Aerospace Engineering Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2737

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End date: 2009Subject: search.filters.subject.Engineering, Aerospace

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    Application of Compound Compressible Flow to Hypersonic Three-Dimensional Inlets
    (2009) Bussey, Gillian Mary Harding; Lewis, Mark J.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A method for correcting flow non-uniformities and incorporating multiple oblique shocks waves into compound compressible flow is presented. This method has several applications and is specifically presented for the problem of creating a streamline-traced hypersonic three-dimensional inlet. This method uses compound compressible flow theory to solve for the freestream flow entering a pre-defined duct with a desired downstream profile. This method allows for multiple iterations of the design space and is computational inexpensive. A method is also presented for modeling a laminar or turbulent boundary layer to compare inlet designs and to determine the viscous correction to the inlet. Two different Mach 6 designs were evaluated, with a rectangular capture area and circular combustor with a uniform temperature, pressure, and Mach number profile. Comparison with other three-dimensional inlets indicates those designed with this method demonstrate good inviscid performance. These inlets also have the ability to correct incoming flow non-uniformities.
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    Pressure-Constrained, Reduced-DOF, Interconnected Parallel Manipulators with Applications to Space Suit Design
    (2009) Jacobs, Shane Earl; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation presents the concept of a Morphing Upper Torso, an innovative pressure suit design that incorporates robotic elements to enable a resizable, highly mobile and easy to don/doff spacesuit. The torso is modeled as a system of interconnected, pressure-constrained, reduced-DOF, wire-actuated parallel manipulators, that enable the dimensions of the suit to be reconfigured to match the wearer. The kinematics, dynamics and control of wire-actuated manipulators are derived and simulated, along with the Jacobian transforms, which relate the total twist vector of the system to the vector of actuator velocities. Tools are developed that allow calculation of the workspace for both single and interconnected reduced-DOF robots of this type, using knowledge of the link lengths. The forward kinematics and statics equations are combined and solved to produce the pose of the platforms along with the link tensions. These tools allow analysis of the full Morphing Upper Torso design, in which the back hatch of a rear-entry torso is interconnected with the waist ring, helmet ring and two scye bearings. Half-scale and full-scale experimental models are used along with analytical models to examine the feasibility of this novel space suit concept. The analytical and experimental results demonstrate that the torso could be expanded to facilitate donning and doffing, and then contracted to match different wearer's body dimensions. Using the system of interconnected parallel manipulators, suit components can be accurately repositioned to different desired configurations. The demonstrated feasibility of the Morphing Upper Torso concept makes it an exciting candidate for inclusion in a future planetary suit architecture.
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    Comparison of Optic Flow in the Visible Light and Infrared Specturms
    (2008) Chinn, Michael William; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Insects use a method of Wide Field Integration (WFI) to navigate efficiently through unknown environments. Using these natural paradigms, various WFI based forms of navigation can be implemented based on electro-mechanical vision devices on robotic vehicles. However, under low light and/or suspended particles in the environment, these methods become less useful. One solution to this problem is to use infrared vision sensors rather than visible light sensors. This would allow insect-like navigation for autonomous vehicles under a variety of lighting conditions, including a total lack of visible light. The results show that, using infrared sensors, it is possible to navigate under a variety of lighting conditions, even where visible light sensors become ineffective.
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    A Study of Selected Aspects of Electromagnetic Formation Flight
    (2008) Gardner, Peter Nathaniel; Sedwick, Raymond; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Electromagnetic Formation Flight (EMFF) is a technique for electromagnetically controlling the relative position and velocity of satellites in close proximity, without using propellant.\nAn optimal design for an EMFF system for clusters of small satellites was calculated. Trends in parameters were identiï¬ ed, taking into account thermal issues.\nA power transfer system, using strongly coupled magnetic resonance, was simulated, using the same coils as the EMFF system. The eï¬ ciencies were calculated for the same parameters.\nA scheme for EMFF control was tested, in which two satellites at a time were active, with their dipoles aligned with each other on-axis. This system was shown to keep clusters of four satellites within speciï¬ ed boundaries.
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    Three-Dimensional Motion Coordination in a Time-Varying Flowfield
    (2009) Hernandez-Doran, Sonia; Paley, Derek A; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Decentralized algorithms that stabilize three-dimensional formations of unmanned vehicles in a time-varying flowfield have applications in environmental monitoring in the atmosphere and ocean. This thesis provides Lyapunov-based algorithms to control a system of self-propelled particles traveling in three dimensions at a constant speed relative to a spatiotemporal flowfield. A particle's inertial velocity is the sum of its velocity relative to the flowfield plus the velocity of the flowfield. Multiple particles can be steered to form parallel, helical, and circular formations. A special case of the three-dimensional model is also studied, in which the particles travel on the surface of a sphere. In this case, we provide Lyapunov-based algorithms that stabilize circular formations in a time-varying flowfield on a rotating sphere. Because we are interested in using unmanned-vehicle formations for environmental monitoring, we simulate our results using numerical simulations of time-varying flowfields that resemble tornadoes and hurricanes.
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    UNDERSTANDING THE ROLE OF HEAT RECIRCULATION IN ENHANCING THE SPEED OF PREMIXED LAMINAR FLAMES IN A PARALLEL PLATE MICRO-COMBUSTOR
    (2009) Veeraragavan, Ananthanarayanan; Cadou, Christopher P; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation investigates the role of heat recirculation in enhancing the flame speeds of laminar flames stabilized in a parallel plate reactor by: 1) developing analytical models that account for conjugate heat transfer with the wall and 2) making measurements of temperature profiles in a simulated microcombustor using non-intrusive FTIR spectroscopy from which heat recirculation is inferred. The analytical models have varying degrees of complexity. A simple heat transfer model simulates the flame by incorporating a concentrated heat release function along with constant temperature wall model. The next level model accommodates conjugate heat transfer with the wall along with a built in heat loss model to the environment. The heat transfer models identify the thermal design parameters influencing the temperature profiles and the Nusselt number. The conjugate heat transfer model is coupled with a species transport equation to develop a 2-D model that predicts the flame speed as an eigenvalue of the problem. The flame speed model shows that there are three design parameters (wall thermal conductivity ratio ( &kappa ), wall thickness ratio ( &tau ) and external heat loss parameter ( NuE )) that influence the flame speed. Finally, it is shown that all these three parameters really control the total heat recirculation which is a single valued function of the flame speed and independent of the velocity profile (Plug or Poiseuille flow). On the experimental side, a previously developed non-intrusive diagnostic technique based on FTIR spectroscopy of CO2 absorbance is improved by identifying the various limitations (interferences from other species, temperature profile fitting, ... etc) and suggesting improvements to each limitation to make measurements in a silicon walled, simulated microcombustor. Methane/Air and Propane/Air flames were studied for different equivalence ratios and burning velocities. From the temperature profiles it can be seen that increasing the flame speed pushes the flames further up the channel and increases the combustors inner gas and outer wall temperatures (measured using IR thermography). The temperature profiles measured are used to make a 2-D heat recirculation map for the burner as a function of the equivalence ratio and burning velocity. The experimental results are compared to the analytical models predictions which show a linear trend between flame speed and heat recirculation.
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    Mechanisms of Sediment Entrainment and Transport in Rotorcraft Brownout
    (2009) Johnson, Bradley Stephen Curtis; Leishman, J. Gordon; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    To advance the understanding of the phenomenon of rotorcraft brownout, a dual-phase flow environment induced by a small-scale rotor hovering above a sediment bed was studied using high-speed flow visualization and particle image velocimetry (PIV). The high frame rate of the camera, combined with advanced particle recognition and tracking software, permitted an understanding of the temporal evolution of the rotor wake in ground effect simultaneously with the processes of sediment entrainment and transport by the rotor flow. High-resolution near-wall PIV measurements showed that large excursions in the surface boundary layer were produced by the convecting rotor wake vortices. These excursions acted to suppress an equilibrium state in the boundary layer within the zone of vortex impingement on the ground. The highest sediment entrainment levels were observed to occur within this impingement zone, which can be attributed to the increase in groundwash and wall shear produced beneath the vortices. Once entrained, significant quantities of sediment were then trapped and locally suspended by the vortex-induced upwash field. This effect resulted in a noticeable level of intermittency in the initial vertical transport of sediment from the ground. The ground and upwash flow velocities were shown to strengthen significantly during the viscous merging of adjacent wake vortices. This mechanism proved fundamental in defining the concentration of suspended sediment, as well as the maximum height to which sediment could be transported. Sediment particles reaching sufficient heights were observed to recirculate into the rotor wake, and convect back towards the ground at a high speed. This process caused sediment ejection by means of bombardment or "splash." The classical process of saltation bombardment was also visualized for larger particles whose inertia prevented them from being suspended in the vortical flow. While providing new insight into the time- and length-scales associated with sediment transport by a rotor wake, the observations made here also bring into question the validity of equilibrium particle flux models currently being used for brownout simulations.
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    Experimental Investigation of the Mechanical Properties and Auxetic Behavior of Iron-Gallium Alloys
    (2009) Schurter, Holly Marie; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Iron-gallium alloys (known as Galfenol) are a unique material that have shown great potential for numerous applications. They exhibit a strong magneto-mechanical coupling, otherwise known as magnetostriction, which lends itself very well to transducer applications, from the nano-scale to macro scale. In addition, Galfenol is one of only a few metal alloys known to exhibit large auxetic or negative Poisson's ratio behavior. In order to develop any Galfenol-based applications, it will be necessary to understand its mechanical behavior. The goal of the research presented in this thesis therefore is to measure the elastic properties of Galfenol for a range of compositions in order to create a database, as well as present trends in the elastic properties. This is achieved through tensile testing of single-crystal Galfenol dogbone-shaped specimens and through resonant ultrasound spectroscopy (RUS) of small parallelepiped samples.
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    Stochastic Properties of Wide Field Integrated Optic Flow Measurements
    (2009) Owen, Scott; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Wide Field Integration (WFI) is a biologically inspired method of spatially decomposing optic flow estimates to extract relevant behavioral cues for navigation. In this thesis, a framework is developed that allows the direct application of a Kalman filter to improve the state information extracted from optic flow measurements. In addition, the noise properties of optic flow measurements are characterized, and an architecture to propagate the uncertainty in optic flow measurements to WFI state estimates is formalized. The closed-loop performance of a ground robot maneuvering in a straight tunnel using WFI outputs is then analyzed using three different algorithms to compute optic flow. The performance of the robot is characterized by its ability to track the tunnel centerline, and the accuracy of the WFI state estimates are compared with the true state estimates using a visual motion capture system. Lastly, the Kalman filter is implemented on a ground robot and the modified closed-loop performance is analyzed.
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    Development and Validation of a Bidirectionally Coupled Magnetoelastic FEM Model for Current Driven Magnetostrictive Devices
    (2009) Graham, Frank; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A bidirectionally coupled magnetoelastic model (BCMEM) has been extended to include electric currents in its magnetic finite element formulation. This enables the model to capture the magnetoelastic behavior of magnetostrictive materials subjected to elastic stresses and magnetic fields applied not only by permanent magnets but also by current carrying coils used often in transducer applications. This model was implemented by combining finite element solutions of mechanical and magnetic boundary value problems using COMSOL Multiphysics 3.4 (Finite Element Modeling software) with an energy-based non-linear magnetomechanical constitutive model. The BCMEM was used to simulate actuator load lines and four point bending results for Galfenol, which were then compared to experimental data. The model also captured the ΔE effect in Galfenol. The BCMEM can be used to study and optimize the design of future current driven magnetostrictive devices.