Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item DIRECT FUSION DRIVE BASED ON CENTRIFUGAL MIRROR CONFINEMENT(2023) Carson, Jerry Lee; Sedwick, Raymond J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A concept for direct fusion drive based on centrifugal mirror confinement of thermonuclear plasmas (DFD-CM) is described. In centrifugal mirrors, electric and magnetic fields are combined to confine the plasma within a rapidly rotating annulus of burning plasma fixed between two mirror magnets. High-energy fusion products leave the reactor core at a rate determined by the velocity of plasma rotation and the strength of the mirrors. Those departing through the aft jet-side mirror deposit their energy in a “warm plasma” which then expands through a magnetic nozzle to deliver jet power in the 100-1000 kW range. Fusion products departing through the forward, power-side mirror are converted to electricity to power the reactor. Moderate thrusts at attractive specific impulses (15000+ seconds) are possible. Findings are presented on centrifugal mirror reactor dynamics in propulsion applications, to include new insights into the relationship between mirror and centrifugal components of plasma confinement. Additionally, analysis is presented on reactor operability limits and characterization of viable configurations based on power density, technology constraints, and the ability to self-power. Physics of the warm plasma are discussed, to include estimates for fusion energy deposition. Finally, considerations for Alfvén’s “frozen-in” theorem relative to fusion plasmas and magnetic nozzle performance will be outlined.Analysis indicates the DFD-CM system can self-power, and would be relatively compact. For the 200 kW delivered jet power system, the volume of burning plasma in the CM fusion reactor is estimated to be on the order of 1 m3. Self-powering in propulsion applications requires DFD-CM reactor operation at M_θ>9. This in turn requires electric fields ranging from 40-90 MV/m, and mirror strengths up to 15T. The main losses in the propulsion system are due to heating and ionizing the propellant. These losses decrease with increasing specific impulse. This work has resulted in four contributions. To start, it is the first analysis of the end-to-end performance of direct fusion drive based on centrifugal mirror confinement of the burning plasma. It demonstrates that the concept is thermodynamically feasible with nominal cycle efficiencies of 50 percent based on fusion energy entering the propulsion system. The second contribution is characterization of CM fusion reactor performance and operability. A particular finding is that self-powering DFD-CM reactors in propulsion applications may need to operate at centrifugal Mach numbers greater than 9, as previously mentioned. The third contribution is the development and preliminary application of a set of engineering models of the reactor, warm plasma, and plasma acceleration and expansion. These models are considered moderate fidelity in that they account for first order effects, as well as salient second order effects. The fourth contribution is identifying the possibility that the burning plasma in the reactor and the warm plasma may be electrically coupled. The nature and implications of any coupling are uncertain, and the current research proceeds assuming that the coupling does not occur. However, the question indicates the need for further research.Item SYNTHESIS AND CHARACTERIZATION OF ENERGETIC NANOMATERIALS WITH TUNABLE REACTIVITY FOR PROPULSION APPLICATIONS(2020) Kline, Dylan Jacob; Zachariah, Michael R.; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Combustion is the world’s leading energy conversion method in which a fuel and oxidizer react and release energy, typically in the form of heat. Energetic materials (propellants, pyrotechnics, and explosives) have combustion reactions that are so fast that they are generally limited by how quickly the fuel and oxidizer can reach each other. Recent research has employed nanomaterials to reduce the distance between reactants to increase energy release rates. This dissertation attempts to uncover and quantify structure-function relationships in energetic nanomaterials by modifying chemical and physical properties of the materials and characterizing the observed changes using new diagnostic tools. This dissertation begins with the development of diagnostic tools that can capture the dynamics of energetic material combustion using a high-speed color camera to measure temperature. This tool has also been modified into a high-speed microscope that allows for spatial and temperature measurements at microscale length (µm) and time (µs) scales. Changes to chemical formula have been explored for energetic nanomaterial systems, though visualization of the reaction dynamics limited detailed results on reaction mechanisms. The first study performed here probed the role of gas generation vs. thermal effects in energy release rate where it was found that combustion inefficiencies from reactive sintering could be mitigated by introducing a gas-generating oxidizer. To explore combustion improvements in the fuel, a metal fuel nanoparticle manufacturing method was explored, though the combustion performance was again limited by reactive sintering. Another effort to reduce reactive sintering with a gas generator proved successful, but also unveiled the importance of different heat transfer mechanisms for propagation. The role of physical architecture on propellant combustion was also investigated to improve efficiency and versatility in solid propellants. It was found that addition of a poor thermal conductor to a propellant mixture increased the propagation rate of the material and this was attributed to the result increase in burning surface area resulting from inhomogeneous heat transfer. Lastly, this dissertation explores a method to remotely ignite materials using microwaves and titanium nanoparticles. This work sets the stage for a remotely staged solid propellant architecture that would provide control over solid propellant combustion in-operando.Item COMPARATIVE ANALYSIS OF MINIATURE INTERNAL COMBUSTION ENGINE AND ELECTRIC MOTOR FOR UAV PROPULSION(2017) Chiclana, Branden; Cadou, Christopher; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis compares the performance of an engine/fuel tank based propulsion system to a motor/battery based propulsion system of equal total mass. The results show that the endurance of the engine/fuel system at the same thrust output is approximately 5 times greater than that of the motor/battery system. This is a direct result of the fact that the specific energy of the fuel is 20 times that of the lithium-polymer batteries used to power the motor. A method is also developed to account for the additional benefits of fuel consumption (and hence weight reduction) over the course of the flight. Accounting for this effect can increase endurance exponentially. Taken together, the results also demonstrate the dramatic performance improvements that are possible simply by replacing motor/battery systems with engine/fuel systems on small unmanned air vehicles.Item Optimal Propulsion System Design for a Micro Quad Rotor(2011) Harrington, Aaron Michael; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Currently a 50 gram micro quad rotor vehicle is being developed in collaboration with Daedalus Flight Systems. Optimization of the design at this scale requires a systematic study to be carried out to investigate the factors that affect the vehicles performance. Endurance of hovering vehicles at this scale is severely limited by the low efficiencies of their propulsion systems and rotor design and optimization has been performed in the past in an attempt to increase endurance, but proper coupling of the rotor with the motor has been lacking. The current study chose to investigate the factors that had the greatest effect on the vehicle's endurance through analysis of the propulsion system. Therefore, a coupled aerodynamic and structural analysis was carried out that incorporated low Reynolds number airfoil table lookup in order to predict micro rotor performance. A parametric study on rotor design was performed further determine the effect of different rotor designs on hover performance. The experiments performed showed that airfoil camber had the biggest impact on rotor efficiency and other factors such as leading edge shape, number of blades, max camber location, and blade planform taper only had negligible influence on performance. Systematic studies of the interactions between micro rotor blades operating in close proximity to each other were performed in order to determine the changes in rotor efficiency that might occur in a compact quad rotor design. Tests done on the effect of rotor separation demonstrated that there is a negligible interaction between rotors operating near each other. Brushless motors were also tested systematically and characterized by their torque, rpm, and efficiency. It was found that the maximum efficiency of the motors tested was only 60%, which has significant effects on the efficiency of the coupled system. A method for rotor and motor coupling was also established that utilized the motor efficiency curves and the known torque and rotational speed of the rotors at their operating thrust. Through this, it was found that propulsion system efficiency could be increased by 10% by simply using the proper motor and rotor combination. Further, coupled design would have additional benefits and could increase vehicle efficiency further.Item Experimental Characterization of Slot Film Cooling Flows With Minimally Intrusive Diagnostics(2008) Raffan, Fernando; Marshall, Andre; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The performance of a propulsion system is directly proportional to its operating temperature; therefore, an optimum operation regime will undoubtedly generate intense thermal loads on system components. If the system is designed for reusability and/or long range missions, it may be necessary to perform active cooling of critical components to prevent premature failure of the system. One such method is film cooling, in which a layer of relatively cool gas is injected near the surface to be protected. This work describes the use of minimally intrusive diagnostics to characterize the kinematics, thermal dynamics and heat transfer of slot film cooling flows over a wide range of blowing ratios, generating a comprehensive database for detailed analysis, as well as for further use by model developers.Item Modeling of a High Energy Density Propulsion System Based on the Combustion of Aluminum and Steam(2007-12-13) Eagle, W. Ethan; Cadou, Christopher P; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents a thermodynamic analysis of a novel Rankine cycle aluminum/steam combustion power system being developed for use in Unmanned Underwater Vehicles (UUVs). The analysis is performed using a system modeling tool developed by the NASA Glenn Research Center called Numerical Propulsion System Solver (NPSS). Thermodynamic models of the individual components are created and linked together in NPSS, which then solves the system by enforcing mass and energy conservation. Design and off-design conditions are simulated and predicted performance is compared with predictions made by two other research groups. The simulations predict that this power system could provide at least five-fold increases in range and endurance for the US Navy's 'Sea Horse' UUV. A rudimentary sensitivity analysis is used to identify the factors which most strongly influence the performance of the design. Lastly, recommendations for future work and possible model improvements are discussed.