[aspect-devel] Aspect-devel Digest, Vol 12, Issue 3

[Wolfgang Bangerth]

John,

> I've attached a plot showing the basal and surface heat flow for a
> spherical shell model I'm currently running.  The Ra number is ~ 7.66e5.
>   The model has not completely reached steady state yet, but if the
> trend continues there will be a distinct gap between the surface and
> basal heat flow.  The .prm file I used to run the model is also attached.

Can you post a picture of the solution at the time corresponding to the 
end of the plot you show? If this setup is anything similar to the ones 
I've made in this geometry then you shouldn't expect to run into any 
steady-state limit at all. Rather, you get one set of blobs rising at 
the very beginning and then a long phase where hot material streams up 
to the surface. The heat flux will then look like in your graph. But 
it's not a steady state -- it simply moves heat from the bottom into the 
domain but not out of the top, like in your graph. This takes a long 
time until the system finally converts to some more chaotic movement. 
See for example here:
   http://www.math.tamu.edu/~bangerth/step-32.2d.convection.gif
So if you're still in the initial phase where nothing happens for a long 
time, then I wouldn't expect the heat flux at the top and bottom to equal.


> In terms of resolution, I did 4 initial global refinement steps, 3
> initial adaptive refinement steps, and the coarsening and refinement
> fractions are, respectively, 0.05 and 0.3.
>
> I'll try increasing the refinement fraction and initial refinements to
> see if this reduces the gap between the global and surface heat fluxes.
> I am bit surprised that the mesh parameters above did not adequately
> resolve the basal boundary layer, if this is also the issue in my models.

Can you post a picture of the mesh as well?

Best
  W.

-- 
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Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/