Mechanical Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2795
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Item Diversity and Novelty: Measurement, Learning and Optimization(2019) Ahmed, Faez; Fuge, Mark; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary objective of this dissertation is to investigate research methods to answer the question: ``How (and why) does one measure, learn and optimize novelty and diversity of a set of items?" The computational models we develop to answer this question also provide foundational mathematical techniques to throw light on the following three questions: 1. How does one reliably measure the creativity of ideas? 2. How does one form teams to evaluate design ideas? 3. How does one filter good ideas out of hundreds of submissions? Solutions to these questions are key to enable the effective processing of a large collection of design ideas generated in a design contest. In the first part of the dissertation, we discuss key qualities needed in design metrics and propose new diversity and novelty metrics for judging design products. We show that the proposed metrics have higher accuracy and sensitivity compared to existing alternatives in literature. To measure the novelty of a design item, we propose learning from human subjective responses to derive low dimensional triplet embeddings. To measure diversity, we propose an entropy-based diversity metric, which is more accurate and sensitive than benchmarks. In the second part of the dissertation, we introduce the bipartite b-matching problem and argue the need for incorporating diversity in the objective function for matching problems. We propose new submodular and supermodular objective functions to measure diversity and develop multiple matching algorithms for diverse team formation in offline and online cases. Finally, in the third part, we demonstrate filtering and ranking of ideas using diversity metrics based on Determinantal Point Processes as well as submodular functions. In real-world crowd experiments, we demonstrate that such ranking enables increased efficiency in filtering high-quality ideas compared to traditionally used methods.Item UNDERSTANDING DIRECT BOROHYDRIDE - HYDROGEN PEROXIDE FUEL CELL PERFORMANCE(2013) Stroman, Richard O'Neil; Jackson, Gregory S; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Direct borohydride fuel cells (DBFCs) generate electrical power by oxidizing aqueous BH4- at the anode and reducing an oxidizer, like aqueous H2O2 for an all-liquid fuel cell, at the cathode. Interest in DBFCs has grown due to high theoretical energy densities of the reactants, yet DBFC technology faces challenges such as side reactions and other processes that reduce cell efficiency and power generation. Relationships linking performance to cell design and operation will benefit from detailed and calibrated cell design models, and this study presents the development and calibration of a 2D, single-cell DBFC model that includes transport in reactant channels and complex charge transfer reactions at each electrode. Initial modeling was performed assuming ideal reactions without undesirable side reactions. Results were valuable for showing how design parameters impact ideal performance limits and DBFC cell voltage (efficiency). Model results showed that concentration boundary layers in the reactant flow channels limit power density and single-pass reactant utilization. Shallower channels and recirculation improve utilization, but at the expense of lower cell voltage and power per unit membrane area. Reactant coulombic efficiency grows with decreasing inlet reactant concentration, reactant flow rate and cell potential, as the relative reaction rates at each electrode shift to favor charge transfer reactions. To incorporate more realistic reaction mechanisms into the model, experiments in a single cell DBFC were performed to guide reaction mechanism selection by showing which processes were important to capture. Kinetic parameters for both electrochemical and critical heterogeneous reactions at each electrode were subsequently fitted to the measurements. Single-cell experiments showed that undesirable side reactions identified by gas production were reduced with lower reactant concentration and higher supporting electrolyte concentration and these results provided the basis for calibrating multi-step kinetic mechanism. Model results with the resulting calibrated mechanism showed that cell thermodynamic efficiency falls with cell voltage while coulombic utilization rises, yielding a maximum overall efficiency operating point. For this DBFC, maximum overall efficiency coincides with maximum power density, suggesting the existence of preferred operating point for a given geometry and operating conditions.Item CONCEPTUAL UNDERSTANDING AND THE USE OF HAND-SKETCHING IN MECHANICAL ENGINEERING DESIGN(2008-04-29) Grenier, Ashley Lynn; Schmidt, Linda; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the Mechanical Engineering Design Process, sketching has been used as a tool to foster engineers' work. However, with the integration of the computer, computer tools and software are replacing what many previously did by hand. Capstone Mechanical Engineering sketching assignments and final reports were analyzed with sketch coding schemes, including the New Content-Based Sketch Coding Scheme that was created for this research. The "Mechanical Engineering Visual Design Mediums Concept Inventory" was created to begin to understand the current role of sketching and students' conceptual understanding of sketching and CAD within the Mechanical Engineering design process. Literature and previous research enriched the content of the Concept Inventory. Sketching assignments and data from students' design notebooks were analyzed to obtain more breadth and natural data. With the various data and analyses, insight on sketching in the Mechanical Engineering Design Process is obtained.Item Vehicle Shaping for Mine Blast Damage Reduction(2006-07-28) Genson, Kevin William; Fourney, William; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)When a buried explosive is detonated beneath a target (such as a vehicle), the target is rapidly loaded by flying ejecta, high pressure gas, and shock waves. This paper explores how changes in the shape of the underside of a target affect the total impulse captured from the detonation of a buried charge. The effects of changes in target height and charge burial depth are also examined. Testing was conducted on dihedral target plates using 0.636 gram charges. These were buried in saturated sand at three depths, and shaped targets were placed at four heights above the surface. The impulse applied to the plate by the exploding charge was determined through analysis of high speed digital video recordings. Changing the geometry of the target reduced the impulse by up to 45%. Increasing standoff distance reduced impulse by up to 70%.