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The tire is one of the most complex subsystems of the vehicle. It is, however, the least understood of all the components of a car. Without a good tire model, the vehicle simulation handling response will not be realistic, especially for maneuvers that require a combination of braking/traction and cornering. Most of the simplified theoretical developments in tire modeling, however, have been limited to on-road tire models. With the availability of powerful computers, it can be noted that majority of the work done in the development of off-road tire models have mostly been focused on creating better Finite Element, Discrete Element, or Boundary Element models. The research conducted in this study deals with the development of a simplified tire brush-based tire model for on-road simulation, together with a simplified off-road wheel/tire model that has the capability to revert back to on-road trend of behavior on firmer soils. The on-road tire model is developed based on observations and insight of empirical data collected by NHSTA throughout the years, while the off-road tire model is developed based on observations of experimental data and photographic evidence collected by various terramechanics researchers within the last few decades. The tire model was developed to be used in vehicle dynamics simulations for engineering mobility analysis. Vehicle-terrain interaction is a complex phenomena governed by soil mechanical behavior and tire deformation. The theoretical analysis involved in the development of the wheel/ tire model relies on application of existing soil mechanics theories based on strip loads to determine the tangential and radial stresses on the soil-wheel interface. Using theoretical analysis and empirical data, the tire deformation geometry is determined to establish the tractive forces in off-road operation. To illustrate the capabilities of the models developed, a rigid wheel and a flexible tire on deformable terrain is implemented and output of the model was computed for different types of soils; a very loose and deformable sandy terrain and a very firm and cohesive Yolo loam terrain. The behavior of the wheel/tire model on the two types of soil is discussed. The outcome of this work shows results that correlate well with the insight from experimental data collected by various terramechanics researchers throughout the years, which is an indication that the model presented can be used as a subsystem in the modeling of vehicle-terrain interaction to acquire more insight into the coupling between the tire and the terrain. / Ph. D.

The Gate Turn-Off (GTO) Thyristor has the best voltage blocking and current conducting capabilities among all known high power semiconductor devices. To improve its dynamic performances to meet the increased demand in high-performance high-power applications, a special driving technique, namely unity gain turn-off, is studied. Several innovative approaches, which realize this driving requirement, are proposed, analyzed and experimentally demonstrated in this dissertation. The Emitter Turn-Off Thyristor (ETO) is a new family of high power semiconductor devices that is suitable for megawatt power electronics application. ETOs with voltage and current ratings of 4.0~6.0 kV and 1.0~4.0 kA, have been developed and demonstrated. These power levels are the highest in silicon power devices and are comparable to those of the GTO. Compared to the conventional GTO, the ETO has a much shorter storage time, voltage controlled turn-off capability, and a much larger reverse biased safe operation area (RBSOA). These combined advantages make the ETO based power system simpler in terms of dv/dt snubber, di/dt snubber and over current protection, resulting in significant savings at the system level. Experimental and numerical simulation results that demonstrate the advantages of the ETO are presented. A new family of snubberless turn-off GTO, the Resonant Gate Commutated Thyristor (RGCT) is proposed and investigated. By using a transient high commutation voltage, the RGCT can achieve unity turn-off gain and snubberless turn-off capability even with a relatively high gate loop stray inductance. Therefore conventional GTOs with flexible gate lead can be used to achieve the state-of-the-art performance similar to that of the Integrated Gate Commutated Turn-Off thyristor (IGCT). Detailed current commutation analysis and experimental results are presented. A novel equivalent circuit model for the GTO under the unity gain turn-off is proposed. This model is composed of a step current source, which represents the open-base PNP turn-off behavior, in series with a diode that represents the GTO's gate-cathode junction. This equivalent circuit can be used to analyze the turn-off transient behavior of a system employing this GTO. A new mechanism that dominates the failure of the GTO under the unity gain turn-off condition is identified and analyzed. Innovative hybrid GTO-based devices all have significant gate lead stray inductance. During the turn-off transition, this stray inductor will interact with the turn-off voltage source, the junction capacitance of the GTO's gate-cathode, causing effective current injection into the GTO's emitter junction when the voltage on the device is already high. Design guidelines and solutions for different types of GTO-based hybrid devices are provided. / Ph. D.

Woodstove emission of atmospheric pollutants has been a growing concern in the last two decades, and catalytic combustors have been used in woodstoves to reduce emissions. Field tests of EPA-certified catalytic stoves have demonstrated that emission factors increase substantially after a few seasons of use, and catalyst degradation is a suspected cause. Previously, an in-field test developed to assess catalyst condition was performed on a group of catalytic stoves in field use. In the current study, a laboratory test apparatus and procedure for the evaluation of woodstove catalysts was developed to verify the accuracy of the field test. Bench tests were performed on 24 aged catalysts retrieved from the field-tested stoves. In the bench test, steady-state conversions of CO and propene were measured at discrete temperatures ranging from 100°C to 400°C. At a temperature of 400°C, the average CO conversion of the aged catalysts was 94.8% and the average propene conversion was 83.1%. Comparison of individual catalyst data did not show a strong correlation between field measurements and bench test data. It is concluded that inaccuracies in the field test are responsible for the lack of correlation, and modifications to the field tests are recommended. In addition to the experimental work, a flow model of a catalytic woodstove was developed to better understand the interaction between the combustion process and the fluid mechanics within a woodstove. Evaluations of a catalytic woodstove under a set of baseline operating conditions show that the catalyst is not a significant source of frictional pressure loss in a catalytic stove-flue system. The model also predicts that increasing the flue crosswind velocity from 0 to 5 m/s will increase the mass flow rate through the stove by 21%. / Master of Science

Undertaking a work of architecture utilizing modular construction is, in most cases, a design project dominated, or at least driven by, the most technical aspects of architecture. Technical aspects which haven't been completely figured out yet. Rather than making the decision to use a pre-determined structural system in the project before going through the design process, my thesis offers an example of how a more traditional and balanced approach can improve resulting buildings. In addition, rather than allowing the technology of the module to create the form of the building, show how a thorough study of program and form can influence the structure, even in an endeavor which usually requires such hard-nosed engineering. / Master of Architecture

The primary purpose of this research was to examine institutional characteristics of four-year, public colleges and universities that closed off-site locations between 2012 and 2019 through the lens of resource dependence theory. As institutions attempt to maximize their available resources and make the best use of existing resources, there will inevitably be moments where an off-site location will come into question. Over the eight years of the study, the US Department of Education recorded the closure of 7,508 educational locations across all types of educational institutions. This study examined the closure trends that existed for public colleges and universities across the period and looked for institutional characteristics associated with a heightened risk of closing off-site locations. The results of the study indicate that most of the public closures came from a small number of institutions, with 62% of the closed off-site locations coming from 18 of the 365 institutions in the study. After examining the overall trend, data was analyzed from 365 institutions across ten self-reported variables. These research findings indicate two primary variables that significantly affected the closure of off-site locations and suggest the struggle between the access mission of public universities and prestige-maximizing behavior can drive institutional decision making. The study concludes with recommendations for future research.

Trade-offs in resource allocation underlie key life history traits of organisms. My dissertation focuses on the size-number trade-off in clonal broods of offspring using the polyembryonic wasp, Copidosoma bakeri parasitizing immature stages of the moth Agrotis ipsilon. I aim to characterize responses of wasp brood size and individual body mass by manipulating the environments in order to understand the allocation pattern in the size number trade-off. In reviewing the functional forms of trade-off relationships in relation to resource constraints, I distinguish among three main trade-off types based on graphical representations of the relationship between the trade-off variables: linear, convex (inverse), and concave. The size-number trade-off in C. bakeri shows convex relationship. Characteristics of the trade-off are sex specific: female broods have larger body mass but smaller brood size than do male broods. When food intake of the host was increased, the trade-off between wasp body mass and brood size for both sexes shifts toward both higher wasp brood size and higher body mass. When the host has better access to food late in development, the size-number trade-off curve moves up and to the right on the graph. However, the trait combinations shift along the same trade-off curve toward greater wasp body mass but smaller brood size when the host development time is shorter due to more resources in early in development. I also investigate temperature effects on the size-number trade-off. C. bakeri brood size significantly increases with high temperature early in host development. There is no shift in the allocation pattern of the size-number trade-off with temperature. Finally, I test effects of body mass on longevity, fecundity, and mating competitiveness of C. bakeri. Larger body size increases female longevity, and mated females produce more eggs than unmated females. There are no significant relationships between male body mass and longevity or mating competitiveness. Mating reduces male longevity independent of body mass. The different impact of body mass on fitness between male and female wasps suggests the observed sex-specific allocation patterns of the size-number trade-off. Implications of the experiments and possible follow-up work are discussed.

The computer program WHEEL is a mathematical model which predicts off-road vehicle performance characteristics. The program was developed using empirical relationships resulting from mobility tests on conventional-sized trucks and tires. The model was subsequently validated by comparing the model's predicted values of vehicle performance parameters, such as net drawbar pull, slip, sinkage and torque, with field test results for conventional-sized vehicles. However, validity of the model for predicting the off-road mobility of vehicles with large diameter tires was not established. The purpose of this study was to provide this validation. Values of net drawbar pull and slip for a Case 2390 tractor with 70.2" diameter driven wheels predicted by computer program WHEEL compare favorably with traction data obtained from tractor performance tests conducted by the University of Arizona Department of Agricultural Engineering. Therefore, the model may be used confidently to analyze performance of vehicles with large diameter wheels.