• Strategic bidding for price-maker hydroelectric producers

      Rebennack, Steffen; Steeger, Gregory M.; Balistreri, Edward J. (Edward Jay); Boushell, Thomas; Kaffine, Daniel; Newman, Alexandra M.; Simões, M. Godoy (Colorado School of Mines. Arthur Lakes Library, 2014)
      Hydropower is arguably the most important and widely used renewable energy source in the world. Deregulation has led to the use of auction-based markets while a growing desire for efficient and renewable energy sources has rekindled modeling efforts in the energy sector. Producers that can impact prices with their production quantities are termed price makers, whereas producers that have no influence on prices are termed price takers. We ask: What is the revenue-maximizing production schedule for both single and multiple price-maker hydroelectric producers in a deregulated, bid-based market? We begin by reviewing the problem in which producers submit bids to the day-ahead market, the bidding problem. Following the review, we model the problem over multiple stages for (i) a single price maker assuming deterministic inflows, (ii) a single price maker assuming stochastic inflows, and, finally, (iii) multiple price makers assuming deterministic inflows. Decomposition algorithms, like Benders decomposition and stochastic dual dynamic programming, are commonly used to solve multi-stage problems like ours. In all the above cases, our methodology aims to extend the stochastic dual dynamic programming algorithm. The market interaction between producers creates a revenue function with jump discontinuities. Because of the discontinuities, we use mixed-integer linear programming to model the revenue, thus precluding us from solving the problem with either of the aforementioned algorithms. To overcome this difficulty, we pair Lagrangian relaxation with either Benders decomposition or stochastic dual dynamic programming, in the deterministic and stochastic cases. In addition to often yielding better bounds and solutions, we prove our method never yields worse bounds. For multiple price-maker producers, we consider each price maker's bidding decision in a non-cooperative Nash-Cournot game, in which we seek a Nash equilibrium for all of the price-maker producers' bids in every stage. Unlike current approaches, when one exists, our method returns an equilibrium that is preferred by all price makers.
    • Design-analogy performance parameter system (D-APPS)

      Turner, Cameron J.; Lucero, Briana M.; Linsey, Julie S.; Lucena, Juan C.; Blacklock, Jenifer; Berger, John R.; Gaylord Murray, Sylvia; Rolston, Jessica Smith, 1980- (Colorado School of Mines. Arthur Lakes Library, 2014)
      Analogical reasoning is not the only approach for achieving innovation, but it is a highly effective and noted method. To avoid relying on chance identification of analogies through unique individual knowledge and experience, this research considers the potential impact of a system where an engineer could begin with their existing design, specify to a computer a set of critical functions and desired design performance improvements, and be returned with design analogies intended to inspire avenues for design improvements. This system, called Design Analogy Performance Parameter System (D-APPS), implements performance metric matching to retrieve examples and stimulate analogical mapping, enabling innovative design advances. This dissertation presents a proof-of-concept D-APPS tool organized into 3 major areas: 1) critical functions and flows in the use of analogy mapping, 2) frameworks for performance metrics, and 3) an application enacting this frameworks called: Design Repository & Analogy Computation via Unit-Language Analysis (DRACULA) software package. For a given design problem, critical functions are those which are the most important product functions to meet the product requirements and customer needs. Functions which are commonly used in a given design domain provide an optimal target for demonstrating D-APPS with a limited set of database examples that satisfies the most common functions. A study of function usage in the student design repositories of three universities revealed the high prevalence of a small set of functions for the domains represented in those repositories. Akin to the functions, the critical flows are also characterized in this dissertation as those that are most pertinent to satisfying the Key Performance Parameters (KPPs) of a product. Organizing the many technical performance metrics in engineering design, such as lift or drag, is categorized in D-APPS. Studies were conducted to investigate and propose a framework for organizing metrics and facilitating metrics-based design example retrieval. The efforts generated a classification of performance metrics similar to the functional basis vocabulary of function and flow terms. The generated taxonomy used dimensional analysis to organize performance metrics by their composite, generalized units of measure (e.g., mass, length, time), augmented by functions as defined by bond graph characteristics. The culmination of this research is the DRACULA application, comprised of a repository and search algorithm. The design repository developed from the frameworks established with this dissertation allow for isomorphic matching of the functional models when dissected into engineering performance parameters and functional characteristic categories. Comparison of the models is performed utilizing graph theory to connect the functions and flows of the target and analog solutions, resulting in analogies capable of increasing abstraction.
    • Chemo-elastic behavior of reconstructed Li-ion battery cathode particles with phase transformation: a numerical and analytical investigation

      Berger, John R.; Malave, Veruska; Mustoe, Graham G. W.; Kee, R. J.; Martin, P. A.; Reimanis, Ivar E. (Ivar Edmund) (Colorado School of Mines. Arthur Lakes Library, 2014)
      The chemo-mechanical response of 3-D reconstructed and idealistic Li[subscript x]CoO[subscript 2] cathode particles has been elucidated with the implementation of an isothermal microscale numerical and analytical solution. The electrode stress-strain state is delineated upon the contribution of: i) phase transformation; ii) anisotropy and crystallographic orientation; iii) Li-composition inhomogeneity; iv) particle morphology and size; and v) composition-dependent chemical-expansion coefficient, [beta]. Diffusion-induced stresses (DIS) can be quite extreme with increasing particle size, Li concentration and discharge rate. Peaks of DIS locally emerge in the vicinity of concave features and protuberances of the anisotropic-elastic actual morphologies. In some cases, the severity of DIS indicate proneness to particle fragmentation. It is shown that phase-transition-induced stresses detrimentally contribute to abrupt changes in the particle mechanical behavior. The strong anisotropic chemo-elastic field induces the evolution of bands of Li-composition, chemical strains, and high-peak stresses. These occurrences are considered to be irrespective of the particle morphology but are highly dependent on the grain crystallographic orientation. Deleterious phase-transformation-induced stress bands are also found within the particle structure and are closely related to bands of chemical-misfit strains. It is demonstrated that [beta] is a key parameter in demarcating the chemo-stress-strain state of the Li[subscript x]CoO[subscript 2] cathode material. Under the linearity of [beta], both the stress-induced diffusion (SID) and DIS are dramatically more affected than when [beta] is constant. Hence, non-linear volumetric changes in the cathode structure can undermine its mechanical integrity. Because the chemo-elastic phenomena emanate in a reciprocate fashion, the linear-[beta]-based hydrostatic-stress gradients significantly facilitate Li diffusion under both charge-and discharge conditions comparing to the classical-Fickian-diffusion case. Subsequently, the stress-decoupling model promotes greater DIS due to composition inhomogeneity.
    • Beneficiation of plasma display panels

      Taylor, Patrick R.; Esquibel, Matthew; Anderson, Corby G.; Mishra, Brajendra (Colorado School of Mines. Arthur Lakes Library, 2014)
      A literature review, thermodynamics, and experimental testing were used to develop a beneficiation method for plasma display panels. The proposed process includes cutting the adhered glass, separating the front and back glass, acid leaching the glass panels separately, precipitating indium hydroxide, and precipitating rare earth oxalates. This process has the advantage of not requiring the glass to be crushed. Combining the front and back glass into one leaching stage followed by a two-stage precipitation is an option, but further test work is required. It was found that the best leach conditions for the ITO powder during testing was a temperature of 90°C, agitation rate of 600 rpm, 2.0054 g/L, 1M H2SO4, and 4 hours of leaching time. 99% of the indium was extracted at a grade of 96%. Leaching results suggest the process is controlled by the chemical reaction. The indium hydroxide precipitation was found to be optimal at a pH of 6, agitation rate of 400rpm, temperature of 25°C, 84 g/L NaOH, and a precipitation time of 90 minutes.96% of the indium was recovered as a hydroxide at a grade of 97%. The acidic leaching of the rare earth phosphor powder was found to be best at a temperature of 70°C, agitation rate of 600 rpm, 1M H2SO4, 2.5g/L, and 4 hours of leaching time. 99% of the REES were extracted with these parameters. Leaching results suggest the process is controlled by the chemical reactions. The parameters were then used on the phosphor glass and extracted 69% of the REEs at a grade of 10%. Rare earth oxalate precipitation results showed that it was possible to recover 98% of the REEs. Combined leaching experiments showed promise in extracting both indium and the REEs, but further work is required. A two-stage precipitation was attempted on the combined leach solution. The first stage is an indium hydroxide precipitation and the second stage is a rare earth oxalate precipitation. The precipitation results were encouraging, but a high indium concentration is required for the first precipitation stage to be selective. Further work is required on the two-stage precipitation parameters.
    • Micro-mechanical aspects of hydraulic fracture propagation and proppant flow and transport for stimulation of enhanced geothermal systems: a discrete element study

      Gutierrez, Marte S.; Tomac, Ingrid; Frenzel, Christian; Mustoe, Graham G. W.; Berger, John R.; Wu, Yu-Shu (Colorado School of Mines. Arthur Lakes Library, 2014)
      The study presented in this thesis uses micro mechanical approach to better understand hydraulic fracture initiation, propagation, proppant flow and transport and proppant settling during hydraulic fracturing of enhanced geothermal systems. Discrete Element Method (DEM) is used in two dimensions to address some of the current problems of hot dry rock fracturing. In particular, Bonded Particle Model (BPM) is used to simulate granite behavior and hydraulic fracturing. BPM is further improved using a novel convective-conductive heat transport model for studying hydro-thermo-mechanical fracturing processes. The new contributions regarding micromechanical understanding of fracturing fluid and rock behavior coupling, effect of fracturing fluid properties on fracture shape, branching, secondary fracturing and the relationship between tensile and shear micro-cracks are presented. The effects of temperature difference between fracturing fluid and surrounding rock on fracture initiation and propagation, as well as, heating of the fluid and cooling of the rock during fracture propagation are studied. Along with the process of hydraulic fracturing proppant is placed in the fracture for keeping its stable long-term aperture. Proppant is transported in the fracture in dense slurries with high viscosity fluids. The Discrete Element Method is coupled with Computational Fluid Dynamics (DEM-CFD) for studying horizontal proppant flow and transport in narrow fracture zone and proppant settling in a narrow rough granite fracture. High proppant concentrations are usually used in practice, but such systems exhibit frequent particles collisions, especially where the ratio of fracture width and particle diameter is small. The new contact model is built within DEM-CFD code that accounts for effects of fluid lubrication force on particle collisions. A thin layer of fluid between two approaching particles yields the lubrication force that dissipates particle kinetic energy. As a result, in high viscosity fluid particles remain in close vicinity and start to form agglomerate, while fluid flows around it. A comprehensive study that investigates the effects of fluid viscosity, particle and fracture width, and pressure drop and proppant concentration is given. Better understanding of conditions that lead to particle agglomerations and proppant clogging is obtained for horizontal proppant flow and transport and proppant settling in rough granite fracture.
    • Tailored reclaimed water irrigation effects on turfgrass visual quality, rootzone salinity, nitrogen species, and denitrifying microorganisms in the vadose zone

      Munakata Marr, Junko; Cochran, James; Leinauer, Bernd; Lowe, Kathryn; Cath, Tzahi Y. (Colorado School of Mines. Arthur Lakes Library, 2014)
      Water is essential for any functioning society, but drinking water supplies are becoming increasingly insufficient for current and future demands. To alleviate stress on diminishing potable water resources, reclaimed water can be a viable option for replacement in many different schemes, like turfgrass irrigation. Irrigating turfgrass with reclaimed water can reduce demand on potable water supplies and provide essential nutrients for turfgrass health and aesthetic appeal, but can also be associated with nitrate leaching to groundwater and salt accumulation in the rootzone. The purpose of this study was to address concerns surrounding the use of tailored reclaimed water for turfgrass irrigation by measuring turfgrass visual quality, rootzone salinity, nitrogen leaching, and the abundance of denitrifying microorganisms in the vadose zone during irrigation with reclaimed water. In this study, tailored reclaimed water from the Mines Park sequencing batch membrane bioreactor was utilized in a semi-arid environment to irrigate 67% of a turfgrass area, consisting of buffalograss and Kentucky bluegrass, while the remaining 33% was fertilized with granular fertilizer and irrigated with potable water from the City of Golden drinking water treatment plant. For the second study year, all turfgrass plots receiving reclaimed water were tailored with calcium nitrate-nitrogen to achieve 15 mg L-1 of nitrate (NO3--N), while for the third year 50% of the reclaimed water plots were dosed with calcium nitrate to achieve 8 mg L-1 of NO3--N (a more representative concentration in the reclaimed water industry) and the remaining were dosed at 15 mg L-1 NO3--N. The turfgrass plant health was monitored on a weekly basis, with both a qualitative visual assessment and quantitative digital imaging analysis. The accumulation of salts and the fate and transport of NO3- throughout the vadose zone were monitored both from monthly soil pore water samples and soil samples taken before, during, and after the growing season. The abundance of denitrifying microbial communities was also analyzed from soil samples. Throughout this study, 198 x 103 L of potable water and 27 kg of 20-10-5 granular fertilizer were saved by irrigating turfgrass with tailored reclaimed water rather than irrigating with potable water supplemented with granular fertilizer. This study also found no aesthetic differences between using tailored reclaimed water or potable water for turfgrass irrigation, though sodium adsorption ratio values were higher in plots irrigated with reclaimed water (particularly Kentucky bluegrass plots). Nitrate concentrations for both irrigation water types in the soil pore water and soil were higher throughout the spring and fall months, nirK denitrifying genes for both irrigation water types (potable and reclaimed) were seasonally lower in the spring and fall months, and nirK genes were more abundant than nirS genes; nosZ denitrifying genes were not detected.
    • Middle Bakken wettability evaluation using NMR T2 forward modeling and mineralogy

      Wempe, Wendy; Kerimov, Abdulla; Prasad, Manika; Graves, Ramona M.; Kazemi, Hossein (Colorado School of Mines. Arthur Lakes Library, 2014)
      Determination of the wettability of rocks is one of the crucial elements in reservoir characterization. It affects the recovery efficiency, relative permeability, and volumetric reserves calculations. Assuming wrong wetting conditions may result in inaccurate reserves estimation and could be detrimental to improved and enhanced hydrocarbon recovery processes. There are several conventional methods based on fluid displacement, such as USBM and Amott-Harvey, to determine wettability indices. However, these methods are time-consuming and expensive in tight unconventional reservoir core plugs. The approach developed by Looyestijn and Hofman (2005) was applied to determine a wettability index of preserved Middle Bakken core plugs using Nuclear Magnetic Resonance (NMR) transverse relaxation time (T2) data. In addition, a new simple approach was developed to predict likelihood wettability indices using the mineralogical content from X-ray Diffraction (XRD) data. The overall goal of computing wettability index (WI) is to identify ways in which we can significantly reduce the amount of time and cost of developing a representative wettability index in preserved Middle Bakken plugs, without changing the preserved state of the core. The main assumption in our approach is that cleaned, adjacent core properties are representative of the preserved core properties, such as helium connected porosity, absolute air permeability, Dean Stark saturation, mineralogy, etc. NMR T2 measurements in the adjacent, cleaned plugs were measured to develop the pore size distribution that is representative of the preserved plugs. To determine NMR wettability indices of the preserved Middle Bakken plugs, T2 relaxation measurements of preserved, and cleaned adjacent brine saturated plugs, bulk produced brine and oil under ambient conditions are used in the Looyestijn and Hofman (2005) NMR forward model. From NMR forward modeling, it is concluded that the preserved Middle Bakken plugs appear to be intermediate to fairly oil-wet. NMR wettability indices vary between -0.04 and -0.54. Also, to predict the wettability indices of the Middle Bakken plugs, a very simple approach based on previously published contact angle measurements on polished carbonate and silicate mineral surfaces was developed. Our results from this analysis conclude that the given plugs are likely oil-wet. Predicted likelihood wettability indices vary between -0.08 and -0.64. Likelihood wettability indices were matched with NMR wettability indices. The significance of this research study is to reduce time and cost in determining the wetted state.
    • Committing to coal and gas: long-term contracts, regulation, and fuel switching in power generation

      Kaffine, Daniel; Fell, Harrison; Rice, Michael; Davis, Graham A.; Lange, Ian; Navidi, William Cyrus; Rebennack, Steffen (Colorado School of Mines. Arthur Lakes Library, 2014)
      Fuel switching in the electricity sector has important economic and environmental consequences. In the United States, the increased supply of gas during the last decade has led to substantial switching in the short term. Fuel switching is constrained, however, by the existing infrastructure. The power generation infrastructure, in turn, represents commitments to specific sources of energy over the long term. This dissertation explores fuel contracts as the link between short-term price response and long-term plant investments. Contracting choices enable power plant investments that are relationship-specific, often regulated, and face uncertainty. Many power plants are subject to both hold-up in investment and cost-of-service regulation. I find that capital bias is robust when considering either irreversibility or hold-up due to the uncertain arrival of an outside option. For sunk capital, the rental rate is inappropriate for determining capital bias. Instead, capital bias depends on the regulated rate of return, discount rate, and depreciation schedule. If policies such as emissions regulations increase fuel-switching flexibility, this can lead to capital bias. Cost-of-service regulation can shorten the duration of a long-term contract. From the firm's perspective, the existing literature provides limited guidance when bargaining and writing contracts for fuel procurement. I develop a stochastic programming framework to optimize long-term contracting decisions under both endogenous and exogenous sources of hold-up risk. These typically include policy changes, price shocks, availability of fuel, and volatility in derived demand. For price risks, the optimal contract duration is the moment when the expected benefits of the contract are just outweighed by the expected opportunity costs of remaining in the contract. I prove that imposing early renegotiation costs decreases contract duration. Finally, I provide an empirical approach to show how coal contracts can limit short-term fuel switching in power production. During the era prior to shale gas and electricity market deregulation, I do not find evidence that gas generation substituted for coal in response to fuel price changes. However, I do find evidence that coal plant operations are constrained by fuel contracts. As the min-take commitment to coal increases, changes to annual coal plant output decrease. My conclusions are robust in spite of bias due to the selective reporting of proprietary coal delivery contracts by utilities.
    • Pulsed PECVD synthesis of metal dichalcogenide thin films for sustainable energy applications

      Wolden, Colin Andrew; Sentman, Christopher; Agarwal, Sumit; Ohno, Timothy R. (Colorado School of Mines. Arthur Lakes Library, 2014)
      The current world energy demand is ~15 TW and growing, with >85% of production coming from non-renewable sources. The technologies for renewable energy exist, but to achieve this unprecedented scale of production at affordable cost will require developing alternative, earth abundant materials and develop new ways to produce them. Metal dichalcogenide (MS2, MSe2) are a class of semiconductors with unique optical, electrical and catalytic properties with potential applications in sustainability. The aim of this thesis was to develop a pulsed plasma-enhanced chemical vapor deposition (PECVD) as a novel approach for well controlled synthesis of stoichiometric thin films of FeS2 and WS2, establish their intrinsic material properties, and explore their potential in renewable energy applications. First, pulsed PECVD was developed for self-limiting growth of pyrite (cubic FeS2), a potential absorber for thin film solar cells. This material has promising attributes for photovoltaics, but poor device performance experienced to date has been attributed to the difficulty of controlling stoichiometry, avoiding marcasite phase impurities (orthorhombic FeS2), and surface defects. To mitigate these issues, several techniques rely on a post deposition sulfur annealing step, which would not be amenable for large scale manufacturing. In this work, self-limiting growth of FeS2 was accomplished using a continuous flow of Fe(CO)5 and H2S diluted in argon. The onset of thermal CVD was identified to be at ~300 °C, and films produced by thermal CVD contained sub-stoichiometric pyrrhotite. In contrast, pulsed PECVD produced stoichiometric FeS2 films without the need for post-deposition sulfurization. Films contained a mixture of pyrite and marcasite, though the latter could be minimized using a combination of high duty cycle, low temperature, and low plasma power. Conversely, marcasite rich films could be produced using low duty cycles and high plasma power. Both pyrite- and marcasite-rich films displayed similar optical properties with a band gap of ~1 eV and an absorption coefficient of ~10[superscript 5] cm[superscript -1]. Pyrite displayed relatively higher photoconductivity, but the absolute response was poor and solid-state devices fabricated with pyrite showed no rectifying behavior, indicating that this material may not be suitable for PV. Another energy application explored was the use of FeS2 as a cathode for Li batteries because of its high energy density. Here the composition was shown to have an impact. Pyrite films showed high initial discharges near 890 mA*hr/g. Similar capacities were observed initially for marcasite, but these films degenerated after a few cycles. The generality of pulsed PECVD for dichalcogenide synthesis was tested by applying the lessons gained from depositing pyrite to WS2. Stoichiometric WS2 thin films were produced by simply replacing Fe(CO)5 with W(CO)6. Films were deposited by thermal CVD and continuous wave (CW) PECVD for comparison, and it was found that pulsed PECVD delivered the best crystalline quality at combinations of high plasma power and intermediate duty cycles ([tau] = 0.50 - 0.67). This was attributed to the observation that pulsing produced transients with significantly enhanced plasma intensity relative to CW PECVD. Moreover the orientation of the films could be controlled through choice of duty cycle and thickness. WS2 was demonstrated to be catalytically active for hydrogen evolution reaction (HER), as films deposited on fluorine-doped tin oxide with an increased density of edge sites was shown to reduce the HER onset potential from 340 mV to 240 mV vs. RHE. Pulsed PECVD may also be promising for synthesizing WS2 nanocrystals, which could be formed in abundance under certain operating conditions.
    • Acoustic monitoring of hydraulic stimulation in granites

      Gutierrez, Marte S.; Hood, John Calvin; Mooney, Michael A.; Revil, André, 1970- (Colorado School of Mines. Arthur Lakes Library, 2014)
      Enhanced Geothermal Systems (EGS) have substantial potential as a domestic energy source and is well suited as an alternative to diversify the national energy portfolio due to its high levels of heat and recoverable energy. Hydraulic fracture stimulation of low permeability EGS reservoir rock is widely employed to develop this resource and is generally required to make unconventional resources an economically viable resource. Significant challenges for EGS technology include poor connectivity between injection and production wells during stimulation and difficulty predicting fracture growth (Tester, et al. 2006). This, coupled with notable advances in oil and gas recovery, has made hydraulic fracture mechanics the subject of considerable study. Acoustic emissions, or microseisms, contribute greatly to these studies and have been employed on a wide range of topics in rock mechanic studies. At Colorado School of Mines, acoustic emission technology has been employed to monitor stimulation of cubic granite samples under heated and true triaxial stress environments to simulate deep reservoir conditions. Recorded AE activity was used to determine proper location of production well placement while additional analysis on the fracture process using characteristics such as wave amplitude and hit rates were used to identify stages of activity during fracture propagation. Study of the spatial and time dependence of the initiation and growth of rock fractures is critical to understanding the processes that govern fracture behavior and require details that are not accessible to alternative methods of analysis. Acoustic emissions can provide crucial information and represent an important part of rock mechanics studies.
    • Modeling the activated sludge process with gravity clarification using mixed-integer nonlinear programming

      Figueroa, Linda A.; Guerra, Andres; Huggins, Richard G.; Spear, John R.; Munakata Marr, Junko; Eggert, Roderick G.; Cohen, Ronald R. H. (Colorado School of Mines. Arthur Lakes Library, 2014)
      The activated sludge process (ASP) is widely used to remove organics and nutrients from domestic wastewater. Traditional ASP designs are based on a paradigm of strict regulation, cheap energy, and overdesign. Because of this regulation first paradigm, engineers rely heavily on experience based design approaches, empirical studies, and iterative methods to produce ASP designs that meet regulatory targets. This dissertation improves upon these typical design approaches by applying a rigorous mathematical methodology for reducing combined investment and operating costs associated with ASP designs. An explicit mathematical programming model, using the Activated Sludge Model 3 and the double exponential layered settling model, was used to find ASP designs that represent the lowest combined costs. The model was presented as a Mixed-Integer Nonlinear Programming (MINLP) problem with complementarity constraints and solved using a random-multi start method. Uncertain factors were varied singly, and as a group, allowing the model to draw probabilistic inference about the reliability of least-cost ASP designs. Multiple solutions to the problem were obtained that reduced costs compared to a typical design solution by up to 25%. Perturbation of optimization model parameters was used to identify important parameters contributing to cost variability in excess of 40%. Quantitative safety factors (QSFs) were calculated using sample-averaged approximation optimization that included the probabilistic nature of model parameters. Lastly, a robust-optimal ASP design was obtained using QSFs that reduced costs compared to a typical design by 18% and which represented a risk of performance degradation due to uncertainty of less than 5%. Synthesis of the activated sludge and settler models with MINLP produced the following improvements from typical designs: High numbers of solutions improved confidence that MINLP methods can be used to design and control ASPs more efficiently and at a lower cost. Uncertainty was decreased by identifying important parameters that significantly impact optimal ASP costs. QSFs were used to decide which unit processes and operations required overdesigned to account for parameter uncertainty. In addition, the inclusion of equilibrium conditions as complementarity constraints increased model credibility as compared to earlier ASP optimizations.
    • Block copolymers for alkaline fuel cell membrane materials

      Knauss, Daniel M.; Li, Yifan; Boyes, Stephen G.; Wu, David T.; Herring, Andrew M.; Dorgan, John R. (Colorado School of Mines. Arthur Lakes Library, 2014)
      Alkaline fuel cells (AFCs) using anion exchange membranes (AEMs) as electrolyte have recently received considerable attention. AFCs offer some advantages over proton exchange membrane fuel cells, including the potential of non-noble metal (e.g. nickel, silver) catalyst on the cathode, which can dramatically lower the fuel cell cost. The main drawback of traditional AFCs is the use of liquid electrolyte (e.g. aqueous potassium hydroxide), which can result in the formation of carbonate precipitates by reaction with carbon dioxide. AEMs with tethered cations can overcome the precipitates formed in traditional AFCs. Our current research focuses on developing different polymer systems (blend, block, grafted, and crosslinked polymers) in order to understand alkaline fuel cell membrane in many aspects and design optimized anion exchange membranes with better alkaline stability, mechanical integrity and ionic conductivity. A number of distinct materials have been produced and characterized. A polymer blend system comprised of poly(vinylbenzyl chloride)-b-polystyrene (PVBC-b-PS) diblock copolymer, prepared by nitroxide mediated polymerization (NMP), with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) or brominated PPO was studied for conversion into a blend membrane for AEM. The formation of a miscible blend matrix improved mechanical properties while maintaining high ionic conductivity through formation of phase separated ionic domains. Using anionic polymerization, a polyethylene based block copolymer was designed where the polyethylene-based block copolymer formed bicontinuous morphological structures to enhance the hydroxide conductivity (up to 94 mS/cm at 80 °C) while excellent mechanical properties (strain up to 205%) of the polyethylene block copolymer membrane was observed. A polymer system was designed and characterized with monomethoxy polyethylene glycol (mPEG) as a hydrophilic polymer grafted through substitution of pendent benzyl chloride groups of a PVBC-b-PS. The incorporation of the hydrophilic polymer allows for an investigation of the effect of hydration on ionic conductivity, resulting in the increase in membrane water affinity, enhancement of conductivity and reduced dependence of conductivity on relative humidity. A study of crosslinking of block copolymers was done wherein the crosslinking occurs in the non-matrix phase in order to maintain mechanical properties. The formation of a cationic crosslinked structure improves the mechanical integrity of the membrane in water while showing little deleterious effect on ionic conductivity and mechanical properties.
    • Advanced characterization techniques in understanding the roles of nickel in enhancing strength and toughness of submerged arc welding high strength low alloy steel multiple pass welds in the as-welded condition

      Liu, Stephen; Sham, Kin-Ling; Olson, D. L. (David LeRoy); Mishra, Brajendra; Findley, Kip Owen; Steele, John P. H.; Young, George (Colorado School of Mines. Arthur Lakes Library, 2014)
      Striving for higher strength along with higher toughness is a constant goal in material properties. Even though nickel is known as an effective alloying element in improving the resistance of a steel to impact fracture, it is not fully understood how nickel enhances toughness. It was the goal of this work to assist and further the understanding of how nickel enhanced toughness and maintained strength in particular for high strength low alloy (HSLA) steel submerged arc welding multiple pass welds in the as-welded condition. Using advanced analytical techniques such as electron backscatter diffraction, x-ray diffraction, electron microprobe, differential scanning calorimetry, and thermodynamic modeling software, the effect of nickel was studied with nickel varying from one to five wt. pct. in increments of one wt. pct. in a specific HSLA steel submerged arc welding multiple pass weldment. The test matrix of five different nickel compositions in the as-welded and stress-relieved condition was to meet the targeted mechanical properties with a yield strength greater than or equal to 85 ksi, a ultimate tensile strength greater than or equal to 105 ksi, and a nil ductility temperature less than or equal to -140 degrees F. Mechanical testing demonstrated that nickel content of three wt. pct and greater in the as-welded condition fulfilled the targeted mechanical properties. Therefore, one, three, and five wt. pct. nickel in the as-welded condition was further studied to determine the effect of nickel on primary solidification mode, nickel solute segregation, dendrite thickness, phase transformation temperatures, effective ferrite grain size, dislocation density and strain, grain misorientation distribution, and precipitates. From one to five wt. pct nickel content in the as-welded condition, the primary solidification was shown to change from primary delta-ferrite to primary austenite. The nickel partitioning coefficient increased and dendrite/cellular thickness was refined. Austenite decomposition temperatures into different ferrite products were also suppressed to refine the effective ferrite grain size with increasing nickel. Finally, dislocation density and strain increased and a more preferred orientation behavior was observed. At five wt. pct nickel, a precipitate in the form of MnNi3 or FeNi3 was observed. Its presence in both inter and intragranular regions enhanced strength and toughness by limiting the ferrite grain size and precipitation strengthening.
    • Hydrogen induced damage in pipeline steels

      Findley, Kip Owen; Angus, Garrett R.; Matlock, David K.; Speer, J. G. (Colorado School of Mines. Arthur Lakes Library, 2014)
      The hydrogen induced cracking (HIC) resistance of several grades of plate steels was investigated using electrolytic hydrogen charging. HIC generated by electrolytic charging was also compared to the industrial standard test for HIC, the NACE standard TM0284. The electrolytic charging (EC) apparatus was designed to optimize the reproducibility of the HIC results and the robustness of the components during long charging times. A characterization study on the EC apparatus was undertaken. Alterations to applied current density and charging time were conducted on a highly susceptible plate steel, 100XF, to assess HIC damage as a function of charging conditions. Intermediate current densities of 10 to 15 mA/cm2 produced the greatest extent of cracking without significant corrosion related surface damage. The hydrogen charging time did not greatly affect the extent and depth of cracking for test times between 24 to 48 hours. Thus, for subsequent experiments, the applied current density was set to 15 mA/cm2 and the charging time was set to 24 hours. Plate steel grades X52, X60, X70, and 100XF were prestrained in tension to various levels and then electrolytically charged with hydrogen or tested with the NACE standard TM0284 test (solution A) saturated with H2S(g) to induce HIC. Prestrain was introduced to assess its impact on HIC. Hydrogen damage was quantified with the crack ratios defined in the NACE Standard TM0284. The results from the EC and NACE methods were very comparable to one, with respect to the magnitude of cracking and the trends between alloy and pre-strain conditions observed. Both methods showed that HIC substantially increased for the high strength 100XF steel compared to the lower strength alloys. This is consistent with NACE recommendations for HIC resistance steels, which suggests that alloy strength should be less than 116 ksi (800 MPa) or 248 HV (22 HRC). The HIC results were largely independent of the pre-strain levels imposed within the statistical accuracy of the evaluation method employed. The total, irreversibly trapped, and diffusible hydrogen amounts were measured or estimated for each condition using a LECO interstitial analyzer and the American Welding Society method for measuring diffusible hydrogen concentrations. The total amount of diffusible hydrogen was highest for the 100XFalloy and lowest for the X52 alloy. The amount of trapped hydrogen was similar for all the alloys, implying that the number of irreversible trap sites were comparable. However, the diffusible hydrogen content was greatest for the 100XF alloy and lowest for the X52 alloy, which is believed to be related to the relatively high amount of grain boundary area and high dislocation density of the 100XF alloy. A qualitative analysis on the effect of microstructure and nonmetallic inclusions on HIC was performed and produced results that confirmed findings from literature. Cracking was observed around nonmetallic inclusions such as sulfides and oxides in the metal matrix. For materials in which both inclusion types were present, X60 and X70, HIC originated and was observed most often around sulfide type inclusions.
    • Shape correspondences: local to global

      Szymczak, Andrzej; Liang, Luming; Petrella, Anthony J.; Mehta, Dinesh P.; Sava, Paul C.; Hoff, William A. (Colorado School of Mines. Arthur Lakes Library, 2014)
      Finding correspondences between two or more shapes is a fundamental and still unsolved problem in computer graphics and computer vision. Typically, one is interested in finding correspondence between similar objects (e.g. shapes representing different four-legged animals) or deformed versions of the same object (e.g. model of a human in different poses). The problem often suffers from ambiguities, which are brought about by shape symmetry, point slippage, edge stretching and shrinking. Most approaches to shape correspondence put restrictions on the deformation model: for example, matching techniques tailored for near isometric, area preserving or articulated deformations have been developed. Ideally, one would like to design an optimization based approach that would produce an optimal correspondence subject to constraints on the deformation model. However, setting up an optimization problem that can reliably provide a high quality solution and, at the same time, is computationally tractable, has been a major challenge. The correspondence problem solutions are often broken into three stages: 1. extract salient features in the input shapes; 2. perform rough matching of the salient features using descriptors; 3. globally register two shapes based on the rough matching. We propose several new contributions to different stages of this framework. First, we design a local shape descriptor based on the classical Spin Image. Our descriptor (Spin Contour) is essentially the contour of the original Spin Image. It provides considerably higher quality matching results while making comparisons between the descriptors more efficient. Second, we introduce the Geodesic Spin Contour, a variant of the Spin Contour suitable for non-rigid near-isometric shape matching by replacing the Euclidean-based spin coordinates with geodesic-based coordinates. This descriptor compares favorably with state-of-the-art local shape descriptors when for matching shapes deformed in a near-isometric manner. The Geodesic Spin Contour is suitable for partial matching, i.e. matching shapes with missing parts. Third, we develop a fully automatic surface registration scheme. This method matches near-isometric shapes by globally minimizing the geodesic distance differences between pairs of features. Finally, we extend the Iterative Closest Point (ICP) scheme to nonrigid non-isometric registration. Instead of using 1-1 mapping, we use many-many mapping to recover the nontrivial underlying deformation.
    • Lightweight Mg-based composites with thermodynamically stable interfaces by in-situ combustion synthesis

      Kaufman, Michael J.; Jo, Ilguk; Gorman, Brian P.; Vidal, Edgar E.; Mustoe, Graham G. W.; Midson, Stephen (Colorado School of Mines. Arthur Lakes Library, 2014)
      Lightweight Mg-based composites have been produced by in-situ combustion synthesis of the Al-Ti-C reaction system. The characteristics of the in-situ composites were investigated in terms of phase evolution and interfacial stability using various analysis techniques. The structural analysis results showed that full conversion of the Al-Ti-C reactants into spherical TiC reinforcements with sizes around 1[mu]m was achieved by the combustion reaction. In-situ formed TiC had less oxygen and higher Al contents at the interface than ex-situ formed TiC; these clean interfaces with an Al layer on the reinforcements were shown to yield interfacial stability. For these reasons, the in-situ composites exhibited higher theoretical densities and also good mechanical properties compared with ex-situ produced composites. The interfacial characteristics of molten Mg with the Al-Ti-C reactants and the commercial TiC+Al substrates were evaluated using an infiltration technique under an argon atmosphere. Infiltration length increased with time at temperature, yielding activation energies (Ea) for each system. The value of Ea for the Al-Ti-C system (307.31kJ/mol) is lower than that for the other system (350.84kJ/mol); the high Ea value indicates that the infiltration is not a simple viscosity-controlled phenomenon but involves a chemical reaction. Formation of the Al3Ti phase was observed from the crystal structural analysis of the infiltrated area; thus, existence of reaction promoting the wetting of Mg. The phase evolution, reaction mechanism and kinetics of the Al-Ti-C reaction were studied using DSC and HT-XRD. It was confirmed that, along with the melting of Al, there was formation of Al3Ti by reaction between Al and Ti. A detailed structural analysis indicates that, the reaction mechanism involves melting of Al followed by formation and growth of Al3Ti, which then contacts the graphite powder and initiates the combustion reaction. The effect of important process parameters, such as the Al content and the reactant sizes, on the microstructure of the resulting in-situ composites is discussed. Feasibility and castability of the composites were investigated by high pressure die casting the composite preforms into automotive parts and durability tests were conducted on the cast parts.
    • Rock fall mitigation for an open pit mine experiencing substantial rock fall from overblasting

      Higgins, Jerry D.; Cybulski, Paige G.; Lupo, John F.; Santi, Paul M. (Paul Michael), 1964- (Colorado School of Mines. Arthur Lakes Library, 2014)
      Rock fall is a common hazard in open pit mines causing safety concerns for workers, transportation routes and may adversely affect mine production. To reduce and mitigate rock fall hazards, a benched slope design is normally used and, occasionally, additional mitigation may be necessary in areas with excessive rock fall hazards. Newmont's Boddington Gold Mine in Australia is experiencing substantial rock fall in the south portion of their open pit mine due to rock damage from blasting resulting in highly fractured wall rock. This has increased the volume of rock fall experienced in the mine, and the rock fall has caused accumulation of debris on benches and crest loss, reduced bench width, in some parts of the mine by as much as 40 percent. The loss of bench width has reduced the effectiveness of the benches for rock fall mitigation and allowed rock fall to travel much farther down slope than desired for safety. Because of these conditions, there is a 20 meter exclusion zone near the rock walls in the mine, reducing production and impairing safety conditions. The mine is currently mitigating the rock fall by draped mesh, spot bolts, cable lashing and benches originally excavated at 8 meters in width. As the open pit is deepened, a more permanent rock fall mitigation method is desired. Newmont proposed several modified bench designs to be evaluated. The new bench designs were evaluated by modeling rock fall on the existing and proposed bench designs using the Colorado Rock Fall Simulation Program (CRSP) and RocFall. Newmont provided rock fall data for modeling that included the normal coefficient of restitution and rock fall video from the open pit. Rock fall kinetic energies, bounce heights and velocities on existing benches and proposed benches were examined on five cross-sections from the open pit to assess which bench design had the most efficient rock fall mitigation. The importance of testing the normal coefficient of restitution and use of rock fall video for rock fall modeling were also examined, as well as the slope steepness versus rock fall run out with the new bench designs.
    • Evaluation of low salinity waterflooding in carbonates using simulation and economics, An

      Hoffman, B. Todd; Althani, Mohammed G.; Tutuncu, Azra; Wu, Yu-Shu (Colorado School of Mines. Arthur Lakes Library, 2014)
      Improving oil recovery by low salinity waterflooding (LSWF) has gained a lot of attention in the last two decades. The effect of LSWF was demonstrated by coreflooding experiments in several core samples from sandstone and carbonate reservoirs around the world. This effect has also been shown in a field scale by some field pilot trials. While the exact mechanisms that cause increased recovery due to LSWF are not fully understood, most agree that changes in wettability and interfacial tension are the reasons that LSWF perform better than high salinity waterflooding (HSWF). LSWF can therefore be modeled by changing the property that determines the effect of wettability in fluid flow equations, which is the relative permeability. In this research, coreflooding results from a carbonate reservoir are used to find the relation between the relative permeability curves for HSWF and LSWF. A numerical simulation model of the coreflooding experiment showed that the relative permeability for the LSWF can be estimated by changing only one parameter in the Corey-type relative permeability equation of the HSWF: residual oil saturation. An application of this result was performed on a full-field simulation model to evaluate the effect of LSWF using simulation and economics. The field model was built for a carbonate reservoir in the Madison formation of Wyoming. The simulation results showed an increase in the recovery by more than 5% of the oil in place by using LSWF instead of HSWF. An economic analysis was performed to determine if the additional oil would justify the expense of making low salinity water. With proper assumptions of the construction and operating costs of a water desalination plant, a development plan with LSWF showed a higher net present value than a development with HSWF. This research provides a practical approach to evaluate the effect of LSWF on certain fields using simulation. It provides a screening tool to quickly evaluate the oil gain from the LSWF before spending money on core samples testing for further research.
    • Refining magnetic amplitude methodology for use in the presence of remanent magnetization

      Li, Yaoguo; Coleman, Camriel A.; Andrews-Hanna, Jeffrey C.; Swidinsky, Andrei (Colorado School of Mines. Arthur Lakes Library, 2014)
      The magnetic method is a common geophysical technique used to detect and image magnetically susceptible sources. Interpretation of magnetic data can be difficult in the presence of remanent magnetization. Remanence can alter the total magnetization to an unknown direction and hinder the interpretation of 3D susceptibility models by leading to incorrect shape and size of the sources. The magnetic amplitude method is an effective tool for interpretation of magnetic data in such settings. Amplitude data are the amplitude of the anomalous magnetic field and are weakly dependent on magnetization direction. The data are often used to bypass challenges posed by the presence of remanently magnetized materials as they not rely on known magnetization direction. 3D amplitude inversion plays a particularly important role in quantitative interpretation of magnetic data affected by remanence. Inversion of amplitude data results in an effective susceptibility model capable of delineating geologically interpretable anomalies where susceptibility modeling approaches struggle. Challenges remain, however, with the use of amplitude method. The first challenge is that a methodology for determining the noise statistics relating to amplitude data and associated inversion has not been well developed, hindering the ability to properly estimate the data misfit associated with an inverse model and therefore the model itself. The second challenge is amplitude data, while successful at delineating remanent source bodies, do not contain direction information. This limitation makes it difficult to recover dipping structures affected by remanence. These challenges are the focus of my work. I investigate amplitude error statistics to address the first challenge. I analytically derive the propagation of errors associated with calculating amplitude data and confirm the derivation by implementing parametric bootstrapping. The investigation reveals that the noise in amplitude data is approximately equal to that of the total-field anomaly data. Having characterized the relationship between noise in total-field anomaly and amplitude data, I estimate the noise in total-field anomaly datasets. Using synthetic and field data, I demonstrate that equivalent source technique can recover accurate estimates of noise in magnetic datasets. I use this estimate for inversion of amplitude data to aid in recovering optimal models. I show that noise in magnetic datasets can be estimated by equivalent source technique and that the estimate can be used in inversion resulting in increased confidence in the recovered model. Following this work, I address the second challenge of estimating the magnetization direction. I implement a method to recover the missing direction information using an effective susceptibility model. I segment the amplitude inversion into distinct anomalous bodies and assume a constant magnetization direction for each. Assuming that the effective susceptibility provides a sufficiently accurate representation of the magnitude of the magnetization, I then solve a least-squares problem to recover the magnetization directions of multiple source bodies simultaneously. This approach is able to recover magnetization direction from datasets containing both single and multiple anomalies. The direction estimate can be used in susceptibility inversion to recover accurate dipping structures of anomalies. My work improves amplitude method by increasing confidence in interpretation and by broadening the scope of the method. I demonstrate that a reliable noise estimate can be obtained using equivalent source technique and used to recover an optimal effective susceptibility model. Using the effective susceptibility model, magnetization direction can then be estimated for single and multiple anomaly datasets. Following my research, amplitude data can now be used to fully characterize magnetization in both magnitude and direction.
    • Three-dimensional facies and process-regime variability in shelf-edge deltas: implications for shelf-margin progradation and deepwater sediment delivery

      Plink-Björklund, Piret; Laugier, Fabien J.; Nummedal, Dag; Carr, Mary; Hoffman, B. Todd; Sarg, J. F. (J. Frederick) (Colorado School of Mines. Arthur Lakes Library, 2014)
      Prograding shelf-slope systems are the main constituents of continental margins. In particular, shelf-edge deltas are the primary mechanism by which shelf margins are constructed and play a critical role in the delivery of sediment to the shelf edge, as well as facilitating sediment dispersal to the slope and basin floor. The overall architecture of shelf-edge deltas and their association to the shelf margin and deepwater deposits is well-understood from seismic data; however, much remains to be understood about the mechanisms by which sediment is brought to and partitioned along the shelf edge, and downslope. The shelf edge is a zone of significant gradient change separating a relatively flat-lying shelf from a steeper slope region, and has a physiographic expression that can be observed in 2-D and 3-D seismic data and in seismic-scale, dip-parallel, continuous outcrops; however, the physiographic shelf edge needs to be defined in well log datasets or non-continuous outcrops. Defining this zone of gradient change is essential because it segregates areas dominated by shelf currents and waves from areas where sedimentation is governed by gravity-driven processes. Moreover, the location of the shelf edge must be known in order to understand the linkage between shelf-edge deltas and their coeval slope and basin floor deposits. In the Tanqua depocenter of the Karoo Basin (South Africa), the Permian Kookfontein Formation is exposed at seismic scale in 3-D outcrops on a series of mountainsides. The Kookfontein Formation consists of stacked shelf-slope clinothems that occur as gently basinward-dipping, generally upward-coarsening packages that can be walked out across 21 km in depositional-dip and depositional-strike orientations. The quality and aerial extent of the exposure permits investigation at multiple stratigraphic scales and allows detailed analyses of the 3-D linkage between sedimentation from the shelf to the slope. This study (Chapters 2-3) focuses on three clinothems that prograded to the northeast. First, two independent methods were used to identify the shelf-edge position: the shelf-edge zone was determined by facies distribution, as well as clinothem thickness changes and gradient breaks. In particular, results from this dissertation show that a transition from predominantly shelf-current and wave deposits to gravitational deposits, together with the increase in degree and style of soft-sediment deformation, correlates with the position of gradient increase and clinothem thickening, and thus defines the shelf-edge position. Recognition of the shelf edge permits 3-D documentation of the distribution of facies along the shelf edge and from shelf to slope. Two main varieties of shelf and shelf-edge depositional environments are recognized along the Kookfontein shelf margin and indicate spatial variation in process-regime dominance along the shelf edge. In places, the shelf and shelf-edge deposition occurred from river-dominated deltas with gravitational delta-front deposits. Basinward of such shelf-edge zones, the slope is sand-rich, channelized (with channels widening downslope), and rich in slump and collapse features. In other places, the shelf and shelf-edge deposits indicate considerable tidal reworking. This tidal influence was recognized by the occurrence of facies with bidirectional paleocurrent signatures, thickening-thinning trends that approach a neap-spring tidal cyclicity, and deposits that indicate repeated and systematic fluctuations in current velocities. Tidal deposits occur as thin, localized depositional units, as well as laterally-extensive zones along the shelf edge. Thin, localized packages of tidal deposits associated with mouth bars and distributary channels indicate that tidal currents were locally amplified in topographically-restricted areas. Laterally-extensive zones of significant tidal influence indicates large-scale topographically-restricted areas, possibly between delta lobes, or that decreased fluvial drive allowed tidal currents to have greater effects. Basinward of tide-influenced shelf-edge zones, the slope is largely devoid of sand, shelf-edge-delta deposits are thinner, and only one small channel was observed. This analysis suggests that process-regime variability along the shelf edge exercises significant control on the character of shelf-edge progradation, slope channelization, and sediment delivery to the deepwater areas. Though process regime variability is locally observed along the shelf edge, the shelf-edge deltas of the Kookfontein Formation are fluvial-dominated. Data from Clinothem 6 is compared to high-resolution outcrops datasets from other fluvial-dominated shelf-edge delta-to-slope systems (Chapter 4). These outcrops include the Eocene Battfjellet Formation in the Central Basin of Spitsbergen; the Eocene Sobrarbe Formation in the Ainsa Basin, Spain; and the Fox-Hills-Lewis Formations in the Washakie Basin, Wyoming, U.S.A. Results from this chapter highlight greater variability in the processes of delta progradation, shelf-margin accretion, and sediment delivery than previously recognized in fluvial-dominated shelf-edge deltas. In particular, this study indicates that within fluvial-dominated shelf-edge deltas, processes of shelf-margin accretion and deepwater sediment delivery can be controlled by sediment failure, hyperpycnal flows, episodic bypass from distributary channel avulsions, or a combination thereof. This investigation also includes a case study of deriving simple geologic concepts from outcrops, and integrating them with quantitative outcrop data into novel rule-based reservoir models to address the impact of fine-scale stratigraphy on flow performance in deepwater lobe systems (Chapter 5). Data was collected from well-exposed outcrops of the Permian Skoorsteenberg Formation in the Tanqua Karoo Basin. Simple geologic concepts of lobe hierarchy, within-bed lithofacies distribution, and bed amalgamation were derived from outcrop analysis and form the foundation of the models. Two end member models were constructed: 1) a complex of deepwater lobe elements that were only subdivided into lobe sandstone and overbank mudstone; and 2) a complex of deepwater lobe elements constructed from individual sedimentation units with distinct trends in lithofacies and associated rock properties. Simplified flow performance simulated within each model highlights the significant impact that heterogeneity related to individual bed-scale trends within the lobe elements has on reservoir performance at the complex scale.