Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29-31). / The importance of process in successful and effective technology and product development is widely recognized in industry. Tools, such as Technology Readiness Levels (TRLs) and various metrics, have been developed and successfully used to guide and strategically plan R&D processes, allocate resources, and calibrate expectations. Similarly, one might hypothesize that academic research might also benefit from similar tools that would assist both researchers and funding organizations. A research assessment tool should: 1) facilitate planning and communication; 2) effectively gauge progress; and 3) accommodate and capture the diverse scope of academic research. However, the inherent open-endedness and exploratory nature of research makes it difficult to quantify or characterize research progress. This work aims to develop an academic research measurement process, embodied as a tool called Research Maturity Levels (RMLs), that divides research activities into four main components: 1) background knowledge, 2) problem and question formulation, 3) procedures and results, and 4) resources. Within each component, the RML guides researchers through a process of increasing maturity levels. Additionally, each component includes mechanisms to formalize iterations and "eureka" moments-when directions and plans may change based upon a new knowledge. Preliminary evaluation suggests that the tool has promise as a comprehensive measurement tool. It is hoped that this work will result in a tool that can facilitate planning, help to measure and communicate research progress, and encompass the diverse scope of academic research goals. / by Ming Leong. / S.M.

Thesis (Nav. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 71). / Over the next 5 years, MIT Sea Grant is tasked with locating and photographing Didemnum Vexillum, an invasive species which threatens New England fishing habitats. Didemnum research is conducted in the photosynthesis zone of the coastal shelf using photography and radiometry instruments. In order to streamline Didemnum research, a new, low cost and modular AUV was designed and built to replace Odyssey IV as the primary Didemnum research vehicle. This new AUV is a shallow cruising vehicle with a depth rating of 100 meters. With a weight of less than 50 kg, the AUV can easily be launched and recovered by hand from Sea Grant's 25 ft vessel. Although specifically designed to support Didemnum research, the AUV incorporates a flexible and modular design which allows it to be reconfigured for existing Didemnum missions or upgraded with additional sensors and payload. Incorporating a separate, interchangeable Li-Polymer Battery pack allows the vehicle to achieve both a high mission duty cycle and extended bottom time. The Didemnum Cruiser also serves as a prototype for future vehicles in the AUV Lab. / by Eric D. Brege. / Nav.E.and S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (leaves 68-69). / by Jaehyun Kim. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 35-36). / Earthships are passive solar buildings with renewable power, water harvesting, and sewage systems, designed to be off grid with minimal reliance on public utilities, and use recycled and natural materials. Due to high initial capital cost and resources needed, earthships have primarily been implemented in developed countries. However, the self-sufficiency earthships offer through their subsystems presents an opportunity for resource-constrained environments. Three earthship projects have been developed in Africa, each serving a unique purpose and overcoming different obstacles. Through earthship design principles, technical reports, and lessons learned from each project, this paper aims to outline design considerations for those who are interested in implementing an earthship in Africa. / by Sade Kailani Nabahe. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 145-156). / Cleavage decohesion and shear dislocation nucleation are two basic modes of localized deformation in crystal lattices, which normally result from instability of the atomic configuration driven by mechanical forces. The critical state of instability and its thermal activation mechanisms can be quantitatively determined by analyzing the energetics of the lattice system. In this thesis, the unit processes of configurational instability of crystal lattices under various non-uniform structural and/or chemical environments are characterized by systematically probing the atomistic potential energy landscape of each system using the state of the art configurational space sampling schemes. The problems studied are homogeneous dislocation nucleation in a perfect crystal by nanoindentation, dislocation emission and cleavage decohesion at atomically sharp crack tips, and chemically-enhanced bond breaking in a wet silica nanorod. These processes are studied in a unified manner such that two important types of properties are determined: one is the athermal load at which the instability takes place instantaneously without the aid of thermal fluctuations, and the other is the stress-dependent activation energy used for an estimate of the kinetic rate of transition. Along the way, important aspects concerning the atomistic characterization of configurational instability are revealed. Of particular note is extending the continuum instability criterion to detect atomic defect nucleation. We demonstrate that a local instability criterion can be applied to identify dislocation nucleation in the case of indentation, considering that the relatively small strain gradient beneath the indenter will lead to a mode of long wavelength phonon instability suitable for a study / (cont.) by the local continuum approach. In addition, the chemical effect on stress-driven lattice instability is revealed via the study on reactivity of a silica nanorod with water. We identify distinct competing mechanisms of hydrolysis which are rate-controlling at different load regimes. The ensuing stress-mediated switch of rate-limiting steps of hydrolysis quantitatively demonstrates the impact of finding the detailed molecular mechanisms on a realistic estimate of the activation rate when configurational instability occurs within a chemically reactive environment. Implications regarding the analysis of chemically-assisted brittle fracture are also discussed. / by Ting Zhu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaves 57-60). / The contribution of this thesis is the development of tractable computational methods for reducing the complexity of two classes of dynamical systems, finite alphabet Hidden Markov Models and Jump Linear Systems with finite parameter space. The reduction algorithms employ convex optimization and numerical linear algebra tools and do not pose any structural requirements on the systems at hand. In the Jump Linear Systems case, a distance metric based on randomization of the parametric input is introduced. The main point of the reduction algorithm lies in the formulation of two dissipation inequalities, which in conjunction with a suitably defined storage function enable the derivation of low complexity models, whose fidelity is controlled by a guaranteed upper bound on the stochastic L2 gain of the approximation error. The developed reduction procedure can be interpreted as an extension of the balanced truncation method to the broader class of Jump Linear Systems. In the Hidden Markov Model case, Hidden Markov Models are identified with appropriate Jump Linear Systems that satisfy certain constraints on the coefficients of the linear transformation. This correspondence enables the development of a two step reduction procedure. / (cont.) In the first step, the image of the high dimensional Hidden Markov Model in the space of Jump Linear Systems is simplified by means of the aforementioned balanced truncation method. Subsequently, in the second step, the constraints that reflect the Hidden Markov Model structure are imposed by solving a low dimensional non convex optimization problem. Numerical simulation results provide evidence that the proposed algorithm computes accurate reduced order Hidden Markov Models, while achieving a compression of the state space by orders of magnitude. / by Georgios Kotsalis. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / Includes bibliographical references (p. 97-109). / Recent developments in shape-based modeling and data acquisition have brought three-dimensional models to the forefront of computer graphics and visualization research. New data acquisition methods are producing large numbers of models in a variety of fields. Three-dimensional shape-based matching and registration (alignment) are key to the useful application of such models in areas from automated surface inspection to cancer detection and surgery. The three-dimensional models in these applications are typically huge. State-of-the-art simulations in computational fluid dynamics produce upward of four terabytes of data per second of flow. Research-level magnetic resonance imaging (MRI) resolutions can reach 1 cubic micro-meter. As a result, object registration and matching algorithms must handle very large amounts of data. The algorithms developed in this thesis accomplish automatic registration and matching of three-dimensional voxelized models. We employ features in a wavelet transform domain to accomplish registration. The features are extracted in a multiresolutional format, thus delineating features at various scales for robust and rapid matching. Registration is achieved through seeking peaks in sets of rotation quaternions using a voting scheme, then separately identifying translation. The method is robust to occlusion, clutter and noise. The efficacy of the algorithm is demonstrated through examples from solid modeling and medical imaging applications. / by Julie S. Chalfant. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 147-155). / Thermoelectric materials are capable of solid-state direct heat to electricity energy conversion and are ideal for waste heat recovery applications due to their simplicity, reliability, and lack of environmentally harmful working fluids. Recently, nanostructured thermoelectrics have demonstrated remarkably enhanced energy conversion efficiencies, primarily due to a reduction in lattice thermal conductivity. Despite these advances, much remains unknown about heat transport in these materials, and further efficiency improvements will require a detailed understanding of how the heat carriers, electrons and phonons, are affected by nanostructures. To elucidate these processes, in this thesis we investigate nanoscale transport using both modeling and experiment. The first portion of the thesis studies how electrons and phonons are affected by grain boundaries in nanocomposite thermoelectric materials, where the grain sizes are smaller than mean free paths (MFPs). We use the Boltzmann transport equation (BTE) and a new grain boundary scattering model to understand how thermoelectric properties are affected in nanocomposites, as well as to identify strategies which could lead to more efficient materials. The second portion of the thesis focuses on determining how to more directly measure heat carrier properties like frequency-dependent MFPs. Knowledge of phonon MFPs is crucial to understanding and engineering nanoscale transport, yet MFPs are largely unknown even for bulk materials and few experimental techniques exist to measure them. We show that performing macroscopic measurements cannot reveal the MFPs; instead, we must study transport at the scales of the MFPs, in the quasi- ballistic transport regime. To investigate transport at these small length scales, we first numerically solve the frequency-dependent phonon BTE, which is valid even in the absence of local thermal equilibrium, unlike heat diffusion theory. Next, we introduce a novel thermal conductivity spectroscopy technique which can measure MFP distributions over a wide range of length scales and materials using observations of quasi-ballistic heat transfer in a pump-probe experiment. By observing the changes in thermal resistance as a heated area size is systematically varied, the thermal conductivity contributions from different MFP phonons can be determined. We present the first experimental measurements of the MFP distribution in silicon at cryogenic temperatures. Finally, we develop a modification of this technique which permits us to study transport at scales much smaller than the diffraction limit of approximately one micron. It is important to access these length scales as many technologically relevant materials like thermoelectrics have MFPs in the deep submicron regime. To beat the diffraction limit, we use electron-beam lithography to pattern metallic nano dot arrays with diameters in the hundreds of nanometers range. Because the effective length scale for heat transfer is the dot diameter rather than the optical beam diameter, we are able to study nanoscale heat transfer while still achieving ultrafast time resolution. We demonstrate the modified technique by measuring the MFP distribution in sapphire. Considering the crucial importance of the knowledge of MFPs to understanding and engineering nanoscale transport, we expect these newly developed techniques to be useful for a variety of energy applications, particularly for thermoelectrics, as well as for gaining a fundamental understanding of nanoscale heat transport. / by Austin Jerome Minnich. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 94-96). / Introduction: Rotorcraft engines can lose up to 70% of the potential chemical energy of their fuel as waste heat. Harvesting this waste heat and converting it to useful work would improve the efficiency and power output of the engine. Figure 1 shows two possible engine systems in which a secondary engine could be used to harvest waste heat. For the gas turbine engine in Figure 1A, the main source of waste heat is the enthalpy of the engine's exhaust gases. In the case of the spark ignition engine in Figure 1B, there are three sources of waste heat: the enthalpy available in the exhaust gases, the heat rejected by the coolant loop, and the heat rejected by the oil loop. For each engine system, the heat from waste heat engine is rejected to the ambient air. Possible candidate systems for waste heat recovery include closed cycle systems such as the Rankine and Brayton engines. Rankine engines typical use water as a working fluid. The performance of water-based Rankine engines suffer from low pressures in the working fluid at the temperatures of the ambient and, therefore, require large low pressure expanders and condensers to operate efficiently. Organic working fluids have higher vapor pressures and can be used in Rankine engines instead of water. The higher vapor pressures of these fluids allow the use of smaller expanders. However, organic working fluids are limited to temperatures below 250 C, which is substantially lower than the typical temperatures available in the waste streams. Brayton engines can operate at higher temperatures using inert gases such as helium and argon as working fluids. In either of these engines, the turbomachinery and heat exchangers must remain leak tight as the working fluid is cycled through at high temperatures and high pressures. As a consequence of this requirement, these cycles will not be considered further in this work. Thermoelectric devices, on the other hand, do not require leak tight passages or turbomachinery. These are compacted and are expected to have a higher reliability since they have no moving parts. These advantages have motivated this study on thermoelectrically-based waste heat engine. For a thermoelectrically-based waste heat engine to be feasible, it must be capable of absorbing and rejecting large amounts of heat in part to compensate for the low efficiencies of thermoelectric materials. It must also be light weight and compact to address concerns of power to weight ratios and space constraints in rotorcraft. Therefore, the waste heat engine must be designed to minimize thermal resistance while also minimizing the mass and volume of the heat exchangers. / by Victoria D. Lee. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1991. / Includes bibliographical references (p. 365-381). / by Randall D. Manteufel. / Ph.D.