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Using MFIX-DEM to Probe the Dynamics of Crystal Mushes

Using MFIX-DEM to Probe the Dynamics of Crystal Mushes. George Bergantz , Jill Schleicher University of Washington. (with thanks to Alain Burgisser for many discussions). "No one believes the results of computational fluid dynamics except the one who performed the calculations,

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Using MFIX-DEM to Probe the Dynamics of Crystal Mushes

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  1. Using MFIX-DEM to Probe the Dynamics of Crystal Mushes George Bergantz, Jill Schleicher University of Washington (with thanks to Alain Burgisser for many discussions)

  2. "No one believes the results of computational fluid dynamics except the one who performed the calculations, And everyone believes experimental results except the one who performed the experiment.” --anon (cited by P.J. Roache, “Verification and Validation in Computational Science”, 1998, pg. 273)

  3. It’s a multiscale world! • Compositional, mechanical diversity reflects progressive non-linear feedback among scales

  4. Understanding the physics of volcanoes These are fluidized beds!

  5. Geological observations/questions motivate approach: • Complex crystal cargo, “antecrysts” • Rapid “unlocking” and mixing of crystal mushes • Old crystals in zero age erupted rocks • Picrites, other OIB systems erupted mushes • What controls the time dependence and emergent behavior of crystal-rich systems?

  6. Sandes et al., Nature 2011

  7. Porous media flow Increasing mass flux Stable void bubble Chimney/bypass

  8. Note strength hysteresis from particle-particle contacts Philipp and Badiane, 2013, Localized fluidization in a granular medium, Phys. Rev. E, 87, 042206

  9. Problems recovering critical state behavior with continuum method • Non-affine deformation (!) • Continuum method imposes particle-scale kinematics • Emergent features like shear band evolution not recovered • Real particle systems can show formally chaotic behavior at all Reynolds numbers

  10. Multiphase flow theories and methods Increasing resolution and cost

  11. “Correcting” for viscous fluid Yang and Hunt, Physics of Fluids, 2006

  12. Mixing? • Which kind: particle-particle? Particle-fluid? Fluid-fluid? • Random vs. perfect mixture • Lacey index (one of over 30!) for particle-particle, zero for fully segregated, unity for perfectly random

  13. Scaling of open-system processes • Not many “natural” scales • Dimensionless velocity U* scales as f(Re, Ar, H, f, e)

  14. Run simulations

  15. Magmas? • Mushes may fail in a Mohr-Coulomb sense that sets the initial scale and volume of decompaction • Mixing efficiency is dictated by the open-system tempo and length scale • A whole lot more needs to be done to establish the verisimilitude of these efforts

  16. Thanks

  17. Time dependence in ‘tapered beds’ is complex • Porous flow • Creation of a decompacted volume with a more compacted region above • Necking of initial size into a “straw” • Mixing bowl created

  18. Self-similarity suggested by scaling

  19. Morphodynamics of unconfined dense mush Johnsen et al., Phys. Rev. E, 2008

  20. Porosity change only 3% Johnsen et al., Phys. Rev. E, 2008

  21. Decompaction from top down Johnsen et al., Phys. Rev. E, 2008

  22. Dense multiphase flow much more complex than dilute • Non-affine deformation • Stress transmission arises stochastically from particle “stress chains” • Local emergence of strength and strain partitioning not necessarily related in any simple way to external or forcing length scales

  23. Mixing index

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