Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. [247]-252). / Characterizing the strain-dependent behavior of technological Nb₃Sn superconducting strand has been an important subject of research for the past 25 years. Most of the effort has focused on understanding the uniaxial tension and compression effects and applying this information to improve predictive scaling laws which are used for superconducting magnet design. However, the strain state of the strand in an actual magnet winding is often a complicated combination which includes uniaxial tension or compression, bending, and transverse compression. A bending mechanism was designed and used to characterize the bending strain behavior of two different types of Nb₃Sn superconducting strand at 4.2K in a magnetic field. Results showed that the critical current of the strand increased up to an applied bending strain between 0.2-0.3% and then decreased with continued applied strain. / by David L. Harris. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 75). / This thesis reviews the design of two scaled mechanical end effectors that mimic the digging of Ensis directus, the Atlantic Razor Clam. Modeled after a 0.5x Ensis scale device, the end effectors are 1.0x and 2.0x Ensis scale. The end effectors will be coupled to a pneumatic robotic actuator to explore the nondimensional relationships governing the digging dynamics of razor clams in littoral substrates. Such dynamics could be exploited to construct novel mimetic engineering devices which would provide an order-of-magnitude improvement over existing subsea burrowing and anchoring technologies. / by Mario Attilio Bollini. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 110-114). / Integrated simulations have been used to predict and analyze the integrated behavior of large, complex product and technology systems throughout their design cycles. During the process of integration, uncertainties arise from many sources, such as material properties, manufacturing variations, inaccuracy of models and so on. Concerns about uncertainty and robustness in large-scale integrated design can be significant, especially under the situations where the system performance is sensitive to the variations. Probabilistic simulation can be an important tool to enable uncertainty analysis, sensitivity analysis, risk assessment and reliability-based design in integrated simulation environments. Monte Carlo methods have been widely used to resolve probabilistic simulation problems. To achieve desired estimation accuracy, typically a large number of samples are needed. However, large integrated simulation systems are often computationally heavy and time-consuming due to their complexity and large scale, making the conventional Monte Carlo approach computationally prohibitive. This work focuses on developing an efficient and scalable approach for probabilistic simulations in integrated simulation environments. A predictive machine learning and statistical approach is proposed in this thesis. / (cont.) Using random sampling of the system input distributions and running the integrated simulation for each input state, a random sample of limited size can be attained for each system output. Based on this limited output sample, a multilayer, feed-forward neural network is constructed as an estimator for the underlying cumulative distribution function. A mathematical model for the cumulative probability distribution function is then derived and used to estimate the underlying probability density function using differentiation. Statistically processing the sample used by the neural network is important so as to provide a good training set to the neural network estimator. Combining the statistical information from the empirical output distribution and the kernel estimation, a training set containing as much information about the underlying distribution as possible is attained. A back-propagation algorithm using adaptive learning rates is implemented to train the neural network estimator. To incorporate a required cumulative probability distribution function monotonicity hint into the learning process, a novel hint-reinforced back-propagation approach is created. The neural network estimator trained by empirical and kernel information (NN-EK estimator) can then finally be attained. To further improve the estimation, the statistical method of bootstrap aggregating (Bagging) is used. Multiple versions of the estimator are generated using bootstrap resampling and are aggregated to improve the estimator. A prototype implementation of the proposed approach is developed and test results on different models show its advantage over the conventional Monte Carlo approach in reducing the time by tens of times to achieve the same level of estimation accuracy. / by Wei Mao. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 52). / Harbor seal whiskers have a unique surface structure that dramatically reduces vortex induced vibrations as they move through the water. Concurrently with rigid whisker experiments, this project focuses on the design and testing of a flexible model. The rubber model was cast with integrated Kevlar strings, for tensioning purposes, and accelerometers to measure vibration data. The whisker model was mounted to the carriage in the MIT tow tank where it could be towed at a variety of speeds and tension settings. Accelerometer data clarity was a significant problem, but gradual improvements to the whisker mounting design allowed higher quality data to be gathered at a larger range of towing speeds. Using this data we observed correlations between towing speed, vibration frequency, g forces, and displacement in the whisker's vertical axis of motion. Further work could be done to examine whisker motion in multiple axes, as well as with different angles of attack. / by Christopher D. Gerber. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 89-98). / Erythrocytes, better known as red blood cells, among various functions, are mainly tasked with the oxygen transport in vertebrates through blood circulation. Red blood cells are packed with the hemoglobin, an oxygen-binding molecule, and have unique biophysical properties that are critical in enabling the oxygen delivery and optimization of the blood flow in large vessels and capillaries. These properties such as cellular deformability, biconcave shape, and proper hemoglobin function are compromised in a range of diseases known as anemic disorders. Quantifying these alterations provides a tool for studying pathobiology of these diseases and guides the search for the cure or novel treatments. Interferometric microscopy in various forms has been suggested as a tool for measuring some of these biophysical properties. However, current interferometric techniques suffer from one or a combination of the following shortcomings: (1) precision of the biophysical measurements is limited due to limits on the measurement sensitivity, (2) absence of a practical solution for clinical settings to conduct high-throughput and comprehensive biophysical measurements on a cellular basis, (3) ignoring cell-to-cell variability in molecular specific information such as cellular hemoglobin concertation in conventional interferometric measurements, In several steps, we have made advancements to the state-of-the-art technology in each of these areas. We have particularly shown the capabilities of our platforms in studying a genetic anemic disorder known as sickle cell disease (SCD). Through these studies and in collaboration with our clinical partners, we have investigated the treatment effects on SCD patients, and have introduced novel biomarkers relevant in quantifying the pathophysiology of the anemic disorders. These technology developments open new horizons in which interferometric microscopy serves as a powerful platform for studying anemic disorders and potentially / by Poorya Hosseini. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 133-142). / We revisit the classic problem of buckling of thin spherical shells under uniform pressure and explore the effect that geometric imperfections can have on their buckling behavior. Since the 1960s, numerous theoretical and computational studies have addressed the imperfection sensitivity of buckling of thin elastic shells. However, there is a lack of precise experiments to corroborate these predictions, especially for spherical shells, which is the central topic of this thesis. First, we develop a novel fabrication technique to produce thin hemispherical elastic shells by the coating of spherical molds with a polymer solution. Upon curing the thin liquid film yields the elastic structure of nearly constant thickness. We experimentally investigate the drainage dynamics, the final thickness, and its uniformity. Our results are directly compared with theoretical and numerical analyses. Secondly, we study the buckling of spherical shells that contain a precisely engineered geometric imperfection. Our shell fabrication technique allows us to introduce a single dimple-like defect with controllable geometric properties. We systematically vary the amplitude and width of the defect, and then we present a quantitative relationship between the critical buckling pressure and the defect geometry. Our results can be predicted by both the finite element method and numerical simulations of a reduced shell theory model. Finally, we fabricate hemispherical bilayer shells containing a defect. To do so, we coat two different polymer solutions, layer by layer, onto the hemispherical molds containing a defect. We find that the bilayer shell can self-repair or self-aggravate the geometric imperfections due to residual swelling. Hence, the critical buckling pressure can be increased or decreased over time depending on the order of coating of each polymer layer. The fabrication technique and experimental results presented in this thesis open exciting new avenues in the study of the buckling of spherical shells, and we hope that it will instigate a resurgence of interest in this classic but important field of mechanics. / by Anna Lee. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 109-110). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / This thesis studies material flow control policies for automobile manufacturing systems. Various control policies are implemented in simulations of manufacturing systems to test whether they increase the efficiencies of the systems in terms of specific performance measures of interest. Among the control policies, Control Point Policy (CPP) is deeply studied, because this policy is designed for controlling complex manufacturing system with multiple product types. First, fundamental research in CPP is presented to understand the effects of the parameters on single product type manufacturing systems. Then, multiple product type, assembly-disassembly systems are studied with various control policies, including hybrid policies. Finally, a real automobile manufacturing system case study is presented, and various control policies are experimented on in the simulation model. Because the evaluations of performances are done by simulations, the speed of simulation becomes a very important problem. This thesis therefore presents a new approach to accelerating the speed of simulation. / by Chiwon Kim. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaf 29). / This paper illustrates the construction and installation of a public piece of art, hidden within which is an enclosed and private meditation space. In making the piece, the artist was influenced by the works of others as well as by her own previous works and personal experiences. The theory of deep touch pressure can be extrapolated to associate encapsulation within small, enclosed spaces with relaxation and the relief of anxiety. Through the fluid process of aesthetic development, the work evolved towards completion and fulfillment of the piece's goals. The result was a basket-like structure containing a close and comfortable space for decompression. Geared towards the MIT community, the piece also explored the effects of isolation and connectivity. Viewer interaction, made possible by a period of public display, remains a critical component of this artwork. There are various directions in which to move forward with the investigation, one of which is to explore the dynamics of multiple pieces in a single location. / by Sheila A. Longo. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaves 50-52). / Over 250,000 people in the United States currently live with a spinal cord injury and approximately 11,000 new cases occur every year. People with spinal cord injuries experience a significant reduction in quality of life due to the many problems that arise from damage to the spinal cord including paralysis and loss of sensation below the location of injury, loss of bowel and bladder function, loss of sexual function, and impaired respiration. Despite considerable ongoing research in the area of nerve regeneration by various institutions, satisfactory treatment for spinal cord injury has not yet been discovered. Previous studies have had considerable success in facilitating the regeneration of severed peripheral nerves through the use of collagen based implants used to bridge the resulting gap between the severed nerve stumps. The current study aims to apply this same regenerative approach to a defect created in the spinal cord of adult rats. The objective is to evaluate the efficacy of three different collagen implants toward the regeneration of the spinal cord. The experimental spinal cord injury was a complete transection at T7 and T9 and the removal of the spinal cord segment between the two transections, creating a 5 mm gap. / (cont.) This study contained four experimental groups. Group I was the control group. The animals in this group had a complete spinal cord transection as described above but received no implantation. Group II received a resorbable dura replacement sheet of collagen, 1 mm thick, cut from the BioGide(® membrane which was placed extradurally over the dorsal aspect of the wound site. Group III used the BioGide® membrane as a wrap which bridged the gap between the two cord stumps. Group IV used a collagen tube, fabricated using a freeze-drying process, to bridge the gap. Histological analysis at 6 weeks after implantation showed Groups III and IV to have more longitudinally oriented reparative tissue filling the defect area as well as fewer fluid-filled cysts. Quantitative analysis of axonal regeneration showed the collagen implants to be supportive of the regeneration of axons into the center of the defect. / by Rahmatullah H. Cholas. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / Includes bibliographical references (p. 141-142). / by Mohamed Mustapha Khemira. / Ph.D.