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Full-Text Articles in Engineering Science and Materials

Investigating The Physical Mechanisms That Impact Electric Fields In The Atmosphere, Greg M. Lucas Jan 2017

Investigating The Physical Mechanisms That Impact Electric Fields In The Atmosphere, Greg M. Lucas

Aerospace Engineering Sciences Graduate Theses & Dissertations

The underlying physics and dynamics of the atmosphere drive electric currents and establish electric fields in a phenomenon known as the global electric circuit (GEC). The GEC has been observed and modeled with limiting assumptions and parameterizations in previous research. This thesis describes the incorporation of a physics-based GEC modeling scheme into a sophisticated climate model to describe the evolution of GEC currents, ground-ionosphere potential, electric fields, and conductivity within the atmosphere. Supporting measurements of atmospheric electric fields over time were used to describe the impact of local meteorological changes and assess the GEC contribution to near-surface electric fields.

The ...


Nonlinear Dispersive Elastic Waves In Solids: Exact, Approximate, And Numerical Solutions, Romik Khajehtourian Jan 2017

Nonlinear Dispersive Elastic Waves In Solids: Exact, Approximate, And Numerical Solutions, Romik Khajehtourian

Aerospace Engineering Sciences Graduate Theses & Dissertations

Wave motion lies at the heart of many disciplines in the physical sciences and engineering. For example, problems and applications involving light, sound, heat, or fluid flow are all likely to involve wave dynamics at some level. A particular class of problems is concerned with the propagation of elastic waves in a solid medium, such as a fiber-reinforced composite material responding to vibratory excitations, or soil and rock admitting seismic waves moments after the onset of an earthquake, or phonon transport in a semiconducting crystal like silicon. Regardless of the type of wave, the dispersion relation provides a fundamental characterization ...


Autonomous Mission Design In Extreme Orbit Environments, David Allen Surovik Jan 2016

Autonomous Mission Design In Extreme Orbit Environments, David Allen Surovik

Aerospace Engineering Sciences Graduate Theses & Dissertations

An algorithm for autonomous online mission design at asteroids, comets, and small moons is developed to meet the novel challenges of their complex non-Keplerian orbit environments, which render traditional methods inapplicable. The core concept of abstract reachability analysis, in which a set of impulsive maneuvering options is mapped onto a space of high-level mission outcomes, is applied to enable goal-oriented decision-making with robustness to uncertainty. These nuanced analyses are efficiently computed by utilizing a heuristic-based adaptive sampling scheme that either maximizes an objective function for autonomous planning or resolves details of interest for preliminary analysis and general study. Illustrative examples ...