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  • 1
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    An Adaptive Lattice Boltzmann Scheme for Modeling Two-Fluid-Phase Flow in Porous Medium Systems (2016)
    Wiley
    Details
    Publication Date: 2016-03-10
    Description: We formulate a multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) to simulate two-fluid-phase flow in porous medium systems. The MRT LBM is applied to simulate the displacement of a wetting fluid by a non-wetting fluid in a system corresponding to a microfluidic cell. Analysis of the simulation shows widely varying time scales for the dynamics of fluid pressures, fluid saturations, and interfacial curvatures that are typical characteristics of such systems. Displacement phenomena include Haines jumps, which are relatively short duration isolated events of rapid fluid displacement driven by capillary instability. An adaptive algorithm is advanced using a level-set method to locate interfaces and estimate their rate of advancement. Because the displacement dynamics are confined to the interfacial regions for a majority of the relaxation time, the computational effort is focused on these regions. The proposed algorithm is shown to reduce computational effort by an order of magnitude, while yielding essentially identical solutions to a conventional fully coupled approach. The challenges posed by Haines jumps are also resolved by the adaptive algorithm. Possible extensions to the advanced method are discussed. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Electrification in Mesoscale Updrafts of Deep Stratiform and Anvil Clouds in Florida (2019)
    American Geophysical Union
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    Publication Date: 2019-01-21
    Description: Airborne observations in deep stratiform and anvil clouds showed extensive layers of 10- to 40-kV/m electric fields colocated with highly stratified uniform radar reflectivity of 20 to 25 dBZ from 5- to 9-km altitude. Size distributions with numerous small- and intermediate-sized ice crystals (mostly aggregates) and large aggregates were observed in these regions. We infer that the uniform electric field, radar reflectivity, and broad particle size distributions were the result of mesoscale updrafts, confirmed by high-resolution images of particles showing diffusional growth and no riming. No measurable supercooled liquid water was found in these regions from −10 to −45 °C. Calculated particle collision rates from observed distributions were 〉5 × 10 3 collisions per cubic meter per second in this volume. Laboratory results show that weak charge separation occurs when ice particles collide and separate even in the absence of supercooled water. We infer that charge separation occurred in the mesoscale updrafts via a noninductive mechanism in which ice particles growing by diffusion collide and transfer charge without supercooled water being present. These regions with strong, uniform fields, stratified radar reflectivity, and broad size distributions also occurred in anvils that barely reached the melting zone. Thus, we deduce that the nonriming collisional mechanism acts at middle to upper cloud levels and is not dependent upon electrification occurring near the melting zone. This mechanism should produce two oppositely charged layers of charge with the top layer residing on smaller particles often existing near the top of the cloud. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 3
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    Rationales for the Lightning Launch Commit Criteria (2016)
    In:  CASI
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    Publication Date: 2019-07-12
    Description: Since natural and triggered lightning are demonstrated hazards to launch vehicles, payloads, and spacecraft, NASA and the Department of Defense (DoD) follow the Lightning Launch Commit Criteria (LLCC) for launches from Federal Ranges. The LLCC were developed to prevent future instances of a rocket intercepting natural lightning or triggering a lightning flash during launch from a Federal Range. NASA and DoD utilize the Lightning Advisory Panel (LAP) to establish and develop robust rationale from which the criteria originate. The rationale document also contains appendices that provide additional scientific background, including detailed descriptions of the theory and observations behind the rationales. The LLCC in whole or part are used across the globe due to the rigor of the documented criteria and associated rationale. The Federal Aviation Administration (FAA) adopted the LLCC in 2006 for commercial space transportation and the criteria were codified in the FAA's Code of Federal Regulations (CFR) for Safety of an Expendable Launch Vehicle (Appendix G to 14 CFR Part 417, (G417)) and renamed Lightning Flight Commit Criteria in G417.
    Keywords: Documentation and Information Science; Meteorology and Climatology; Launch Vehicles and Launch Operations
    Type: NASA/TP-2016-219439 , KSC-E-DAA-TN38051
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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