ParStokes and ice shelves

Extension of Elmer in computational glaciology

ParStokes and ice shelves

Postby mewo2 » 28 Apr 2015, 18:05

I've been trying to run some small test simulations of an ice shelf using ParStokes, with an eye towards scaling up to looking at the long-term evolution of Larsen C. Unfortunately, I don't seem to be able to get the parallel solver to converge to anything remotely sensible. Identical runs with the standard Navier-Stokes solver work fine, as do similar runs with grounded geometry (both ParStokes and Navier-Stokes). As far as I can tell, it's just the combination of ParStokes and ice shelf type boundary conditions which breaks down.

So, two questions:

  • Is there anything in particular that has to be done to get ParStokes to play nice with Neumann boundary conditions? As far as I can tell from the code, it should "just work", but is there something I've missed?
  • Has anybody successfully used ParStokes in an ice shelf setup? Is there any special configuration required?

Thanks,
Martin
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Re: ParStokes and ice shelves

Postby tzwinger » 30 Apr 2015, 09:01

Dear Martin,
if your "normal" Stokes solver produced a solution, then - in principle - the ParStokes should do so, too.
Could you please indicate which part of ParStokes refuses to converge: the outer (GCR) system or one of the block-preconditioning sub-problems?
Do you have grounding-line dynamics switched on? Perhaps there is an incompatibility in these procedures, which, to my knowledge, haven't been tested with the block pre-conditioner.

Best wishes,

Thomas
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Re: ParStokes and ice shelves

Postby mewo2 » 01 May 2015, 14:23

Initially, using the actual ice shelf geometry, I thought that the GCR was failing to converge. However, I've been trying to reduce things to a simpler test case, and when I use a simple square geometry, I get (fairly slow) convergence of the GCR, but to a nonsensical result.

I haven't been using any grounding line dynamics - the domain is fully floating, with velocities specified along the upstream and lateral boundaries, and pressure boundary conditions (using the Buoyancy USF) on the downstream and lower boundaries.

I've attached a test case you can try for yourself. The "normal" Stokes solution is generated by seq.sif and the ParStokes by par.sif.
Attachments
parstokes-shelf.tgz
Test case .sif and .geo
(2.47 KiB) Downloaded 411 times
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Re: ParStokes and ice shelves

Postby mika » 05 May 2015, 09:57

Hi,

In the section of Boundary Condition 3 one should have

Normal-Tangential FlowVar = Logical True

instead of the original specification

Normal-Tangential Velocity = Logical True

After this change the simple test case appears to work for me.

- Mika
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