[CIG-LONG] Corner Flow Velocity unstable at initial condition

[Walter Landry]

Karen Paczkowski <karen.paczkowski at yale.edu> wrote:
> The top BC is vx = 1 and vy =0, the left is vx = 0 and vy = -1, the
> boundary conditions for the right and bottom use the input files to
> give them the values of the analytic solution.  The velocity gradient
> in the top left corner spans the length of 10% of the box size along
> the top and left side.

The boundary conditions are over-specified .  If vx and vy are set on
all the boundaries, then the numerical scheme will produce
instabilities like this.  For the first step, it is not so bad because
the boundary conditions are close enough.  But for the second step,
notice that the mesh has distorted a bit on the right and bottom.  Now
the boundary conditions are really not right, and you get artifacts
like what you see.

I took out the boundary conditions for the right and bottom, and got
reasonable results.  I also set the right and bottom boundaries to be
static, so that they will not distort.  I have attached a new input
file.  Let me know if you have any more problems.

Cheers,
Walter Landry
walter at geodynamics.org
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