[CIG-SHORT] Friction Solver optimization

[Brad Aagaard]

Romain,

You should be able to put Neumann BC on any boundary. For example, even 
if you overlap a Neumann BC with a Dirichlet BC, the Neumann BC just 
doesn't contribute. You do need sufficient Dirichlet constraints on each 
side of the fault to prevent rigid body motion. Instead of a Neumann BC 
you can also try a Dirichlet BC with just the node on the fault removed 
from the Dirichlet BC.

If the above suggestions don't resolve the issue, please send a diagram 
of your geometry and BC.

Regards,
Brad


On 08/04/2015 06:43 AM, Romain Jolivet wrote:
> Dear Brad, Matt, Charles and other Pylith developers,
>
> I am currently trying to optimise the solver in an experiment I am
> running and I am having some difficulties getting my run to go
> faster...
>
> The problem is 2D and has a fault cutting from top to bottom (with
> some angle).  Since I gravity is “on”, I have to prescribe adequate
> boundary conditions, particularly at the bottom of the model. As the
> fault cuts the entire domain, one of its node belongs as well to the
> bottom set of nodes. On this set of nodes, I therefore cannot impose
> DirichletBC (otherwise, I am fixing to many degrees of freedom on the
> node that also belongs to the fault). I therefore have imposed
> Neumann BC, with normal traction opposing gravity forces at the
> bottom of the domain.
>
> When I try to use fieldsplit (to speed things up, following one of
> your tutorials, a few years back), the linear solver does not run
> since PETSc issues some NANORINF norm. When I remove the fault from
> the model, it runs fine. I guess this is because one node of my
> domain has 2 types of constraints (one Neumann BC and some frictional
> BC). Is that correct? Should I keep going that way or is it a bad
> idea in general (to mix Neumann and friction on the same node)?
>
> Cheers, Romain
>
> —————————————————————————————————————
> ————————————————————————————————————— Romain Jolivet Postdoctoral
> Fellow
>
> University of Cambridge Department of Earth Sciences Bullard Labs
> Madingley Rise Madingley Road Cambridge CB3 0EZ United Kingdom
>
> email: rpj29 at cam.ac.uk Phone: +44 1223 748 938 Mobile: +44 7596 703
> 148
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