[aspect-devel] Some interesting (pathological?!) behaviour of particles ... Do we need CVI here?

Rene Gassmoeller rene.gassmoeller at mailbox.org
Wed Jul 20 14:48:44 PDT 2016

Hi Gerry,

I suppose you refer to the clustering of particles as seen in the
attached screenshot (created from the data you sent us)? That is indeed
pathological and most likely caused by the local divergence of the
velocity inside of cells and could be helped by CVI. However, have you
noted that in this example the mesh is increasingly coarsened within the
first timesteps, so that the largest part of the computation is done on
a 4 by 4 grid? As far as I recall from the hackathon we have not been
able to produce this behavior with more usual resolutions, and I vaguely
remember that the local velocity divergence within cells converges to
zero second-order with mesh size.

Could you add the following line to the "Mesh refinement" subsection of
your parameter file and repeat the computation? That should ensure a
constant mesh:

  set Time steps between mesh refinement       = 0

One thing that is interesting about this model is that the default
parameters apparently only lead to coarsening of the mesh, but no
refinement is happening. The default mesh refinement criterion is
"thermal energy density" (essentially the gradient of rho*cp*T) and this
quantity is zero across the whole model, so this is a border case. Would
be interesting to see why this is happening, but the reasonable thing
for your purpose is most likely to just prevent mesh changes completely.



On 07/19/2016 01:59 AM, Thieulot, C.A.P. (Cedric) wrote:
> Hi Gerry, 
> you make me currious. Do you have a plot to share ?
> Ce/
> On 19 Jul 2016, at 05:05, Elbridge Gerry Puckett <egpuckett at ucdavis.edu> wrote:
>> Hi Rene and Cedric,
>> Check out the SolKz benchmark as in the ASPECT manual, but with particles running around in the flow.
>> Do we need CVI here?
>> - G
>> <solkz.prm>_______________________________________________
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