Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 23). / As part of an ongoing effort to better understand and treat locomotor disorders, an over-ground therapeutic robot prototype to study recovery of locomotion after spinal cord injury in rodents is under development. One key element of the therapeutic robot is a system to support the partial body weight of a freely-moving rodent. This paper discusses the design requirements, fabrication, modeling, calibration and preliminary analysis of a highly back-drivable bodyweight support system prototype. In addition, a closed loop feedback control system was designed, simulated, constructed and tested. Hardware limitations were identified, and alternative control techniques were explored. / by Michaëlle Ntala Mayalu. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Access to drinking water is a growing issue and one of the key challenging of the twenty first century. The rapid depletion of current supply sources (aquifers, rivers, lake...) urges to find solutions, especially cost and energy efficient processes to desalinate seawater. Reverse osmosis is a membrane process for purification of seawater, invented in 1940's, which has evolved ever since, to become nowadays the most efficient process for desalination. We discuss the shortcomings of this technology, and identify bio-fouling to be the main cause of irreversibility (thus costs) in this process. After observation of solutions developed by Nature to deter bio-fouling (especially for marine species), surface micro-topography and chemistry have been identified as the two effective anti-fouling strategies. We introduce a brand new technology to create micro- and nano-patterned surfaces that is compatible with a wide variety of chemical compounds. A proof of concept is introduced with the first prototypes of wrinkled surfaces created with Initiated Chemical Vapor Deposition; Stiff polymeric coatings form wrinkles when deposited on pre-stretched soft elastomeric substrates. We are showing, both theoretically and experimentally, that the characteristics of these wrinkles can be tuned very easily. Mimicking Nature requires creating more complicated micro-topographies than the sinusoid-like pattern obtained with uniform coatings and substrates. We are showing with a numerical model that local stiffening of the substrate can be used to direct and control the buckling of the coating. In order to gain the full control of this design strategy, an inverse method is needed to establish how to treat the substrate in order to obtain a desired micro-topography. We set up the foundations of this inverse mechanical model, and develop an algorithm for a simple case. / by Damien Eggenspieler. / S.M.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 81-82). / The MIT MEng Team worked at Konarka Technologies, the world leader organic photovoltaic panels (OPV) manufacturer, on several improvement projects. The concentration was on operations improvement as well as production information tracking and analysis. This thesis report, however, focuses primarily on the implementation of a continuous improvement culture. Tools to implement the SS methodology, such as 5S Audit, Kaizen board and Kanban board, were provided, and operators were trained. A layout improvement solution was developed, and a plan for implementation recommended. The new layout was designed to increase visual control of the processes and to reduce movement of material by 85%. Each phase of the project went through review and discussion to encourage operator involvement in order to develop a continuous improvement culture. / by Gregorio Colaci. / M.Eng.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 67-74). / This thesis justifies photovoltaic (PV)-powered electrodialysis (ED) as an energy and cost-effective means of desalinating groundwater in rural India and presents the design requirements for a village-level system. Saline groundwater, which underlies 60% of India, can negatively impact health as well as cause a water source to be discarded because of its taste. A quarter of India's population lives in villages of 2000-5000 people, many of whom do not have reliable access to electricity. Most village-scale, ongrid desalination plants use reverse osmosis (RO), which is economically unviable in off-grid locations. Technical and ethnographic factors are used to develop an argument for PV-ED for rural locations, including: system capacity, biological and chemical contaminant removal; water aesthetics; recovery ratio; energy source; economics of water provision; maintenance; and the energetic and cost considerations of available technologies. Within the salinity range of groundwater in India, ED requires less specific energy than RO (75% less at 1,000 ppm and 30% less at 3,000 ppm). At 2,000 ppm, this energetic scaling translates to a 50% lower PV power system cost for ED versus RO. PV-ED has the potential to greatly expand the reach of desalination units for rural India. Additionally, a theoretical model for an electrodialysis system is presented and validated through experimental trials. / by Natasha C. Wright. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Discovering highly active and stable catalysts for electrochemical energy conversion and storage is essential to envision a new generation of renewable energy applications. Mixed ionic and electronic conductors (MIECs) such as Lai.xSrxCoO₃-[delta] (LSC₁₁₃) and Lai-xSrxCo1-yFeyO3-[delta] (LSCF₁₁₃) are currently utilized for applications including oxygen permeation membranes and solid oxide fuel cells (SOFCs), but alternative materials with higher catalytic activity and stability are required for intermediate temperature (500 - 700 °C) oxide electrocatalysts. In this thesis, two promising strategies, 1) Ruddlesden-Popper (RP) oxides and 2) surface decoration on the MIEC oxides are proposed to design highly active oxide materials and improve the fundamental understanding of the oxygen electrocatalysis at intermediate temperature. The oxygen surface exchange kinetics of a-axis-oriented La2NiO4+[delta] (LNO) thin films increases with decreasing film thickness. Increasing volumetric strains in the LNO films at elevated temperatures are correlated with increasing surface exchange kinetics and decreasing film thickness. Volumetric strains may alter the formation energy of interstitial oxygen and influence on the surface oxygen exchange kinetics of the LNO films. The effect of strontium (Sr) substitution on the oxygen electrocatalysis of RP oxides is also investigated using La2-xSrxNiO4+/-[delta] (LSNO, 0.0 </=Xsr </= 1.0) thin films. A structure reorientation occurs with increasing the Sr content, which can result from different energies in each surface. The surface exchange kinetics of LSNO is strongly dependent on the Sr content. This observed surface exchange kinetics can be attributed to the different oxygen adsorption energies and crystallographic orientations. The oxygen surface exchange kinetics of LSC₁₁₃ is significantly enhanced by La0.8Sr0.2CoO3-[delta] (LSM₁₁₃) surface decoration as shown in LSC₂₁₄-decorated LSC₁₁₃. In addition, long-term stability of LSC₁₁₃ is significantly improved by LSM₁₁₃ coverage. The suppression of Sr-enriched particles and substantial changes in the surface cationic ratios are associated with LSM₁₁₃ decoration, which can contribute the enhanced surface exchange kinetics and stability of LSM₁₁₃-decorated LSC₁₁₃. In contrast to the LSC₂₁₄-decorated LSC₁₁₃, LSC₂₁₄ decoration does not lead to the enhancement of the surface exchange kinetics and the long-term stability of LSCF₁₁₃. The change in the surface electronic structure and the suppression of the formation of secondary passive phases as a result of LSC₂₁₄ decoration can be responsible for observed oxygen surface exchange kinetics. / by Dongkyu Lee. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 79-80). / This paper describes the design of a supervisory controller (supervisor) that manages multiple heterogeneous vehicles, i.e., multiple controlled and uncontrolled vehicles, to avoid intersection collisions. Two main problems are addressed: verification of the safety of all vehicles at an intersection, and management of the inputs of controlled vehicles. For the verification problem, we employ an inserted idle-time scheduling approach, where the "inserted idle-time" is a time interval when the intersection is deliberately held idle for uncontrolled vehicles to safely cross the intersection. For the management problem, we design a supervisor that is least restrictive in the sense that it overrides controlled vehicles only when a safety violation becomes imminent. We analyze computational complexity and propose an efficient version of the supervisor with a quantified approximation bound. To mitigate the abrupt changes of control inputs and to reduce the number of unnecessary interventions, we additionally design two optimization problems and provide the supervisor with a more conservative bound. / by Heejin Ahn. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 59-60). / A stirred-cell reverse osmosis setup was used to demonstrate that a seawater reverse osmosis membrane can maintain excellent rejection at pressures as high as 172 bar. However, it was also demonstrated that there was a significant drop in permeability at high pressures - likely due to membrane compaction. A simple visco-elastic model was shown to be able to model the overall shape of the permeability curve in time. However, this model does not match the data well when pressure is removed and then reapplied. From the perspective of membrane performance, RO is feasible at high pressures but distinct challenges are presented by reduced permeability and increased variability in flux. / by Dillon James McConnon. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 149-164). / The aim of the research presented in this thesis is to design optimal wavefronts and subwavelength structures that enhance mechanical effects on the nanoscale, focusing on three types of devices: holographic optical tweezers, broadband solar absorbers, and acoustic waveguides. Much of the work presented is obtained using open source software tools. Advances in spatial wave modulation and nanomaterial fabrication technologies have created many new degrees of freedom for engineering wave-matter interaction. When exploring so many parameters, a large number of full-wave scattering problems must be solved efficiently - calling for a more targeted design approach. We address this challenge by offering computer-automated design frameworks that effectively combine the best computational software developed in physics, numerical analysis, and inverse design. Part I presents computational inverse design methods for structured illumination in holographic optical tweezers. Wave optimization is highly nonconvex by nature, and possesses many local optima due to interference and resonance. By combining a compact Bessel basis and a fast boundary element method, we achieve a 20-fold enhancement in torque per intensity, over a standard circular-polarized illumination, on a model plasmonic nanoparticle. Part II presents mode analysis and numerical parameter-testing strategies for periodic subwavelength structures in optics and acoustics. We first summarize the design and experimental characterization results of a photonic crystal solar absorber with wide-angle spectral selectivity. Next, we discuss a multiscale acoustic model of a phononic crystal with strong spatial dispersion. We are optimistic that our computational frameworks for wavefronts and subwavelength structures can be generalized and applied to other design problems, such as metamaterials, 3d manufacturing, and 3d imaging. / by Yoon Kyung (Eunnie) Lee. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996. / Includes bibliographical references (p. 395-399). / The material properties and dimensional accuracy of metal tooling produced by the Three Dimensional Printing process can be enhanced by increasing the green density of the 3D printed part. Green density is the ratio of metal powder volume to the external volume of the printed part, and is a measure of how tightly packed the powder particles in the printed part are. The central goal of this thesis was to increase the green density of metal parts from the current level of 58% to levels greater than 75%. Two approaches were taken for increasing green density. The first was to utilize bimodal mixtures of metal powders which could be packed to significantly higher densities than the monomodal powders which had been previously used. Three bimodal powder mixtures, with tap densities near 80%, were studied. The second approach was to develop a new powder layering device which could pack these bimodal powders to the tap density during layer creation. New understandings about the relationship between the stresses applied to the powder layer and the resulting packing density changes were required to design this device. Shear cell and unconfined compression tests were performed to characterize the metal powder stress / strain behavior. Particulate stress / strain models, such as the Mohr-Coulomb failure law and the Jenike yield locus theory, were used to interpret the packing behavior of the metal powders under various stress conditions. / (cont.) A simple frictional model of powder behavior was proposed for the low stress levels permissible in the 3DP process. The application of a small static normal stress, in combination with an oscillatory horizontal shear stress, was found to be the most effective means of reducing particle interlocking and provided the best layer densification results. A new layer densification mechanism was constructed and successfully used to generate printed parts with green densities in excess of 75%. Photographic analysis techniques used to analyze part microstructures indicated significant improvements in packing homogeneity. Packing defects between the printed layers were reduced or eliminated. Compositional analysis indicated no significant segregation of the bimodal components during layer spreading. / by Steven Joseph Gregorski. / Ph.D.

Thesis: S.M. in Naval Architecture and Marine Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016. / Thesis: Mech. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 213-217). / Recent advances in small-scale portable computing have lead to an explosion in swarming as a viable method to approach large-scale data problems in the commercial, scientific, and defense sectors. This increased attention to large-scale swarm robotics has lead to an increase in swarm intelligence concepts, giving more potential to address issues more effectively and timely than any single unit. However, the majority of today's autonomous platforms are prohibitively costly and too complex for marketable research applications. This is particularly true when considering the demands required to be temporally and spatially pervasive in a marine environment. This work presents a low cost, portable, and highly maneuverable platform as a method to collect, share, and process environmental data. Our platform is modular, allowing a variety of sensor combinations, and may yield a heterogeneous swarm. Kalman filters are utilized to provide integrated, real-time dynamic self-awareness. In addition to an environmentally savvy platform, we define computational framework and characteristics, which allow complex problems to be solved in a distributed and collective manner. This computational framework includes two methods for scalar field estimation, which rely on low order orthogonal Hermite basis functions. Low order fits provide a natural method for low-pass filtering, thus avoiding ambient noise recovery in the reconstruction process. Real-time sampling and recovery allow for individual and collectively autonomous behaviors driven through globally assessed environmental parameters. Finally, we give evidence that large numbers can cooperatively tackle large-scale problems much more efficiently and timely than more capable and expensive units. This is particularly true when utilizing a unique methodology, presented herein, to best assemble in order to most affectively reconstruct sparse spatial scalar fields. / by Brandon M. Zoss. / S.M. in Naval Architecture and Marine Engineering / Mech. E.