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Evaluation of Multiple Approaches for Solidification Modeling of Advanced Nuclear Reactor Coolants
No full textThis dissertation focuses on developing and validating numerical tools for modeling solidification phenomena in advanced nuclear reactor coolants. The primary objective is to offer cost-effective alternatives to experimental studies and enable rapid simulation of multiphysics reactor transients. To achieve this, a hierarchical structured framework is established. High-fidelity models or experiments inform intermediate-fidelity data, which, in turn, provide training data for multidimensional coarse-mesh models capable of running on a single core and delivering fast results. The first phase of this research focuses on developing a solidification model using the Lattice Boltzmann Method (LBM) for 3D internal transient solidification modeling of Generation-IV nuclear reactor coolants. This model, based on the Total Enthalpy Model coupled with the Partially Saturated Method, addresses both high and low Prandtl numbers under laminar forced conditions. Key findings include the utility of the LBM total enthalpy Partially Saturated Method for solidification modeling, faster computational times compared to conventional Finite Volume Computational Fluid Dynamics (FV-CFD) methods for low Prandtl numbers, and the identification of stability limitations for high Peclet numbers.
In the second phase, we develop an intermediate-fidelity model based on a FV-CFD RANS enthalpy-porosity method, addressing high and low Prandtl numbers. We validate it against experimental data for high Prandtl numbers and against a high-fidelity LBM-LES model for low Prandtl numbers. Incorporating interface turbulence viscosity damping addresses RANS models��� tendency to overestimate heat transfer, enhancing their practical utility despite slightly reduced predictive accuracy compared to LES models.
In the third phase, we introduce a fine-to-coarse mesh upscaling technique enhanced by physics-based closure terms. Employing a data-driven strategy, we fine-tune the model���s closure coefficients utilizing the FV-CFD RANS intermediate-fidelity model on fine meshes. The calibrated coarse-mesh model reliably predicts essential performance metrics, including pressure drop, velocity profile, outlet temperature, and solid thickness distribution. This multidimensional approach marks a notable progression from conventional 1D methods, offering substantial time savings compared to fine-mesh models.
The highlights of this dissertation include (i) an innovative solidification model coupled with turbulence modeling based on LBM (ii) the validation and enhancement of an intermediate-fidelity RANS solidification model by incorporating a turbulence viscosity-damping source, preventing turbulence overproduction at the interface (iii) the development of a fine-to-coarse mesh upscaling solidification model, incorporating physics-based closure terms calibrated through a data-driven approach
Using X-Ray Computed Tomography to Quantify Pore Characteristics in a Shrink-Swell Clay
No full textShrink-swell soils are those which shrink when drying and swell when wetting. This creates cracks that may measure >10 cm in width and >1 m in depth when the soil is dry. These soils have low permeability when wet but allow rapid water movement through cracks when dry. Because of their dynamic nature, these soils can cause infrastructure damage, crush crop roots, and lead to unpredictable rates and concentrations of contaminant transport. Current numerical models are not able to accurately represent the dynamic pore characteristics, and often soil shrink-swell processes are not taken into consideration at all. To better model the potential impacts of dynamic pore networks in a shrink-swell soil, it is necessary to quantify changes in pore characteristics���size distribution, connectivity, and tortuosity���that accompany changes in soil water content. X-ray computed tomography (CT) scanning is a technology used to visualize the internal structure of an object and can be used to observe and quantify porosity in a soil sample. The goal of this project is to improve our understanding of dynamic porosity in shrink-swell soil, using X-ray CT scanning to quantify crack patterns and sizes in shrink-swell soils at multiple water contents. Three intact soil cores were saturated, scanned using Xray CT, then dried and scanned again. Dragonfly, ImageJ, and MATLAB software were used for image processing and analysis of structural and porosity changes within the cores. Our results show a higher number of pores with volumes >1 mm^3 and pores with lengths >5 mm in the dried cores compared to the saturated. A higher connectivity of these pores was observed in the dried cores compared to the saturated. The knowledge gained through this study regarding changes in porosity between saturated and dried cores will improve our understanding of shrink-swell soils, contributing to improvements in shrink-swell soil���s role in regulating hydrological processes
Supplementation of Oral Probiotics to Freshly Weaned Lambs When Transitioning to a High Concentrate Diet in Conjunction with Parasite Resiliency to Copper Wire Boluses
No full textRumen health is vital to post weaning health and performance in all ruminant species. Sheep are fed high concentrate diets to improve growth rate, however, these high concentrate diets can lead to acidosis, or even mortality, if not fed correctly. Acidosis is caused by the increased consumption of grain and a drop in pH. The hypothesis that administering a probiotic supplement to lambs prior to and during the feeding period would improve the post-weaning gain as well as decrease mortality. For this study, 93 finewool lambs (n=93; females, n=45, males, n=48) were weaned at approximately 90 days of age and had an average body weight (BW) of 24.7 Kg. Each lamb was assigned randomly to one of the three treatment groups: Control (CON), Treatment 1 (TRT 1), and Treatment 2 (TRT 2). Lambs assigned to TRT 1 and TRT 2 received an oral dose of probiotics (ProBios, Menomonie, WI), which contained four lactic acid producing bacteria: Enterococcus faecium, Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus plantarum. Lambs in CON received 0g of Probios (n=31, females, n=15; males, n=16), lambs in TRT 1 were administered 10g of Probios on Day 0 (n=31, females, n=15; males, n=16), and lambs in TRT 2 were administered 10g of Probios on Day 0 and Day 7 (n=31, females, n=15; males, n=16). Lambs were housed in groups of three in a fully covered barn with automatic waters. Lambs were sorted into groups by treatment, sex, and initial weight. Lambs were limit fed for 12 days with hay to aid in transition to the high concentrate diet; after the 12 days, they were then fed ad libitum. For six weeks, body weight (BW) and FAMANCHA (FAM) scores were collected. Blood was also collected for the first four weeks and fecal egg counts (FEC) were collected on weeks 1, 4, 5, and 6. There was no interaction between treatment group and weight gain, however, female lambs were statistically lighter when compared to male lambs. Female lambs had a lower FAM score when compared to males.
An additional study of Copper Oxide Wire Particle Boluses (COPWs) was conducted to determine the effectiveness when compared to regularly used anthelmintics. Lambs received an oral drench of Valbazen, Cydectin, and Prohibit (n=44) or a COWP Bolus (n=41). After week one lambs who received oral anthelmintics had a statistically lower FEC when compared to lambs who received COPWs. There was not a significant difference between COPWs and dewormer by Week 2
Probabilistic Clustering Methods for Complex Data and Related Topics
No full textProbabilistic clustering involves identifying mutually exclusive subsets of data in a probabilistic manner by characterizing the probability distribution on the space of partitions, enabling uncertainty quantification. Random partition models serve as prior probability models for probabilistic clustering, which are closely connected to Bayesian nonparametric models involving discrete random structures. This dissertation aims to contribute to the existing literature on probabilistic clustering and related topics by introducing new key concepts and novel methodologies.
First, we offer new perspectives on exchangeable random partition models based on the concept of balancedness and risk equilibrium/penalization priors with respect to a loss function. The balancedness property provides a better understanding of what probabilistic clustering model works better and what does not for different applications. The notion of risk equilibrium and penalization priors, which are not limited to clustering problems, provide the development of objective and regularized prior model probabilities in light of the effect of loss functions.
Next, we suggest Bayesian hierarchical models with non-exchangeable random partition models associated with a graph that represents complex dependence structures. We start by introducing the low-rank horseshoe prior based on random spanning trees, which simultaneously detects structured sparsity and smoothness of high-dimensional parameters associated with the graph. Also, we introduce the graph product partition model where a probability of partition is defined as a product of cohesion functions capturing internal and external connectivity. This formulation does not rely on graph generative assumptions and can be used as a robust alternative for the probabilistic clustering of graphs with node attributes.
Finally, we propose the logistic-beta process, whose logistic transformation yields a stochastic process with common beta marginals that have significant computational benefits. It has great potential in applications to dependent Bayesian nonparametric models involving beta distributions, related to probabilistic clustering of non-exchangeable data. We illustrate with a Bayesian density regression problem based on the newly proposed logistic-beta dependent Dirichlet process
Colonial Calamities: The Politics of U.S. Disaster Relief and Economic Development in Puerto Rico, 1898-1979
No full textWhen Hurricanes Maria and Fiona battered Puerto Rico in 2017 and 2022, it reopened public conversations about Puerto Rico���s colonial status. With thousands out of electricity, displaced from their homes, and ruined economically, then- and only then- did U.S. policymakers debate the appropriate humanitarian response. In addition, the disaster relief aid overseen by the Federal Emergency Management Agency (FEMA) provided only temporary solutions but did nothing to address the ongoing structural issues of Puerto Rico. This type of response was not a new phenomenon. It was just the latest chapter in a century-long history of United States disaster relief operations that continually reinforced Puerto Rico���s colonial status.
This dissertation Colonial Calamities: The Politics of U.S. Disaster Relief in Puerto Rico, 1898-1979, is the first to explore the history of American disaster relief in Puerto Rico from the period 1898-1979. Disasters provide a window to reveal how structures of power determined who ���deserved��� aid and what conditions were attached to it. I argue that after disasters, the relief policies undertaken by U.S. government institutions were justifications to strengthen influence in the region and actually made Puerto Ricans more vulnerable to disasters. The American military, Red Cross, and colonial administrators prioritized short-term mitigation strategies that served U.S. strategic and economic interests. In this way the American colonial government constructed and maintained Puerto Rican vulnerability to disasters and the vagueness of status as subjects/citizens. American policymakers perpetuated the idea that if Puerto Ricans were poor and vulnerable to disasters, it could not have anything to do with the United States or colonialism. However, policymakers also thought that if Puerto Rican poverty and vulnerability to disasters was caused by Puerto Ricans themselves, then the U.S. and only the U.S. could help them. Together, these ideas inscribed Puerto Ricans as inferior, borderline citizens, while at the same time rejecting them as completely alien. To combat these positions and policies, Puerto Ricans developed local networks to promote solidarity and conduct disaster relief without relying on American agencies. This strategy proved important during the latter part of the twentieth century with the increasing effects of climate change causing more frequent disasters
A Tide That Raises All the Boats: The Soviet Threat, NATO, and Marine Corps Innovation, 1969-1991
No full textAfter suffering the bitter defeat of the Vietnam War, the United States Marine Corps entered a nearly two-decade long period of reform and modernization. By the end of the Cold War in 1991, the service had markedly improved its training, equipment, doctrine, and proficiency for mid- and high-intensity conventional conflicts. Notably, the capabilities gained during the 1970s and 1980s remained in place well into the twenty-first century, marking this era as one comparable to the service���s most storied periods of innovation. The existing historical literature of the late-Cold War Marine Corps ascribed the service���s rise either to its military culture or crises in Southwest Asia. Such interpretations, however, overlook the impetus provided by the Soviet military threat and North Atlantic Treaty Organization (NATO) missions. An analysis of multi-archival and multi-service sources ��� including declassified war plans and studies, strategies and concepts, congressional testimony, exercise reports, student papers, journal articles, memoirs, oral histories, interviews with participants, commentary from NATO allies, and related secondary histories ��� demonstrates that the Soviet threat and NATO missions were salient driving influences on Marine Corps innovation during this period. This impetus, ever present, often unacknowledged, and occasionally even strenuously denied, provided the service with a unique azimuth of innovation, one qualitatively different from the id��e fixes of other militaries. The resulting service strategy served as a ���tide that raises all the boats,��� a focus on the severest test ��� a Soviet anti-amphibious defense in Europe ��� that simultaneously rehabilitated the Corps��� political relevance, modernized readiness, and inspired future concepts, all while still preserving flexibility for global employment across the spectrum of conflict. Accordingly, at Cold War���s end, observers praised the Corps as the ���most general-purpose force of the general-purpose forces,��� a service particularly well-suited for the uncertain new security environment. This dissertation advances historical interpretations of the Marine Corps and military innovation in the late-Cold War and demonstrates the effectiveness of threat-based strategies of innovation, providing a case study of value both to scholars of military innovation studies and strategic practitioners
Shell Designs for Tailoring Dissolution Rates of Selective Laser Sintered Pharmaceutical Printlets
No full textWith the advent of personalized medicine, 'Just In Time' manufacturing of solid dosage pharmaceutical formulations is necessary, especially for a pediatric population that has a rapidly changing physiology. Solvent-free additive manufacturing is a promising approach that lends geometric and compositional flexibility to the process. The objective of this study is to investigate the behavior of shell-based designs, predominantly in their ability to affect dissolution rates of additively manufactured (AM) pharmaceutical pills/tablets (printlets). The primary motivation for this work lies in being able to leverage the tailorability of the AM process to control the geometric design of printlets and thus ���tune��� the eventual dissolution rates of these pills in a biological medium. For this, Selective Laser Sintering (SLS) was used to manufacture tablets using a powder mixture consisting of Carbamazepine (CBZ) as the active ingredient (drug), Kollidon VA64 as the excipient (polymer), and gold sheen as the agent with high laser absorptivity. A design of experiments was implemented to investigate the influence of compositional variance (% drug fraction) and geometrical differences (shell thickness) on the manufacturability and mechanical/pharmacokinetic performance of the printlets. Results show a general inverse relationship between structural integrity (as measured by pharmaceutical 'hardness' tests) and drug dissolution rates, as expected. Further, certain shell-breakup events were detectable via dissolution tests, as evidenced by sudden increases in dissolution magnitudes. FTIR and XRD analyses confirmed that there was no appreciable drug degradation. Altogether, this effort yielded a viable approach to 'tune' dissolution rates of certain solid dosage formulations
Design, Development, and Characterization of a 3D Solar Heat Exchanger
No full textThis thesis presents a multifaceted approach to the design, characterization, and development of a 3D Solar heat exchanger, employing state-of-the-art Computational Fluid Dynamics (CFD) and experimental techniques. The Solar Model represents a compact and innovative multi-level heat exchanger, incorporating intricate design elements such as pin-fins, vanes, multiple fluid passages, or channels. The primary objective of this design is to bolster heat transfer efficiency by prolonging the contact duration between the fluid and the heat transfer surfaces. To substantiate the theoretical models and designs, a comprehensive CFD and experimental study of the 3D model was conducted. CFD has proven to be an effective tool in the design and optimization of heat exchangers by considering thermal properties and it has been employed to study different modifications, compare results, and present the best possible combination of variables to ensure optimum performance. The proposed experimental procedure was implemented, with a step-by-step guide for system setup, including the installation of a solar collector, heat exchanger, and fluid circulation system. Measurement devices, comprising of thermocouples and pressure transducers, were placed throughout the system to monitor temperatures, pressure drop, and heat transfer rates under varying experimental conditions.
This comprehensive research endeavor not only explores the theoretical aspects of solar design and optimization using CFD but also validates these models through practical experimentation. The findings emphasize the paramount role of design configurations and parameters, particularly the aspect ratios and how they influence the overall thermal performance of solar systems. This combined approach paves the way for the advancement of efficient solar thermal systems, contributing to sustainable and eco-friendly energy solutions.
Steady state CFD simulations were conducted to study the fluid flow patterns, velocity profiles and temperature distribution of the solar at different aspect ratios. The modified geometry with an aspect ratio of 0.5 led to a more homogenous temperature distribution within the computational domain characterized by well-distributed fluid flow patterns. The modified geometry was then selected for fabrication so a prototype could be characterized experimentally. Experimental results revealed that the overall heat transfer coefficient, U, increased with flow rate. Furthermore, U reached an optimum value between 2.8 and 3.0 l/min, suggesting that the flow behavior inside the solar heat exchanger reached an optimum condition despite depicting higher pressure drop at higher flow rates. In summary, designing, numerically simulating, and experimentally characterizing a solar heat exchanger with features such as long fins and guide vanes proved to be a successful heat exchanger development approach. Such an approach should help the development of heat exchangers for renewable energy applications
Characterizing Effects That Influence Measured Range Hood Capture Efficiency
No full textKitchen range hoods remove harmful contaminants released by cooking, and they are essential for maintaining healthy indoor air quality. Standardized range hood capture efficiency (RHCE) experiments and tests were performed, and the resulting data were used to calculate RHCE, which is a parameter that provides a measure of how contaminants are removed. The goal of the studies reported herein is to improve the repeatability and reproducibility of RHCE tests performed in accordance with ASTM E3087.18. Changes to the standard aligning with the results of these reported studies will contribute to a reduction in error between measurements made at different testing laboratories, as well as a reduction in test variability. Achieving these goals is an essential step in ensuring further widespread adoption of the testing standard and RHCE as a metric, which in turn will lead to improved indoor air quality and human health, along with less energy consumed and greenhouse gas released.
A detailed experimental study was performed to analyze the effect of tracer gas injection rate, emitter assembly surface temperature, and chamber volume on measured RHCE. One study herein found that when the chamber volume was reduced from 36.6 m3 to 21.0m3 then a sample produced average results 3.6%CE lower at its higher operating speed and 7.8%CE lower at its lower operating speed. In contrast, in another study herein, a more extreme volume reduction led to a decrease in RHCE for another sample���s high-speed setting and an increase on its low-speed setting, suggesting that while chamber volume change has a definite effect on measured RHCE, this effect is not always consistent between samples or operating conditions.
Two analytical models were derived to predict chamber and exhaust concentrations during an RHCE test. The second model, which is the more useful model, assumes that there are two bodies of chamber air with limited interaction. It was validated by comparing its predicted results against experimentally measured ones. While the model predicted chamber CO2 concentration within 1.8% for a high-RHCE case, its accuracy was just 14.8% for a low-RHCE case. Further analysis found the model to have a consistent decrease in accuracy with decreasing nominal RHCE. The models can be used to predict performance and trends if one keeps in mind the limitations of the model with regards to its accuracy in specific flow ranges.
Another experimental study was performed herein to characterize the distribution of tracer gas throughout the test chamber. Results of this study confirmed that the concentration of tracer gas decreases as distance from the emitters increases, but that there is also a local zone of relatively low tracer gas concentration along the centerline of the room.
A reference range hood frame without a blower was constructed and tested for comparison against conventional range hoods. This test series aimed to determine whether the fan blower and motor selection impacts low-CE results. Using the exhaust as a prime mover, the reference box achieved capture efficiencies of 96.5% at 250 CFM, 93.3% at 160 CFM, and 81.3% at 100 CFM, outperforming other range hoods while showing lower test variance, with the result that fan and motor installation have a negative effect on RHCE. While design refinement is needed to better satisfy the initial goal of replicating low-RHCE results, the box���s low variance between tests suggests only minor modification of the design should be needed to do so.
A chamber inlet modification was performed and validated to ensure it did not severely impact the quality of measured RHCE. Three units were tested before and after installing the inlet modification. The results show that the inlet modification slightly reduced variance without noticeably affecting mean RHCE in four of five tested cases, but in one case it led to an increase in mean RHCE from 75.6%CE to 87.2%CE accompanied by an increase in variance from 0.94%CE to 3.06%CE. The results of this study found that the inlet change does not noticeably interfere with RHCE measurements
Linking Cardiovascular and Neuromotor Responses to an Orthostatic Challenge
No full textHuman physiology has adapted few responses to changes in the orthostatic gradient typically caused by gravity and postural changes. Sustained alterations to our gravitational environment, whether through bedrest or during human spaceflight missions, are known to elicit multi-system physiological decrements. Previous work has identified potential differences in the responses of males and females.
The current work delivered an acute bout of orthostatic stress to 24 sex-balanced subjects via step-wise increases in lower-body negative pressure (LBNP) levels. During this intervention, subjects performed one of four bimanual coordination tasks. Measures of systemic hemodynamics, autonomic indices, and bimanual coordination task performance were performed. Orthostatic dose-response curves were generated, and a correlation analysis between the metrics of the two systems was performed. Additionally, statistical models were selected that best predict tolerance to the orthostatic challenge using baseline cardiovascular metrics. Models using cardiovascular metrics to best predict task performance were also selected.
The orthostatic challenge was successful in eliciting early and robust cardiovascular responses, especially in metrics related to sympathetic drive. Neuromotor performance changes to the orthostatic challenge, where they occurred, were usually only detectable in the final levels of the LBNP intervention. The most consistent neuromotor responses were increases in the pace of motor inputs, and increases in the variability of forces applied. Baseline cardiovascular health metrics were the best predictors of tolerance. Time-domain autonomic indices of heart rate variability were shown to be the strongest predictors of the increases in the pace of motor inputs. No differences were detected between male and female Index of Tolerance scores.
These results inform our understanding of cardiovascular and neuromotor responses to an orthostatic challenge both in a dose-response manner and an integrative manner. They suggest that neuromotor decrements may occur at the point during an orthostatic challenge at which sympathetic drive becomes the dominant factor in further cardiovascular responses. Data also suggest that sex differences in orthostatic tolerance may not be the result of anatomical and anthropometric differences. Finally, it is proposed that the discovered linkages between the two studied systems may reside in the insula, a structure deep in the brain with functions in both systems