Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item SIMULATION OF MAGNETIC GRANULAR MEDIA USING OPEN SOURCE SOFT SPHERE DISCRETE ELEMENT METHOD(2021) Leps, Thomas; Christine, Hartzell; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Magnetic granular media were investigated using a mutual dipole magnetic model integrated into the open source Soft Sphere Discrete Element Method (DEM) framework LAMMPS and LIGGGHTS. Using the magnetic model and the contact force models from LIGGGHTS, we simulated shear behavior of MagnetoRheological Fluids (MRF). We found that the size distribution of simulated particles significantly affects the qualitative and quantitative behavior of MRF in a simple shear cell. Additionally, including cohesion, rolling resistance, friction and other contact forces affect the simulated shear behavior. By using a high fidelity contact force model along with an accurate size distribution and the mutual dipole magnetic model we were able to accurately match experimental data for an example MRF.We used the DEM model to aid in the development of a novel MRF valve operating on an alternative MRF behavior. Our jamming, MRF valve holds pres- sure through stable, but reversible jamming in the flow path, and is actuated by electropermanent magnets, which require no quiescent current to maintain their magnetization states. These valves do not require the large power draw of con- ventional MRF valves to maintain their state. We were able to accurately predict the experimental jamming behavior of the MRF valve using Finite Element Analysis and LIGGGHTS with magnetization, further validating the model with a non-linear, non-continuum behavior. Our jamming MRF valve was demonstrated in a multi- segmented, elastomeric robot, actuated using MRF. Using the magnetic DEM model coupled with self-gravity, the effects of mag- netism on rubble pile magnetic asteroids were examined. We simulated formation, and disruption of metallic asteroids with remnant magnetizations using LAMMPS with permanent dipoles. We found that rubble pile asteroids, formed from clouds of magnetized grains, coalesce more quickly, and have higher porosities than aster- oids coalesced from unmagnetized grains. Distortion and disruption was affected by magnetization during simulated YORP spin-up. Large fragments with high aspect ratios and low densities were formed from highly magnetized asteroids after disrup- tion, matching the shapes of suspected metallic small bodies. Simulations of grain avalanching on the surface of magnetized asteroids found additional morphological differences from their unmagnetized counterparts, with reduced densities, increased angles of repose, and cornicing.Item Morphing Waveriders for Atmospheric Entry(2019) Maxwell, Jesse R; Oran, Elaine S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary challenge for vehicles entering planetary atmospheres is surviving the intense heating and deceleration encountered during the entry process. Entry capsules use sacrificial ablative heat shields and sustain several g deceleration. The high lift produced by the Space Shuttle geometry resulted in lower rates of heating and deceleration. This enabled a fully reusable vehicle that was protected by heat shield tiles. Hypersonic waveriders are vehicles that conform to the shape of the shock wave created by the vehicle. This produces high compression-lift and low drag, but only around a design Mach number. Atmospheric entry can reach speeds from zero to as high as Mach 40. A morphing waverider is a vehicle that deflects its flexible bottom surface as a function of Mach number in order to preserve a desired shock wave shape. It was demonstrated in this work that doing so retains high aerodynamic lift and lift-to-drag ratio across a wide range of Mach number. Numerical simulations were conducted for case-study waveriders designed for Mach 6 and 8 for flight at their design conditions as well as with variations in angle-of-attack and Mach number. A single-species air model was used between Mach 1 and 12 with the RANS k-omega SST and LES-WALE turbulence models. A seven-species air model was used for Mach 15 at 60km altitude and Mach 20 at 75km. Analytical methods were used to construct a reduced-order model (ROM) for estimating waverider aerodynamic forces, moments, and heating. The ROM matched numerical simulation results within 5-10% for morphing waveriders with variations in angle-of-attack, but discrepancies exceeded 20% for large deviations of rigid vehicles from their design Mach numbers. Atmospheric entry trajectory simulations were conducted using reduced-order models for morphing waverider aerodynamics, the Mars Science Laboratory (MSL) capsule, and the Space Shuttle. Three morphing waveriders were compared to the Space Shuttle, which resulted in reduced heating and peak deceleration. One morphing waverider was compared to the MSL capsule, which demonstrated a reduction in the peak stagnation heat flux, a reduction in the peak and average deceleration, and a reduction in the peak area-averaged heating.Item Performance Measurement, Simulation, and Analysis of the Cox Tee Dee 0.010, the World's Smallest Production Internal Combustion Engine(2006-12-15) Sookdeo, Troy; Cadou, Christopher; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Cox Tee Dee 0.010 is a two-stroke 0.010 cubic inch model engine designed to power small propeller-based hobby aircraft. First manufactured in 1961, it remains the smallest working piston engine ever mass-produced, but no scientific measurements of its performance are available in the open literature. These measurements are important because they could facilitate the development of small unmanned air vehicles. This thesis reports measurements of power output and efficiency using a specialized dynamometer. An unsuccessful attempt is made to correlate the measurements with simulations based on Stanford University's Engine Simulation Program (ESP). Instead, the results are compared to the predictions of a simple zero-dimensional thermodynamic MATLAB simulation of an engine cycle developed at the University of Maryland. Differences and correlations are discussed and the engine performance is analyzed in the context of propulsion systems for small UAVs and for compact power generation.