UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item Identification of State-Space Rotor Wake Models with Application to Coaxial Rotorcraft Flight Dynamics and Control(2019) Hersey, Sean Patrick; Celi, Roberto; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Modern aerodynamic analysis tools, such as free-vortex wake models and CFD-based techniques, include fewer theoretical limitations and approximations than classical simplified schemes, and represent the state-of-the-art in rotorcraft aerodynamic modeling, including for coaxial and other advanced configurations. However, they are impractical or impossible to apply to many flight dynamics problems because they are not formulated in ordinary differential equation (ODE) form, and they are often computationally intensive. Inflow models, for any configuration type, that couple the accuracy of high-fidelity aerodynamic models with the simplicity and ODE form of dynamic inflow-type theories would be an important contribution to the field of flight dynamics and control. This dissertation presents the methodology for the extraction of linearized ODE models from computed inflow data acquired from detailed aerodynamic free-vortex wake models, using frequency domain system identification. These methods are very general and applicable to any aerodynamic model, and are first demonstrated with a free wake model in hover and forward flight, for a single main rotor, and subsequently for the prediction of induced flow off the rotor as well, at locations such as the tail or fuselage. The methods are then applied to the extraction of first order linearized ODE inflow models for a coaxial rotor in hover. Subsequent analysis concluded that free-vortex wake models show that the behavior of the inflow of a coaxial configuration may be higher-order. Also, tip-path plane motion of a coaxial rotor causes wake distortion which has an impact on the inflow behavior. Therefore, the methodology is expanded to the identification of a second order inflow representation which is shown to better capture from all of the relevant dynamics from free-vortex wake models, including wake distortion. With ODE models of inflow defined for an advanced coaxial configuration, this dissertation then presents a comparison of the fully-coupled aircraft flight dynamics, and the design of an explicit modeling-following feedback controller, with both a free-vortex wake identified model and a momentum theory based approach, concluding that accurate inflow modeling of coaxial rotor inflow is essential for investigation into the flight dynamics and control design of advanced rotor configurations.Item Real-Time Pose Based Human Detection and Re-Identification with a Single Camera for Robot Person Following(2017) Welsh, John Bradford; Blankenship, Gilmer; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this work we address the challenge of following a person with a mobile robot, with a focus on the image processing aspect. We overview different historical approaches for person following and outline the advantages and disadvantages of each. We then show that recent convolutional neural networks trained for human pose detection are suitable for person detection as it relates to the robot following problem. We extend one such pose detection network to spatially embed the identity of individuals in the image, utilizing the pose features already computed. The proposed identity embedding allows the system to robustly track individuals in consecutive frames even in long term occlusion or absence. The final system provides a robust person tracking scheme which is suitable for person following.Item Identification of Operators on Elementary Locally Compact Abelian Groups(2015) Civan, Gokhan; Benedetto, John J; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Measurement of time-variant linear channels is an important problem in communications theory with applications in mobile communications and radar detection. Kailath addressed this problem about half a century ago and developed a spreading criterion for the identifiability of time-variant channels analogous to the band limitation criterion in the classical sampling theory of signals. Roughly speaking, underspread channels are identifiable and overspread channels are not identifiable, where the critical spreading area equals one. Kailath's analysis was later generalized by Bello from rectangular to arbitrary spreading supports. Modern developments in time-frequency analysis provide a natural and powerful framework in which to study the channel measurement problem from a rigorous mathematical standpoint. Pfander and Walnut, building on earlier work by Kozek and Pfander, have developed a sophisticated theory of "operator sampling" or "operator identification" which not only places the work of Kailath and Bello on rigorous footing, but also takes the subject in new directions, revealing connections with other important problems in time-frequency analysis. We expand upon the existing work on operator identification, which is restricted to the real line, and investigate the subject on elementary locally compact abelian groups, which are groups built from the real line, the circle, the integers, and finite abelian groups. Our approach is to axiomatize, as it were, the main ideas which have been developed over the real line, working with lattice subgroups. We are thus able to prove the various identifiability results for operators involving both underspread and overspread conditions in both general and specific cases. For example, we provide a finite dimensional example illustrating a necessary and sufficient condition for identifiability of operators, owing to the insight gleaned from the general theory. In working up to our main results, we set up the quite considerable technical background, bringing some new perspectives to existing ideas and generally filling what we consider to be gaps in the literature.