[aspect-devel] Problems with periodic boundary conditions

[Max Rudolph]

Dear All,
I'm trying to set up a simple 2D calculation (in a box) with periodic
boundary conditions. I keep running into the error message below
(about numerical breakdown). A solution is obtained for the first
timestep (0) but for the second timestep the 'numerical breakdown'
error appears. It seems that this error is related to Ra - aspect runs
fine for the low-Ra case but when I increase the layer depth so that
Ra~10^8, there are errors. I tried re-meshing every timestep and
reducing the CFL number to 0.01 to no avail. Is this a known problem?
Either way, do you have any suggestions about how to work around this?

Thanks!
Max

----------------------------------------------------
Exception on processing:

--------------------------------------------------------
An error occurred in line <246> of file
</opt/deal.II-8.1-src/source/lac/trilinos_solver.cc> in function
    void dealii::TrilinosWrappers::SolverBase::execute_solve(const
dealii::TrilinosWrappers::PreconditionBase &)
The violated condition was:
    false
The name and call sequence of the exception was:
    ExcMessage("AztecOO::Iterate error code -2: " "numerical breakdown")
Additional Information:
AztecOO::Iterate error code -2: numerical breakdown
--------------------------------------------------------

Aborting!
----------------------------------------------------

input file used (left file is my modified input file, right file is cookbook.

max at harding:~/aspect_runs$ diff periodic_box.prm
/opt/aspect-dev/cookbooks/future/periodic_box.prm
2c2
< set CFL number                             = 0.01
---
> set CFL number                             = 1.0
4c4
< set Output directory                       = output_pb
---
> set Output directory                       = output
39,41c39,41
<     set X extent = 4.2e6
<     set Y extent = 3.0e6
< #    set Z extent = 5.e5
---
>     set X extent = 1.e6
>     set Y extent = 5.e5
>     set Z extent = 5.e5
58,60c58
<     set Function constants = Ttop=0.0, Tbottom=1000.0, p=0.01,
H=3.0E6, W=4.2e6, pi=3.1415926
<     set Function expression = Tbottom - (Tbottom-Ttop)*y/H +
p*sin(pi*y/H)*cos(2.0*pi*x/W)
<
---
>     set Function expression = if((sqrt((x-1.e5)^2+(y-4.0e5)^2)<5.0e4) | (sqrt((x-3.e5)^2+(y-2.e5)^2)<1.0e5) , 800.0, 0)
85c83
<   set Time steps between mesh refinement = 1                       #
default: 10
---
>   set Time steps between mesh refinement = 10                       # default: 10
100c98
<   set List of postprocessors = velocity statistics, visualization,
temperature statistics, heat flux statistics, basic statistics
---
>   set List of postprocessors = visualization
104,105c102,103
<     set Output format                 = hdf5
<     set Time between graphical output = 0.0
---
>     set Output format                 = vtu
>     set Time between graphical output = 1.e3
max at harding:~/aspect_runs$