Hi all,

I had a problem, when I generate the plate-driven flow in the model.

When I tested with low viscosity and large grid, it was successfully converged.

I extended my model with larger number of repetitions, its solution did not converge anymore.

To solve this problem, I tried to use large number of iterations, coarse grid, removing null-space (net rotation, net surface rotation).

Could you please share your any opinion about this issues?

Thank you in advance,

Here is my input prm file and error massage below.

original.prm (3.4 KB)

Additional information:

The iterative Stokes solver in Simulator::solve_stokes did not

converge.

```
The initial residual was: 4.490404e+22
The final residual is: 4.024511e+18
The required residual for convergence is: 2.661754e+16
See
/data/dynamics/output/spherical/solver_history.txt
for the full convergence history.
The solver reported the following error:
--------------------------------------------------------
An error occurred in line <1287> of file
</opt/dealii/deal.II-v9.4.0/include/deal.II/lac/solver_gmres.h>
in function
void dealii::SolverFGMRES<VectorType>::solve(const MatrixType&,
VectorType&, const VectorType&, const PreconditionerType&) [with
MatrixType = aspect::internal::StokesBlock; PreconditionerType =
aspect::internal::BlockSchurPreconditioner<dealii::TrilinosWrappers::PreconditionAMG,
dealii::TrilinosWrappers::PreconditionBase>; VectorType =
dealii::TrilinosWrappers::MPI::BlockVector]
The violated condition was:
false
Additional information:
Iterative method reported convergence failure in step 1000. The
residual in the last step was 4.02451e+18.
This error message can indicate that you have simply not allowed a
sufficiently large number of iterations for your iterative solver to
converge. This often happens when you increase the size of your
problem. In such cases, the last residual will likely still be very
small, and you can make the error go away by increasing the allowed
number of iterations when setting up the SolverControl object that
determines the maximal number of iterations you allow.
The other situation where this error may occur is when your matrix is
not invertible (e.g., your matrix has a null-space), or if you try to
apply the wrong solver to a matrix (e.g., using CG for a matrix that
is not symmetric or not positive definite). In these cases, the
residual in the last iteration is likely going to be large.
```