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Poor nonlinear solver performance for VEP rheology + particles + continous compositional fields #5734
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After a bit more testing (see attached plot), it looks like the best convergence behavior for the modified Continental Extension cookbook (elasticity added, etc) with particles is obtained by using the cell average (CAV) particle interpolation scheme (+ DG composition field ~ DGC = True). Using the Quadratic or Bilinear Least Squares + limiters (QLS + LIM, BLS + LIM) produces poorer convergence behavior. Using a continuous composition field (default option) with a cell average particle interpolation scheme fails to produce convergence within 200 nonlinear iterations (max value) on multiple time steps. I can do further testing to see if #5685 (@bangerth) or #5754 (@YiminJin) help. At this stage, I think it is sufficient to recommend that users just use a discontinuous composition field with VEP models, as this will be required when #4370 is merged. I will make a note of this in the update continental extension cookbook documentation (working on PR now). |
Just to summarize the discussion at the hackathon: @anne-glerum and @MFraters could not reproduce the problems after switching off the operator splitting for compositional fields, but the behavior remains for @naliboff. |
An update based on further testing:
|
A more detailed summary of the tests mentioned by @anne-glerum, which all use the same PRM file as @MFraters and are broken down into the following cases: Case 1
Case 2
Case 3
Case 4
The main takeaways here are:
|
While updating the continental extension bookmark (see attached PRM), I found that switching between using continuous and discontinuous compositional fields (
set Use discontinuous composition discretization =
true
orfalse
) in combination with particles for track advected properties (viscoelastic stress, strain, and chemical compositions) has a large effect on nonlinear solver convergence behavior.For
set Use discontinuous composition discretization =
true
, the Newton solver will converge in anywhere from ~ 8-16 nonlinear iterations.For
set Use discontinuous composition discretization =
false
, the Newton Solver on many time steps will often reach the maximum number of allowed nonlinear iterations (200) and will clearly not converge to the selected tolerance with further iterations.After discussion with @gassmoeller, this makes intuitive sense as interpolating the particle values to a discontinuous compositional fields makes sense for certain (cell average used here) or all interpolation schemes (cell average was used here).
I have not checked whether using a DG field for a model tracking properties on fields has the same effect, but will follow up with results checking that. I will also test whether this choice influences other viscoelastic benchmarks without plasticity.
Overall, somewhat of a mute point as #4370 enforces using DG compositional fields with viscoelasticity, but certainly useful information in the short term and potentially for future issues.
continental_extension_vep_particles.prm.txt
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