Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1989. / Includes bibliographical references. / by Neil Cooper Singer. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1988. / Includes bibliographical references. / by Vipin Kumar. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 134-136). / A novel, low-cost positioning stage was constructed using a six-axis compliant mechanism driven by three two-axis electromagnetic actuators. The mechanism's monolithic, planar geometry is easily fabricated with low-cost manufacturing processes (such as waterjet machining). The manipulator tolerates ±1 mm actuator misalignment with less than 0.1% full-scale position error. Measurements over a 100x100x100 nm3 work volume displayed resolution better than the sensing capability, 5nm, and open-loop linearity errors less than 0.005% of the full-scale range (100 [mu]m). Measurements over a 100x100x100 [mu]m3 work volume exhibited linearity errors less than 0.20% full-scale. The mechanism's equilateral symmetry and planar geometry restricted thermal drift rates at start-up to 23nm and 4 [mu]tradians over 30 minutes and 0.1°C temperature change. The manipulator, built for $ 2000 (excluding electronics), was successfully tested in a fiber optic alignment application. / by Gordon A.B. Anderson. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaf 22). / This project aims to gain a qualitative view of the three-dimensional vortical structures of a flexible flapping foil at Reynolds number 164. Flexible foils were fabricated, coated with fluorescent dye, and towed with heave and pitch in a large glass tank. The foil cross section is a NACA 0030 foil shape, and the foil has an aspect ratio of 3. Pictures where taken of the vortical structures from planform, wingtip, and isometric views over a range of Strouhal number and kinematic parameters. Results are compared to previous experimental and numerical studies. / by Matthew J. Krueger. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 157-160). / Genome Scanning is a powerful new technique for DNA sequencing. The method presented in this thesis uses an atomic force microscope with a functionalized cantilever tip to sequence single stranded DNA immobilized to a mica surface. The functionalized cantilever tip hybridizes with only one base type (A, C, T, or G) and results in distinct peaks in the AFM-produced image. Genome Scanning has been successful at identifying 40 base strands of synthesized DNA and has been shown to detect a particular base type on 48 kilobase strands of lambda DNA. Currently, Genome Scanning is only accurate to 3-26 bases at a time, however, it can achieve a sequencing speed of 6000 bases/sec. In other words, Genome Scanning can be used to sequence the 3 billion bases of the human genome in 5.78 days. / by Ahmed Elmouelhi. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaves 114-118). / Vehicle rollover represents a significant percentage of single-vehicle accidents and accounts for over 9,000 fatalities and over 200,000 non-fatal injuries each year. Previous automotive research has studied ways for detecting and mitigating rollover on flat ground at high speed, and robotics research has studied the rollover stability of robots on rough terrain at low speed. Accident statistics show, however, that over 80% of rollovers occur when a vehicle departs the roadway and encounters sloped and rough terrain at high speed. This thesis investigates the stability limits imposed by off-road terrain conditions and techniques for measuring vehicle stability in the presence of off-road terrain factors. An analysis of the effects of terrain slope, roughness, and deformability on vehicle rollover stability in road departure scenarios is presented. A simple model that captures the first-order effects of each of these terrain features is presented and used to compare the relative danger posed by each factor. A new stability measure is developed that is valid in off-road conditions, which include sloped, rough, and deformable terrain. The measure is based on the distribution of wheel-terrain contact forces and is measurable with practical sensors. / (cont.) The measure is compared to existing stability measures and is able to detect wheel lift-off with greater accuracy in off-road conditions. The measure is experimentally validated with wheel lift-off detection as well. An uncertainty analysis of the measure is presented that assesses the relative importance of each sensor and parameter in the measure. / by Steven C. Peters. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 81-84). / In the pharmaceutical industry, the conventional tablet manufacturing process, a batch-based process based on solid powder handling, presents challenges such as inhomogeneous blending between Active Pharmaceutical Ingredients (APIs) and excipients, low yield, and low production rate. These difficulties can be resolved by the realization of a continuous manufacturing process through co-processing of APIs and excipients in the liquid-phase solution. A solvent-cast thin film, produced from liquid solution, can then be manufactured into tablets by way of a folding process. In order to design detailed compaction processes and machines, required compression pressure for layer bonding and mechanical properties of materials should also be investigated. The bonding strength of solvent-cast thin film layers was quantitatively measured by lap shear test. Based on this measurement, bonding threshold pressure was proposed as an indicator showing degree of bonding. At the same time, the layer bonding mechanism of solvent-cast thin films was interpreted as an interdiffusion of amorphous polymer chain end segments. In this context, relative contact area, polymer mobility, which is measured by glass transition temperature, and dwell time were proposed as critical factors in determining bonding threshold pressure. The relationships between those critical factors and process parameters such as surface roughness, residual water and excipient concentration, and compression rate were investigated. The mechanical and viscoelastic properties of solvent-cast thin films were also characterized. Solvent-cast thin films showed ductile-brittle transition, i.e., change of indentation hardness and strength factors among tensile properties with respect to residual water concentration. Changes of creep modulus and tensile properties at various stress levels and strain rates were also observed. / by Won Kim. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (leaves 81-82). / In the near future, the baby boomer population will cause a growth in the number of people entering nursing homes. Currently, if people wish to stay out of a nursing home, they must hire a personal aid to take care of daily tasks. A more cost-effective method could be to employ a robotic aid to help with these chores. One such aid is the SmartWalker, a robotic device that would provide health-monitoring sensors, physical support, and help in mobility to the elderly. The focus of this thesis is the design and analysis of the SmartWalker hardware. The design tools necessary to prevent the SmartWalker from slipping, tipping over, and experiencing brake failure are presented. Furthermore, a study of the omnidirectional platform used on the SmartWalker is performed for uneven terrain. It is shown that all of the wheels of the platform touch the ground at the same time. A simulation of a split caster mobility module, the main component of the omnidirectional platform, traversing a bump is also done. This proves that the control algorithms designed for a perfectly flat floor will suffice on an uneven floor. In addition, this thesis discusses the mechanical design that is necessary to build the SmartWalker. The mechanical design focuses on the split caster mobility modules, the slip rings, the frame, and the tradeoffs between strength and weight. / by Matthew J. Spenko. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 275-280). / Many industrial applications involve the transport of multiphase flows through pipes. For instance, the design and operation of oil pipelines and production facilities relies heavily on understanding the hydrodynamics of inultiphase flow. Industrial engineers utilizes multiphase flow simulators to aid in the design and flow assurance of such systems; however, the complexity of the physics and the range of scales involved in the problem require that the numerical algorithms invoke phase averaging methods and rely on empirical models. These assumptions and simplifications often result in predictions which are non-physical or are off by orders of magnitude forcing engineers to implement conservative safety factors to accommodate the large uncertainties. The development of physics based models may reduce the empiricism in the simulators allowing for the creation of more robust and cost effective designs. The work described in this thesis carries out both theoretical and computational investigations of some nonlinear mechanisms governing the interfacial stability and nonlinear evolution of stratified two-phase flows through horizontal channels and pipes. The resulting investigation identifies a strong nonlinear energy transfer mechanism which extracts energy generated by an interfacial instability and transfers it (with possible bi-exponential growth rates) to long wavelength waves which may eventually evolve into large amplitude waves and slugs. Detailed investigations demonstrate the effectiveness of this mechanism in flows ranging from ideal (potential) to turbulent two-phase flows. This thesis consists of three key focus areas. The first section develops a nonlinear potential flow analysis to identify a mechanism composed of a triad of resonantly interacting interfacial waves which are influenced by the Kelvin-Helmholtz interfacial instability. The mechanism that is identified permits the rapid energy transfer from linearly unstable short waves to stable long waves through nonlinear resonant wave interactions. It was found that, depending on the flow conditions, it is possible for linearly stable waves to achieve bi-exponential growth due to the resonant coupling. Extensions of this mechanism to broadbanded wave interactions were found to be in close agreement with experimental measurements. The analysis was also adjusted to examine the special case of sub-harmonic resonant interactions which have been observed in many experimental measurements and it was shown that this special case could still effectively create rapid long wave growth with up to bi-exponential growth rates. The second focus area examines the robustness of the aforementioned potential flow mechanism by identifying if a linear interfacial instability could be effectively coupled with resonant interactions in the presence of viscosity and flow turbulence. Using a linear stability analysis along with direct numerical simulations, comparisons were made against experimental measurements. This analysis was able to accurately identify the bandwidth of unstable interfacial modes as well as predict the existence of the strong sub-harmonic and triad resonances among modes which were reported in the experimental observations. The behavior observed in the numerical simulations demonstrates that the coupled instability-resonance mechanism is capable of existing in more complex two-phase turbulent flows and still permits the rapid exchange of energy from unstable short to linearly stable long wavelength modes. In addition, the numerical simulation results provide high-resolution data sets for which the interfacial stress distributions could quantified and described providing insights into the necessary behavior of future interfacial stress modeling. The final focus area is dedicated to developing a novel nonlinear slug transition criterion which couples the effects of a linear instability with that of nonlinear resonant interaction theory. An energy bounding condition is proposed for which the number of resonant modes which are linearly unstable is minimized allowing for a critical gas velocity to be identified. Comparisons are made against experiments carried out in horizontal channels and good agreement is observed. A heuristic method is proposed which allows for "equivalent" channel flow conditions to be obtained which are representative of the original pipe flow conditions. Unlike previously developed slug transition conditions, this new nonlinear criterion provides predictions which are significantly more accurate when compared against experimental measurements and maintains its accuracy over a large range of pipe diameters, flow conditions, and fluid combinations. / by Bryce K. Campbell. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 125-130). / Near field radiation transfer between objects separated by small gaps is a widely studied field in heat transfer and has become more important than ever. Many technologies such as heat assisted magnetic recording, aerogels, and composite materials with interfacial transport involve heat transfer between surfaces with separations in the nanometer length scales. At separations of only a few nanometers, the distinction between classical thermal conduction and thermal radiation become blurred. Contact thermal conduction is understood through the means of interfacial transport of phonons, whereas thermal radiation is understood by the exchange of heat through the electromagnetic field. Typically conductance values in the far field radiation regime are on the order of 5 W/m²K, whereas contact conductance is on the order of 108 W/m²K. While near field radiation experiments have reached separations down to on the order of 10 nm and measured 10⁴ W/m²K, there are still 4 orders of magnitude change that occurs over 10 nm of separation. However to this day, there does not exist a single unified formalism that is able to capture the relevant physics at finite gaps all the way down to the contact limit. The success of the continuum electromagnetic theory with a local dielectric constant has allowed accurate modeling of thermal transport for materials separated by tens of nanometers. The validity of this approach breaks down at the contact limit as the theory predicts diverging thermal conductance. The nonlocal dielectric constant formalism has successfully been applied to correct this error and predict transport at nanometer separations for metals and nanoparticles. However, success has been limited for deriving nonlocal dielectric constants for insulators as it is both theoretically and computationally more challenging and requires accurate atomic modeling to retrieve a valid continuum dielectric that reproduces the response of the system. In this work, the continuum approach is avoided and an approach is taken which more closely resembles the conduction picture, by performing atomistic modeling of the thermal transport between two semi-infinite media. The interatomic forces of both short-range chemical bonding forces and long ranged electromagnetic forces are included in an atomistic Green's function formalism in order to accurately calculate thermal transport at finite gaps down to the contact limit. With a single, unified formalism the bridge between conduction and radiation is finally achieved. / by Vazrik Chiloyan. / S.M.