A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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    ELECTRICAL AND STRUCTURAL FORMATION OF TRANSIENT LIQUID PHASE SINTER (TLPS) MATERIALS DURING EARLY PROCESSING STAGE
    (2023) Nave, Gilad; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The growing demands of electrification are driving research into new electronic materials. These electronic materials must have high electrical conductivity, withstand harsh environments and high temperatures and demonstrate reliable solutions as part of complete electronic packaging solutions. This dissertation focuses on characterizing the initial stage of the manufacturing process of Transient Liquid Phase Sinter (TLPS) alloys in a paste form as candidates for Pb-free high-temperature and high-power electronic materials.The main objective of this dissertation work is to investigate the factors and decouple the multiple cross effects occurring during the first stage of TLPS processing in order to improve the understanding of material evolution. The work proposes, develops, and conducts in-situ electrical resistivity tests to directly measure material properties and analyze the dynamics at different stages of the material's evolution. The research explores various factors, including alloying elements, organic binders, and heating rates, to understand their effects on the development of electrical performance in electronic materials. More specifically, the work examines the performance of Ag-In, Ag-Sn and Cu-Sn TLPS paste systems. Additionally, packing density and changes in cross-section are investigated using imaging techniques and image processing to gain insights into the early formation of the material's structural backbone. An Arrhenius relationship together with Linear Mixed Models (LMM) techniques are used to extract the activation energies involved with each of the processing stages. The study then develops procedures to model different states of the TLPS microstructures at different heating stages based on experimentally observed data. Using these models, the study uses Finite Element Method (FEM) analysis to verify the experimental results and gain a better understanding and visualization into the involved mechanisms. This investigation not only sheds light on the material's behavior but also has implications for robust additive manufacturing (AM) applications.
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    QUANTIFYING THE ADDED VALUE OF AGILE VIEWING RELATIVE TO NON-AGILE VIEWING TO INCREASE THE INFORMATION CONTENT OF SYNTHETIC SATELLITE RETRIEVALS
    (2022) McLaughlin, Colin; Forman, Barton A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Satellite sensors typically employ a “non-agile” viewing strategy in which the boresight angle between the sensor and the observed portion of Earth’s surface remains static throughout operation. With a non-agile viewing strategy, it is relatively straightforward to predict where observations will be collected in the future. However, non-agile viewing is limited because the sensor is unable to vary its boresight angle as a function of time. To mitigate this limitation, this project develops an algorithm to model agile viewing strategies to explore how adding agile pointing into a sensor platform can increase desired information content of satellite retrievals. The synthetic retrievals developed in this project are ultimately used in an observing system simulation experiment (OSSE) to determine how agile pointing has the potential to improve the characterization of global freshwater resources.
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    SIMULATION OF MAGNETIC GRANULAR MEDIA USING OPEN SOURCE SOFT SPHERE DISCRETE ELEMENT METHOD
    (2021) Leps, Thomas; Christine, Hartzell; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Magnetic granular media were investigated using a mutual dipole magnetic model integrated into the open source Soft Sphere Discrete Element Method (DEM) framework LAMMPS and LIGGGHTS. Using the magnetic model and the contact force models from LIGGGHTS, we simulated shear behavior of MagnetoRheological Fluids (MRF). We found that the size distribution of simulated particles significantly affects the qualitative and quantitative behavior of MRF in a simple shear cell. Additionally, including cohesion, rolling resistance, friction and other contact forces affect the simulated shear behavior. By using a high fidelity contact force model along with an accurate size distribution and the mutual dipole magnetic model we were able to accurately match experimental data for an example MRF.We used the DEM model to aid in the development of a novel MRF valve operating on an alternative MRF behavior. Our jamming, MRF valve holds pres- sure through stable, but reversible jamming in the flow path, and is actuated by electropermanent magnets, which require no quiescent current to maintain their magnetization states. These valves do not require the large power draw of con- ventional MRF valves to maintain their state. We were able to accurately predict the experimental jamming behavior of the MRF valve using Finite Element Analysis and LIGGGHTS with magnetization, further validating the model with a non-linear, non-continuum behavior. Our jamming MRF valve was demonstrated in a multi- segmented, elastomeric robot, actuated using MRF. Using the magnetic DEM model coupled with self-gravity, the effects of mag- netism on rubble pile magnetic asteroids were examined. We simulated formation, and disruption of metallic asteroids with remnant magnetizations using LAMMPS with permanent dipoles. We found that rubble pile asteroids, formed from clouds of magnetized grains, coalesce more quickly, and have higher porosities than aster- oids coalesced from unmagnetized grains. Distortion and disruption was affected by magnetization during simulated YORP spin-up. Large fragments with high aspect ratios and low densities were formed from highly magnetized asteroids after disrup- tion, matching the shapes of suspected metallic small bodies. Simulations of grain avalanching on the surface of magnetized asteroids found additional morphological differences from their unmagnetized counterparts, with reduced densities, increased angles of repose, and cornicing.
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    Simulations of Fire Smoke Movement in High-rise Buildings with FDS
    (2021) Xu, Hongda; Trouve, Arnaud AT; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Fire Dynamics Simulator (FDS) developed by the National Institute of Standards and Technology (NIST) solves a form of the Navier-Stokes equations appropriate for low-speed (Ma < 0.3), thermally-driven flow with an emphasis on smoke and heat transport and has been shown to be capable of simulating the flow and temperature conditions in the vicinity of a fire [1]. In the present study, we evaluate the ability of FDS to simulate pressure dynamics in high-rise buildings, a pre-requisite to the correct simulation of smoke transport far from the fire.The objective of this study is to test the accuracy of FDS for determining the conditions throughout the entire expanse of a 40-story high-rise building featuring an elevator shaft and four stairwells. The output from FDS is first compared to the results generated by a network model called COSMO. The comparison of the two outputs shows that correct results are predicted by FDS. Additionally, more realistic scenarios are simulated with FDS and the results are compared with those of a network model called CONTAM and an in-house MATLAB program. The network model CONTAM and the MATLAB program do not represent the time-dependent thermal mixing process taking place inside the elevator shaft and the stairwells whereas FDS does. The comparison shows the importance of this thermal mixing process that impacts the pressure dynamics and smoke movement inside the building, with implications for the evacuation capability provided by the stairwells.
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    Morphing Waveriders for Atmospheric Entry
    (2019) Maxwell, Jesse R; Oran, Elaine S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The primary challenge for vehicles entering planetary atmospheres is surviving the intense heating and deceleration encountered during the entry process. Entry capsules use sacrificial ablative heat shields and sustain several g deceleration. The high lift produced by the Space Shuttle geometry resulted in lower rates of heating and deceleration. This enabled a fully reusable vehicle that was protected by heat shield tiles. Hypersonic waveriders are vehicles that conform to the shape of the shock wave created by the vehicle. This produces high compression-lift and low drag, but only around a design Mach number. Atmospheric entry can reach speeds from zero to as high as Mach 40. A morphing waverider is a vehicle that deflects its flexible bottom surface as a function of Mach number in order to preserve a desired shock wave shape. It was demonstrated in this work that doing so retains high aerodynamic lift and lift-to-drag ratio across a wide range of Mach number. Numerical simulations were conducted for case-study waveriders designed for Mach 6 and 8 for flight at their design conditions as well as with variations in angle-of-attack and Mach number. A single-species air model was used between Mach 1 and 12 with the RANS k-omega SST and LES-WALE turbulence models. A seven-species air model was used for Mach 15 at 60km altitude and Mach 20 at 75km. Analytical methods were used to construct a reduced-order model (ROM) for estimating waverider aerodynamic forces, moments, and heating. The ROM matched numerical simulation results within 5-10% for morphing waveriders with variations in angle-of-attack, but discrepancies exceeded 20% for large deviations of rigid vehicles from their design Mach numbers. Atmospheric entry trajectory simulations were conducted using reduced-order models for morphing waverider aerodynamics, the Mars Science Laboratory (MSL) capsule, and the Space Shuttle. Three morphing waveriders were compared to the Space Shuttle, which resulted in reduced heating and peak deceleration. One morphing waverider was compared to the MSL capsule, which demonstrated a reduction in the peak stagnation heat flux, a reduction in the peak and average deceleration, and a reduction in the peak area-averaged heating.
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    Modeling of Falling-Particle Solar Receivers for Hydrogen Production and Thermochemical Energy Storage
    (2014) Oles, Andrew; Jackson, Gregory S.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    One of the most important components in a solar-thermal power plant is the central receiver where concentrated solar energy is absorbed in a medium for storage and eventual use in power generation or fuel production. Current state-of-the-art receivers are not appropriate for future power-plant designs due to limited operating temperatures. The solid-particle receiver (SPR) has been proposed as an alternative architecture that can achieve very high temperatures (above 1500 °C) with high efficiency, while avoiding many of the thermal stress issues that plague alternative architectures. The SPR works by having a flow of solid particles free-fall through a cavity receiver while directly illuminated to absorb the solar energy. Because of the high operating temperatures that can be achieved, along with the ability to continuously flow a stream of solid reactant, the SPR has the potential for use as a reactor for either chemical storage of solar energy or fuel production as part of a solar water-splitting cycle. While the operation of the SPR is relatively simple, analysis is complicated by the many physical phenomena in the receiver, including radiation-dominated heat transfer, couple gas-particle flow, and inter-phase species transport via reaction. This work aims to demonstrate a set modeling tools for characterizing the operation of a solid particle receiver, as well as an analysis of the key operating parameters. A inert receiver model is developed using a semi-empirical gas-phase model and the surface-to-surface radiation model modified to account for interaction with the particle curtain. A detailed thermo-kinetic model is developed for undoped-ceria, a popular material for research into solar fuel production. The inert-receiver model is extended to integrate this kinetic model, and further used to evaluate the potential of perovskite materials to enhance the storage capability of the receiver. A modified undoped ceria model is derived and implemented via custom user functions in the context of a computational fluid dynamics simulation of the receiver using the discrete-ordinates method for radiation transfer. These modeling efforts provide a basis for in-depth analysis of the key operating parameters that influence the performance of the solid-particle receiver.
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    Simulation and Analysis of Energy Consumption for an Energy-Intensive Academic Research Building
    (2014) Levy, Jared Michael; Ohadi, Michael M.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The University of Maryland's Jeong H. Kim Engineering Building is a state-of-the-art academic research facility. This thesis describes an energy analysis and simulation study that serves to identify energy saving opportunities and optimum operation of the building to achieve its goals of high energy efficiency and substantial CO2 emission reduction. A utility analysis, including a benchmarking study, was completed to gauge the performance of the facility and a detailed energy model was developed using EnergyPlus to mimic current operation. The baseline energy model was then used to simulate eight energy efficiency measures for a combined energy savings of 16,760 MMBtu, reducing annual energy use by 25.3%. The simple payback period for the proposed measures as a single project is estimated to be less than one year. Due to the high-tech and unique usage of the Kim Engineering Building, including cleanrooms and research labs, this thesis also contributes to the development of energy consumption benchmarking data available for such facilities.
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    Performance Exploration of the Hybrid Memory Cube
    (2014) Rosenfeld, Paul; Jacob, Bruce; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Hybrid Memory Cube (HMC) is an emerging main memory technology that leverages advances in 3D fabrication techniques to create a memory device with several DRAM dies stacked on top of a CMOS logic layer. The logic layer at the base of each stack contains several DRAM memory controllers that communicate with the host processor over high speed serial links using an abstracted packet interface. Each memory controller is connected to several memory banks in the DRAM stack with Through-Silicon Vias (TSVs), which are metal connections that extend vertically through each chip in the die stack. Since the TSVs form a dense interconnect with short path lengths, the data bus between the controller and memory banks can be operated at higher throughput and lower energy per bit compared to traditional Double Data Rate (DDRx) memories, which uses many long and parallel wires on the motherboard to communicate with the memory controller located on the CPU die. The TSV connections combined with the presence of multiple memory controllers near the memory arrays form a device that exposes significant memory-level parallelism and is capable of delivering an order of magnitude more bandwidth than current DDRx solutions. While the architecture of this type of device is still nascent, we present several parameter sweeps to highlight the performance characteristics and trade-offs in the HMC architecture. In the first part of this dissertation, we attempt to understand and optimize the architecture of a single HMC device that is not connected to any other HMCs. We begin by quantifying the impact of a packetized high-speed serial interface on the performance of the memory system and how it differs from current generation DDRx memories. Next, we perform a sensitivity analysis to gain insight into how various queue sizes, interconnect parameters, and DRAM timings affect the overall performance of the memory system. Then, we analyze several different cube configurations that are resource-constrained to illustrate the trade-offs in choosing the number of memory controllers, DRAM dies, and memory banks in the system. Finally, we use a full system simulation environment running multi-threaded workloads on top of an unmodified Linux kernel to compare the performance of HMC against DDRx and "ideal" memory systems. We conclude that today's CPU protocols such as coherent caches pose a problem for a high-throughput memory system such as the HMC. After removing the bottleneck, however, we see that memory intensive workloads can benefit significantly from the HMC's high bandwidth. In addition to being used as a single HMC device attached to a CPU socket, the HMC allows two or more devices to be "chained" together to form a diverse set of topologies with unique performance characteristics. Since each HMC regenerates the high speed signal on its links, in theory any number of cubes can be connected together to extend the capacity of the memory system. There are, however, practical limits on the number of cubes and types of topologies that can be implemented. In the second part of this work, we describe the challenges and performance impacts of chaining multiple HMC cubes together. We implement several cube topologies of two, four, and eight cubes and apply a number of different routing heuristics of varying complexity. We discuss the effects of the topology on the overall performance of the memory system and the practical limits of chaining. Finally, we quantify the impact of chaining on the execution of workloads using full-system simulation and show that chaining overheads are low enough for it to be a viable avenue to extend memory capacity.
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    DYNAMIC BEHAVIOR OF OPERATING CREW IN COMPLEX SYSTEMS: AN OBJECT-BASED MODELING & SIMULATION APPROACH
    (2013) Azarkhil, Mandana; Mosleh, Ali; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    High-risk environments such as the control room of Nuclear Power Plants are extremely stressful for the front line operators; during accidents and under high task load situations, the operators are solely responsible for the ultimate decision-making and control of such complex systems. Individuals working as a team constantly interact with each other and therefore introduce team related issues such as coordination, supervision and conflict resolution. The aggregate impact of multiple human errors inside communication and coordination loops in a team context can give rise to complex human failure modes and failure mechanisms. This research offers a model of operating crew as an interactive social unit and investigates the dynamic behavior of the team under upset situations through a simulation method. The domain of interest in this work is the class of operating crew environments that are subject to structured and regulated guidelines with formal procedures providing the core of their response to accident conditions. In developing the cognitive models for the operators and teams of operators, their behavior and relations, this research integrates findings from multiple disciplines such as cognitive psychology, human factors, organizational factors, and human reliability. An object-based modeling methodology is applied to represent system elements and different roles and behaviors of the members of the operating team. The proposed team model is an extended version of an existing cognitive model of individual operator behavior known as IDAC (Information, Decision, and Action in Crew context). Scenario generation follows DPRA (Dynamic Probabilistic Risk Assessment) methodologies. The method capabilities are demonstrated through building and simulating a simplified model of a steam/power generating plant. Different configurations of team characteristics and influencing factors have been simulated and compared. The effects of team factors and crew dynamics on system risk with main focus on team errors, associated causes and error management processes and their impact on team performance have been studied through a large number of simulation runs. The results are also compared with several theoretical models and empirical studies.
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    The Effects of Urban Development on Sedimentation
    (2012) Gupta, Justin A.; McCuen, Richard H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Channels are the main conduit for floodwater conveyance in a watershed. The channel geometry can change due to a high peak discharge, which causes erosion and subsequent deposition that can change the downstream channel geometry. Urban development can lead to increases in peak discharge, and therefore, channel erosion and flood hazard. The purpose of this research is to assess the effect that urban development has on erosion and downstream deposition. A hydrologic model was built to simulate the effect urban development has on erosion volumes and depths of downstream deposition at the watershed outlet. The results indicated that the amount of erosion and deposition exhibit a non-linear relationship with the level of urban development. Therefore, developing watersheds should plan for a non-linear increase in flood hazard. The model developed can be applied to any watershed with knowledge of some basic regional and local characteristics. Guidelines for the model application were also developed.