• 3-D numerical simulations of conjugate heat transport in vacuum membrane distillation systems with applied membrane heating

      Tilton, Nils; Dudley, Mark; Porter, Jason M.; Cath, Tzahi Y. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Membrane distillation has gained attention recently for its capabilities to treat hyper-saline brine and its compatibility with renewable heat. But the effects of temperature and concentration polarization are major inhibitors to its permeate production and ultimately its commercial viability. To alleviate these effects, we investigate an improvement to vacuum membrane distillation (VMD) such that a thin, thermally conductive, porous metal mesh is placed beneath the membrane. This mesh is heated laterally with low-grade heat to actively heat the membrane and feed, thereby countering effects of temperature polarization. We develop a three-dimensional CFD code to simulate heat and vapor transport conjugately in the feed, membrane, and mesh for this system, which included deriving new equations governing heat and mass in the membrane and mesh. We discretize these governing equations with second-order accurate finite volume methods. These methods are verified using manufactured solutions. We then perform a comprehensive parametric study of fully developed duct flow over a heated plate. We identify the optimal combination of plate properties, duct dimensions, and operating conditions to maximize uniform heating of the duct-plate interface. With this, we identified that decreasing channel width, decreasing inlet flow rate, and increasing plate thickness provided the best results of uniform heating. We then validate our solver against experimental measurements of vapor flux, and determined the best fit for membrane vapor permeability Am. For best fit Am, we were able to reproduce experimental results to within 9% mean error. Following that, we performed a second comprehensive parametric study of the VMD system to investigate the effect of operating conditions, mesh properties, and system geometry on temperature polarization and vapor flux measurements. We observe that polarization effects could be reversed for systems with a high input heat, faster flow rate, slim channel width, thicker mesh, and high vacuum pressure.
    • 4D quantitative interpretation of Jubarte field (Brazil): an integrated approach

      Tura, Ali; Damasceno, Andrea; Simmons, James; Prasad, Manika; Kazemi, Hossein; Vasquez, Guilherme (Colorado School of Mines. Arthur Lakes Library, 2020)
      The use of time-lapse (4D) seismic data and quantitative interpretation is essential in the characterization and monitoring of oil reservoirs. This information reduces reservoir management risk, allows better well designs and placement, and improves history-matching. This work studies the application of 4D quantitative interpretation on the post-salt reservoir of the Jubarte field, a Brazilian deep-water oil field. In this project, I face the challenge of conducting a 4D study using seismic acquisitions only one year apart, which is a short interval to observe significant time-lapse changes. However, a high repeat permanent reservoir monitoring system (PRM) helps detect small time-lapse signals. Conventionally, 4D interpretation is conducted with only PP-wave reflection data. In this thesis, I use 4D PS-wave reflection data as well. I present a novel integrated interpretation of joint PP-PS elastic inversion, as well as PP and PS time-shift volumes. Further, I build a rock physics model from well and core data. A detailed comparative analysis of PP and joint PP-PS inversion shows that the joint inversion results are superior in terms of noise content and spatial continuity. Also, the 4D PP-PS joint inversion estimates show a better match with the rock physics models, allowing for more reliable interpretation. 4D time-shifts are integrated with 4D inversion results to discriminate between pore pressure and fluid saturation changes. I observe that time-shifts and inversion estimates provide information on reservoir properties at different scales. The integrated interpretation of the different 4D seismic attributes brings a much broader view since it uses independent data with complementary information to differentiate the effects of saturation and pore pressure changes as the field produces. The information generated in this project can be used to update Jubarte's flow simulator, for placing new injection and producers wells (which can bring significant savings, considering the high cost of drilling offshore wells), in addition to the improved production.
    • 4D simultaneous PP-PS prestack inversion: the Edvard Grieg field, Norwegian North Sea

      Simmons, James; Daneshvar, Sima; Tura, Ali; Wood, Lesli J.; Martinez, Alex (Colorado School of Mines. Arthur Lakes Library, 2020)
      The Edvard Grieg oil field was discovered in 2007 in the Norwegian North Sea and is operated by Lundin Energy Norway. The field is in the production stage. Production began in November 2015, and water injection began in July 2016. The oil bearing reservoir lies in a half graben in Haugaland High, composed of multi-source sediment accumulation bounded by unconformities as most of deposition occurred subareally. The early Cretaceous to late Triassic reservoir is composed of aeolian sands, fluvial sands, alluvial conglomerates, and shallow marine sands, all capped by a regionally extensive unit of chalk. Reservoir characterization challenges arise from the depositional complexity of the field and detailed analysis must be done to plan for future production. In the oil and gas industry, detailed analysis and inversion is typically done using PP seismic data. In this project, I work to evaluate the benefits of PS data to better characterize the reservoir heterogeneity and understand the effects of production and injection by performing simultaneous PP-PS prestack time-lapse inversion. My analysis begins with theoretical expectations of the PS dataset from a rock physics approach and analysis of the raw seismic and well data. The input PS data has significant signal loss from sand injectites directly above the reservoir, where PP data showed no signal loss, resulting in the PS reservoir interval to contain a 9Hz peak frequency when registered to PP time. Given this information, the expectation of the PS data was to only marginally improve model estimates. Synthetic work was done to assess inversion performance and controlling parameters. Findings show if only PP waves were used for inversion, large offsets would be needed for a partially successful S-impedance inversion, which is not available in the Edvard Grieg survey, due to a maximum 34 degrees incidence angle. This idea is reflected in the prestack PP inversion results for the field data. The prestack PP inversion produces the best estimate for P-impedance, a large improvement from post-stack inversion, however, the resulting S-impedance estimate simply follows the background relationship with the P-impedance term. By performing joint PP-PS inversion, we greatly improve the S-impedance estimates to further characterize the reservoir heterogeneity using Vp/Vs. The seismic data is shot in two vintages, 2016 and 2018, with time-lapse purposes in mind, leading to excellent repeatability (11% NRMS for PP data, 24% NRMS for PS data). Theoretically, the P-impedance estimate is influenced by fluid and pressure changes, while the S-impedance estimate is chiefly influenced by pressure. This discrepancy can be used to separate these two effects in locations where overlap and interference occurs. The inversion results showed that with limited offsets, the PP prestack inversion derived S-impedance change estimate provides no time-lapse interpretation benefits and simply mimics the changes in P-impedance. With PP-PS 4D inversion the S-impedance was able to capture geomechanical changes in the field and aid in the separation of the effects of saturation and pressure. The optimal P-impedance estimate is derived from PP prestack inversion while the optimal S-impedance estimate is derived from PP-PS prestack inversion. This S-impedance is noisier due to the PS data, but is far more accurate and allowed for better identification of reservoir quality heterogeneities from impedance extractions and the generation of facies volumes. Baffles and barriers were identified in the large sand bodies and alluvial section that correlate to the 4D response. S-impedance change is used in conjunction with P-impedance change to create saturation and pressure change maps in the reservoir. The maps are used to determine reservoir compartmentalization, monitor injected fluids, understand water drive, and identify bypass zones. The work in this thesis demonstrates the benefits of 4D joint PP-PS prestack inversion on maximizing the understanding of reservoir quality, heterogeneity, and fluid flow pathways. This information proves invaluable to industry asset teams in making drilling and reservoir management decisions.
    • Across- and along-strike structural and geochronological variations of the Nashoba-Putnam and Avalon terranes, eastern Massachusetts, Connecticut, and Rhode Island, southeastern New England Appalachians

      Kuiper, Yvette; Severson, Allison R.; Trudgill, Bruce, 1964-; Palin, Richard M.; Findley, Kip Owen (Colorado School of Mines. Arthur Lakes Library, 2020)
      A comprehensive structural and geochronologic investigation was combined with existing structural, geochronologic and geophysical data to characterize and interpret across- and along-strike variations associated with the last two major orogenic events that formed the southeastern New England Appalachians of eastern North America. These orogenies are the mid-Paleozoic Acadian orogeny and the late Paleozoic Alleghanian orogeny. The northeast-trending Nashoba-Putnam terrane, located in eastern Massachusetts and Connecticut is part of the Gondwanan-derived microcontinent Ganderia. It is in fault contact with greenschist facies rocks of the Merrimack belt to the west, and with generally low grade rocks of the Avalon terrane to the east. Structural data in the Nashoba-Putnam terrane show five generations of deformation. Structural and metamorphic data are generally consistent with a channel flow model, where a hot, viscous mid- to lower crustal layer flows between relatively cool and more rigid layers, to remove material laterally in an overthickened orogenic belt. The occurrence of contemporaneous localized sinistral movement in schist and distributed dip-slip movement in migmatitic gneiss may represent strain partitioning of lateral movement and ductile extrusion of the channel in a sinistral transpressional regime. Based on new and existing U-Pb geochronology data, ductile deformation and possibly channel flow occurred during the latest Silurian to earliest Carboniferous Acadian orogeny, which resulted from the accretion of the Avalon terrane. Foliation orientations in the northwest-dipping Nashoba-Putnam terrane show a decrease in dip angle from subvertical and moderate dips in the north to moderate and shallow dips in the south, changing in particular at the latitude of Boston, Massachusetts. Furthermore, localized zones of west-trending foliation and west-trending terrane boundary between the Nashoba-Putnam and Avalon terranes occur along the generally northeast-trending foliations and boundary. One of these zones occurs at the latitude on Boston, at the same latitude as the transition from steeper to shallower dipping foliations. The Avalon terrane in southeastern New England is a composite terrane that rifted from Gondwana in the Ordovician and accreted to Laurentia during the Acadian orogeny. U-Pb and Lu-Hf isotopic analyses of zircon in three sedimentary rocks in the western-most Avalon terrane in southeastern New England was carried out to compare the detrital zircon signature with those of other metasedimentary rocks of the southeastern New England Avalon terrane and with Avalonia in eastern Canada. Analyzed samples are isotopically similar to others in the New England Avalon terrane, and to Avalonia in Canada, especially the Gamble Brook Formation in the northern part of Nova Scotia. Finally, detrital zircon of the western Avalon terrane has a mixed source between Baltica and Amazonia. U-Pb analyses of zircon from migmatitic rocks in the southeastern Nashoba terrane, combined with existing 40Ar/39Ar and U-Pb analyses of high temperature minerals suggest a younging of leucosome and high-grade metamorphism from north to south in the Nashoba-Putnam and Avalon terranes. The major transition in ages of leucosome occurs at the approximate latitude of Boston, Massachusetts. Furthermore, west-trending lineaments and a gravity anomaly are visible in aeromagnetic and Bouguer gravity datasets, respectively. The most notable of these west-trending lineaments is located along the latitude of Boston, Massachusetts. This lineament coincides with a change in foliation orientations as outlined above. Furthermore, U-Pb monazite ages along this lineament are late Paleozoic in the Nashoba terrane. In the Avalon terrane, a transition occurs from predominantly middle Paleozoic 40Ar/39Ar hornblende cooling ages relating to the Acadian orogeny to the north and mostly late Paleozoic ages relating to the Alleghanian orogeny to the south. This lineament is therefore interpreted as the ‘Alleghanian Front’, where rocks to the south were affected by the Alleghanian orogeny, while rocks to the north show only minor effects.
    • Active limiting frequency selective surface at X-band

      Nayeri, Payam; Bay, Patrick; Coulston, Christopher; Haupt, Randy L. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Receivers used in wireless communication systems will commonly employ limiters to protect sensitive low-noise electronics from high-power emitters that may be located nearby. Receivers may be designed to operate with signals in the nanowatt (10-9 W) range, while nearby transmitters may be broadcasting hundreds or thousands of Watts of power. The disadvantage of traditional receiver limiters are that they are located downstream from the antenna, which will commonly have gain and increase the amount of power that the limiter must handle. A frequency selective surface with integrated limiter protection is proposed to mitigate this issue by moving the limiting function before the antenna, and this type of receiver protection has had minimal investigation in the existing literature. A new design operating at X-band is proposed using a square-plate element, and is simulated and measured for both small-signal and large-signal conditions. The measurements show that the concept is capable of non-linear limiting behavior with insertion loss comparable to the traditional microstrip limiter approach.
    • Advanced perfluorinated anion exchange membrane polymers and their issues in electrochemical conversion devices

      Herring, Andrew M.; Divekar, Ashutosh G.; Koh, Carolyn A. (Carolyn Ann); Krebs, Melissa D.; Samaniuk, Joseph R.; Pivovar, Bryan S.; Trewyn, Brian (Colorado School of Mines. Arthur Lakes Library, 2020)
      After decades of dedicated efforts in research and development of the polymer electrolyte membranes for electrochemical conversion devices, the technology is nearing their large-scale commercialization. Improvements like utilization of thin mechanically supported membranes (< 15 μm), advanced Pt catalysts with enhanced activity have made the proton-exchange membrane class of polymers very attractive for vehicular fuel cell and other electrochemical conversion applications. However, with the increasing energy demand for the rapidly growing population high performing commercial devices with non-precious catalysts need further attention. Anion exchange membrane polymers perfectly fit this description due to its compatibility with the cheaper electrochemical catalysts. In this work, the potential of novel perfluorinated anion exchange membranes primarily for low-temperature fuel cell applications were tested. Three iterations of polymer membranes with a PTFE backbone were electrochemically, physiochemically, and morphologically characterized to conclude that the six-carbon alkyl spacer chain is the most promising candidate with a high ionic (OH-) conductivity. Ex-situ characterization of this class of polymers was performed to understand the interaction of the hydroxyl charge carrier with the atmospheric CO2 in the ambient air as in a commercial fuel cell device, ambient air is used as an oxidant. It was concluded that the CO2 not only interacts with the ionic domains of the polymer but also hampers the crystallinity of the backbone which could potentially lead to mechanical failures while operating for longer durations. From the knowledge gained from this study, a standard fuel cell device was tested to report the highest air-fed anion exchange membrane fuel cell performance to date (446 mW cm-2). For the first time, the segmented fuel cell hardware was used to understand the spatial differences in the anion exchange membrane fuel cell performance due to the variation in humidification, fuel or oxidant starvation and the durability issues. Over several days of operation, it was found that the cell degrades primarily in the feed inlet section due to difference in the hydration or water accumulation over the channel length. FTIR analysis was performed to prove that the chemical functionality of the membrane changes due to the fuel cell operation. The catalyst-ionomer interface was investigated using polymer dispersion spin-coated on model Si and Ag substrates. From the grazing incident x-ray scattering study, phenomenon like parallel polymer chain alignment with respect to the surface at a higher ionomer thickness and their variation with hydration and type of substrate was investigated. With increasing thickness, the film formation undergoes two transition regimes: formation of crystalline polymer domains followed by intra-molecular alignment of CF2 units within the polymer chain. It was also found that the silver surface is interacting strongly with the polymer. From the knowledge gained, it is recommended to design the catalyst inks with lower ionomer content so that the parallel alignment of the polymer chains is limited to mitigate the mass-transport limitations. This work can serve as a guide to design higher performing catalyst inks, optimal conditions of water management, and ambient air operation to produce higher-performing fuel cell devices. However, learnings can also be applied to other electrochemical devices like water-splitting, electro-dialysis, CO2 reduction, and lead-air batteries. Understanding of the CO2 limitations from this work could also help in designing CO2 sequestration devices containing anion conducting ionic liquids.
    • Advancing continuum and discontinuum models of brittle rock damage and rock-support interaction

      Walton, Gabriel; Sinha, Sankhaneel; Hedayat, Ahmadreza; Ozbay, M. Ugur; Santi, Paul M. (Paul Michael), 1964- (Colorado School of Mines. Arthur Lakes Library, 2020)
      Stress-induced damage and spalling in underground mines continue to remain a major hazard to mining personnel. In order to reduce worker injuries caused by falls of ground, it is necessary to develop techniques through which the mechanisms of pillar damage can be accurately interpreted and supports can be designed to control the anticipated displacements along pillar boundaries. With advancement in numerical modeling techniques, it is now possible to study such rock mechanics problems in detail, but there is a need for improvement in the available approaches before they can be utilized as tools for the design of ground support schemes. The goal of this research is, therefore, to advance continuum and discontinuum models to better reproduce both observed pillar damage mechanisms and the interaction between supports and (unsupported) ground. The associated findings contribute significantly towards improving our understanding of the phenomenological capabilities of continuum and discontinuum modeling approaches and their applications in different mining scenarios. The contents of this thesis can be broadly sub-divided into two sections – continuum (using Itasca’s FLAC3D software) and discontinuum (using Itasca’s UDEC software) analyses of pillar damage and rock-support interaction. In the first section, a rock yield criterion is developed that considers both brittle fracturing at low confinement and shearing at higher confinement. When implemented in FLAC3D pillar models, results consistent with the empirical trend of pillar strength as a function of width to height ratio for granite, conglomerate, and coal were obtained. In terms of site-specific case studies, pillar displacement and stress data from two different sites could be reproduced using this yield criterion. Subsequent investigations on rock-support interaction revealed that continuum models tend to underestimate the effect of support on otherwise unsupported ground, and accordingly is limited in its potential application as a support design tool. In the second portion of this thesis, the Voronoi Bonded Block Modeling (BBM) approach is employed, which represents a material domain by an aggregate of polygonal blocks. Laboratory-scale modeling of a granitic rock was pursued to understand how decisions related to model setup affect the ability of such grain-based models to reproduce various deformation mechanisms. Ultimately, a BBM representation utilizing different elastic properties for the different mineral grains along with inelastic grain properties was necessary to match the pre- and post-peak attributes of the granite under consideration. The input properties from the laboratory-scale models, however, were found to not be directly applicable to pillar-scale simulations because much larger blocks sizes were used in the latter case and blocks sizes are known to exert a significant influence on the macroscopic behavior of BBMs. Accordingly, pillar-scale BBMs were calibrated independently, although the findings regarding model setup decisions from the grain-based BBM are, in part, transferable across scales. For example, the pillar BBMs required an inelastic block representation to simulate the damage process within the confined sections of the pillars, similarly to how the laboratory-scale model also required inelastic grains to replicate the high confinement attributes observed in laboratory triaxial tests. The analysis of rock-support interaction was conducted by comparing the lateral displacements along the pillar edges without support and with various support patterns for both the polygonal and the triangular (also called Trigon) block geometries. The polygonal BBM produced behavioral differences that were closer to empirical field-data assembled from hard rock mines in comparison to the Trigon models. Coal pillars were simulated with elongated, inelastic Voronoi blocks to account for the anisotropic cleating of coal. For the case of the West Cliff longwall mine, this model representation was able to reproduce the pillar displacements at two neighboring sites that had different support patterns by modifying the support in a BBM calibrated to one site to match the support at the adjacent site. This is perhaps the first study to quantitatively demonstrate that BBMs can replicate the influence of rock reinforcement on ground behavior in rock undergoing spalling. Lastly, as BBMs are computationally intensive and cannot easily be applied at the mine-scale in 3D, an integrated modeling approach was established using two different mining case studies. In this approach, the larger-scale stress distribution was assessed using FLAC3D, and the deformation behavior near excavation boundaries (with and without support) under the expected loading path was estimated using a BBM. This study, as a whole, has demonstrated the capabilities of continuum and discontinuum modeling approaches under a variety of conditions, and the proposed approach for studying ground-support interaction has the potential for practical application in the context of site-specific support design.
    • Advancing understanding and prediction of redevelopment impacts on stormwater runoff in semi-arid urban areas

      Hogue, Terri S.; Panos, Chelsea Lynne; Kroepsch, Adrianne; Holley, Jeffrey A.; McCray, John E. (Colorado School of Mines. Arthur Lakes Library, 2020)
      As the global urban population grows, cities are densifying by redeveloping previously developed spaces. “Smart growth” through redevelopment is increasing the impervious coverage of urban areas and impacting the hydrologic regime in uncertain ways. Cities are looking to update current stormwater management criteria, which often exempt redevelopments, based on data-driven decisions informed by watershed-scale hydrologic modeling. Future stormwater management strategies must also consider climate changes and flood mitigation via low impact development (LID). Using the Berkeley neighborhood of Denver, Colorado, we investigated the impacts of redevelopment land use change, along with climate change and LID implementation, on stormwater quantity using a high-resolution, calibrated Stormwater Management Model for PC (PCSWMM). The model includes 170 subcatchments and parcel-scale predictions of impervious cover change for three scenarios of future redevelopment.Simulations of design storms for multiple redevelopment scenarios predict that an increase of 1% in impervious area from redevelopment will increase surface runoff by 1.63% for the 2-yr, 24-hr design storm and by 0.91% for the 100-yr, 24-hr design storm resulting in greater relative flood risks for smaller storm events. When assessing the effectiveness of LID to mitigate increases in runoff from redevelopment, we found that model sensitivity to LID siting and routing parameters can impact the potential for meeting regulatory compliance. Relative sensitivity of runoff volume output to area treated and LID placement was found to be on average 3.0 and 11.2 times higher than the seven most sensitive physical LID and subcatchment parameters. Misunderstandings of model sensitivities can lead to costly decisions that are made based on modeling results. Finally, when assessing the combined impacts of redevelopment land use change and climate change on stormwater dual drainage system resilience, it was found that the system may be able to handle increases in runoff and flooding from redevelopment land use changes or climate changes alone, but likely not both. However, distributed LID implementation in conjunction with redevelopment provides a unique opportunity for increasing system resilience with a small LID footprint. All findings indicate a need to lower the current area threshold for requiring stormwater management with redevelopment within updated stormwater management criteria.
    • Analysis of the influence of ferricrete on hyporheic exchange flows

      Singha, Kamini; Rickel, Ariel; Navarre-Sitchler, Alexis K.; Mangel, Adam (Colorado School of Mines. Arthur Lakes Library, 2020)
      The area of confluence between surface water and groundwater, known as the hyporheic zone, is a natural biogeochemical filter that is dependent on channel morphology and hydraulic conductivity, pressure-driven downwelling and upwelling currents, and stream discharge. In Cement Creek near Silverton, Colorado, deposition of amorphous iron minerals reduces the permeability of the streambed and limits flow through the hyporheic zone. This limited exchange may lower the potential for pollutant attenuation from the metals-loaded waters of Cement Creek within the hyporheic zone. This study found that hyporheic exchange in this system is limited in spatial extent and reduces during low flow when compared to what we would expect from streams without ferricrete. To quantify flow through the hyporheic zone, we used time-lapse electrical resistivity of the streambed and banks of Cement Creek taken over the course of a day in conjunction with a four-hour salt injection tracer test. The solute was constrained within the streambed, with little flow through the banks, and had longer residence times in the hyporheic zone during high flow than at low flow. Slug test data suggested the presence of a zone of lower permeability at 44-cm depth that was likely made of precipitated ferricrete that cemented cobbles together. The comparison of apparent bulk conductivity from the geophysics to in-stream fluid conductivity allowed for the calculation of mass transfer parameters between the stream and hyporheic zone based on the difference in solute retardation patterns in the two breakthrough curves. During high flow, in-stream breakthrough curves displayed slower breakthrough and greater smoothing which is consistent with the geophysical inversion results that indicate higher residence times at high flow. Analyses of low flow data indicated decreased residence time within the subsurface and comparatively faster breakthrough. The hyporheic storage area within Cement Creek, estimated from the modeled capacity coefficient, decreased by two orders of magnitude between high (0.5 m2 as modeled from hysteresis curve and in STAMMT-L) and low flow (0.006 m2 from STAMMT-L model), along with a corresponding decrease in residence times (300 s versus 10 s, respectively).
    • Application of machine learning to gas flaring

      Miskimins, Jennifer L.; Lu, Rong; Bandyopadhyay, Soutir; Eustes, Alfred William; Fan, Yilin; Crompton, James Scott (Colorado School of Mines. Arthur Lakes Library, 2020)
      Currently in the petroleum industry, operators often flare the produced gas instead of commodifying it. The flaring magnitudes are large in some states, which constitute problems with energy waste and CO\textsubscript{2} emissions. In North Dakota, operators are required to estimate and report the volume flared. The questions are, how good is the quality of this reporting, and what insights can be drawn from it? Apart from the company-reported statistics, which are available from the North Dakota Industrial Commission (NDIC), flared volumes can be estimated via satellite remote sensing, serving as an unbiased benchmark. Since interpretation of the Landsat 8 imagery is hindered by artifacts due to glow, the estimated volumes based on the Visible Infrared Imaging Radiometer Suite (VIIRS) are used. Reverse geocoding is performed for comparing and contrasting the NDIC and VIIRS data at different levels, such as county and oilfield. With all the data gathered and preprocessed, Bayesian learning implemented by Markov chain Monte Carlo methods is performed to address three problems: county level model development, flaring time series analytics, and distribution estimation. First, there is heterogeneity among the different counties, in the associations between the NDIC and VIIRS volumes. In light of such, models are developed for each county by exploiting hierarchical models. Second, the flaring time series, albeit noisy, contains information regarding trends and patterns, which provide some insights into operator approaches. Gaussian processes are found to be effective in many different pattern recognition scenarios. Third, distributional insights are obtained through unsupervised learning. The negative binomial and Gaussian mixture models are found to effectively describe the oilfield flare count and flared volume distributions, respectively. Finally, a nearest-neighbor-based approach for operator level monitoring and analytics is introduced.
    • Arrowhead patch slot antenna for 5G applications

      Elsherbeni, Atef Z.; Feng, Yuhao; Aaen, Peter H.; Hadi, Mohammed (Colorado School of Mines. Arthur Lakes Library, 2020)
      With the rapid development of 5th generation mobile network (5G), the need to integrate multiple frequency bands and multiple wireless standards into 5G systems is growing. The antenna is an essential part of the system to ensure communication quality. Therefore, research on antennas and arrays suitable for the 5G frequency bands is of great significance for future wireless communication systems. This thesis reviews recent antenna designs related to 5G systems, especially those based on coplanar waveguide feeding method. Then antenna based on coplanar waveguide feed structure is designed and optimized for better input impedance match and radiation performance. Measurements of the fabricated prototype confirmed the targeted operating frequencies. Furthermore, antenna array configurations are designed and optimized for 5G base stations or terminals. The scanning feature of the antenna array configurations (5 and 15 antenna elements) are investigated for operation in two segments of the licensed lower 5G frequency band (3.55-3.7GHz and 3.7-4.2GHz). Finally, a cavity is further suggested to be added to the bottom of the antenna element to focus the radiated field mainly in one half space and to be used in the array configurations.
    • Assessing the impacts of hydrologic disturbances on urban water supply and demand in the western United States

      Hogue, Terri S.; Blount, Kyle; Ajami, Newsha; Bell, Colin D.; Read, Laura; Singha, Kamini; Smith, Jessica, 1980- (Colorado School of Mines. Arthur Lakes Library, 2020)
      In the semi-arid western U.S., urban water systems are facing growing challenges to both supply and demand associated with growing populations, urban development, wildfires in headwaters basins, and climate change. Wildfire and climate change can alter the volume and timing of water delivery to downstream systems, and projected increases in temperature are expected to increase demand in urban systems. Along the Colorado Front Range, extensive redevelopment is changing the characteristics of the urban systems that drive water demand. To better understand the impacts of disturbance on regional water supply and demand, this dissertation assesses post-fire changes to water yield in a burned watershed in the Rockies and investigates trends in and drivers of urban irrigation, a consumptive use of water, in Denver, Colorado. After the Chippy Creek Fire in 2007, the Mill Creek Basin in Montana experienced abrupt shifts in vegetation, from evergreen forest to shrub/scrub and grasslands, resulting in significant changes in local hydrologic partitioning and altering downstream supplies. Evapotranspiration from the basin decreased by 46%, and water yield increased by 140% during the first decade after the fire with no clear recovery trends. In Denver, temperature and land cover influenced demand for outdoor water use between 1995 and 2018. Increasing temperatures drove significant increases in irrigation rates in 37% of Denver census block groups, and the percentage of water used outdoors increased significantly across the city during this period. Finally, examinations of irrigation rates at the parcel scale in Denver show significant differences between land uses that are associated with variation in impervious land cover. Modeled residential redevelopment scenarios show reductions of 141,000 m3 (114 AF) of residential outdoor use per 1% increase in single-family parcels redeveloped to multi-family units. This work contributes essential insights toward improving the resiliency of water systems and understanding key factors that influence sustainable urban development. Despite the destructive nature of wildfire, results indicate that increases in water yield following fire in headwaters basins can be utilized for downstream urban supply if managers appropriately plan for altered volume and quality. As temperatures rise and indoor water use becomes more efficient or is recycled, outdoor use comprises an increasingly large portion of total urban water demand, posing challenges to climate adaptation within water-limited cities. However, by integrating land use and water planning, the residential redevelopment of urban areas provides opportunities to reduce outdoor demand and design urban green spaces to achieve multiple benefits efficiently.
    • Assessment of alloy 709 accelerated creep properties for use in sodium cooled fast reactors

      Findley, Kip Owen; Kaufman, Michael J.; Carter, Alan; De Moor, Emmanuel; Clarke, Kester; Deinert, Mark R.; Wright, Richard (Colorado School of Mines. Arthur Lakes Library, 2020)
      The high temperature mechanical properties and microstructural development of Alloy 709 were investigated from temperatures ranging from 550 to 650 °C. Constant load creep, stress dip, and stress relaxation tests were carried out to determine the minimum creep rate exponent and activation volume, as well as the activation energy of creep and stress relaxation. Constant load creep tests were interrupted close to the point of minimum creep rate. These interrupted specimens were used to investigate microstructural development during creep conditions using scanning and transmission electron microscopy. The properties measured during mechanical testing and microstructural development observed during microscopy investigation were studied in an effort to identify controlling deformation mechanism. Two physical models are applied to Alloy 709 in an effort to determine the feasibility of the identified controlling deformation mechanism during creep. The mechanical properties and microstructural development of two aged conditions were investigated in an effort to identify the role of precipitate size, spacing, and type on the creep processes taking place in Alloy 709. The minimum creep rate exponent and activation volume, as well as the activation energy of creep and stress relaxation were determined for the differing age conditions. Constant load creep tests of aged specimens were interrupted close to the moment of minimum creep rate. Microstructural development due to aging as well as due to creep conditions, from interrupted specimens, were investigated with scanning and transmission electron microscopy. The variation between the measured high temperature properties of Alloy 709 were related to the physical differences observed during microscopy.
    • Bake hardening behavior of advanced high strength steel grades

      De Moor, Emmanuel; Matlock, David K.; Blesi, Brandon W.; Findley, Kip Owen; Speer, J. G. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Advanced high strength steels (AHSS) have been developed combining high strength and formability, allowing for lightweighting of vehicle structural components. These AHSS components are exposed to paint baking treatments, following straining induced from part forming, which may lead to increased in-service component performance due to a strengthening mechanism known as bake hardening (BH). This study quantified the BH behavior of select AHSS grades. Materials investigated were press hardenable steels (PHS) 1500 and 2000; transformation induced plasticity (TRIP) aided bainitic ferrite (TBF) 1000 and 1200; and dual phase (DP) 1000. The number designations of these grades refer to minimum as received ultimate tensile strengths in MPa. Paint baking was simulated using times and temperatures from 15 to 60 min and 120 to 200 °C, respectively. Samples were prestrained 0, 2, and 5 pct. The effects of time, temperature, and prestrain on the DP and TBF steels were evaluated using uniaxial tensile testing. Because no additional part forming occurs after austenite is quenched to martensite during hot stamping, the PHS grades were not experimentally prestrained and thus BH assessed low temperature tempering (LTT) response. Uniaxial tensile, bend, and microhardness testing were used to evaluate LTT for the same times and temperatures. Yield strength generally increased for the DP and TBF steels with increasing time and temperature. Without prestrain, DP 1000 and TBF 1200 showed similar aging for most conditions. BH exceeded 100 MPa for DP 1000 at the greatest time/temperature. Tensile ductility also remained high for all test conditions without prestrain, typically decreasing by 1 pct or less relative to AR. With the addition of 2 and 5 pct prestrain, different aging behaviors per grade were observed with TBF 1200 showing the greatest BH response followed by TBF 1000. After prestraining, DP 1000 had the smallest BH values. Prestraining TBF 1200 5 pct followed by aging at 200 °C for 60 min resulted in a BH value of 180 MPa. Likewise, BH for TBF 1200 continuously increased with increasing prestrain. Ductility diminished for the DP and TBF steels with increasing prestrain, time, and temperature. Tensile tests for PHS grades showed that yielding transitioned from continuous to discontinuous and yield strengths reached maxima with increasing tempering intensity. The higher carbon PHS 2000 had the greatest BH response and a maximum value of 180 MPa after aging at 200 °C for 15 min. Bend test results for both grades had large scatter and showed no observable trends in bend angle with increasing aging.
    • Carbon formation in direct reduced iron and hot briquetted iron

      De Moor, Emmanuel; Godoy, Michelle P.; Taylor, Patrick R.; Anderson, Corby G. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Carbon formation in the MIDREX© reduction shaft at voestalpine Texas LLC was investigated with computational simulations and physical examination of hot briquetted iron and direct reduced iron. Simulations were carried out utilizing HSC thermodynamic software, ANSYS Fluent computational fluid dynamic software and a material balance analysis. The simulation provided the theoretical amounts of carbon formation possible in the reduction shaft along with temperature and gas distribution profiles. The computational results led to a focused analysis of the transition zone due to the lack of interference with the reduction process, the greater possible range in process condition changes and increased quality control. The physical analysis was carried out utilizing x-ray diffraction, Mössbauer spectroscopy, total carbon content analysis, metallography and TIMA mineralogy. Plant trials were conducted to determine the carbon formation at various operating ranges. Prior to the trials, baseline testing was conducted to determine carbon variance. Additionally, material was collected during a furnace discharge and it was estimated that the bustle region introduces 44% of the total carbon formation. The transition zone trial proved carbon formation could be altered by a change of flow rate. The carbon was positively impacted by a higher transition zone flow rate, specifically a + 20.2 relative carbon percent was experienced with a 1000 SCFM increase of transition zone flow. A temperature change of the discharge material was also experienced due to the endothermic nature of the cracking of methane. Increased temperatures were experienced at the low flow rate set point, which had a positive effect on the briquetting density. The density was closely correlated with briquetting temperature rather than carbon formation.
    • CFD modeling of methane flame, turbulence, and obstacle interaction applied to a longwall coal mine

      Bogin, Gregory E.; Brune, Jürgen F.; Nguyen, Thu; Porter, Jason M.; Rickey, Kelly (Colorado School of Mines. Arthur Lakes Library, 2020)
      The formation of explosive gas zones (EGZs) forming from flammable vapors, gases, or dust pose safety hazards to many industries. An EGZ ignition could occur by faulty electrical equipment, hot streaks from worn bits on a shearer cutting hard rock, rock-on-rock frictional sparks, heat, or fires and result in an explosion, and/or detonation. Agriculture, oil and gas, chemical, and energy industries experience methane-air or organic dust explosion hazards. In many cases, explosions may occur in confined areas with obstacles in the path of flame expansion. By studying the effects of obstacle shape and size on flame propagation and turbulence, a more complete understanding of the interaction of the flame and fluid dynamics has been achieved. Obstacle shape, turbulence model, and spark location were investigated using a single obstacle and flame interaction in the model. Reynolds Averaged Navier Stokes (RANS) models were tested to determine if these simplified turbulence models could capture the flame dynamics and propagation velocities using fewer computational resources compared to the higher fidelity Large Eddy Simulation (LES) turbulence model. Obstacle shapes were varied to examine the impact of shape on methane flame propagation. Results showed that square obstacles caused faster flame propagation around the obstacle compared to hexagons and circles. The square had an average flame speed 26% faster than the circle, and the hexagon was 16% faster than the circle using a k-ω model. Modeling results indicate that variation of the spark location by as a distance as small as 10% of the obstacle diameter can result in a significant difference in flame propagation velocity. Comparing to RANS, an LES turbulence model only increases computational time by 25%. Therefore, the LES turbulence model was used in modeling a simplified 2D longwall mine combustion model. Achieving reasonable computational times while maintaining general flame propagation trends was the main goal of modeling an explosion in a full-scale longwall mine. Investigating different methods of modeling the gob inside the mine showed that a porous media model would not be able to capture effects from turbulence or handle a reacting flow due to a Darcy Flow assumption. As a result, the gob was modeled as a fluid zone with discrete obstacles. Results from the 2D mine model with combustion overpredicted the pressure compared to a 3D model but was still able to track the propagation of the pressure front well when compared to a 3D model. By simplifying the model to 2D, computational time was reduced to three days, compared to three weeks for the 3D model, to simulate a 35ms interval after ignition.
    • CFD simulation of polarization phenomena in direct contact membrane distillation systems

      Tilton, Nils; Lou, Jincheng; Cath, Tzahi Y.; Decaluwe, Steven C.; Ganesh, Mahadevan (Colorado School of Mines. Arthur Lakes Library, 2020)
      Direct contact membrane distillation (DCMD) is a thermal process in which warm feed and cool distilled water flow on opposite sides of a hydrophobic membrane. The temperature difference causes water to evaporate from the feed, travel through the membrane, and condense in the distillate. Because DCMD is insensitive to osmotic pressure, it has emerged as a promising means of concentrating brines to their saturation limit. Studies have shown that temperature and concentration polarization are the two crucial factors affecting DCMD performance in the treatment of hypersaline brines. Temperature polarization refers to a reduction in the transmembrane temperature difference due to heat transfer through the membrane. Concentration polarization describes the accumulation of solutes adjacent to the feed side of the membrane. To date, computational fluid dynamics (CFD) studies of DCMD focus primarily on the challenge of temperature polarization. For high concentration brines, however, concentration polarization is another major challenge that reduces system efficiency and leads to mineral scaling. Temperature and concentration polarization are further complicated by spacers, a mesh-like material that separates and supports tightly packed membrane sheets. These interactions are not well understood, because they are difficult to study experimentally and numerically, and the flow regimes are not fully charted. We consequently develop a tailored in-house CFD code that simulates unsteady two-dimensional heat and mass transport in plate-and-frame DCMD systems with cylindrical spacers. The code uses an efficient combination of finite-volume methods in space, projection methods in time, and recent advances in immersed boundary methods for the spacer surfaces. For DCMD systems without spacers, we perform a comprehensive parametric study of polarization phenomena for a wide range of feed and distillate operating conditions, system length, and co-current versus counter-current operation. We also investigate the system-level performance by measuring the average permeate flux, single-pass water recovery, maximum concentration polarization coefficient, and gained output ratio of DCMD systems with heat recovery. Though the transmembrane vapor flux is small, we observe dramatic increases in solute concentration at the membrane surface, exceeding 1.6 times the feed value. The temperatures, concentration, and vapor flux vary considerably in the downstream direction, and are poorly approximated by common Nusselt and Sherwood correlations. For DCMD systems with spacers, we investigate the impact of the Reynolds number, spacer diameter, and spacer position on polarization and system performance. We show that the impact of spacers can be explained by examining the various steady and unsteady vortical flow structures generated in the bulk and near the bounding plates and membranes. Overall, we show that though unsteady vortex structures tend to mix temperature polarization layers with the bulk, they are not similarly able to mix the thin concentration layers. Rather, vortical structures tend to create regions of preferential salt accumulation. In the vortex shedding regime, the net result is that spacers often increase vapor production at the expense of increasing the risk of mineral scaling.
    • Chalcogenide-based van der Waals-layered materials for enhanced electronic and electromechanical properties

      Ciobanu, Cristian V.; Likith, S. R. J.; Brennecka, Geoffrey; Tucker, Garritt J.; Berger, John R. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Since the successful isolation of graphene via mechanical exfoliation at room temperature, other van der Waals (vdW)-layered or quasi-2D materials have gained significant interest in the scientific and technological communities. Quasi-2D (q2D) materials have been shown to unlock a wide variety of unusual and useful thermoelectric, electronic, optoelectronic, electromechanical, and sensing properties (among others) offering several advantages over conventional bulk 3D materials. From an application standpoint however, between the large band gap of hexagonal boron nitride and the zero band gap of graphene, the semiconductor space is mostly limited to Transition Metal Dichalcogenides (TMDCs) - which are semiconductors. There are several ways to improve the diversity of semiconducting 2D or q2D materials, which can lead not only to new materials, but to new phenomena and applications as well; these include alloying, doping, layering (heterostructuring), or discovering and manufacturing new 2D or q2D materials altogether. In the quest for new, versatile, and multi-functional q2D materials, this thesis presents computational studies based on vdW-corrected density functional theory addressing several directions of increasing the range of electronic and electromechanical properties of chalcogenide-based 2D or q2D materials. These studies pertain to group IV monochalcogenides, bilayer and bulk TMDC heterostructures, and surface-doped TMDCs, and have led, respectively, to (i) the discovery of 39 new and potentially synthesizable monochalcogenides, (ii) understanding the range of band gaps and piezoelectric coeffecients achievable in bilayer TMDCs and the effects of interlayer registry, and (iii) elucidating the physical origins of the p-type doping measured in molybdenum ditelluride in ambient air
    • Chaos and complexity of magnetic spin-wave solitary wave dynamics in the complex cubic quintic Ginzburg-Landau equation

      Carr, Lincoln D.; Wu, Mingzhong; Anderson, Justin Quinn; Callan, Kristine; Benson, David A.; Pankavich, Stephen (Colorado School of Mines. Arthur Lakes Library, 2020)
      We report the development, implementation and complete experimental vindication of a model for complex dynamical behaviors in spin wave envelopes propagating in nonlinear, dissipative driven, damped systems. These backward volume spin waves evolve under attractive nonlinearity in active magnetic thin film-based feedback rings where the major loss mechanisms present in the film are directly compensated by periodic linear amplification. Such a quasi-conservative evolution allows for the self-generation of spin waves and the observation of long-time behaviors $\mathcal{O}(\mathrm{ms})$ which persist for hundreds to tens of thousands of the fundamental round trip time $\mathcal{O}(100~\mathrm{ns})$. The cubic-quintic complex Ginzburg-Landau equation is developed as a predictive, descriptive model for the evolution of spin wave envelopes. Over 180000 nodes hours of computation are used to execute more than 10000 simulations in order characterize the model's six dimensional parameter space. This exploration of parameter space was conducted in full generality, spanning a minimum of eight orders of magnitude for each of three loss terms and five orders of magnitude for higher order nonlinearities. Nine distinct classes of behavior were identified, including four categories of dynamical pattern formation. This work contains the first predicted long time dynamical behaviors for spin waves and analogous physical systems. All four categories of dynamical pattern formation that were identified numerically were then cleanly realized experimentally. Additionally we observed the first known examples of dynamical behaviors for dark solitary waves self-generated under attractive nonlinearity. Our experimental verification of these dynamical regimes show that such ideas are not simply theoretical but in fact occur in the real physical world and are observable in an approachable, tunable spin-wave system which matches the conditions of many other real-world physical systems. It further established that the relatively simple cubic-quintic complex Ginzburg-Landau equation provides a highly accurate, effective, and predictive description of complex spin wave dynamics and should replace the commonly used nonlinear Schr\"odinger equation for these systems. Finally, simulations which model the ring dynamics on the scale round trips were conducted using 130000 node hours over 3000 unique numerical simulations. This yielded a robust general solution for stable bright solitary wave trains evolving under periodic amplification which is the numerical equivalent to the bright solitary wave train initial condition perturbed experimentally to generate soliton fractals and chaotic solitons. Using this novel dynamical equilibrium as an initial condition we developed a mechanism for the generation of bright soliton fractals. Our experimental and numerical works on complex spin wave envelopes in magnetic thin films suggest these systems provide for an approachable, table top, experiment for the study of fundamental nonlinear wave physics. The cubic-quintic complex Ginzburg-Landau model further provides for means for both prediction and verification of results. The physics reported here are expected to be wildly applicable to related fields of physics that are described by isomorphic forms of our model. This includes fields such as nonlinear optics, nonlinear hydrology and Bose-Einstein condensation.
    • Characterization of arc-based additive manufacturing of low carbon steel deposits

      Liu, Stephen; Ream, Jordan; Yu, Zhenzhen; Clarke, Kester; Javernick, Daniel A. (Colorado School of Mines. Arthur Lakes Library, 2020)
      Wire arc additive manufacturing (WAAM) is a technique that involves the use of a computer numeric-controlled (CNC) arc welding torch with an integrated wire feed to deposit metal one layer at a time in the fabrication of a near-net-shape part. Advantages of using WAAM over another additive manufacturing process include high deposition rate, large build volume, and reduced need for expensive equipment such as a vacuum chamber that would be used in a laser-based or electron beam-based process. However, little study has been performed to characterize the metallurgical properties of WAAM builds, particularly regarding the evolution of microstructure and mechanical properties along the entire build dimension with respect to length and width. This work characterized the microstructure, composition of alloying elements, and mechanical properties of ER70S6 carbon steel deposits on a layer-to-layer basis to better understand how the WAAM process affects the properties of the part.The microstructure of the build was characterized from layer to layer to determine how microstructural changes take place during the WAAM process. It was found that the as-solidified material formed a variety of ferrite microstructures, mostly acicular ferrite within large columnar prior austenite grains decorated with grain boundary ferrite and Widmanstätten ferrite at the prior austenite grain boundaries. Between subsequent passes, volumes of the prior deposit are heat treated by the process thermal conditions to form a heat affected zone, similar to that found in weldments. Irregular pockets of lath martensite and martensite-austenite-carbide (MAC) microconstituents were found dispersed in the HAZ along the length of the deposit and along the build direction. Also, in the heat affected zones, the as-deposited ferrite would be tempered into polygonal ferrite in the center of the build, due to the heat generated by the arc deposition. The composition of alloying elements was found to increase within each layer, from bottom to top. With remelting of the top regions of each prior layer during the additive manufacturing process, the richer composition near the top of the deposit would be incorporated into the subsequent layer. Arc stirring and pool mixing would uniformize the composition but partition during solidification will again create a composition gradient in this subsequent pass. This process repeats throughout the entire height of the build elevating gradually, but continuously, the concentration of the alloying elements. The mechanical properties were characterized through microhardness measurements to examine fluctuations within the build. Hard regions of martensite were found in the reheated zones of the earlier passes of a build. With subsequent deposits, however, the initially formed hard and soft regions were tempered to result in a more homogenized ferritic microstructure with lower hardness. Except for the initial and end transients, the remainder of a WAAM build would exhibit a relatively uniform microstructure and hardness.