Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 37). / High precision sensing is a widely applicable technology that ranges in use case from manufacturing, mobile devices, and robotics among more. Specifically inspired by the need for a high precision orientation sensing for an underwater inspection robot with high maneuverability, we explore the design of an underwater-capable sensor that can provide fast response and easy integration into the overall architecture of the robot. Ultimately, the sensor design opted for cost-minimization (<$50) in tandem with the high precision capabilities to create a design that would be further accessible. The sensor array consists of three Time-of-Flight sensors, each having +/- 1 mm precision and accuracy. The sensors sit in a triangular formation to allow for 3-point range finding and thereby constrain the sensing input to locate the robot in 3D space. In addition, custom fabrication of Printed Circuit Boards and implementation of an Extended Kalman Filter allow for integration into nearly and robot, while this was specifically designed for EVIE (Ellipsoidal Vehicle for Inspection and Exploration), a current project within d'Arbelloff Lab. For the sake of yielding useful data for position and orientation, the sensor array outputs a vector of Distance perpendicular to the surface, Yaw difference, and Pitch Difference. This is then fed back into the trajectory planning algorithms onboard EVIE. With full EKF implementation, and tuned noise parameters, the system exhibited precision and response beyond the typical sensor range.Typical accuracy of the Perpendicular Distance measure output was found to be +/-.52 mm while the Pitch and Yaw respectively held accuracy of +/- 20° and +/- 5°. / by Lawrence "Zack" Bright. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 193-198). / In recent years edge fracture has become a challenge in the manufacturing industry with the dramatical increase in the application of light-weight materials such as Advanced High Strength Steels (AHSS) and aluminum alloys. A premature edge cracking is observed in components with blanked/trimmed/pierced edges during the subsequent metal forming process. To understand the underlying physical mechanism and to establish a reliable CAE model, the thesis carries out a comprehensive experimental and numerical investigation on edge fracture of a commercially available DP780 steel sheet. The study reveals that it is the substantial plastic deformation introduced during the out-of-plane sheet blanking process that compromises the material ductility within the Shear Affected Zone (SAZ), and subsequently causes the edge to fracture prematurely under the in-plane edge stretching. To simulate the fracture behavior under such a complex a loading path, the fracture initiation is modeled using the concept of a scalar damage indicator that consists of two parts which are accumulated at different stages. The first one is accumulated during the sheet blanking process, referred to as pre-damage, while the second part is produced by the following metal forming. In such a modeling frame work, a corner stone is to determine the first part of pre-damage within the SAZ. This is achieved by a hybrid experimental and numerical method. Aided by microscopic examinations on cracked surfaces, the study shows that the pre-damage distribution within the SAZ follows an exponential function that drops from the critical value of unity at the edge surface to zero over the width of the SAZ. The obtained pre-damage is then introduced as the initial damage value during the following metal forming process. Based on a detail experimental characterization, a plasticity and fracture model is introduced to describe the material behavior under investigation. The model is based on the von Mises yield condition, a non-associated Hill'48 flow potential and an isotropic hardening law, together with the MMC fracture locus description with dependence on both stress triaxiality and Lode angle parameter. The proposed model successfully predict edge fracture in numerical simulation. / by Kai Wang. / Ph. D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Bibliography: leaf 35. / by Neil Vincent Hamblin. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / "September 2005." / Includes bibliographical references (p. [281]-283). / The goal of the MIT micro-engine project is to develop high-speed rotating Power MEMS (Micro-Electro-Mechanical Systems) using computer chip fabrication technologies. To produce high power (10-50 W) in a small volume (less than one cubic centimeter), the micro-turbo-machinery must be spun at a rotational speed on the order of million rpm. This ultra-high rotational speed, together with the small length-to-diameter ratio (L/D<0.07) limited by the chip manufacturing technology, entails many challenges in the design of the bearing system, such as an ultra-high whirl ratio of over 20 (compared with a whirl ratio of 2 for large-scale journal bearings) and a DN number of order 10 million mm-rpm. The thesis presents a newly developed theory for the hydrostatic gas journal- bearings for the micro-engine devices. To investigate the underlying physical mechanisms, fluid models are established to analytically calculate the hydrostatic, hydrodynamic, and damping bearing forces. It is found from first principles that the hydrodynamic force due to viscous drag becomes dominant with an L/D<<1 and acts in the opposite direction of the hydrodynamic force due to rotor pumping action. / (cont.) As a result, the net destabilizing hydrodynamic force can vanish for certain bearing geometries, causing singular behavior in the whirl instability limit. Thus, the ultra-short bearing is suggested to enable a large DN number and a high whirl ratio in the micro-journal-bearing system. A novel variation of the axial-flow hydrostatic micro gas journal-bearing concept is introduced, which yields anisotropy in bearing stiffness. By departing from axial symmetry and introducing biaxial symmetry in hydrostatic stiffness, the bearing's top speed is increased and the fabrication tolerance requirements are substantially relieved. The third-order nonlinear resonances in the micro-journal-bearing system are investigated by both analytical models and numerical simulations, and the predictions from these models agree well with the experimental observations. The model predicts a subharmonic resonance in the isotropic journal-bearing system, with a slow rotating noncircular orbit such that the symmetry of the system is broken by itself in the nonlinear resonance. / (cont.) Furthermore, the anisotropic journal-bearing system is found to be able to engage in multi-type nonlinear resonances: superharmonic resonances at one third of the natural frequencies, subharmonic resonances at three times the natural frequencies, and combinations (such as the average) of the two natural frequencies. The conditions under which these resonances can occur are derived analytically and are then verified by numerical simulation. / by Lixian Liu. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (p. 123-125). / In this thesis, I develop the conceptual design of the spacecraft required for human-Lunar and human-Mars exploration. The requirements for these vehicles are derived in the context of the NASA Concept Exploration & Refinement project. Similarly, the concepts generated are intended to operate within the transportation architecture developed during this project. Therefore, this thesis serves as a vehicle-level design exercise. Four vehicle architecture options are synthesized by combining system concepts in a logical fashion. These four options are evaluated on several performance criteria, and one vehicle design concept is selected for detailed modeling. In addition, I investigate the conceptual design of the airlock system, as a system-level design exercise. This research project culminated in a set of vehicle concept designs and design recommendations for NASA. / by Brenden P. Epps. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 220-228). / Diesel particulate filters (DPF) are an effective means for meeting increasingly stringent emissions regulations that limit particulate matter. Over time, ash primarily derived from metallic additives in the engine oil accumulates in DPFs. Lubricant-derived ash increases pressure drop and reduces fuel economy. After long time periods, the accumulation of ash may lead to irreversible plugging in DPFs, which necessitates periodic filter removal and cleaning. This thesis examines the sources for lubricant-derived ash in engines and explores potential opportunities to reduce ash emissions. The research studies changes in lubricant composition in the engine via advanced in-situ diagnostics and computer modeling of species transport in the power cylinder. These changes are directly related to ash emissions and the effectiveness of the lubricant in protecting engine components. In the first part of this thesis, sampling techniques are employed to determine the composition of the lubricant in critical locations in the engine system, where oil is lost by liquid oil consumption and vaporization. The first practical in-situ FTIR measurements of lubricant composition at the piston and liner interface are obtained with a novel diagnostics system employing Attenuated Total Reflection (ATR) spectroscopy. This information is used to create a mass balance for ash-related elements and a framework for modeling the distribution of ash-related species in the engine. In the second part of this thesis, a novel approach to condition the lubricant at a fixed station in the oil circuit is explored as a potential means to reduce ash emissions. This study examines the performance of an innovative oil filter that releases no additives into the lubricant, yet enhances the acid control function typically performed by detergent and dispersant additives. The filter has the potential to be used as a replacement for detergent additives in a lubricant formulation, or enhance additive effectiveness there-by allowing in an increase in oil drain interval. This research will assist in the development of new formulations for diesel lubricants that minimize detrimental effects on DPFs, while providing adequate protection to engine components. / by Simon A.G. Watson. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 57-62). / In this thesis, I present a procedure by which to transfer greater than 25 mm² areas of high-quality graphene synthesized via low-pressure chemical vapor deposition from copper foil to porous support substrates. Large-area, high quality graphene on a porous support would serve as a platform by which to create high efficiency porous graphene membranes for use in liquid and gas-phase separation technologies. In this procedure, we transfer greater than 25 mm² areas of graphene with few holes and tears to both gold Quantifoil Holey Carbon transmission electron microscope grids with 1.2 [mu]m diameter pores and to Sterlitech polycarbonate track etch membranes with 200 nm diameter pores by bonding the substrates to the graphene then wet-etching the copper. The resulting membrane quality is characterized via Raman spectroscopy, scanning electron microscopy, diffraction patterning, and aberration-corrected scanning transmission electron microscopy. / by Sean C. O'Hern. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 87-89). / Full automation of repetitive and/or specialized tasks has become a preferred means to meet the needs of manufacturing industries. However, some tasks cannot be fully automated due to their complexity or the nature of the work environment. In such cases, semi-automation through human-robot collaboration is a strong alternative that still maintains a high level of efficiency in task execution. This thesis focused on the control and coordination issues of the Supernumerary Robotic Limbs (SRL); a pair of wearable robotic limbs that are a potential solution to these issues. The first purpose of this study was to adequately model the collaborative aspect of a task that is conventionally performed by two coworkers. This was achieved through the Coloured Petri Nets (CPN) tool, which was able to model the collaboration between two coworkers by using the SRL and its operator instead. The second purpose of this work was to evaluate how to implement a sensor suit to establish reliable communication between the SRL and its operator. Using data-driven methods for detection, we were able to monitor the operator's current state. By combining this data with the CPN task model we were able to relay the operator's intentions to the SRL. This enabled the SRL to follow the CPN process model in a timely and coordinated manner together with its operator. The third and final section of this thesis focused on considering the interchangeability of roles between the SRL and its operator. We used a datadriven approach to model a task where the SRL and its operator had to perform a simultaneous dynamic task. This was performed by using teach by demonstration techniques on process data from two workers. A control algorithm was then extracted from the actions of the supporting worker. Both the process model and the sensor suit, together with the detection algorithms, were implemented and validated using the first prototype of the SRL. Results show that the SRL was successful in autonomously coordinating with its operator and completing an intercostal assembly task. / by Baldin Adolfo Llorens - Bonilla. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000. / Includes bibliographical references (p. 132). / by Nicolas Oriol Hoyos. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 39). / This thesis analyses the front wheel of the Leveraged Freedom Chair (LFC) an all-terrain, off-road wheelchair with two distinct models: one for the developing world and one specifically for American riders. The functional requirements of performance and price, were designated by the start-up company Global Research Innovation and Technology (GRIT), which makes the LFC. This study includes comparisons between the original rubber wheel, which is currently being used as the front wheel of the LFC, and alternative wheels available for purchase. The goal was to find a new wheel which could be implemented for future manufacturing to increase the lifespan of the LFC, improve the ride quality and efficiency of production. Based on performance it is concluded that a pneumatic wheel of comparable geometry to the original rubber wheel is the best alternative for the American chair where maintenance is more routine and replacement parts and service are readily available. For the developing world future work is necessary to either improve the quality of the original rubber wheel or select a low cost, low maintenance alternative. / by Sara Elizabeth Falcone. / S.B.