[aspect-devel] "Not converge" problem with variable viscosity.

[Shangxin Liu]

Hi;

Just follow up the old problem that our model runs very slow and cannot
converge with variable viscosity in high global refinement degree (> 2). We
used to think this is due to the time-consuming computation algorithm of
S40RTS initial condition. But I have tried other initial conditions and
this still cannot converge in 3 or higher global refinement degree. We are
using several depth-dependent viscosity model such as the mantle radial
viscosity profile of Steinberger (only radial viscosity part of steinberger
model) or a simple four layer viscosity profile from lithosphere to CMB.
The common phenomenon is that they all can converge quite fast up to only 2
global refinement degree. However, when we make the meshing denser to try 3
or higher global refinement degree, the code just keeps running and cannot
finish (converge).

I have tried making the tolerance up to 10^-4, but the code with 3 or
higher global refinement still cannot finish until the wall time limit. I
also have excluded the possibility that this is due to the large number of
post processing. Because when I run the code with constant viscosity or
just prescribe a narrow viscosity range of 1e20-1e22, the code can converge
very fast. I also used the cell material average operation in the Material
Model subsection but it still cannot solve the problem.

I suppose this is also why the steinberger material model with higher (> 2)
global refinement degree takes very long time and cannot finish.

The attachment is our prm file and two viscosity profiles we're using. Any
suggestions to solve this long-standing problem?

Best,

Shangxin
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