2d Ice Shelf without Grounding Line

Extension of Elmer in computational glaciology

2d Ice Shelf without Grounding Line

Postby Reinhard » 18 Jul 2014, 17:19

Hi Elmers,

I have troubles with an ice-shelf model (prognostic, 2D, flowline, no grounding line). I start from a block, prescribe the flux at the back and the pressure at the bottom & front. I do get nice steady state profiles, however, the final shape unfortunately depends strongly on the time-stepping size and the spatial gridding (I attached a snapshot for dt=0.03,0.1,0.3 years). The system becomes more instable when increasing the horizontal resolution; using the Normal-Tangential Velocity at the bottom does not work.

Does anybody have experience with simple ice-shelf models that do not include a grounding line? I would be grateful if somebody could have a look at the attached zip file ("make compile all2d" should make it run).

Greetings, Reinhard
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Reinhard
 
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Re: 2d Ice Shelf without Grounding Line

Postby gagliar » 18 Jul 2014, 18:18

Hi Reinhard,

I had a look in your sif file. Did you check that you really have a constant flux in your inflow boundary?
If you really have constant BC then i would expect that the steady solution is not a function of the time step...

Regards
Olivier
gagliar
 
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Re: 2d Ice Shelf without Grounding Line

Postby Reinhard » 19 Jul 2014, 01:41

Hi Olivier,

thanks for the quick reply. To prescribe the flux, I scale the x-velocity in the incoming BC with the ice thickness of the current time step. I double checked (depth+height)*velocity_X in Paraview and it stays constant at the inflow boundary (x=0). However, for the case of zero accumulation the flux varies by about 3 % for x>0. Something is still wrong here.
Reinhard
 
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Re: 2d Ice Shelf without Grounding Line

Postby Reinhard » 25 Jul 2014, 18:16

To finish this thread: As suspected by Olivier the Case more or less works. I did some more testing with with the time stepping and the horizontal resolution and it turns out that for a given grid the solution is consistent if the time steps are small enough (e.g. 0.05 and below). I still have problems when using the Normal-Tangential Velocity coordinate system at the ice-shelf bottom as indicated in the "buoyancy" documentation.
Reinhard
 
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