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<p>A new type of flexible silicon solar cell has been fabricated by interconnecting solar cell die on a flexible substrate. The fabrication process is described in this thesis. The solar cell die were diced using two methods. One method was to dice a solar cell completely through. The other method was to dice a solar cell from its back partially and then cleave through. To study the effects of different dicing methods on the performance of solar cell die, storage delay time measurement was employed to determine the lifetime of excess electrons in the p region of the two types of solar cell die. A laser beam induced current (LBIC) scanning technique was employed to study the electrical performance of the two types of solar cell die. The carrier diffusion lengths of two types of solar cell die were also determined by traveling light spot diffusion length measurement.</p><p>The theoretical response of a solar cell was compared to experimental results at various incident light angles. OpticLab software was used to model the incident light angle and lens spacing dependence of solar cell performance.</p> / Thesis / Master of Applied Science (MASc)

This research is intended to better understand the structural behavior of steel bridge beams that have experienced section loss near the bearings. This type of deterioration is common in rural bridges with leaking expansion joints, which exposes the superstructure to corrosive road deicing solutions. Seventeen beams from 4 decommissioned structures throughout Virginia were tested to induce web shear failure near the bearing locations and measured for load, vertical displacement, and web strain behavior. The strain was measured using a digital image correlation (DIC) system to create a digital strain field at equal loading and beam displacement intervals during testing. The data recorded during these large-scale tests was compared to several existing methods for calculating the shear capacity of the damaged beams. Finally, the most appropriate method of these approaches was identified based on accuracy, conservatism, and ease of implementation for load rating. When using load rating methods to determine a steel beam's capacity, this study also recommends that the effective area of the web used in determining the percentage of remaining thickness should consist of the bottom 3 inches of the web and should extend the length of the bearing plus one beam height excluding any areas without any noticeable section losses. / Master of Science / Older bridge structures typically include a rubber joint near the ends to allow for expansion and contraction of the bridge due to heating and cooling from the weather. In many cases, these joints will get damaged due to impacts from vehicle tires and other environmental disturbances. Damage to these joints allows for water to leak through, which, while not in of itself harmful, also allows melting snow to carry road salts laid in the winter to spread onto the underlying bridge steel. These salts cause aggravated corrosion of the steel beams below the bridge's deck, resulting in damage or collapse of the bridge itself. The goal of this study was to characterize this damage and determine how it affects the remaining capacity of the bridge. This objective was achieved by testing 17 beams from 4 out of service bridges with varying damage levels. A load was applied near the damaged ends to determine their behavior during loading, to locate areas of high strain resulting from corrosion, and find the beam's capacity. Several methods to predict the remaining strength in corroded steel beams were compared and recommendations made based on accuracy and conservatism.

This thesis describes development of the DRACO plasma simulation code. DRACO is an electro-static (ES) code which uses the particle-in-cell (PIC) formulation to track plasma particles through a computational domain, and operates within the Air Force COLISEUM framework. The particles are tracked on a non-standard mesh, which combines the benefits of a Cartesian mesh with the surface-resolving power of an unstructured mesh. DRACO contains its own mesher, called VOLCAR, which is also described in this work. DRACO was applied to a fully kinetic simulation of an ion-beam neutralization. The thruster configuration and running parameters were based on the NASA's 40cm NEXT ion thruster. The neutralization process was divided into three steps. Electron dynamics was studied by assuming an initial beam neutralization, which was accomplished by injecting both electrons and ions from the optics. Performing the simulation on a full-sized domain with cell size much greater than the Debye length resulted in a formation of a virtual anode. Decrease of the cell size to match the Debye length was not feasible, since it would require a million-fold increase in the number of simulation nodes. Instead, a scaling scheme was devised. Simulations were performed on thruster scaled down by a factor of 100, but its operating parameters were also adjusted such that the produced plasma environment did not change. Loss of electrons at the boundary of the finite simulation domain induced a numerical instability. The instability resulted in a strong axial electric field which sucked out electrons from the beam. It was removed by introducing an energy based particle boundary condition. Combination of surface scaling and energy boundary resulted in physically sound simulation results. Comparison were made between the Maxwellian and polytropic temperatures, as well as between simulation electron density and one predicted by the Boltzmann relationship. The cathode was modeled individually from the beam by introducing a positively charged collector plate at a distance corresponding to the beam edge. The local Debye length at the cathode tip was too small to be resolved by the mesh, even if mesh-refinement was incorporated. Since the simulation was not concerned with the near-tip region, two modifications were performed. First, the a limiting value of charge density at the tip was imposed. Second, the cathode potential was allowed to float. These two modifications were necessary to prevent development of a strong potential gradient at the cathode tip. The modified cathode model was combined with ion injection from the optics to model the actual beam neutralization. Three configurations were tested: a single thruster, a 2x2 cluster with individual cathodes and a similar cluster with a single large neutralizer. Neither of the cases achieved neutralization comparable to one in the base-line pre-neutralized case. The reason for the discrepancy is not known, but it does not seem to be due a loss of electrons at the walls. The difference could be due to limited extent of the modeled physics. An additional work is required to answer this question. / Master of Science

High levels of noise have historically been present in the interior of aircrafts. This causes passenger, pilot, and other aircraft employee fatigue as well as speech interference and discomfort issues. In general aviation aircraft, little has been done to reduce the noise in the interior of fuselages. Noise transmitting into the cabin of a single engine aircraft is complex. Researchers have identified areas of noise transmission in general aviation aircraft to include the windshield, exhaust, side windows, and little through the engine firewall. Sources originally noted that structure-borne and airborne noise transmission paths were equal contributors to interior energy penetration of single-engine aircraft. However, additional studies found that airborne noise transmission paths dominate interior energy transmission for single-engine aircraft. Energy transmits mostly through the front of the aircraft via the windshield. Little goes through the engine firewall, which contradicts the original assumption that engine vibration contributed to large noise transmission into the cabin of the aircraft via the firewall. Airborne noise and some exhaust noise transmit through the firewall, but not near as much as noise that transmits through the windshield. Reducing interior aircraft noise levels is a complicated joint effort, combining propeller radiation control; fuselage wall reduction methods; exhaust emission regulation, management of air turbulence; some propeller, wake-induced vibration control; and a little engine vibration restraint. For minimum propeller acoustic propagation, it is important to control propeller radiation by using techniques such as increasing the number of blades, altering blade airfoil (especially using a felix or grooved design); applying small angle of attack; utilizing swept blades; decreasing blade diameter; lowering tip speed; and reducing the load on a propeller (i.e. by controlling the blade thickness, tip volume, and blade shape). Controlling the vibration in the fuselage skin can also help to reduce interior noise. Some early attempts were made using ribs/stiffeners, tuned dampers, and a limp mass double wall. More recently, dynamic vibration absorbers have been utilized, quite successfully, to reduce fuselage skin vibration and thus, interior noise levels. Attempting to control the exhaust emission and induced vibration from air turbulence has contributed to lower airplane cabin noise levels as well. For large aircrafts, the strategic location of luggage compartments and bathrooms help in keeping the interior quiet. Most importantly for small single-engine aircraft, the windshield has been found to contribute heavily to aircraft interior noise levels. Currently, the use of active control methods (especially the active structural acoustic control methods) and the utilization of dynamic vibration absorbers (a form of passive noise control) are the most popular techniques to reduce interior aircraft noise levels. In small general aviation aircraft, the blade passage frequency (bpf) and the first few harmonics have been found to be the largest contributor to noise transmitting into the fuselage. This project analyzes a two degree-of-freedom (DOF) dynamic vibration absorber in hopes of reducing windshield vibration of a Cessna 150 fuselage at the fundamental blade passage frequency of approximately 87 Hz and thus, reducing noise transmitting into the interior of the aircraft. This research project is unique in several ways. First, numerous passive noise control techniques have been utilized to control vibration and acoustics on an aircraft, but none have used the two degree of freedom Distributed Vibration Absorbers (DVA) employed in this project, as a noise reduction method on the windshield of an aircraft. Secondly, little research has been done on analyzing noise transmission into small, single engine general aviation aircraft, which is conducted in the work here. Third, little work has been done on analyzing and reducing noise propagation through the windshield of a small engine aircraft, which is also analyzed in this project. Finally, the modal analysis conducted on the windshield of the small engine plane is one of the few modal decompositions that has been conducted on a small general aircraft windshield. / Master of Science