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Mechanical Engineering - Master's degree

Mostrando recursos 1 - 20 de 3.447

  1. Hydrodynamic performance of multi-component structures in oscillatory flow, from blow-out preventer to dual Cylinder interference

    Fan, Dixia
    As one of the key components for the wellhead integrity, the Blow-out Preventer (BOP) is designed and constructed to prevent abnormal pressure change in the well and keep the blow-out from happening, and therefore is essential for the whole well- being of the offshore drilling system, and this calls for a careful investigation on the understanding of the BOP dynamics and its effect on the whole system. However, due to the complexity of the structure itself, the hydrodynamics of the BOP are difficult to model and therefore is the main focus on this thesis. First a general overview will be...

  2. Electrohydrodynamic (EHD) printing of microparticle streams for additive manufacturing

    Guan, Yue, S.M. Massachusetts Institute of Technology
    Electrohydrodynamic (EHD) printing can be used to fabricate high resolution (~100 nm) features at high rates (~10 kHz), and is compatible with a wide range of materials. However, conventional EHD printing techniques focus only on homogeneously dispersed functional inks, including nanoparticulate materials, molecular and polymers. This thesis explores EHD printing of liquids containing microparticles. For printing, liquids containing microparticles with a diameter of ~1-10 pm are prepared, which sediment upon loading into the capillary tip. A single-tip EHD apparatus enabling pulsed delivery of kilovolt signals, high speed imaging, and measurement of charge transfer to the substrate has been constructed. Using...

  3. Characterization of the exhaust gas condensate pH values of gasoline engines

    Jain, Lakshya
    Exhaust Gas Recirculation has been used in gasoline engines to reduce NOx formation and part-load throttle loss for many years. More recently, there is a trend towards down-sizing and turbocharging engines as the strategy helps to improve fuel economy. Cooled low pressure EGR complements down-sizing-turbocharging in direct injection gasoline engines and has the potential to further improve efficiency. When exhaust gas gets cooled down below its dew point in an EGR cooler, the contained water vapor condenses on the cooler walls and dissolves some of the exhaust gases, which may make the condensate corrosive. For this reason, the extraction point...

  4. Robust motion planning for autonomous tracked vehicles in deformable terrain

    Lee, Sang Uk, S.M. Massachusetts Institute of Technology
    Ensuring the safety of autonomous vehicles during operation is a challenging task. Numerous factors such as process noise, sensor noise, incorrect model etc. can yield uncertainty in robot's state. Especially for tracked vehicles operating on rough terrain, vehicle slip due to vehicle terrain interaction affects the vehicle system significantly. In such cases, the motion planning of the autonomous vehicle must be performed robustly, considering the uncertain factors in advance of the real-time navigation. The primary contribution of this thesis is to present a robust optimal global planner for autonomous tracked vehicles operating in off-road terrain with uncertain slip. In order...

  5. Methods to measure and relate the viscoelastic properties of brain tissue

    Mijailovic, Aleksandar S
    Measurement of brain tissue elastic and viscoelastic properties is of interest for modeling traumatic brain injury, understanding and creating new biomarkers for brain diseases, improving neurosurgery procedures and development of tissue surrogate materials for evaluating protective strategies (e.g., helmets). However, accurate measurement of mechanical properties of brain tissue is challenging due to the high compliance and complex mechanical behavior of this tissue, including nonlinear viscoelastic behavior, poroelastic deformation, and failure mechanisms. Thus, reported measurements of the elastic and viscoelastic moduli of brain tissue vary by several orders of magnitude. This thesis highlights three mechanical characterization techniques for brain tissue: rheology,...

  6. Agile quadrotor maneuvering using tensor-decomposition-based globally optimal control and onboard visual-inertial estimation

    Riether, Fabian
    Over the last few years, quadrotors have become increasingly popular amongst researchers and hobbyist. Although tremendous progress has been made towards making drones autonomous, advanced capabilities, such as aggressive maneuvering and visual perception, are still confined to either laboratory environments with motion capture systems or drone platforms with large size, weight, and power requirements. We identify two recent developments that may help address these shortcomings. On the one hand, new embedded high-performance computers equipped with powerful Graphics Processor Units (GPUs). These computers enable real-time onboard processing of vision data. On the other hand, recently introduced compressed continuous computation techniques for...

  7. Wheel design optimization for locomotion in granular beds using resistive force theory

    Slonaker, James (James C.)
    Inspired by hypotheses of Resistive Force Theory, a general dimensionless form for granular locomotion has been discovered, which instructs how to scale size, mass, and driving parameters to relate dynamic behaviors of different locomotors in the same granular media. These scalings are experimentally confirmed with wheel pairs of various shapes and sizes under many driving conditions in a common sand bed. How the relations may be derived alternatively by assuming Coulombic yielding and how the relations can be augmented to predict wheel performance in different ambient gravities is also explained. Next, a rotating-flap wheel that consists of a central hub...

  8. Designing metal grid contacts for four-terminal tandem solar cells

    Sofia, Sarah E. (Sarah Elizabeth)
    Flat-panel tandem solar cells have demonstrated the potential to exceed the efficiencies of their single-junction constituents. However, robust rules for tandem solar cell design are currently lacking, slowing the development of cost-effective implementations of this technology. The four-terminal (4T) architecture stacks electrically independent sub-cells and avoids current-matching losses, resulting in two main advantages over the conventional integrated two-terminal (2T) architecture: a higher energy yield and a loosened constraint on material bandgap combinations. Because both sub-cells are contacted independently in a 4T tandem, multiple stacked semi-transparent contacts are needed, causing significant shading and series resistance losses. Moreover, for stationary flat panel...

  9. Internal tides near steep topographies

    Sroka, Sydney Glass
    The primary contributions of this thesis include the first stages of development of a 2D, finite-volume, non-hydrostatic, [sigma]-coordinate code and beginning to apply the Dynamically Orthogonal field equations to study the sensitivity of internal tides to perturbations in the density field. First, we ensure that the 2D Finite Volume (2DFV) code that we use can accurately capture non-hydrostatic internal tides since these dynamics have not yet been carefully evaluated for accuracy in this framework. We find that, for low-aspect ratio topographies, the z-coordinate mesh in the 2DFV code produces numerical artifacts near the bathymetry. To ameliorate these stair-casing effects, and...

  10. Effect of synthesis conditions on large and persistent photoconductivity in chemical bath deposited cadmium sulfide thin films

    Yin, Han, S.M. Massachusetts Institute of Technology
    Persistent photoconductivity (PPC) has been observed in numerous semiconductors and dielectrics. It refers to the phenomenon that photoconductivity can last for a long time after photo-excitation is terminated. In most cases, the causes of PPC are unknown, and the connections between synthesis conditions, composition, morphology, and PPC are unexplored. Here, we study the effect of chemical bath deposition parameters on PPC in CdS thin films, including bath temperature, concentration of reactants, deposition time, stirring speed and cation source. By tuning the chemical conditions during deposition, we achieved near stoichiometric CdS thin films exhibiting large photoconductive responses (up to 109 times...

  11. Standard operating procedure for Highly Accelerated Life Testing (HALT) : design and standardization of fixture setup for circuit boards

    Chew, Dexter Xuan Han
    This thesis deals with the introduction of Highly Accelerated Life Testing (HALT) in a multinational corporation as part of a reliability improvement process for printed circuit boards (PCBs). More specifically, the thesis focuses on drafting a standard operating procedure (SOP) to standardize the fixture setup process so as to minimize variation in vibrational responses attributed to fixture setup. This study proposes a three phase approach to meet the objective. The first phase aims to minimize variation in the gauges and the vibration table. A gauge repeatability and reproducibility (gauge R&R) test is conducted on two triaxial accelerometers to determine the...

  12. Analysis and implementation of laboratory automation system

    Secundo, Rafael Garcia
    Quest Diagnostics is a large company that analyzes millions of medical specimens every day using a variety of analytical equipment. It is implementing a fully automated line in a major laboratory. The automation line is Quest's first major automation initiative and will serve as a pilot for future initiatives. An important element of implementing this initiative is the transition from manual to automated specimen handling operations. Furthermore, it is crucial to model the behavior of the newly automated production system. This thesis discusses the risk analysis performed on the transition from manual operations into automated as well as a discrete...

  13. Fabrication of anti-reflective and imaging nanostructured optical elements

    Choi, Hyungryul
    Moth eyes minimize reflection over a broad band of angles and colors and lotus leaves minimize wetting over a broad range of breakthrough pressures by virtue of subwavelength structures patterned on their respective surfaces; similar examples of organisms exploiting geometry to attain properties unavailable in bulk materials are abundant in nature. These instances have inspired applications to man-made structures, collectively known as functional materials: for example, self-cleaning/anti-fogging surfaces, and solar cells with increased efficiency. I fabricated a functional surface where both wetting and reflectivity are controlled by geometry. Using a periodic array of subwavelength-sized high aspect ratio cones, patterned on...

  14. Correlative elemental and electrical micro-analysis of laser fired contacts in silicon solar cells

    Yen, Patricia, S.M. Massachusetts Institute of Technology
    Photovoltaic (PV) energy is an abundant and clean alternative to conventional energy sources, which pose an irreversible threat to the environment. For PV to reach cost parity with conventional energy, advances like laser-fired contacts must be adopted to improve cost levers like solar cell efficiency and industrial throughput. This work examines the relationship between laser-processing on the structure and property of solar cells, with the goal of (1) characterizing the differences between using two lasers simultaneously (double-shot lasing) versus a single laser for LFC processing, and (2) using the new findings to optimize industrial LFC efforts. Electrical properties such as...

  15. Product availability improvement for an analytical consumables supply chain : distribution and transportation

    Han, Yan, M. Eng. Massachusetts Institute of Technology
    This thesis work focuses on supply chain operation optimization on column consumables at Waters Corporation in order to improve product availability to 95% to customers. This thesis project is conducted by collaboration of Han, Hua and Lee as a team through interviewing stakeholders, performing historical data analysis and model simulation. Hua's thesis focuses on safety stock allocation in different stages of column supply chain and Lee's thesis focuses on replenishment policy of products with consistent high demands and production policy for build-to-order products. This thesis focuses on improving product availability of products with relatively low demands and high variability. Due...

  16. Production ramp-up of a hardware startup : developing inventory management strategies and establishing a framework for vendor selection

    Gokaram Narayana Murthy, Rakshith
    It is imperative for hardware startups to have a clear plan of action while scaling-up production. Manufacturing and operations related activities should be accorded the same importance as design and engineering. New Valence Robotics Corporation (NVBOTS), a high-technology automated 3D printing manufacturing startup was experiencing high growth. The demand for their 3D printers was rising and they were looking to expand into new markets. In order to ramp up production and meet growing needs of the market, it was an absolute necessity to restructure their production planning and inventory management strategies. Inventory is the life-blood of every organization and mandates...

  17. Developing Highly Accelerated Life Test (HALT) method to improve product robustness and shorten development cycle

    Chang, Chun-Ming, M. Eng. Massachusetts Institute of Technology
    Highly Accelerated Life Testing (HALT) is often used to identify the latent defects for the printed circuit boards (PCBs) during the early stage of the product development process. The inconsistency in executing HALT may not reveal the maximum amount of design weaknesses or intermittent failures, which would eventually lead to the premature product failure in the field and incur additional warranty expenses. The scope of this project has focused on establishing the standardized operating procedure (SOP) for Highly Accelerated Life Testing (HALT) using the DMAIC methodology for the electronic components such as printed circuit boards (PCBs) to help identify these...

  18. First pass yield analysis and improvement at a low volume, high mix semiconductor equipment manufacturing facility

    Anand, Shaswat
    "Improve quality, you automatically improve productivity " - W. Edwards Deming Quality is the heart and soul of any manufacturing unit. Quality metric stagnation at a high mix semiconductor equipment manufacturing facility was the motivation for this project. An analysis was done to understand the working and importance of the quality metrics, First Pass Yield and Quality Notifications per Module, to understand the reasons for its stagnation over the past couple of years at the assembly plant. Also module specific study was done to understand the trends in the quality improvement and the improvements achieved on different modules assembled at...

  19. Characterization of inertial measurement unit placement on the human body upon repeated donnings

    Vanegas, Morris Dwight
    Given projections of an increase in the number of consumers wearing sensors in the upcoming years coupled with NASA's technological roadmap for future human space exploration, there is a need to understand and appropriately incorporate the variability of humans during the use of sensors that extract human activity and diagnostics. Accurate estimations of variability in multiple donnings of sensor suites may aid algorithm development for wearable motion capture systems that make use of Inertial Measurement Units (IMUs). The accuracy of any algorithm incorporating these sensors is limited by the accuracy of the sensor to segment calibration. In this study, 22...

  20. Comparison of experimental results and theory for two laboratory hydraulic fracture apparatus

    Quinn, Timothy Sean
    by Timothy Sean Quinn.

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