[aspect-devel] Van Keken et al. 2008 subduction benchmark

Wolfgang Bangerth bangerth at tamu.edu
Fri Dec 9 13:42:06 PST 2016

On 12/09/2016 12:12 PM, Max Rudolph wrote:
> I did not try the modification to allow a linear ramp. The problem that I
> encountered was not associated with the pressure field in the wedge. It was
> actually along the subduction interface where the downgoing plate meets the
> over-riding plate. There is a discontinuity in the velocity field there. The
> velocity field is locally divergence-free but it may not be divergence-free in
> the integral sense when interpolated using the finite element basis functions.

That's one possible issue. When you say that it's locally divergence free, 
does this also hold at the points along the interface?

> One possible work-around would be to prescribe zero dynamic pressure
> throughout the rigid downgoing and over-riding plate (the correct solution).
> Doing so would mean prescribing all of the degrees of freedom for every node
> in the prescribed velocity region. I think that this would be a very
> straightforward modification of the prescribed velocity plugin. Maybe we can
> chat for a few minutes about this at the ASPECT dinner?

Sure. Yours sounds like a reasonable solution. I don't recall who wrote this 
plugin, so I don't know how difficult it would be to implement what you 
suggest; but it can't be very difficult at all.


Wolfgang Bangerth          email:                 bangerth at colostate.edu
                            www: http://www.math.colostate.edu/~bangerth/

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