Denis, thanks a lot for your answer and links that you provided.
However, my solution becomes in a way that the displacement values on that
boundary abnormally grow
even without assigning new boundary condition in a time loop. I attach
figures on the zero step (correct) and on the first step (wrong).
I do the following these things on each iteration:
1) recompute rhs vector - system_rhs (which is zero for my problem),
2) compute matrix terms that are on the dirichlet boundary:
for (auto cell = dof_handler.begin_active(); cell!=dof_handler.end();
++cell) {
cell_matrix = 0; cell_rhs = 0; fe_values.reinit(cell);
for (unsigned int face_number=0;
face_number<GeometryInfo<dim>::faces_per_cell; ++face_number) {
if (cell->face(face_number)->at_boundary()) {
// boundary index
int id = cell->face(face_number)->boundary_id();
if (boundary_displacement.find(id) !=
boundary_displacement.end()) {
//compute cell_matrix
Then call function
hanging_node_constraints.distribute_local_to_global(cell_matrix, cell_rhs,
local_dof_indices, system_matrix, system_rhs);
3) Then apply functions to account Dirichlet boundary condition:
VectorTools::interpolate_boundary_values(dof_handler, boundary_id,
DirichletHandler, boundary_values);
MatrixTools::apply_boundary_values (boundary_values,
system_matrix,
solution,
system_rhs);
Can you give some advice how to make it correct?
<https://lh3.googleusercontent.com/-O_1geVdTAOc/Wo2eOCPcdWI/AAAAAAAAA44/s_OauNpGhwcv2d4h3nmBinL40UhP7-S7ACLcBGAs/s1600/iter0.jpg>
<https://lh3.googleusercontent.com/-wHZAFJbU0bI/Wo2egOHamAI/AAAAAAAAA5A/6QJqcgEqD8MiPR5DNLF34OWMF3qX9QZvQCLcBGAs/s1600/iter1.jpg>
On Tuesday, February 20, 2018 at 10:51:17 PM UTC+3, Denis Davydov wrote:
>
> Hi Ilya,
>
> I am not away of principally simple solution, the RHS simply contains your
> bilinear form times interpolated values at constrained DoFs.
> What you can do is to loop over a subset of cells (those which are at the
> boundary), still assemble the local matrix and do
> constraints.distribute_local_to_global() which takes global matrix and RHS.
>
> Or you can use constrained_linear_operator
> <https://www.dealii.org/developer/doxygen/deal.II/group__constraints.html#ga59c2f70370213d436cb9fade9d813478>,
>
> see this <https://groups.google.com/d/msg/dealii/A8dQs5i2n8A/YotvqvGwEgAJ>
> forum discussion.
>
> Please also study this
> <https://groups.google.com/d/msg/dealii/xo3Fa_olNwM/ObOuJPP2JT0J> thread,
> which covers similar question.
>
> Regards,
> Denis.
>
> On Tuesday, February 20, 2018 at 4:46:19 PM UTC+1, Bryukhanov Ilya wrote:
>>
>> Hi,
>>
>> I consider elastic problem and forces and displacements on boundaries are
>> changing with time. I don't want to compute FEM matrix
>> on each step. How to correctly simulate the task? I know that there is a
>> simple solution, but my solution is incorrect :)
>> I have two variables for the system_matrix and rhs_vector. I try to
>> recompute rhs_vector on each step and dirichlet condition
>> is accounted by calling "intepolate_boundary values +
>> apply_boundary_values" on each step with system_matrix and rhs_vector
>> variables inside.
>> I think that I should use initial matrix and the matrix which is modified
>> by Dirichlet procedure and assign latter to the initial matrix on each step?
>> Am I corrent or there is some other solution?
>>
>>
>>
>>
>>
>>
>>
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