Hi Tri Dat,
was is your current status on this?
Can you provide a minimal example in terms of number of elements and
process count where the problem occurs?
Kind regards
Bernd
On 11/28/2015 01:30 AM, Tri Dat NGO wrote:
Hi Birger and Alex,
Thank you very much for your shares and your advices.
I confirm that installing SuperLU solved my problem in the homogeneous
case.
But when trying to run my tests in heteogeneous media, I got the same
convergence problem as Birger:
"Newton: Caught exception: "NumericalProblem
[newtonSolveLinear:../dumux/nonlinear/newtoncontroller.hh:389]: Linear
solver did not converge"
I don't get any convergence at all, even with very small time steps.
Any hints are welcome.
@ Alex: Did you try run your test with fully implicit cc model? From
my experience, in general, cc model works correctly in parallel
(parallel run are faster than sequentiel run) but not box model.
Best regards,
Tri Dat
2015-11-26 17:26 GMT+01:00 Alexander Kissinger
<[email protected]
<mailto:[email protected]>>:
Hi Birger and Tri Dat,
are you not getting any convergence at all or do you get
convergence at a smaller time step size?
Do you get the error in the first Newton step of a time step or in
between somewhere?
I have similar problems for parallel computations with bad aspect
ratios (300:10). Additionally I have horizontal layers with large
differences in permeability. I am using AMG (also with SuperLU as
coarse solver) and the fully implicit box model (1p2c).
Running the same grid sequentially leads to much larger time step
sizes until my time step is constrained by the linear solver.
I also ran the my grid for a homogeneous case with simplified
physics which the linear solver was able to handle.
I assume that the problem in my case is a combination of
heterogeneities and the bad aspect ratio.
Unfortunately I was not able to resolve the problem. Some actions
that slightly improved the behavior were:
(1) In amgproperties.hh setting the Preconditioner from
Dune::SeqSSOR to Dune::SeqILUn (This also improved convergence
behavior of the linear solver for the sequential case)
(2) If you use Dune ALUGrud. Try setting METIS_PartGraphRecursive
in your alugrid.cfg file. Another point I observed is that the
partitioning method played a huge role. Metis worked the best for me.
(3) In amgbackend.hh increasing the coarsen target to a value
larger than 2000 (for example 10000, 50000 or 100000). In the
following line:
Dune::Amg::Parameters params(15,2000,1.2,1.6,Dune::Amg::atOnceAccu);
You can see the effect of the latter when you set the linear
solver verbosity to 2 in your input file:
[LinearSolver]
Verbosity = 2
AMG will print the different agglomeration levels for each Newton
step. If you increase the coarsen target there should be fewer
levels. On the highest level the coarse solver (SuperLU) is used.
The convergence in my case improved with increasing number of
unknowns in the highest level. The downside to this is that it
takes much more time to solve the coarse linear system with
SuperLU which for me meant that I was much faster in the
sequential case than in the parallel one in the end. But maybe you
have more luck.
Best regards
Alex
On 11/26/2015 04:05 PM, Birger Hagemann wrote:
Hi Tri Dat,
I had recently the same problem with parallel computation on a
realistic reservoir grid where also the horizontal dimensions are
much larger than the vertical. The error message was the same.
Bernd gave me the hint to install SuperLU. However, after
installing SuperLU the error was only changed to:
“Newton: Caught exception: "NumericalProblem
>>[newtonSolveLinear:…/dumux/dumux/nonlinear/newtoncontroller.hh:380]:
>>Linear solver did not converge"
Maybe installing SuperLU will solve your problem. My problem is
also still unsolved, thus, any hints are welcome. I am also using
a fully implicit cell-centered model. The same simulation is
working when started on only one processor and the same model is
working in parallel on more simple grids.
Kind regards
Birger
*Von:*Dumux [mailto:[email protected]] *Im
Auftrag von *Tri Dat NGO
*Gesendet:* Dienstag, 24. November 2015 20:07
*An:* DuMuX User Forum
*Betreff:* Re: [DuMuX] Convergence problem for 3D simulations (2p
cell-centered model, ALUGrid)
Sorry, I forgot to add my files.
Kind regards,
Tri Dat
2015-11-24 20:03 GMT+01:00 Tri Dat NGO <[email protected]
<mailto:[email protected]>>:
Hi Dumuxers,
I would like to run parallel simulations of CO2 injection into a
3D reservoir of which the horizontal extents are much higher than
the vertical one: Lx/Lz = Ly/Lz >> 1 (e.g. a reservoir of 1000m x
1000m x 50 m). A 2p cell-centered model is used.
The domain is described on a cartesian grid of 100x100x100 (1E+6)
cells. The CO2 is injected into the domain at X=500m and Y =
500m by using the Peaceman's well model (bhp). The pressure at
the boundaries perpendicular to the Y-axis is set to the initial
hydrostatic pressure. All others boundaries are no-flux Neumann
boundaries. At the first step, we consider, for simplicity, an
homogeneous reservoir. You can find in attachment the *.hh files
of my test.
The simulation converges only if the reservoir is anisotropic
(Kxx/Kzz = Kyy/Kzz >>1), meaning that the medium is lowly
permeable in Z-direction. Nevertheless, when the domain is
isotropic (Kxx = Kzz), a problem occurs: Newton solver did not
converge. The error message is "MathError
[mgc:/home/share/soft/dumux-2.6/include/dune/istl/paamg/amg.hh:825]:
Coarse solver did not converge".
Moreover, the same test works correctly on isotropic but thicker
domains (e.g. 1000m x 1000m x 250 m, the grid is always of
100x100x100).
I don't understand why a same test works on a grid but not on
another grid. Is this related to the numerical scheme
(fully-implicit, cell-centered)?
Any help will be greatly appreciated!
Kind regards,
Tri Dat
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