[aspect-devel] Difficulties with tracers and material model

[Wolfgang Bangerth]

Hi Adriaan,

> - Running particle tracers crash with the message "Particle count unexpectedly
> changed". This happens mostly when timesteps are large (CFL number is large).
> I suspect that the tracers postprocessor might not be ready for particles
> leaving through velocity boundaries?

Is a "velocity boundary" one where the normal velocity is (or may be) nonzero? 
Eric has already suggested one solution. We may want to make this more robust 
but I'd like to know a bit more about the case you are considerig.


> - 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 "Max nonlinear iterations" and/or "Nonlinear solver scheme" is set in the
> input file, one is not able to turn off the nonlinear iterative solver by
> setting "Nonlinear iteration" to false.

I think here it would be useful to have an input file (maybe based on a simple 
one from the tests/ directory, or based on box.prm) along with an explanation 
of what you expect to happen.

In any case, thanks for the feedback!
Cheers
  W.

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