<p> Environmental concerns are driving the automotive industry towards more sustainable and efficient forms of transportation such as electric vehicles. The electric drivetrains present in the various types of electric vehicles are much more efficient than traditional internal combustion engine drivetrains and produce fewer greenhouse gases. The most popular type of motor used in electric vehicle drivetrains is the permanent magnet synchronous motor. This can be attributed to its inherent high power density, large torque to weight ratio, and high reliability and efficiency. Advanced control techniques for permanent magnet synchronous motor drives must be developed in order to meet the high performance and efficiency demands of modern electric vehicles. Application of the nonlinear control method known as sliding mode control is the focus of this work. Both first order and higher order sliding mode methods are considered. These control methods provide robustness to modeling inaccuracies, internal parameter variations, and external disturbances. In addition to permanent magnet synchronous motors, the sliding mode control methods are also applied to the buck-boost type DC-DC converter. DC-DC converters have found extensive applications, ranging from consumer electronics to electric vehicles and smart grid synchronization. Computer simulation studies verify the efficacy of the proposed control techniques.</p>

<p> Wind turbines typically rely on feedback controllers to maximize power capture in below-rated conditions and regulate rotor speed during above-rated operation. However, measurements of the approaching wind provided by Light Detection and Ranging (lidar) can be used as part of a preview-based, or feedforward, control system in order to improve rotor speed regulation and reduce structural loads. But the effectiveness of preview-based control depends on how accurately lidar can measure the wind that will interact with the turbine. </p><p> In this thesis, lidar measurement error is determined using a statistical frequency-domain wind field model including wind evolution, or the change in turbulent wind speeds between the time they are measured and when they reach the turbine. Parameters of the National Renewable Energy Laboratory (NREL) 5-MW reference turbine model are used to determine measurement error for a hub-mounted circularly-scanning lidar scenario, based on commercially-available technology, designed to estimate rotor effective uniform and shear wind speed components. By combining the wind field model, lidar model, and turbine parameters, the optimal lidar scan radius and preview distance that yield the minimum mean square measurement error, as well as the resulting minimum achievable error, are found for a variety of wind conditions. With optimized scan scenarios, it is found that relatively low measurement error can be achieved, but the attainable measurement error largely depends on the wind conditions. In addition, the impact of the induction zone, the region upstream of the turbine where the approaching wind speeds are reduced, as well as turbine yaw error on measurement quality is analyzed.</p><p> In order to minimize the mean square measurement error, an optimal measurement prefilter is employed, which depends on statistics of the correlation between the preview measurements and the wind that interacts with the turbine. However, because the wind speeds encountered by the turbine are unknown, a Kalman filter-based wind speed estimator is developed that relies on turbine sensor outputs. Using simulated lidar measurements in conjunction with wind speed estimator outputs based on aeroelastic simulations of the NREL 5-MW turbine model, it is shown how the optimal prefilter can adapt to varying degrees of measurement quality. </p>

<p>Lignocellulosic biomass is a renewable, sustainable resource that can replace or supplement fossil fuels use for liquid fuels and chemicals. However, its recalcitrant structure including interwoven cellulose, hemicelluloses, and lignin biomacromolecules is challenging to deconstruct. Pretreating biomass so that it can be converted to useful liquids dominates process economics. Many pretreatment methods exist, but most require hazardous chemicals or processing conditions. Many ionic liquids (ILs), salts molten below 100&deg;C, can be used to deconstruct lignocellulosic biomass and are less hazardous than the volatile organic compounds typically used. </p><p> While effective, relatively safe, and recyclable, ILs are expensive. To reduce costs, dilution with other safe compounds is desirable, if there is no impact on deconstruction efficiency. Glycerol, a food additive, is inexpensive and becoming even more so since it is a by-product of the burgeoning biodiesel industry. Use of glycerol as an additive or diluent for ILs is extensively evaluated in this work. </p><p> Rice hulls are an abundant biomass, with over 100 million tons produced per year, but with little practical use. The IL 1-ethyl-3-methylimidazolium formate ([C2mim][O2CH] or EMIM Form) when mixed with an equal amount of glycerol has been shown to be effective in pretreating rice hulls. Ambient pressure, a pretreatment temperature of 110&deg;C, and a reaction time of three hours produced rice hulls that could be enzymatically hydrolyzed to give reasonably good glucose and xylose yields considering the recalcitrance of this silica-armored biomass. </p><p> The IL [C2mim][O2CH] was also effective when mixed with an equal amount of glycerol to pretreat loblolly pine, a fast-growing softwood. Loblolly pine was pretreated at 140&deg;C for three hours to produce a solid rich in cellulose and hemicelluloses, while a lignin-rich product could be precipitated from the IL. Similar products were obtained from pretreatment with a mixture of 75% 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc] or EMIM Ac) and 25% glycerol. Enzymatic hydrolysis of the pretreated solids gave glucose, mannose, and xylose yields up to 18 times that of the raw pine. </p><p> Viscosity measurements of pure glycerol, [C2mim][O2CH], [C2mim][OAc], and IL-glycerol mixtures were very different at ambient temperature, but were similar at typical biomass pretreatment temperatures. Biomass pretreated by mixtures with higher viscosity tended to give better carbohydrate yields after enzymatic hydrolysis. Higher excess molar volumes, <i>V_m^E</i>, tended to align with better carbohydrate yields after enzymatic hydrolysis. This phenomenon may relate to more energy put into shearing flow of the IL-glycerol-biomass system resulting in biomass particle shearing or stretching that allowed better solvent access into the biomass. </p>

<p> The flow surrounding a scaled model vertical-axis wind turbine (VAWT) at realistic operating conditions was studied. The model closely matches geometric and dynamic properties&mdash;tip-speed ratio and Reynolds number&mdash;of a full-size turbine. The flowfield is measured using particle imaging velocimetry (PIV) in the mid-plane upstream, around, and after (up to 4 turbine diameters downstream) the turbine, as well as a vertical plane behind the turbine. Ensemble-averaged results revealed an asymmetric wake behind the turbine, regardless of tip-speed ratio, with a larger velocity deficit for a higher tip-speed ratio. For the higher tip-speed ratio, an area of averaged flow reversal is present with a maximum reverse flow of &ndash;0.04<i>U</i>_&infin;. Phase-averaged vorticity fields&mdash;achieved by syncing the PIV system with the rotation of the turbine&mdash;show distinct structures form from each turbine blade. There are distinct differences in the structures that are shed into the wake for tip-speed ratios of 0.9, 1.3 and 2.2&mdash;switching from two pairs to a single pair of shed vortices&mdash;and how they convect into the wake&mdash;the middle tip-speed ratio vortices convect downstream inside the wake, while the high tip-speed ratio pair is shed into the shear layer of the wake. The wake structure is found to be much more sensitive to changes in tip-speed ratio than to changes in Reynolds number. The geometry of a turbine can influence tip-speed ratio, but the precise relationship among VAWT geometric parameters and VAWT wake characteristics remains unknown. Next, we characterize the wakes of three VAWTs that are geometrically similar except for the ratio of the turbine diameter (D), to blade chord (c), which was chosen to be <i> D/c</i> = 3, 6, and 9, for a fixed freestream Reynolds number based on the blade chord of <i>Re_c</i> =16,000. In addition to two-component PIV and single-component constant temperature anemometer measurements are made at the horizontal mid-plane in the wake of each turbine. Hot-wire measurement locations are selected to coincide with the edge of the shear layer of each turbine wake, as deduced from the PIV data, which allows for an analysis of the frequency content of the wake due to vortex shedding by the turbine. Changing the tip-speed ratio leads to substantial wake variation possibly because changing the tip-speed ratio changes the dynamic solidity. In this work, we achieve a similar change in dynamic solidity by varying the <i> D/c</i> ratio and holding the tip-speed ratio constant. This change leads to very similar characteristic shifts in the wake, such as a greater blockage effect, including averaged flow reversal in the case of high dynamic solidity (<i>D/c</i> = 3). The phase-averaged vortex identification shows that both the blockage effect and the wake structures are similarly affected by a change in dynamic solidity. At lower dynamic solidity, pairs of vortices are shed into the wake directly downstream of the turbine. For all three models, a vortex chain is shed into the shear layer at the edge of the wake where the blade is processing into the freestream.</p><p>

In this dissertation, I develop a new theoretical framework for the modeling, pricing analysis, and computation of solutions to electric power supply chains with power generators, suppliers, transmission service providers, and the inclusion of consumer demands. In particular, I advocate the application of finite-dimensional variational inequality theory, projected dynamical systems theory, game theory, network theory, and other tools that have been recently proposed for the modeling and analysis of supply chain networks (cf. Nagurney (2006)) to electric power markets. This dissertation contributes to the extant literature on the modeling, analysis, and solution of supply chain networks, including global supply chains, in general, and electric power supply chains, in particular, in the following ways. It develops a theoretical framework for modeling, pricing analysis, and computation of electric power flows/transactions in electric power systems using the rationale for supply chain analysis. The models developed include both static and dynamic ones. The dissertation also adds a new dimension to the methodology of the theory of projected dynamical systems by proving that, irrespective of the speeds of adjustment, the equilibrium of the system remains the same. Finally, I include alternative fuel suppliers, along with their behavior into the supply chain modeling and analysis framework. This dissertation has strong practical implications. In an era in which technology and globalization, coupled with increasing risk and uncertainty, complicate electricity demand and supply within and between nations, the successful management of electric power systems and pricing become increasingly pressing topics with relevance not only for economic prosperity but also national security. This dissertation addresses such related topics by providing models, pricing tools, and algorithms for decentralized electric power supply chains. This dissertation is based heavily on the following coauthored papers: Nagurney, Cruz, and Matsypura (2003), Nagurney and Matsypura (2004, 2005, 2006), Matsypura and Nagurney (2005), Matsypura, Nagurney, and Liu (2006).

Offshore floating wind turbines represent the future of wind energy. However, significant challenges must be overcome before these systems can be widely used. Because of the dynamics of offshore floating wind turbines—surge, sway, heave, roll, pitch, and yaw—and the resulting interactions between the rotor and generated wake, the aerodynamic analysis methods and design codes that have found wide use throughout the wind energy industry may be inadequate. Application of these techniques to offshore floating wind turbine aerodynamics may result in off-optimal designs, effectively handicapping these next-generation systems, thereby minimizing their full potential. This dissertation will demonstrate that the aerodynamics of offshore floating wind turbines are sufficiently different from conventional offshore and onshore wind turbines, warranting the use of higher fidelity analysis approaches. It will outline the development and validation of a free vortex wake code, the Wake Induced Dynamics Simulator, or WInDS, which uses a more physically realistic Lagrangian approach to modeling complex rotor-wake interactions. Finally, results from WInDS simulations of various offshore floating wind turbines under different load conditions will be presented. The simulation results indicate that offshore floating wind turbine aerodynamics are more complex than conventional offshore or onshore wind turbines and require higher fidelity analysis approaches to model adequately. Additionally, platform pitching modes appear to drive the most aerodynamically-significant motions, followed by yawing modes. Momentum balance approaches are shown to be unable to accurately model these dynamic systems, and the associated dynamic inflow methods respond to velocity changes at the rotor incorrectly. Future offshore floating wind turbine designs should strive to either minimize platform motions or be complementarily optimized, via higher fidelity aerodynamic analysis techniques, to account for them. It is believed that this dissertation is the first in-depth study of offshore floating wind turbine aerodynamics and the applicability of various analysis methods.^

Doctor of Philosophy / Department of Electrical and Computer Engineering / Balasubramaniam Natarajan / The number of wireless devices is predicted to skyrocket from about 5 billion in 2015 to 25 billion by 2020. Therefore, traffic volume demand is envisioned to explode in the very near future. The proposed fifth generation (5G) of mobile networks is expected to be a mixture of network components with different sizes, transmit powers, back-haul connections and radio access technologies. While there are many interesting problems within the 5G framework, we address the challenges of energy-related management in a heterogeneous 5G networks. Based on the 5G architecture, in this dissertation, we present some fundamental methodologies to analyze and improve the energy efficiency of 5G network components using mathematical tools from optimization, control theory and stochastic geometry. Specifically, the main contributions of this research include: • We design power-saving modes in small cells to maximize energy efficiency. We first derive performance metrics for heterogeneous cellular networks with sleep modes based on stochastic geometry. Then we quantify the energy efficiency and maximize it with quality-of-service constraint based on an analytical model. We also develop a simple sleep strategy to further improve the energy efficiency according to traffic conditions. • We conduct a techno-economic analysis of heterogeneous cellular networks powered by both on-grid electricity and renewable energy. We propose a scheme to minimize the electricity cost based on a real-time pricing model. • We provide a framework to uncover desirable system design parameters that offer the best gains in terms of ergodic capacity and average achievable throughput for device-to-device underlay cellular networks. We also suggest a two-phase scheme to optimize the ergodic capacity while minimizing the total power consumption. • We investigate the modeling and analysis of simultaneous information and energy transfer in Internet of things and evaluate both transmission outage probability and power outage probability. Then we try to balance the trade-off between the outage performances by careful design of the power splitting ratio. This research provides valuable insights related to the trade-offs between energy-conservation and system performance in 5G networks. Theoretical and simulation results help verify the performance of the proposed algorithms.

<p> There is a global need for energy technologies that reduce the adverse impacts of societal progress and that address today's challenges without creating tomorrow's problems. Life cycle impact assessment (LCIA) can support technology developers in achieving these prerequisites of sustainability by providing a systems perspective. However, modeling the early-stage scale up and impacts of technology systems may lead to unreliable or incomplete results due to a lack of representative technical, spatial, and temporal data. The goal of this dissertation is to support the acceleration of clean energy technology development by providing information about the regional variation of impacts and benefits resulting from plausible deployment scenarios. Three emerging energy technologies are selected as case studies: (1) brine management for carbon dioxide sequestration; (2) carbon dioxide capture, utilization, and sequestration; (3) stationary fuel cells for combined heat and power in commercial buildings. In all three case studies, priority areas are identified where more reliable data and models are necessary for reducing uncertainty, and vital information is revealed on how impacts vary spatially and temporally. Importantly, moving away from default technology and waste management hierarchies as a source of data fosters goal-driven systems thinking which in turn leads to the discovery of technology improvement potentials.</p>

Numerical and experimental investigations of tidal current energy extraction have been conducted in this study. A laboratory-scale water flume was simulated using commercial computational fluid dynamics (CFD) code FLUENT. In the numerical model, the tidal current turbine is represented with an actuator disk, which produces a pressure drop associated with energy loss. The free water surface is considered in the model using a volume of fluid method and is allowed to deform freely. Numerical results identified that a localised wake is formed behind the tidal current turbine and there is considerable localised flow acceleration around and most especially, under the energy extraction device. A free water surface drop is visualised in the model results due to the energy extraction and this free surface drop is believed to have an impact on the recovery of turbine wake. The influence of other parameters like water depth, ambient turbulence and flow speed on the tidal current energy extraction are also testified, based on the numerical model. Numerical results demonstrated that, because of the existence of a free water surface, tidal turbine interaction with the flow is a complicated three dimensional problem. Therefore, completely using the theoretical methods of wind turbines for tidal current turbine study would be inappropriate. Two physical tests were deigned for the experimental investigation of energy extraction from tidal currents and were carried out under different testing conditions: one was in moving water using a natural open channel and the other was in still water using a towing tank. Comparing experimental and numerical results of wake velocity profiles, good qualitative agreement has been obtained, which proves that the proposed numerical model can provide essential insight into the mechanism of wake development behind tidal current turbines. Experimental results also confirmed that, although moving water is the real operational condition of tidal turbines, a towing tank is still an ideal facility for the experimental study of tidal turbines, especially at the early stages of understanding of the detailed physical processes governing the performance of rotors and turbine wake behaviour. This study is a comprehensive investigation into tidal current energy extraction at laboratory scale. Environmental impact of tidal current energy extraction is further recognized and an appropriate experimental facility for the model testing of tidal energy extraction devices is recommended.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2010. / Thesis Advisor(s): Julian, Alexander L. ; Cristi, Roberto. "June 2010." Description based on title screen as viewed on July 16, 2010. Author(s) subject terms: Regenerative Braking, dynamic braking, rheostatic braking, all electric vehicle, all electric ship. Includes bibliographical references (p. 127-128). Also available in print.