Kinetic Simulation of Air Flow Around Hollow Cylinder Flare Configuration

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76912/1/AIAA-2002-3299-777.pd

Narrow Dust Jets in a Diffuse Gas Coma: A Natural Product of Small Active Regions on Comets

Comets often display narrow dust jets but more diffuse gas comae when their eccentric orbits bring them into the inner solar system and sunlight sublimates the ice on the nucleus. Comets are also understood to have one or more active areas covering only a fraction of the total surface active with sublimating volatile ices. Calculations of the gas and dust distribution from a small active area on a comet's nucleus show that as the gas moves out radially into the vacuum of space it expands tangentially, filling much of the hemisphere centered on the active region. The dust dragged by the gas remains more concentrated over the active area. This explains some puzzling appearances of comets having collimated dust jets but more diffuse gaseous atmospheres. Our test case is 67P/Churyumov-Gerasimenko, the Rosetta mission target comet, whose activity is dominated by a single area covering only 4% of its surface.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98552/1/0004-637X_749_1_29.pd

Development of a General Purpose 3D DSMC Flow Solver on Unstructured Meshes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76553/1/AIAA-2003-3776-874.pd

Monte-Carlo Model for Dust/Gas Interaction in Rarefied Flows

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76515/1/AIAA-2005-4832-757.pd

DSMC Simulation of the Cometary Coma

The study of the comet coma, or its tenuous atmosphere, is a major space application of rarefied gas dynamics, which requires modeling the gas flow in a wide range of Knudsen number. For weak to moderate comets, only the subsolar region of the coma is in a collision dominated regime. In the low density regions of the upper atmospheres of the planets and the planetary satellites and the middle to outer coma of comets the intermolecular mean free path becomes longer then the characteristic length of the problem, which makes using of conventional methods of computational gas dynamics problematic and implies the requirement to model the system based on the Boltzmann equation. Here we present results of a first application of a fully parallelized implementation of Direct Simulation Monte Carlo for axisymmetric cometary comae. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87931/2/696_1.pd

Application of the Monte Carlo Method in Modeling Transport and Acceleration of Solar Energetic Particles

The need for quantitative characterization of the solar energetic particle (SEP) dynamics goes beyond being an academic discipline only. It has numerous practical implications related to human activity in space. The terrestrial magnetic field shields the International Space Station (ISS) and most uncrewed missions from exposure to SEP radiation. However, extreme SEP events with hard energy spectra are particularly rich in hundreds of MeV to several GeV protons that can reach the altitudes of the Low Earth Orbit (LEO). These protons have a high penetrating capability, thus producing significant radiation hazards for human spaceflight. SEPs also have a significant effect on the atmosphere. Sudden ionization of the upper atmosphere at high latitudes that occurs during polar cap absorption (PCA) events can block high frequency (HF) communication for hours, affecting communication with aircraft on intercontinental high-altitude flights. Another effect of SEPs in the atmosphere is creating NOx molecules in the upper atmosphere that can deplete the atmospheric ozone population. The paper also presents an analysis of (1) how various pitch angle diffusion coefficient approximations affect the properties of the simulated SEPs population and (2) discusses how pitch angle scattering when SEPs are beyond 1 AU affects a SEP event decay phase at the Earth's orbit

Numerical Simulation of Dust in a Cometary Coma: Application to Comet 67P/Churyumov-Gerasimenko

The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. With a limited amount of available observational data, planning of the mission as well as the interpretation of measurements obtained by instruments on board the spacecraft requires modeling of the dusty/gas environment of the comet. During the mission, the collision regime in the inner coma will change starting from transitional to fully collisionless. As a result, a physically correct model has to be valid at conditions that are far from equilibrium and account for the kinetic nature of the processes occurring in the coma. A study of the multi-species coma of comet 67P/Churyumov-Gerasimenko is presented in our previous paper, where we describe our kinetic model and discuss the results of its application to cases that correspond to the different stages during the mission. In this work, we focus on numerical modeling of the dust phase in the coma of comet 67P/Churyumov-Gerasimenko and its interaction with the surrounding gas. The basic phenomena that govern the dynamics and energy balance of the dust grains are outlined. The effect of solar radiation pressure and the nucleus gravity in limiting the maximum liftable mass of the grains is discussed. The distribution of the terminal velocity of the dust grains as a function of subsolar angle is derived in the paper. We have found that in the regions with high gradients of the gas density, spike-like features can form in the dust flow. The obtained results represent the state of the coma in the vicinity of the nucleus for a series of stages throughout the Rosetta mission. The implications of the model results for future measurements by the GIADA instrument are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90750/1/0004-637X_732_2_104.pd

Hot carbon corona in Mars’ upper thermosphere and exosphere: 1. Mechanisms and structure of the hot corona for low solar activity at equinox

Two important source reactions for hot atomic carbon on Mars are photodissociation of CO and dissociative recombination of CO + ; both reactions are highly sensitive to solar activity and occur mostly deep in the dayside thermosphere. The production of energetic particles results in the formation of hot coronae that are made up of neutral atoms including hot carbon. Some of these atoms are on ballistic trajectories and return to the thermosphere, and others escape. Understanding the physics in this region requires modeling that captures the complicated dynamics of hot atoms in 3‐D. This study evaluates the carbon atom inventory by investigating the production and distribution of energetic carbon atoms using the full 3‐D atmospheric input. The methodology and details of the hot atomic carbon model calculation are given, and the calculated total global escape of hot carbon from the assumed dominant photochemical processes at a fixed condition, equinox ( L s  = 180°), and low solar activity ( F 10.7 = 70 at Earth) are presented. To investigate the dynamics of these energetic neutral atoms, we have coupled a self‐consistent 3‐D global kinetic model, the Adaptive Mesh Particle Simulator, with a 3‐D thermosphere/ionosphere model, the Mars Thermosphere General Circulation Model to provide a self‐consistent global description of the hot carbon corona in the upper thermosphere and exosphere. The spatial distributions of density and temperature and atmospheric loss are simulated for the case considered. Key Points Hot C corona is simulated at the fixed condition within our frameworks Background atmosphere greatly impacts the structure of hot C corona The estimated global escape rates of hot C is 5.9 x 1023 s‐1Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/107587/1/jgre20239.pd

One-dimensional unsteady fluid motion between two infinite walls

We considered an incompressible fluid motion driven by space-dependent body force. For a one-dimensional case, the problem was solved analytically, with the arbitrary choice of body force coordinate dependence. It was shown that unsteady fluid flow can be represented as a series of separate modes, each with its own characteristic response time. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70559/2/PHFLE6-14-7-2572-1.pd

Unsteady Fluid Motion Between Two Infinite Walls Under Variable Body Force

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77247/1/AIAA-2002-3079-152.pd