Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (p. [173]-181). / by Ujjwal Sinha. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 67). / This thesis discusses the design, characterization and optimization of a low-cost additive rapid-prototyping tool head for a technology known as Fused Filament Fabrication for use in an educational curriculum. Building a 3D printer represents an excellent educational opportunity as it requires knowledge in electronics, mechanics, and thermal-fluids engineering; this particular design also includes a flexural bearing, introducing students to a new and important class of machine element. Polymer flow through the extruder is modeled as pipe flow with pressure drops using Bernoulli's equation with viscous losses; the model predicts that the pressure required to extrude is proportional to 1/d⁴' , where d is the nozzle diameter. Three different extruder designs are considered; a piston-based design, an auger-based design, and a pinch-wheel design. The pinch wheel design best meets the functional requirements after comparing the designs based on factors such as complexity and controllability. Flexural bearings are selected to provide a preload against the polymer filament; HDPE was chosen to be the flexure material after considering factors such as water-jet machinability and yield stress to elastic modulus ratio. Thermal imaging shows that the temperature profile along the heater barrel is not uniform, with the largest variation being 80±2.8°C in large part due to errors in heater wire distribution during assembly. An exponential relationship is observed between the force required to extrude versus the temperature of the heater barrel with the force required to extrude dropping to between 1 and 2N in the range of 200 to 240°C. This data suggests trade-offs between maintaining a reasonable extruding pressure and maintaining good build resolution and speed. A discussion of the low cost rapid prototyping cycle follows, as well as instructions for assembly and use of the extruder. The paper ends with several suggestions to improve extruder performance and a list of ideas for bringing the extruder costs down. / by Aaron Eduardo Ramirez. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (leaves 129-131). / by Matthew Sweetland. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994. / Includes bibliographical references (leaves 93-95). / by Kuo-Chun Wu. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / Includes bibliographical references (leaves 88-90). / by Nicolas G. Hadjiconstantinou. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (leaves 95-99). / In recent years, there has been a large increase in the use of autonomous underwater vehicles (AUV) for numerous military, commercial, and scientific missions. These include mapping, oceanographic data collection, and search and recovery. The list of the key technologies for AUV research includes communications, power, navigation, design, vehicle tracking and sensor fusion. Despite rapid progress in some of these areas, a number of barriers exists. This thesis offers a novel approach to address these issues by utilizing an Autonomous Surface Craft (ASC) with a wetbay from which to launch an AUV, including a launch capability. This paper also discusses the fusion of sensors required by these two vehicles, including computer resources, sonar images, and power. A new method is described by which an ASC can be tracked through the use of a towed underwater modem increasing the communication range over two kilometers. This thesis describes how an ASC tracks an AUV by configuring two modems together in a short baseline acoustic array. Results of this tracking show less than four meters of error under difficult real-world test conditions. / (cont.) Discussed are the advantages of transmitting the information obtained in the AUV modem transmission via surface communications. A tracking ASC maintaining close proximity to the AUV allows a larger bandwidth of underwater communication, increasing the flow of information. Expanded flow enables multiple assets to communicate over long-ranges. The impact of these contributions will expand the capabilities of autonomous vehicles. / by Robert R. Williams. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29). / The distribution of clean, drinkable water is a problem that has been addressed in all civilizations. The most common form of transportation today, is the use of pressurized pipelines to carry the water long distances, but damage to the pipes, such as leaks, can cause considerable losses. The difficulty in detecting these leaks prompted this work, which attempts to find a reliable method of recognizing a leak and suggest possible designs that could be implemented on a pipe-navigating robot. This design would use thin flaps, or "leaves," that would be forced outward by the rapid pressure drop formed in proximity to the leak. In order to determine the characteristic behavior of the system, several simulations, with a circular hole as the leak, were ran that showed that the significant pressure gradient existed only within distance on the order of the diameter of the leak. To validate these results, a high precision pressure sensor was used to try and measure the pressure gradient, but the pressure sensor was too large sense a pressure difference. Therefore, rubber strips were used to emulate the use of "leaves" to perceive the leak. This confirmed the simulation results, as the rubber strips had to be incredibly close to the leak in order to be affected. Furthermore, once the strip was pulled up against the leak, the friction created between the wall and the strip became strong enough that it could be utilized. Both the simulation and experimental results suggest that the leak detecting module should start near the leak. Next, instead of detecting the leak via a motion towards the leak, the module should instead take advantage of the large frictional force that occurs when the leaf has made contact with the leak. Further experiments could include testing the magnitude of the frictional force and creating a prototype. / by James Torres. / S.B.

Thesis (Sc.D.) Massachusetts Institute of Technology. Dept. of Mechanical Engineering, 1948. / Vita. / by Minghua Lee Wu. / Sc.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / 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 115-120). / We investigate the deployment of a thin elastic rod onto a rigid substrate and study the resulting coiling patterns. In our approach, we combine precision model experiments, scaling analyses, and computer simulations towards developing predictive understanding of the coiling process. Both cases of deposition onto static and moving substrates are considered. We construct phase diagrams for the possible coiling patterns, e.g. meandering, stretched coiling, alternating loops, and translated coiling, and characterize them as a function of the geometric and material properties of the rod, as well as the height and relative speeds of deployment. The various modes selected and their characteristic length-scales are found to arise from a complex interplay between gravitational, bending, and twisting energies of the rod, coupled to the geometric nonlinearities intrinsic to their large deformations. We give particular emphasis to the first sinusoidal mode of instability, which we find to be consistent with a Hopf bifurcation, and rationalize the meandering wavelength and amplitude. Throughout, we systematically vary natural curvature of the rod as a control parameter, which has a qualitative and quantitative effect on the pattern formation, above a critical value that we determine. Upon establishing excellent quantitative agreement between experiments and simulations with no fitting parameters, we perform a numerical survey to relate the pattern size to the relevant length-scales arising from material properties and the setup geometry, and quantify the typical strain levels in the rod. The universality conferred by the prominent role of geometry in the deformation modes of the rod suggests using the gained understanding as design guidelines, in the original applications that motivated the study. These include the coiling of carbon nanotubes and the deployment of submarine cables and pipelines onto the seabed. / by Mohammad Khalid Jawed. / S.M.

Thesis: M. Eng. in Manufacturing, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 95-98). / Product reliability, quality, and performance are essential for all companies, especially high technology manufacturing startups looking to scale-up successfully. Company image and reputation can be heavily impacted by product failures. The cost of failures in-house and at the customer will only increase as a company scales up. Failure mitigation is critical to the success of a product and its company throughout the entire product lifecycle. This thesis proposes an ideal Failure Mitigation Strategy (FMS) that provides a methodology and framework with linear process workflow and easy to follow steps that lead to the reduction of cost from failures. Establishing a strong FMS will assist the company in learning from their failures while reducing the total number and average cost of failure events. The ideal FMS was tailored to and implemented at New Valence Robotics Corporation (NVBOTS) in Boston, Massachusetts, as a case study. The ideal FMS consists of failure tracking, failure analysis, and multi-method failure resolution. Failure events are first observed and properly documented via the failure tracking system. Failure tracking data is then processed during failure analysis using a total cost model to automatically prioritize and down select the most impactful failure event types. Root cause analysis is then performed on the top priority failure event types. Finally a robust multi-method failure resolution methodology uses an economical combination of design and process changes along with testing to eliminate or reduce the cost of those failures. Over 200 failure events were tracked, including 50 unique failure event types, accounting for over $75,000 in costs at NVBOTS. A unified and improved tracking system was implemented at NVBOTS along with a powerful analysis framework. Failure analysis was performed, prioritizing the failures by total cost and a failure resolution framework was designed to implement the solutions to the top priority failure event types. The ideal Failure Mitigation Strategy offered in this thesis provides NVBOTS and other entities a framework that allows for full understanding of the current failure landscape as well as a systematic method to reduce the impact from failures through elimination and mitigation. / by Derek S. Straub. / M. Eng. in Manufacturing