[aspect-devel] New feature that helps with convergence issues due to viscosity jumps

[Magali Billen]

This sounds very interesting, can you explain in simple terms what this change does... that is why or how does it allow the solver to converge more quickly with strong viscosity jumps (or gradients?)?  

Also, do you recommend using this with the Material averaging parameter on or off ? 

I ask because i am currently building subduction models with strong viscosity gradients, and also have convergence challenges (although I am just at the beginning of trying different parameters, etc...)

Sent from my iPhone

> On Jun 23, 2018, at 1:14 AM, Diogo Louro Lourenco <dlourenco at ucdavis.edu> wrote:
> 
> Hi all,
> 
> There is a new feature in ASPECT that helps if you are experiencing solver convergence issues. I was having troubles with convergence due to viscosity jumps of 100x in the mid-mantle while using gplates to prescribe surface velocities. Even for (unrealistic) viscosity jumps of more than 1000x across the 660 km, ASPECT will still converge now. It should help too with other problems that involve localized viscosity jumps in the domain.
> 
> To use it add "GMRES solver restart length" to the Solver parameters section in your .prm file. This is the number of iterations that define the GMRES solver restart length. The value used so far as default in ASPECT was 50 (still the default value if you don't change it). Using a value of 200 fixed my problem. You should keep in mind that the higher the value, the slower the simulation will become, because it increases the memory usage of the solver.
> 
> Thanks to Rene for finding the solution to the problem!
> Hope it helps those who run into the same issue!
> Diogo
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