Hi Peter,
Thanks for your reply. I have PBC in all the 3 directions ( I have included
the code snippet above for only 1 direction). In addition to this, I want
to apply compression in 1 direction.
I checked the constraints using
AffineConstraints::is_consistent_in_parallel() and it returned 1. So, that
does not seem to be the issue. I found this problem with multiple processes
even with the step-45 example. Everything works fine when I have DBC
instead of PBC.
Thanks in advance,
On Sun, Jul 4, 2021 at 1:44 AM 'peterrum' via deal.II User Group <
dealii@googlegroups.com> wrote:
> Dear Raghunandan,
>
> I don't quite understand what you want to accomplish. You are setting PBC
> constraint between the left and right face and after that you apply DBC on
> the left face? Is that about right?
>
> My first guess would be that you constraints are somewhere not globally
> consistent. Maybe you could try to check them
> with AffineConstraints::is_consistent_in_parallel(). There is also the
> function AffineConstraints::make_consistent_in_parallel(), which might also
> help. Latter is quite a new function so we might have missed some corner
> cases.
>
> Hope this helps,
> PM
>
> On Sunday, 4 July 2021 at 03:36:28 UTC+2 r...@iastate.edu wrote:
>
>> Hello team,
>>
>> I am running a 3D simulation with periodicity in all 3 directions.
>> I have defined the periodic boundary conditions using (similarly in the
>> other 2 directions) -
>>
>>
>>
>>
>> *DoFTools::make_periodicity_constraints(dof_handler,
>> /*b_id*/ 0, /*b_id*/
>> 1, /*direction*/
>> 0, constraints);*
>> and the deformation of the box using -
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> *IndexSet selected_dofs_x; std::set< types::boundary_id >
>> boundary_ids_x= std::set<types::boundary_id>();
>> boundary_ids_x.insert(0);
>> DoFTools::extract_boundary_dofs(dof_handler,
>> fe.component_mask(y_displacement),
>> selected_dofs_x,
>> boundary_ids_x); unsigned int nb_dofs_face_x =
>> selected_dofs_x.n_elements(); IndexSet::ElementIterator dofs_x =
>> selected_dofs_x.begin(); double relative_displacement_x = 0.0;
>> if(timestep<=020) relative_displacement_x = 5e-4; else
>> if(timestep%02==0) relative_displacement_x = 2e-4; else
>> relative_displacement_x = 0.0; for(unsigned int i = 0; i <
>> nb_dofs_face_x; i++) { constraints.add_line (*dofs_x);
>> constraints.set_inhomogeneity(*dofs_x, (apply_dirichlet_bc ?
>> relative_displacement_x : 0.0)); dofs_x++; }*
>> This works fine when run using a single process. But when increased to 2
>> processes, it pauses after few time steps without any error message. When
>> used more than 2 processes, it does not converge in the first time step
>> itself. I am not sure what is causing the problem.
>>
>> I also tested it with step-45. It works fine with 1 and 2 processes. But
>> when 4 processes are used, it gives out the following error:
>> [100%] Built target step-45
>> Refinement cycle 0
>> Assembling...
>> Computing preconditioner...
>> Solving...
>>
>> ----------------------------------------------------
>> Exception on processing:
>>
>>
>> ----------------------------------------------------
>> Exception on processing:
>>
>> --------------------------------------------------------
>> An error occurred in line <457> of file
>> </usr/include/deal.II/lac/solver_cg.h> in function
>> void dealii::SolverCG<VectorType>::solve(const MatrixType&,
>> VectorType&, const VectorType&, const PreconditionerType&) [with MatrixType
>> = Step45::SchurComplement<dealii::TrilinosWrappers::PreconditionJacobi>;
>> PreconditionerType = dealii::TrilinosWrappers::PreconditionAMG; VectorType
>> = dealii::TrilinosWrappers::MPI::Vector]
>> The violated condition was:
>> false
>> Additional information:
>> Iterative method reported convergence failure in step 65. The residual in
>> the last step was 4.56146e-06.
>>
>> 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.
>>
>> I would appreciate any pointers on the possible mistakes I might be
>> making.
>>
>> Best regards,
>> Raghunandan.
>>
>> --
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--
*Raghunandan Pratoori*
Graduate Student
Aerospace Engineering <https://www.aere.iastate.edu/> | Iowa State
University
2048 Howe Hall | <srhi...@iastate.edu>515-708-6767
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