A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Bending Properties of an Extensile Fluidic Artificial Muscle(Frontiers, 2022-04-13) Garbulinski, Jacek; Wereley, Norman M.Low stiffness, large stroke, and axial force capabilities make Extensile Fluidic Artificial Muscles (EFAMs) a feasible soft actuator for continuum soft robots. EFAMs can be used to construct soft actuated structures that feature large deformation and enable soft robots to access large effective workspaces. Although FAM axial properties have been well studied, their bending behavior is not well characterized in the literature. Static and dynamic bending properties of a cantilevered EFAM specimen were investigated over a pressure range of 5–100 psi. The static properties were then estimated using an Euler-Bernoulli beam model and discrete elastic rod models. The experiments provided data for the determination of bending stiffness, damping ratio, and natural frequency of the tested specimen. The bending stiffness and the damping ratio were found to change fourfold over the pressure range. Experimentally validated bending properties of the EFAM presented insights into structural and control considerations of soft robots. Future work will utilize the data and models obtained in this study to predict the behavior of an EFAM-actuated continuum robot carrying payloads.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 Design and Analysis of New Gasification Apparatus based on the Standard Cone Calorimeter(2012) Liu, Xuan; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A simple, inexpensive, safe version of pyrolysis apparatus is developed base on the standard cone calorimeter (ASTM E 1354). A controllable oxygen concentration (0% to 21% by volume) environment in the vicinity of 80 mm by 80 mm square sample positioned under the cone radiant heater is achieved by means of "Controlled Atmosphere Pyrolysis Apparatus". Valid gasification mass loss rate measurements have been obtained for both poly(methyl methacrylate) (PMMA) and polypropylene (PP) samples under external heat fluxes of 35kW/m^2 and 50kW/m^2. Reasonable value of thermal conductivity for PMMA is measured. With the thermal conductivity and parameters defined by Differential Scanning Calorimeter (DSC) of PMMA, the gasification mass loss rate is well simulated using Thermo-Kinetic Model of Burning (ThermaKin).Item Design and Performance of a Ducted Coaxial Rotor in Hover and Forward Flight(2010) Lee, Timothy Edward; Leishman, J. Gordon; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A ducted contra-rotating coaxial rotor system was designed and tested to assess its potential use as a micro aerial vehicle (MAV). Performance measurements (thrust and power) of the system in hover and forward flight were obtained. The influence of several design parameters (rotor spacing, duct inlet shape, position of rotors within the duct, and tip clearance) on performance was determined. Performance measurements of the unducted coaxial rotor, as well as the unducted/ducted single rotor configurations, were also obtained to give a performance baseline for the ducted coaxial rotor. The aerodynamic characteristics of the isolated duct were assessed from loads measurement and surface flow visualization. While the net system performance of operating the coaxial rotor within the confines of a duct was not always improved, the ducted coaxial rotor concept is still attractive for a MAV based on total attainable thrust for a given rotor size and other operational benefits.Item Design of a Novel Portable Flow Meter for Measurement of Average and Peak Inspiratory Flow(2009) Jamshidi, Shaya; Johnson, Arthur T; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The maximum tolerable physical effort that workers can sustain is of significance across many industrial sectors. These limits can be determined by assessing physiological responses to maximal workloads. Respiratory response is the primary metric to determine energy expenditure in industries that use respirator masks to protect against airborne contaminants. Current studies fail to evaluate endurance under conditions that emulate employee operating environments. Values obtained in artificial laboratory settings may be poor indicators of respiratory performance in actual work environments. To eliminate such discrepancies, equipment that accurately measures peak respiratory flows in situ is needed. This study provides a solution in the form of a novel portable flow meter design that accurately measures average and peak inspiratory flow of a user wearing an M40A1 respirator mask.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%.