[CIG-LONG] CIG-LONG Digest, Vol 43, Issue 14

[Walter Landry]

Karen Paczkowski <karen.paczkowski at yale.edu> wrote:
> Hi Walter,
> 
> I tried adding a slab velocity into the program you sent me and have
> been having issues.  I have attached an xml file with the simplest
> case I tried.  It is just the hydrostatically balanced box you sent
> me, but instead of vx = vy = 0 on the left hand side, it has vx=0 and
> vy = -1.  I expected the down going velocity on the left side would
> cause mass to be pulled into the simulation box on the right hand side
> (like in a cornerflow problem), but instead I just get a velocity
> field that is straight down everywhere.  I feel like it may be
> creating mass at the top boundary, but I'm not sure.  If I set vy=0 on
> the top of the box I get the results I expect, but I would prefer to
> not do that since I would like to track the finite deformation of the
> top interface.

The Stokes equations do not have a frame of reference.  You have to
set them through the boundary conditions.  So at some place in your
simulation you have to set the vertical velocity to zero.  You could
do this on the right side, on the left side, in a corner, or in the
middle.  But you have to do it somewhere.

For this case, if you want mass to be pulled in from the right side,
then set vy=0 on that boundary, but do not set vx.  That would
simulate an infinite reservoir on the right side.

Cheers,
Walter Landry
walter at geodynamics.org