end, optical coupling to devices was addressed. For dense three-dimensional integration of photonic devices, vertical coupling between photonic planes is necessary. Therefore, this thesis begins with the design and simulation of vertical couplers. These couplers utilize evanescent coupling between two overlapping inversely tapered waveguides, which ensure efficient coupling due to optical impedance matching. These couplers are designed to exhibit coupling efficiencies in excess of 98.4%, equivalent to a 0.07 dB coupling loss. The technique of evanescent coupling between overlapping inverse tapers is then applied to electro-absorption modulators (EAMs). A design for low-loss evanescent coupling from a waveguide to a Ge EAM is modeled and optimized. The design implements lateral evanescent coupling from overlapping inverse taper structures. Simulation results show that the coupling efficiency into and out of the modulator can be as high as 99%, equivalent to a 0.04 dB coupling loss. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 97-104). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/78240 2012-01-01T05:00:00Z