In this thesis two kinds of phase change i.e., solid state phase transformation in steels and solid-to-liquid phase transformation in paraffin, have been modeled and numerically simulated. The solid state phase transformation is modeled using the phase field theory while the solid-to-liquid phase transformation is modeled using the Stokes equation and exploiting the viscous nature of the paraffin, by treating it as a liquid in both states.The theoretical base of the solid state, diffusionless phase transformation or the martensitic transformation comes from the Khachaturyan's phase field microelasticity theory. The time evolution of the variable describing the phase transformation is computed using the time dependent Ginzburg-Landau equation. Plasticity is also incorporated into the model by solving another time dependent equation. Simulations are performed both in 2D and 3D, for a single crystal and a polycrystal. Although the model is valid for most iron-carbon alloys, in this research an Fe-0.3\%C alloy is chosen.In order to simulate martensitic transformation in a polycrystal, it is necessary to include the effect of the grain boundary to correctly capture the morphology of the microstructure. One of the important achievements of this research is the incorporation of the grain boundary effect in the Khachaturyan's phase field model. The developed model is also employed to analyze the effect of external stresses on the martensitic transformation, both in 2D and 3D. Results obtained from the numerical simulations show good qualitative agreement with the empirical observations found in the literature.The microactuators are generally used as a micropump or microvalve in various miniaturized industrial and engineering applications. The phase transformation in a paraffin based thermohydraulic membrane microactuator is modeled by treating paraffin as a highly viscous liquid, instead of a solid, below its melting point.  The fluid-solid interaction between paraffin and the enclosing membrane is governed by the ALE technique. The thing which sets apart the presented model from the previous models, is the use of geometry independent and realistic thermal and mechanical properties. Numerical results obtained by treating paraffin as a liquid in both states show better conformity with the experiments, performed on a similar microactuator. The developed model is further employed to analyze the time response of the system, for different input powers and geometries of the microactuator. / <p>QC 20130219</p>

The role played by power converting circuits is extremely important to almost any electronic system built today. Circuits that use converters of any type depend on power that is consistent in form and reliable in order to properly function. In addition, today's demands require more efficient use of energy, from large stationary systems such as power plants all the way down to small mobile devices such as laptops and cell phones. This places a need to reduce any losses to a minimum. The power conversion circuitry in a system is a very good place to reduce a large amount of unnecessary loss. This can be done using circuit topologies that are low loss in nature. For low loss and high performance, soft switching topologies have offered solutions in some cases. Also, limited study has been performed on device aging effects on switching mode power converting circuits. The impact of this effect on a converter's overall efficiency is theoretically known but with little experimental evidence in support. In this thesis, non-isolated buck type switching converters will be the main focus. This type of power conversion is widely used in many systems for DC to DC voltage step down. Newer methods and topologies to raise converter power efficiency are discussed, including a new synchronous ZVT topology . Also, a study has been performed on device aging effects on converter efficiency. Various scenarios of voltage conversion, switching frequency, and circuit components as well as other conditions have been considered. Experimental testing has been performed in both cases, ZVT's benefits and device aging effects, the results of which are discussed as well.

The effect of in-situ or redistributed stress on solute transport in fractured rocks is one of the major concerns for many subsurface engineering problems. However, it remains poorly understood due to the difficulties in experiments and numerical modeling. The main aim of this thesis is to systematically investigate the influences of stress on solute transport in fractured rocks, at scales of single fractures and fracture networks, respectively. For a single fracture embedded in a porous rock matrix, a closed-form solution was derived for modeling the coupled stress-flow-transport processes without considering damage on the fracture surfaces. Afterwards, a retardation coefficient model was developed to consider the influences of damage of the fracture surfaces during shear processes on the solute sorption. Integrated with particle mechanics models, a numerical procedure was proposed to investigate the effects of gouge generation and microcrack development in the damaged zones of fracture on the solute retardation in single fractures. The results show that fracture aperture changes have a significant influence on the solute concentration distribution and residence time. Under compression, the decreasing matrix porosity can slightly increase the solute concentration. The shear process can increase the solute retardation coefficient by offering more sorption surfaces in the fracture due to gouge generation, microcracking and gouge crushing. To study the stress effects on solute transport in fracture systems, a hybrid approach combing the discrete element method for stress-flow simulations and a particle tracking algorithm for solute transport was developed for two-dimensional irregular discrete fracture network models. Advection, hydrodynamic dispersion and matrix diffusion in single fractures were considered. The particle migration paths were tracked first by following the flowing fluid (advection), and then the hydrodynamic dispersion and matrix diffusion were considered using statistic methods. The numerical results show an important impact of stress on the solute transport, by changing the solute residence time, distribution and travel paths. The equivalent dispersion coefficient is scale dependent in an asymptotic or exponential form without stress applied or under isotropic compression conditions. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small. Outstanding issues and main scientific achievements are also discussed. / QC 20111011

Doctor of Philosophy / Department of Educational Leadership / Sarah Jane Fishback / A new group of learners is emerging in the adult learning environment as a result of the United States being at war for more than 10 years. More than two million warriors served in the Global War on Terrorism (GWOT). Educational institutions across the United States are experiencing growing numbers of students who are military combat veterans of the GWOT. These numbers will continue to grow as more of them transition back into life after combat. These students are arriving in class with varying levels of combat trauma experience and possibly Post Traumatic Stress Disorder (PTSD), major depression, Traumatic Brain Injury (TBI) or a combination of these and other difficulties. The purpose of this research was to learn from military veteran students how their combat experience affects them in the classroom. Specifically it looked at the types of combat experiences they have and the types of physical and mental effects they report experiencing while attending and participating in educational learning activities. This research h sought to gain insight into how combat experience influences the learning experience for GWOT military combat veterans who participate in an educational learning environment. It explored the types of experiences these students bring into that learning environment and how their participation in learning activities is affected.