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 PLATE AND MICRO-SCALE STRUCTURES: ANALYSIS AND EXPERIMENTS(2008-12-08) Vechery, Mary Elizabeth; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Within this work, plate and micro-scale structures are studied. Methodologies are developed to analyze the laminate stiffness, residual forces, moments and stresses, and deformations in these thin composite laminate structures to facilitate better designs, enable device characterization, and enhance device performance. Specific devices studied in this work are cantilevered and clamped-clamped PZT resonators of various lengths, widths, and laminate thicknesses. In order to better understand the behavior of these devices, analytical and experimental methods have been developed. The analytical methods are based on linear and nonlinear beam and plate models, with reduced-order models developed to study dynamic behavior. Parameter identification techniques have been applied to characterize residual stress induced deformation of micro-scale structures. Extensive data has been collected through careful experiments to aid the development of identification techniques and to determine device deflections and individual device residual stress values. An analytical model has been developed to describe the behavior of thin composite laminate plate-like structures. Since an exact solution for plate mode shapes does not exist for all boundary conditions, appropriate combinations of orthogonal functions are assumed for the mode shapes of a plate with all edges simply supported or all edges clamped. These functions make the development of reduced-order models possible for these boundary conditions. In addition, these plate-like structures are asymmetric isotropic laminates. A procedure was applied to calculate the stiffness, forces and moments for a laminate comprised of multiple isotropic layers regardless of symmetry. Parametric identification techniques were developed to identify system parameters and to characterize residual stress induced deformation in plate and micro-scale structures. These techniques are based on linear and nonlinear beam models and reduced-order methodologies, and they enable the first characterization of residual stress in PZT micro scale devices post-fabrication and release processing. The obtained results indicate that post-release residual stress measurements in devices can be considerably different from the corresponding measurements made before release.Item Self-consistent simulation of radiation and space-charge in high-brightness relativistic electron beams(2007-06-25) Gillingham, David; O'Shea, Patrick G; Antonsen, Thomas M.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to preserve the quality of relativistic electron beams through transport bend elements such as a bunch compressor chicane is increasingly difficult as the current increases because of effects such as coherent synchrotron radiation (CSR) and space-charge. Theoretical CSR models and simulations, in their current state, often make unrealistic assumptions about the beam dynamics and/or structures. Therefore, we have developed a model and simulation that contains as many of these elements as possible for the purpose of making high-fidelity end-to-end simulations. Specifically, we are able to model, in a completely self-consistent, three-dimensional manner, the sustained interaction of radiation and space-charge from a relativistic electron beam in a toroidal waveguide with rectangular cross-section. We have accomplished this by combining a time-domain field solver that integrates a paraxial wave equation valid in a waveguide when the dimensions are small compared to the bending radius with a particle-in-cell dynamics code. The result is shown to agree with theory under a set of constraints, namely thin rigid beams, showing the stimulation resonant modes and including comparisons for waveguides approximating vacuum, and parallel plate shielding. Using a rigid beam, we also develop a scaling for the effect of beam width, comparing both our simulation and numerical integration of the retarded potentials. We further demonstrate the simulation calculates the correct longitudinal space-charge forces to produce the appropriate potential depression for a converging beam in a straight waveguide with constant dimensions. We then run fully three-dimensional, self-consistent end-to-end simulations of two types of bunch compressor designs, illustrating some of the basic scaling properties and perform a detailed analysis of the output phase-space distribution. Lastly, we show the unique ability of our simulation to model the evolution of charge/energy perturbations on a relativistic bunch in a toroidal waveguide.