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

[Austermann, Jacqueline]

Hi Shangxin,

I agree with you that the step that takes long is probably the Stokes solver and not initializing or post-processing and that convergence becomes much slower when using more complex viscosity profiles. However, I've run global models with global resolution 4, similar viscosity profile to yours and linear solver tolerance of 10^-4 and it converges. I had it run for 30 or so timesteps (the first ones take the longest) with a CFL number of 0.2. I don't recall the exact number of CPUs and runtime for that, but probably something like 600 CPUs for a day or so.
Could you specify how many CPUs you are using and for how long you are running it before it times out?

Thanks!
Jacky


On Aug 6, 2015, at 2:44 PM, Shangxin Liu wrote:

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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