Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1991. / Includes bibliographical references (leaves 161-166). / by Akhil J. Madhani. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 62-64). / The need to understand plastic deformation in amorphous covalently bonded materials arose from the unique mechanical properties of disordered intergranular layers in nc-TiN/a-Si₃N₄ ceramic composites. Silicon was chosen as a model disordered network solid for the purpose of conducting feasible atomistic computer simulations of plastic deformation. Amorphous silicon structures were created by melting and quenching using a molecular dynamics algorithm. These structured were plastically deformed by conjugate gradient static energy minimization. Atomic level analysis was carried out using appropriately generalized notions of stress and strain. Plastic deformation was found to occur in a series of discrete stress relaxations, each one of which was accompanied by a well localized atomic level rearrangement. The transforming regions were roughly ellipsoidal in shape and involved the cooperative motion 100-500 atoms spanning a length scale of 0.7-2.5nm. This length scale is large in comparison to the typical thickness of disordered intergranular layers in nanocrystalline ceramic composites, indicating that the plastic relaxation process in such intergranular layers cannot be the same as the one found in bulk amorphous covalent solids. / by Michael J. Demkowicz. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 201-212). / Moving contact line problems involving polymeric materials and other complex fluids are encountered in many applications such as coating flows, gravity-driven drainage, and spin-coating operations. Viscous, capillary, inertial and gravitational forces can all be important in these flows depending on the scale and speed of the spreading process. In this research, a number of benchmark problems involving moving contact lines of viscous Newtonian and non-Newtonian polymeric fluids have been studied using non-invasive optical techniques. A detailed study of viscous Newtonian and non-volatile liquids spreading on smooth horizontal and inclined substrates is presented. A phase-modulated interference microscope was used to enable the simultaneous measurement of both the inner (microscopic) length scale and the outer (macroscopic) flow scale in addition to the intermediate matching region. The resulting measurements of both the apparent contact angle and lateral scale of the precursor wetting film agree quantitatively with theoretical predictions for the spreading of a van der Waals fluid over a wide range of capillary numbers (10-6 < Ca < 10-1). It is also shown that the dynamic contact angle of a perfectly wetting Newtonian fluid is not only a function of the capillary number (the Hoffman-Voinov-Tanner law), but also depends on a logarithmic correction to this relationship, which is often overlooked. It is shown that both the microscopic and macroscopic length scales affect this logarithmic correction. Our measurements are in good quantitative agreement with available theoretical predictions. In addition to the steady, isothermal spreading of fluids, we have studied instabilities of volatile liquid films spreading on thermally conductive surfaces. / (cont.) When a drop of volatile silicone oil is deposited on the surface of a smooth silicon wafer, its thickness decreases with time in a power-law form as it spreads under the action of capillarity. At a critical thickness, traveling waves can be observed on the free surface of the film, and a confocal microscope was used to measure the amplitude, frequency, and non-linear evolution of these waves. We interpret these waves in terms of Marangoni instabilities induced by surface tension gradients close to the contact line, generated by liquid evaporation. The spreading of highly entangled polymer melts (Z > 10) on a solid surface is also considered. Our experiments confirm the existence of a non-Newtonian 'foot' region in the vicinity of the moving contact line for highly entangled polymer melts. Our experimental results of the lateral and vertical scales of this 'foot' are in fair agreement with available theoretical predictions. The transient spreading motion of an ideal elastic 'Boger' fluid (consisting of a dilute solution of high molecular weight polymer dissolved in a viscous Newtonian solvent) is also investigated. It is shown that the spreading rate of this model elastic fluid is smaller than is observed for corresponding Newtonian fluid drops of similar size and viscosity due to the viscoelastic effects. A foot-like structure is detected at the leading edge of the droplet for these unentangled, elastic fluids as well ... / by Hossein Pirouz Kavehpour. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (p. 157-162). / by Jason Douglas Hintersteiner. / M.S.

Thesis (M. Eng. in Manufacturing)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 143-145). / A semiconductor capital equipment manufacturing plant is a high-mix low-volume manufacturing environment where the complex products produced requires skilled manual assembly and expensive raw materials. The semiconductor capital equipment industry is sporadic with high demand variability and hence, semiconductor capital equipment manufacturers must be able to allocate resources to meet demand at minimum cost to maintain their manufacturing competitiveness. This thesis draws heavily on the research done at Varian Semiconductor Equipment, a manufacturer of ion implantation machines for the semiconductor industry, over a period of seven months as part of the Master of Engineering in Manufacturing program at the Massachusetts Institute of Technology and aims to enable Varian to make optimal resource allocation, capacity planning and personnel decisions that will allow it to meet demand at minimum cost. The goal of this thesis is achieved through the development of three optimization models, a labor flexibility framework, and an inventory management policy. The first optimization model, resource optimization for cost minimization, will allow Varian to determine the optimal combination of workers and assembly bays for each production process that will allow it to meet demand at minimum cost. The second optimization model, labor cost minimization, will enable Varian to determine the optimal combination of regular time and overtime that will allow it to meet demand at minimum labor cost. The final model, labor flexibility, will allow Varian to determine the optimal movement of workers that will allow the Varian's plant to meet demand with the minimum total cost of work hours to be provided. The final model is based on a labor flexibility framework introduced in this thesis. We also present an inventory management policy to manage certain assemblies produced at Varian's supermarket build area that will allow Varian to reduce those assemblies' safety stock levels by 30%. / by Lohithaksha Chengappa. / M.Eng.in Manufacturing

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references. / Data was collected in order to determine the career paths followed by graduates of MIT's mechanical engineering department. The data was obtained with the help of the Alumni Association of MIT. Data was obtained on current occupations for the graduating classes of 1967 through 1997. These occupations were sorted in to more general categories and then the categories were plotted in terms of percentage of graduates per year. Anomalies were found over the initial study of every fifth class from 1972 through 1997. An expansion was made in the data analyzed to every other year from the class of 1967 through 1997 as well as every year from 1969 through 1974. Using this more comprehensive data set, it was concluded that most graduates, approximately two-thirds of each class, pursue careers in either engineering or management. Over the years following graduation, the percentage of engineers decreases while the percentage of managers increases. / by Catherine A. Kelly. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 65). / Solarclave is a solar-powered autoclave designed for use in rural health clinics in developing countries. The autoclave must sufficiently sterilize medical instruments to ensure that they can safely be used in providing patient care. The medical instruments are sterilized in a pressure cooker that is heated by concentrated sunlight from a parabolic reflective surface. Previous iterations and testing of the Solarclave proved that sunlight and a pressure cooker could sufficiently sterilize equipment. However, usability problems and cost constraints require that the design be further improved before dissemination can occur. Critical design decisions that this work makes include updating the reflective structure, the pressure cooker, and the pressure cooker insulation. The combination of choices must meet user needs and provide sufficient sterilization at a minimum cost. A reflective structure was selected based on its low cost and listed ability to meet existing power consumption needs. A mathematical model was created to estimate the actual usable power output of the selected reflective structure based on its dimensions and reflectivity, as well as expected intensity of solar radiation. Furthermore, a thermal circuit model was developed to predict the temperature over time inside the pressure cooker as a function of input power, pressure cooker dimensions, and insulation material choice. The mathematical model was evaluated by measuring the temperature outside the pressure cooker over time, recording all relevant parameters, and comparing the results to those predicted by the model. The results indicated that the theoretical input power estimate was too high, but that the thermal circuit was an appropriate approach to modeling the heat loss of the system. The usability of the system showed major improvements in terms of ease-of-use, but needs further design in terms of its aesthetics. / by Louise E. van den Heuvel. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 65-69). / In this work we consider dynamical systems that are subjected to intermittent instabilities. The presence of intermittent instabilities can be identified by large amplitude spikes in the time series of the system or heavy-tails in the probability density function (pdf) of the response. We formulate a method that can analytically approximate the response pdf (both the main probability mass and heavy-tail structure) for systems where intermittency is important to quantify. The method relies on conditioning the probability density function on the occurrence of an instability and the separate analysis of the two states of the system, the unstable state and the otherwise stable state with no intermittent events, according to a total probability law argument. In the stable regime we employ steady state assumptions, which lead to the derivation of the conditional response pdf using standard methods for random dynamical systems. The unstable regime is inherently transient and to analyze this regime we characterize the response under the assumption of an exponential growth phase and a subsequent decay phase until the system is brought back to the stable attractor. The separation into a stable regime and unstable regime, allows us to capture the heavy-tailed statistics associated with intermittent instabilities. We illustrate the method on three prototype intermittent systems and show that the analytical approximations compare favorably with direct Monte Carlo simulations. We consider the following applications: an intermittently unstable mechanical oscillator excited by correlated noise; a complex mode in a turbulent signal with fixed frequency, where nonlinear mode interaction terms are replaced by a stochastic drag and additive white noise forcing; and a stochastic Mathieu equation, featuring intermittent parametric resonance. / by Mustafa A. Mohamad. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996. / Includes bibliographical references (p. 57-60). / by Matthew Bartschi Wall. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1962. / Vita. / Includes bibliographical references (leaves 88-93). / by Arthur Edward Bergles. / Ph.D.