8,726 research outputs found
A simulation of solar convection at supergranulation scale
We present here numerical simulations of surface solar convection which cover
a box of 303.2 Mm with a resolution of
31582, which is used to investigate the dynamics of scales
larger than granulation. No structure resembling supergranulation is present;
possibly higher Reynolds numbers (i.e. higher numerical resolution), or
magnetic fields, or greater depth are necessary. The results also show
interesting aspects of granular dynamics which are briefly presented, like
extensive p-mode ridges in the k- diagram and a ringlike distribution
of horizontal vorticity around granules. At large scales, the horizontal
velocity is much larger than the vertical velocity and the vertical motion is
dominated by p-mode oscillations.Comment: Contribution to the proceedings of the workshop entitled "THEMIS and
the new frontiers of solar atmosphere dynamics" (March 2001), 6 pages, to
appear in Nuovo Cimento
Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings
Granular packings slowly driven towards their instability threshold are
studied using a digital imaging technique as well as a nonlinear acoustic
method. The former method allows us to study grain rearrangements on the
surface during the tilting and the latter enables to selectively probe the
modifications of the weak-contact fraction in the material bulk. Gradual ageing
of both the surface activity and the weak-contact reconfigurations is observed
as a result of repeated tilt cycles up to a given angle smaller than the angle
of avalanche. For an aged configuration reached after several consecutive tilt
cycles, abrupt resumption of the on-surface activity and of the weak-contact
rearrangements occurs when the packing is subsequently inclined beyond the
previous maximal tilting angle. This behavior is compared with literature
results from numerical simulations of inclined 2D packings. It is also found
that the aged weak-contact configurations exhibit spontaneous restoration
towards the initial state if the packing remains at rest for tens of minutes.
When the packing is titled forth and back between zero and near-critical
angles, instead of ageing, the weak-contact configuration exhibits "internal
weak-contact avalanches" in the vicinity of both the near-critical and zero
angles. By contrast, the stronger-contact skeleton remains stable
Cellular Automaton for Realistic Modelling of Landslides
A numerical model is developed for the simulation of debris flow in
landslides over a complex three dimensional topography. The model is based on a
lattice, in which debris can be transferred among nearest neighbors according
to established empirical relationships for granular flows. The model is then
validated by comparing a simulation with reported field data. Our model is in
fact a realistic elaboration of simpler ``sandpile automata'', which have in
recent years been studied as supposedly paradigmatic of ``self-organized
criticality''.
Statistics and scaling properties of the simulation are examined, and show
that the model has an intermittent behavior.Comment: Revised version (gramatical and writing style cleanup mainly).
Accepted for publication by Nonlinear Processes in Geophysics. 16 pages, 98Kb
uuencoded compressed dvi file (that's the way life is easiest). Big (6Mb)
postscript figures available upon request from [email protected] /
[email protected]
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