Rarefied gas dynamic simulations of planetary atmospheric systems




Hoey, William Andrew

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My doctoral research involves the advanced numerical simulation of rarefied (low-pressure) planetary atmospheres and volcanism with advanced physical modeling, in application of the Direct Simulation Monte Carlo (DSMC) method. This method is the approach of choice for modeling a wide range of continuum-to-rarefied systems - in which the average spacing between molecules in the flow becomes comparable to the flow length scales, and in which traditional means of computing fluid dynamics with the partial differential equations of continuum theory break down. DSMC is a probabilistic technique by which the motions and collisions of representative molecules are computed. Multiple gas species are modelled, along with non-equilibrium radiation, high speed collisions, photochemistry, and a wide range of other relevant physics. Comprehensive atmospheric simulations are computed in parallel on one- and three-dimensional domains that, depending on the scope of a particular project, can span entire atmospheric systems from planetary surface through vacuum. These projects are ongoing efforts in modeling and understanding global-scale atmospheric flows and the processes by which such flows are populated and propagated, and they represent advancements of the state-of-the-art in planetary atmospheric simulation. I have produced and presented research on four distinct topics: 1) simulations of the complete atmosphere of Jupiter's volcanic moon Io including sublimation and plasma-sputtering processes; 2) the creation of a novel neutral density model for Earth's upper-atmosphere in partnership with Los Alamos' ISR division; 3) multi-species simulations of the rarefied gas dynamic, transfer, and escape processes of the Pluto-Charon system; and 4) investigations of the canopy unsteadiness and development of transient filamentary structure as observed by the New Horizons probe at the Ionian Tvashtar plume site. In the course of these projects, and using my research group's existing planetary-science DSMC code as a foundation, I have developed a novel, generalized framework for rarefied atmospheric simulation that enables efficient and thorough construction of entire upper-atmospheric models. My dissertation offers an analysis of the methodology of rarefied gas dynamic planetary atmospheric simulation, in addition to discussion of each project's scientific context, the results of my simulations, and their relevance toward the explanation of various observed phenomena in planetary atmospheric science.


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