[aspect-devel] Difficulties with tracers and material model

[A.B.M. Graas]

Hi there,

No worries. Actually, I found out later that the problem is not caused by
the material model but rather by strain rate values in the corners. This is
more or less the same problem and should be easy to reproduce. An
demonstration input file is here: http://pastebin.com/5LCvM9fT. Just tested
it with the latest version. It might be necessary to alter the visual range
of your viewer to find the strain rate values, since they are extremely
small. However, in other experiments they can become significantly large
and even invalidate the set-up.

Thanks for looking at this and let me know when you need any additional
information,

Adriaan





2013/6/30 Timo Heister <heister at math.tamu.edu>

> Dear Adriaan,
>
> sorry for net getting back to your email earlier.
>
> >>> - In many of my models I model plasticity by using a Material Model
> >>> implementing the new Interface. Often, though not always, there are
> >>> unexpected
> >>> irregularities (viscosity jumps) in the corners. I found  that the
> >>> evaluate()
> >>> method of the Material Model is never called with a position Point in
> the
> >>> corners before the Stokes equation is solved. However, afterwards the
> >>> evaluate() method is called by the Viscosity postprocessor.
> >>
> >>
> >> You mean the point is never in a corner when assembling the linear
> >> systems, but it may be in a corner when using a postprocessor? That is
> >> correct --  we assemble linear systems using Gauss quadrature formulas
> where
> >> all quadrature points are in the interior of a cell. But we do output
> data
> >> using evaluation points that are the vertices of cells.
> >>
> >> Can you explain how this leads to problems in your models?
> >
> > If I understand this correctly the problem is limited to the
> visualization?
> > (here is an example VTU screenshot:
> > http://img196.imageshack.us/img196/5954/corners.png)
>
> Can you explain what the material model is and what you expect to see
> here? This image highlights some bug for sure (be it in your material
> model, the solver, or in the output).
>
> > What I intend to do is flipping on and off the "Nonlinear iteration"
> > parameter in the input file. However, even when "Nonlinear iteration" is
> > false, and "Nonlinear solver scheme" is set (f.e. to "iterated IMPES")
> > nonlinear iterations are executed. This is the case for box.prm and the
> > parameter file I send you.
>
> "Nonlinear iteration" was a left over parameter that did not have any
> effect. Therefore, I removed this parameter. You should use "Nonlinear
> solver scheme".
>
> Best,
> Timo
>
> --
> Timo Heister
> http://www.math.tamu.edu/~heister/
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