Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item ANALYSIS OF SCYE BEARING MOTION AS APPLICABLE TO THE DESIGN OF A MORPHING SPACESUIT(2011) Bradshaw, Heather; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis describes research supporting the development of the Morphing Upper Torso spacesuit design, which uses robotic augmentation of a rear-entry pressure suit to adjust torso dimensions. This concept has the potential to provide increased mobility, easier ingress/egress of the suit, and reduced astronaut workload during extravehicular operations. A range of motion study has been conducted in which subjects wore simulated shoulder scye bearings while performing selected tasks, with the intent to measure human motion in relation to scye bearing motion. Results of the study include an investigation of the neutral pose of the scye bearings in Earth gravity, an analysis of the angular range of motion observed for the right scye bearing, and the development of a heuristic model to predict scye bearing position and orientation as a function of known arm pose.Item The Design Fabrication and Flight Testing of an Academic Research Platform for High Resolution Terrain Imaging(2011) Billingsley, David Daniel; Hubbard, James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis addresses the design, construction, and flight testing of an Unmanned Aircraft System (UAS) created to serve as a testbed for Intelligence, Surveillance, and Reconnaissance (ISR) research topics that require the rapid acquisition and processing of high resolution aerial imagery and are to be performed by academic research institutions. An analysis of the requirements of various ISR research applications and the practical limitations of academic research yields a consolidated set of requirements by which the UAS is designed. An iterative design process is used to transition from these requirements to cycles of component selection, systems integration, flight tests, diagnostics, and subsystem redesign. The resulting UAS is designed as an academic research platform to support a variety of ISR research applications ranging from human machine interaction with UAS technology to orthorectified mosaic imaging. The lessons learned are provided to enable future researchers to create similar systems.Item MODELING OF WATER-BREATHING PROPULSION SYSTEMS UTILIZING THE ALUMINUM-SEAWATER REACTION AND SOLID-OXIDE FUEL CELLS(2011) Waters, Daniel Francis; Cadou, Christopher P; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis investigates the use of solid oxide fuel cells (SOFCs) to consume waste hydrogen and improve the overall performance of a Hybrid Aluminum Combustor (HAC): a novel underwater power system based on the exothermic reaction of aluminum with seawater. The system is modeled using a NASA-developed framework called Numerical Propulsion System Simulation (NPSS) by assembling thermodynamic models developed for each component. Results show that incorporating the SOFC is not beneficial in cases where venting hydrogen overboard is permissible. However, when venting hydrogen is not permissible - which is the situation for most missions - the HAC-SOFC provides a 5 to 7 fold increase in range/endurance compared to equivalent battery powered systems. The utility of NPSS was demonstrated for evaluating and optimizing underwater propulsion system performance. Methodologies for predicting how system volume and mass scale with power were also developed to enable prediction of power and energy density.Item Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME)(2011) Greenwood, Eric; Schmitz, Fredric H; Hubbard, James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A new methodology is developed for the construction of helicopter source noise models for use in mission planning tools from experimental measurements of helicopter external noise radiation. The models are constructed by employing a parameter identification method to an assumed analytical model of the rotor harmonic noise sources. This new method allows for the identification of individual rotor harmonic noise sources and allows them to be characterized in terms of their individual non-dimensional governing parameters. The method is applied to both wind tunnel measurements and ground noise measurements of two-bladed rotors. The method is shown to match the parametric trends of main rotor harmonic noise, allowing accurate estimates of the dominant rotorcraft noise sources to be made for operating conditions based on a small number of measurements taken at different operating conditions. The ability of this method to estimate changes in noise radiation due to changes in ambient conditions is also demonstrated.Item THE EFFECTS OF FINITE-RATE REACTIONS AT THE GAS/SURFACE INTERFACE IN SUPPORT OF THERMAL PROTECTION SYSTEM DESIGN(2011) Beerman, Adam Farrell; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gas-surface modeling is dependent on material type and atmospheric reentry conditions. Lower molecular collisions at the low pressure trajectories make it more likely for occurrences of nonequilibrium, or finite-rate, reactions. Equilibrium is often assumed at the surface of a material as it is a subset of nonequilibrium and is easier to compute, though it can lead to overly conservative predictions. A case where a low density material experiences a low pressure trajectory and designed for equilibrium is the Stardust Return Capsule (SRC) with the Phenolic Impregnated Carbon Ablator (PICA) as its heatshield. Post-flight analysis of the recession on the SRC found that the prediction from the equilibrium model can be more than 50% larger than the measured recession. The Modified Park Model was chosen as the finite-rate model as it contains simple four reactions (oxidation, sublimation, and nitridation) and has been previously used to study individual points of the SRC trajectory. The Modified Park Model cannot model equilibrium so a model BFIAT was developed that allows finite-rate reactions to be applied to the surface for a certain length of time. Finite-rate sublimation was determined to be reaction of importance in the Park Model for SRC-like conditions. The predicted recession on the SRC heatshield experienced a reduction in its overprediction; the finite-rate predictions fall with the measurement error of the recession at three points on the heatshield. The recession reduction was driven by a significant reduction in char formation. There was little change in the pyrolysis gas rate. The finite-rate model was also applied to simulations of various arc-jet tests that covered a range of heating conditions on the surface of the PICA material. Comparison to this experimental data further showed the role of finite-rate reactions and sublimation in the Park Model and conditions that favor the nonequilibrium assumption (heating over 1000 W/cm2). For the emerging PICA material, used for the Mars Science Laboratory and one of two material choices for the Crew Exploration Vehicle, and SRC-like trajectories, a finite-rate model was developed such that the more robust nonequilibrium assumption can be applied to design processes to reduce heatshield mass.Item A DYNAMICS-BASED FIDELITY ASSESSMENT OF PARTIAL GRAVITY GAIT SIMULATION USING UNDERWATER BODY SEGMENT BALLASTING(2011) Mirvis, Adam Daniel; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In-water testing is frequently used to simulate reduced gravity for quasi-static tasks. For dynamic motions, however, the assumption has been that drag effects invalidate any data, and in-water testing has been dismissed in favor of complex and restrictive techniques such as counterweight suspension and parabolic flight. In this study, motion-capture was used to estimate treadmill gait metrics for three environments: underwater and ballasted to 1 g and to 1/6th g, and on dry land at 1 g. Ballast was distributed anthropometrically. Motion-capture results were compared with those for a simulated dynamic walker/runner, and used to assess the effect of the in-water environment on simulation fidelity. For each test case, the model was tuned to the subject's anthropometry, and stride length, pendulum frequency, and hip displacement were computed. In-water environmental effects were found to be sufficiently quantifiable to justify using in-water testing, under certain conditions, to study partial-gravity gait dynamics.Item Human Gait Based Relative Foot Sensing for Personal Navigation(2010) Spiridonov, Timofey N.; Pines, Darryll J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Human gait dynamics were studied to aid the design of a robust personal navigation and tracking system for First Responders traversing a variety of GPS-denied environments. IMU packages comprised of accelerometers, gyroscopes, and magnetometer are positioned on each ankle. Difficulties in eliminating drift over time make inertial systems inaccurate. A novel concept for measuring relative foot distance via a network of RF Phase Modulation sensors is introduced to augment the accuracy of inertial systems. The relative foot sensor should be capable of accurately measuring distances between each node, allowing for the geometric derivation of a drift-free heading and distance. A simulation to design and verify the algorithms was developed for five subjects in different gait modes using gait data from a VICON motion capture system as input. These algorithms were used to predict the distance traveled up to 75 feet, with resulting errors on the order of one percent.Item Smart Fabric sensors for foot motion monitoring(2010) Castano Salcedo, Lina Maria; Flatau, Alison B.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Smart Fabrics or fabrics that have the characteristics of sensors are a wide and emerging field of study. This thesis summarizes an investigation into the development of fabric sensors for use in sensorized socks that can be used to gather real time information about the foot such as gait features. Conventional technologies usually provide 2D information about the foot. Sensorized socks are able to provide angular data in which foot angles are correlated to the output from the sensor enabling 3D monitoring of foot position. Current angle detection mechanisms are mainly heavy and cumbersome; the sensorized socks are not only portable but also non-invasive to the subject who wears them. The incorporation of wireless features into the sensorized socks enabled a remote monitoring of the foot.Item Design and Performance of a Ducted Coaxial Rotor in Hover and Forward Flight(2010) Lee, Timothy Edward; Leishman, J. Gordon; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A ducted contra-rotating coaxial rotor system was designed and tested to assess its potential use as a micro aerial vehicle (MAV). Performance measurements (thrust and power) of the system in hover and forward flight were obtained. The influence of several design parameters (rotor spacing, duct inlet shape, position of rotors within the duct, and tip clearance) on performance was determined. Performance measurements of the unducted coaxial rotor, as well as the unducted/ducted single rotor configurations, were also obtained to give a performance baseline for the ducted coaxial rotor. The aerodynamic characteristics of the isolated duct were assessed from loads measurement and surface flow visualization. While the net system performance of operating the coaxial rotor within the confines of a duct was not always improved, the ducted coaxial rotor concept is still attractive for a MAV based on total attainable thrust for a given rotor size and other operational benefits.Item Performance Prediction of Scalable Fuel Cell Systems for Micro-Vehicle Applications.(2010) St. Clair, Jeffrey Glen; Cadou, Christopher P; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Miniature (< 500g) bio-inspired robotic vehicles are being developed for a variety of applications ranging from inspection of hazardous and remote areas to environmental monitoring. Their utility could be greatly improved by replacing batteries with fuel cells consuming high energy density fuels. This thesis surveys miniature fuel cell technologies and identifies direct methanol and sodium borohydride technologies as especially promising at small scales. A methodology for estimating overall system-level performance that accounts for the balance of plant (i.e. the extra components like pumps, blowers, etc. necessary to run the fuel cell system) is developed and used to quantify the performance of two direct methanol and one NaBH4 fuel cell systems. Direct methanol systems with water recirculation offer superior specific power (400 mW/g) and specific energy at powers of 20W and system masses of 150g. The NaBH4 fuel cell system is superior at low power (<5W) because of its more energetic fuel.