UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
204 results
Search Results
Item A CAUSAL INFORMATION FUSION MODEL FOR ASSESSING PIPELINE INTEGRITY IN THE PRESENCE OF GROUND MOVEMENT(2024) Schell, Colin Andrew; Groth, Katrina M; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pipelines are the primary transportation method for natural gas and oil in the United States making them critical infrastructure to maintain. However, ground movement hazards, such as landslides and ground subsidence, can deform pipelines and potentially lead to the release of hazardous materials. According to the Pipeline and Hazardous Materials Safety Administration (PHMSA), from 2004 to 2023, ground movement related pipeline failures resulted in $413M USD in damages. The dynamic nature of ground movement makes it necessary to collect pipeline and ground monitoring data and to actively model and predict pipeline integrity. Conventional stress-based methods struggle to predict pipeline failure in the presence of large longitudinal strains that result from ground movement. This has prompted many industry analysts to use strain-based design and assessment (SBDA) methods to manage pipeline integrity in the presence of ground movement. However, due to the complexity of ground movement hazards and their variable effects on pipeline deformation, current strain-based pipeline integrity models are only applicable in specific ground movement scenarios and cannot synthesize complementary data sources. This makes it costly and time-consuming for pipeline companies to protect their pipeline network from ground movement hazards. To close these gaps, this research made significant steps towards the development of a causal information fusion model for assessing pipeline integrity in a variety of ground movement scenarios that result in permanent ground deformation. We developed a causal framework that categorizes and describes how different risk-influencing factors (RIFs) affect pipeline reliability using academic literature, joint industry projects, PHMSA projects, pipeline data, and input from engineering experts. This framework was the foundation of the information fusion model which leverages SBDA methods, Bayesian network (BN) models, pipeline monitoring data, and ground monitoring data to calculate the probability of failure and the additional longitudinal strain needed to fail the pipeline. The information fusion model was then applied to several case studies with different contexts and data to compare model-based recommendations to the actions taken by decision makers. In these case studies, the proposed model leveraged the full extent of data available at each site and produced similar conclusions to those made by decision makers. These results demonstrate that the model could be used in a variety of ground movement scenarios that result in permanent ground deformation and exemplified the comprehensive insights that come from using an information fusion approach for assessing pipeline integrity. The proposed model lays the foundation for the development of advanced decision making tools that can enable operators to identify at-risk pipeline segments that require site specific integrity assessments and efficiently manage the reliability of their pipelines in the presence of ground movement.Item Insulating Materials for an Extreme Environment in a Supersonically Rotating Fusion Plasma(2024) Schwartz, Nick Raoul; Koeth, Timothy W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fusion energy has long been sought as the “holy grail” of energy sources. One of the most critical remaining challenges in fusion is that of plasma-facing materials, even denoted by the National Academies of Science. The materials challenge is particularly acute for centrifugal mirrors, an alternative concept to the industry-standard tokamak that may offer a more efficient scheme with a faster path to development. The centrifugal mirror incorporates supersonic rotation into a conventional magnetic mirror scheme, providing three primary benefits: (1) increased confinement, (2) suppression of instabilities, and (3) plasma heating through shear flow. However, this rotation, which is driven by an axial magnetic field and a radial electric field, requires the magnetic field lines to terminate on electrically insulating surfaces to avoid “shorting” the plasma. This unique requirement presents a novel materials challenge: the insulator must not only resist irradiation and thermal damage, but also be an excellent electrical insulator and thermal conductor that can be actively cooled. To address this materials challenge, the Centrifugal Mirror Fusion Experiment (CMFX) was developed at the University of Maryland. CMFX serves as a test bed for electrically insulating materials in a fusion environment, as well as a proof-of-concept for the centrifugal mirror scheme. To guide the design of future power plants and better understand the neutronand ion flux on the insulators, a zero-dimensional (0-D) scoping tool, called MCTrans++, was developed. This software, discussed in Chapter 2, demonstrates the ability to rapidly model experimental parameter sets in CMFX and predict the scaling to larger devices, informing material selection and design. Assuming the engineering challenges have been met, the centrifugal mirror has been demonstrated as a promising scheme for electricity production via fusion energy. One of the key aspects to the operation of CMFX is the high voltage system. This system, discussed in Chapter 3, was developed in incremental stages, beginning with a 20 kV, then 50 kV pulsed power configuration, and finally culminating in a 100 kV direct current power supply to drive rotation at much higher voltages, creating an extreme environment for materials testing. This work identified hexagonal boron nitride (hBN) as a promising insulator material. Computational modeling (Chapter 4) demonstrated hBN’s superior resistance to ion-irradiation damage compared to other plasma-facing materials. Additionally, fusion neutrons are crucial for assessing both material damage and power output. Chapter 5 details the neutronics for CMFX, including 3He proportional counters, which have been installed on CMFX to measure neutron production. In parallel, Monte Carlo computational methods were used to predict neutron transport and material damage in the experiment. Ultimately, a materials test stand was installed on CMFX to expose electrically insulating materials to high energy fusion plasmas (Chapter 6). Comparative analysis of hBN and silicon carbide after exposure revealed superior performance of hBN as a plasma-facing material. Two primary erosion mechanisms were identified by surface morphology and roughness measurements: grain ejection and sputtering, both more pronounced in silicon carbide. This work advances our understanding of insulating material behavior in fusion environments and paves the way for the development of the next-generation centrifugal mirror fusion reactors. Chapter 7 discusses conclusions and proposes future work. In particular this section suggests some changes that may allow CMFX to operate at much higher voltages, unlocking higher plasma density and temperature regimes for further material testing.Item ELECTROLYTE AND INTERPHASE DESIGN FOR HIGH-ENERGY AND LONG-LIFE LITHIUM/SULFURIZED POLYACRYLONITRILE (Li/SPAN) BATTERIES(2024) Phan, An Le Bao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lithium/sulfurized polyacrylonitrile (Li/SPAN) recently emerged as a promising battery chemistry with theoretical energy density beyond traditional lithium-ion batteries, attributed to the high specific capacities of Li and SPAN. Compared to traditional sulfur-based cathodes, SPAN demonstrated superior sulfur activity/utilization and no polysulfide dissolution issue. Compared to batteries based on layered oxide cathodes, Li/SPAN shows two significant advantages: (1) high theoretical energy density (> 1000 Wh kg-1, compared to around 750 Wh kg-1 of Li/LiNi0.8Mn0.1Co0.1O2) and (2) transition-metal-free nature, which eliminates the shortcomings associated with transition metals, such as high cost, low abundance, uneven distribution on the earth and potential toxicity. The success of Li/SPAN chemistry with those two critical advantages would not only relief the range and cost anxiety persistently associated with electric vehicle (EV) applications, but also have great implications for the general energy storage market. However, current Li/SPAN batteries still fall far behind their true potential in terms of both energy density and cycle life. This dissertation aims to provide new insights into bridging the theory-practice gap of Li/SPAN batteries by appropriate interphase and comprehensive electrolyte designs. First, the effect of Li/SPAN cell design on energy density and cycle life was discussed using relevant in-house developed models. The concept of “sensitivity factor” was established and used to quantitatively analyze the influence of input parameters. It was found that the electrolyte, rather than SPAN and Li electrodes, represents the bottleneck in Li/SPAN development, which explains our motivation to focus on electrolyte study. Another remarkable finding is that although not well-perceived, electrolyte density has a great impact on Li/SPAN cell-level energy density. Second, design principles to achieve good electrode-electrolyte compatibility were explored. Novel approaches to promote the formation of more protective, inorganic-rich interphases (SEI or CEI) were proposed and validated with proper experiments, including electrochemical tests, material characterizations (such as SEM, XPS, NMR, IR, Raman), and their correlations. Finally, based on the principles discussed in previous chapters, we developed a new electrolyte that simultaneously offers good electrochemical performance (Li CE > 99.4%, Li-SPAN full-cells > 200 cycles), decent ionic conductivity (1.3 mS cm-1), low density (1.04 g mL-1), good processability (higher vapor pressure than conventional carbonates, b.p. > 140 °C), and good safety. Outlook and perspective will also be presented. Beyond Li/SPAN, we believe that our findings regarding cell design as well as electrolyte solvation structure, interphases chemistry, and their implications on electrochemical performance are also meaningful for the development of other high-energy battery chemistries.Item AN INTEGRATED ASSESSMENT OF THE FUTURE “HYDROGEN ECONOMY”: DECARBONIZATION POTENTIAL, SOCIETAL IMPLICATIONS, AND POLICY APPROACHES(2024) O'Rourke, Patrick Robert; Hultman, Nathan; Public Policy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently clean hydrogen has captured the attention of policy communities, as evidenced by the publication of hydrogen “roadmaps” or “strategies” by dozens of nations. This is partly because it can be produced from numerous primary energy resources and utilized in a plethora of ways to enable decarbonization. However, there remain open questions as to how the energy carrier should contribute toward carbon dioxide (CO2) mitigation. Additionally, less is known about its impacts on other societal objectives and whether government plans for hydrogen are driven by realistic expectations regarding its ability to facilitate emissions reductions. This dissertation involves three studies which simulate energy transitions within the Global Change Analysis Model (GCAM), each aiming to help illuminate hydrogen’s potential impact on society. First, clean hydrogen supply and demand within the context of decarbonization is investigated. In this research, it is found that hydrogen could be a decentralized energy carrier, as a large portion of its production is enabled by onsite production (i.e., at the location of the end user). In terms of demand, although it will represent a smaller portion of global final energy compared to alternatives, hydrogen enables CO2 mitigation in difficult-to-electrify end uses (e.g., satiating demand for industrial high-temperature heat). The second topic of this dissertation examines hydrogen’s potential implications for the water-energy-food nexus. It is found that clean hydrogen production is unlikely to be a large source of water demand, however, its availability in the forthcoming energy transition could cause larger indirect changes in water demand for many regions of the world. Additionally, clean hydrogen availability is found to enable lower staple crop prices, as it provides a method of reducing CO2 associated with fertilizer manufacturing. Lastly, this dissertation analyzed the Japanese and Korean national hydrogen plans. Aligning with the results from the first research topic of this work, hydrogen’s use within their economies is lower than alternative decarbonization strategies (e.g., direct electrification). As a result, the national plans of both nations are found to be overestimating the scale of hydrogen supply. Further, both countries are generally setting numerical goals for hydrogen deployment in areas of the economy that are less economically efficient compared to alternative sectors where it could both facilitate decarbonization as well as bolster their economies.Item INTERFACES IN THIN-FILM SOLID-STATE BATTERIES(2024) Castagna Ferrari, Victoria; Rubloff, Gary GWR; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The lack of a diagnostics approach to monitor interface kinetics in solid-state batteries (SSBs) results in an incomplete knowledge of the mechanisms affecting device performance. In this study, a new protocol for process control of SSB interface formation and their evolution during operation is presented. Thin-film SSBs and diagnostic test devices that are composed by a permutation of isolated layers were simultaneously fabricated using sequential sputtering deposition and in-situ patterning using shadow masks. Physics-based electric circuit models were designed for deconvolution of impedance profiles, which enabled an evaluation of bulk properties and space-charge layers at interfaces individually and during operation under different states-of-charge. Relative permittivity values of fundamental battery components (cathode, electrolyte and anode) were calculated as a function of the frequency and the applied voltage. Interfacial impedances, as well as space-charge layers formed at heterojunctions during charge and discharge processes, were successfully deconvoluted using the diagnostic test devices and electric circuit modeling. The cathode-electrolyte interphase was kinetically stable under a voltage window of 0 – 3.6 V vs Cu, and it had an estimated ionic conductivity of the order of 10-9 S/cm, hence it is a localized limiting factor for Li+ transfer. The anode-electrolyte interphase was thermodynamically stable upon completion of the fabrication process, but it became kinetically unstable during charge and discharge cycles. Hence, the proposed diagnostics protocol enlightened the necessity of implementing interfacial engineering on these interphases in the future for improvement of cyclability and stability of SSBs and ionic devices.Item VOLUMETRIC SOLAR ABSORBING FLUIDS AND THEIR APPLICATIONS IN TWO-PHASE THERMOSYPHON(2024) Zhou, Jian; Yang, Bao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A two-phase thermosyphon is a passive system utilizing gravity to transfer working fluids. The working fluids of a two-phase thermosyphon must undergo vaporization and condensation in the same system. Two-phase thermosyphons can also be used as solar collectors. Traditional solar collectors utilize surface absorbers to convert incident solar radiation into thermal energy, but those systems feature a large temperature difference between the surface absorbers and heat transfer fluids, resulting in a reduction in the overall thermal efficiency. Volumetric solar absorbing fluids serve both as solar absorbers and heat transfer fluids, therefore significantly improving the overall efficiency of solar collectors. Comparing to pure fluids, nanofluids possess both enhanced thermal conductivity and solar absorption capacity as volumetric absorbing fluids. Nanofluids, when serving as volumetric solar absorbing fluids, are so far reported to work only at relatively low temperatures and in a single-phase heat transfer regime due to stability issue. This research investigates the possibility of using nanofluids, especially graphene oxide (GO) nanofluids, as volumetric solar absorbing fluids in two-phase thermosyphons. Despite their reputation as both stable and solar absorptive among nanofluids, graphene oxide nanofluids still deteriorate quickly under boiling-condensation processes (~100 °C). The solar transmittance of the GO nanofluids declines from 38 to 4%, during the first 24 h of testing. Further investigation shows that the stability deterioration is caused by the thermal reduction of GO nanoparticles, which mainly featured with de-carboxylation and de-hydroxylation. A commercial dye named acid black 52, when dissolved in water, exhibits great broadband solar absorption properties and excellent stability. It remains stable for over 199 days in two-phase thermosyphon, and their transmittance in solar spectral region varies less than 9%. The stability of acid black 52 aqueous solution is further confirmed with the 191-day enhanced radiation test, as it shows less than 5% transmittance change in solar spectral region.Item DIRECT INK WRITING SOLID-STATE LI+ CONDUCTING CERAMICS FOR NEXT GENERATION LITHIUM METAL BATTERIES(2024) Godbey, Griffin Luh; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global pursuit of safer and higher-capacity energy storage devices emphasizes the crucial link between the microstructures of electrochemically active materials and overall battery performance. The emergence of solid-state electrolytes featuring multi-layered, variable porosity microstructures presents fresh opportunities for developing the next generation of rechargeable batteries. However, this advancement also brings forth novel challenges in terms of device integration and operation. In this dissertation, solid-state Li-ion conducting electrolytes were 3D printed to enhance the performance of porous electrolyte layers within porous-dense-porous trilayer systems.LLZO-based garnet electrolyte scaffolds were fabricated via 3D printing using direct ink writing (DIW), facilitating the generation of scaffolds with minimal tortuosity and constriction in comparison to previous porous scaffolds manufactured through tape casting. Rheological techniques, including stress and time sweep tests, were employed to characterize the DIW inks and discern their conformal and self-supporting properties. The analysis focused on ink characteristics critical for Direct Ink Writing (DIW), emphasizing properties essential for achieving high aspect ratio printing and minimal constriction in 3D structures. Drawing from this ink research, two distinct 3D architectures, columns and grids, were fabricated. Column structures were utilized in assembling Li-NMC622 and Li-SPAN cells, with detailed discussions highlighting improvements in printing and sintering outcomes. Notably, NMC622, characterized by larger particle sizes, demonstrated complete infiltration within 3D printed porous networks, yielding a promising specific capacity of 169.9 mAh/g with minimal capacity fade. Further optimization involved integrating a porous 3D scaffold to facilitate SPAN infiltration in Li-SPAN cells, resulting in a specific capacity of 1594 mAh/g, albeit with significant capacity fade. The Li-S was implemented into a grid structure achieving 763 mAh/gS with less than 0.25% capacity loss over 16 cycles. Lastly, comprehensive morphology analysis was conducted to evaluate the effectiveness of our optimal DIW structures and to inform future enhancements of such cells.Item OPTIMAL PROBING OF BATTERY CYCLES FOR MACHINE LEARNING-BASED MODEL DEVELOPMENT(2024) Nozarijouybari, Zahra; Fathy, Hosam HF; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation examines the problems of optimizing the selection of the datasets and experiments used for parameterizing machine learning-based electrochemical battery models. The key idea is that data selection, or “probing” can empower such models to achieve greater fidelity levels. The dissertation is motivated by the potential of battery models to enable theprediction and optimization of battery performance and control strategies. The literature presents multiple battery modeling approaches, including equivalent circuit, physics-based, and machine learning models. Machine learning is particularly attractive in the battery systems domain, thanks to its flexibility and ability to model battery performance and aging dynamics. Moreover, there is a growing interest in the literature in hybrid models that combine the benefits of machine learning with either the simplicity of equivalent circuit models or the predictiveness of physics-based models or both. The focus of this dissertation is on both hybrid and purely data-driven battery models. Moreover, the overarching question guiding the dissertation is: how does the selection of the datasets and experiments used for parameterizing these models affect their fidelity and parameter identifiability? Parameter identifiability is a fundamental concept from information theory that refers to the degree to which one can accurately estimate a given model’s parameters from input-output data. There is substantial existing research in the literature on battery parameter identifiability. An important lesson from this literature is that the design of a battery experiment can affect parameter identifiability significantly. Hence, test trajectory optimization has the potential to substantially improve model parameter identifiability. The literature explores this lesson for equivalent circuit and physics-based battery models. However, there is a noticeable gap in the literature regarding identifiability analysis and optimization for both machine learning-based and hybrid battery models. To address the above gap, the dissertation makes four novel contributions to the literature. The first contribution is an extensive survey of the machine learning-based battery modeling literature, highlighting the critical need for information-rich and clean datasets for parameterizing data-driven battery models. The second contribution is a K-means clustering-based algorithm for detecting outlier patterns in experimental battery cycling data. This algorithm is used for pre-cleaning the experimental cycling datasets for laboratory-fabricated lithium-sulfur (Li-S) batteries, thereby enabling the higher-fidelity fitting of a neural network model to these datasets. The third contribution is a novel algorithm for optimizing the cycling of a lithium iron phosphate (LFP) to maximize the parameter identifiability of a hybrid model of this battery. This algorithm succeeds in improving the resulting model’s Fisher identifiability significantly in simulation. The final contribution focuses on the application of such test trajectory optimization to the experimental cycling of commercial LFP cells. This work shows that test trajectory optimization is s effective not just at improving parameter identifiability, but also at probing and uncovering higher-order battery dynamics not incorporated in the initial baseline model. Collectively, all four of these contributions show the degree to which the selection of battery cycling datasets and experiments for richness and cleanness can enable higher-fidelity data-driven and hybrid modeling, for multiple battery chemistries.Item ELECTROLYTE AND INTERFACE DESIGNATION FOR HIGH-PERFORMANCE SOLID-STATE LITHIUM METAL BATTERIES(2024) Zhang, Weiran; Wang, Chunsheng; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The demand for advanced battery technology is intensifying as electric energy becomes the foundation of modern technologies, such as smart devices, transportation, and artificial intelligence. Batteries play a crucial role in meeting our increasing energy demands and transitioning towards cleaner and more sustainable energy sources. However, range anxiety and safety concerns still hinder the widespread application of battery technology.Current Li-ion batteries, based on graphite anode, have revolutionized battery technology but are nearing the energy density limits. This necessitates the development of metal batteries, employing lithium metal as anode which eliminates host materials that do not contribute to capacity, thereby offering 10 times higher specific capacity. Recent research on lithium metal batteries has seen a significant surge, with growing knowledge transitioning from Li+ intercalation chemistry (graphite) to Li metal plating/stripping. The electrolyte, which was previously regarded as an inert material and acting as a Li+ ion transportation mediator, has gradually attracted researchers’ attention due to its significant impact on the solid electrolyte interphase (SEI) and the Li metal plating/stripping behaviors. Compared to the traditional liquid electrolytes, solid-state lithium metal batteries (SSLMB) have been regarded as the holy grail, the future of electric vehicles (EVs), due to their high safety and potential for higher energy density. However, there are notable knowledge gaps between liquid electrolytes and solid-state electrolytes (SSEs). The transition from liquid-solid contact to solid-solid contact poses new challenges to the SSLMB. As a result, the development of SSLMB is strongly hindered by interface challenges, including not only the Li/SSE interfaces and SSE/cathode interfaces but also SSE/SSE interfaces. In this dissertation, I detailed our efforts to highlight the role of electrolytes and interfaces and establish our understanding and fundamental criteria for them. Building on this understanding, we propose effective and facile engineering solutions that significantly enhance batterie metrics to meet real-world application demand. Rather than simply introducing new compositions or new designations, we are dedicated to introducing our understanding and mechanism behind it, we hope the scientific understanding, the practical solution, and the applicability to various systems can further guide and inspire the electrolyte and interface designation for next-generation battery technology.Item ENERGY ANALYSIS OF A METRO TRANSIT SYSTEM FOR SUSTAINABILITY AND EFFICIENCY IMPROVEMENT(2023) Higgins, Jordan Andrew; Ohadi, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The industrial sector in the US accounted for 33% of the overall energy consumption and 23% of total GHG Emissions in 2022, necessitating the need for energy efficiency and decarbonization of this sector. This study identifies common opportunities and challenges while performing energy audits for the State of Maryland public transportation maintenance complex and proposes site-specific energy efficiency measures. Utilizing performance indices such as Energy Use Intensity (EUI) and load factor from end-use energy data, as well as walkthrough observations from energy audits, energy efficiency measures specific to each facility were formulated to augment the overall energy performance. Additionally, energy modeling helped pinpoint the additional scope of energy efficiency improvements that could have potential significant energy performance improvements and reduce on-site GHG emissions. Among the energy conservation measures considered, the re-sizing and decarbonization of HVAC equipment has the greatest contribution to energy and GHG savings, with a 100% decrease in natural gas, a 37% decrease in electricity use annually, and net decrease of 272 Mton CO2. This study aims to highlight the similarities and differences in existing transportation and maintenance facilities and the applicable technology(ies) that could streamline and serve as a guide for energy audits for transportation maintenance facilities by demonstrating the most common energy efficiency measures and subsequent achievable savings for these facilities.