Dear Daniel and Timo,
Thank you very much for your advises. I have figured out the problem with
the periodic constraints but I do not know where this problem comes from.
Let me explain the issue more. As I mentioned earlier, I have applied
periodic BC for displacement field and I want to apply boundary
displacement as well using constraints.set_inhomogeneit. I mean,
u(0,y)=u(L,y)+delta_x for the left and right faces and
u(x,0)=u(x,L)+delta_y for the bottom and top faces.
The following is my periodic constraints and the code for boundary
displacement.
//////////////////////////////////////////////////////////////////////////////////
template <int dim>
void Solid<dim>::make_constraints(const int &it_nr)
{
if (it_nr > 1)
return;
constraints.clear();
const bool apply_dirichlet_bc = (it_nr == 0);
DoFTools::make_periodicity_constraints(dof_handler,
/*b_id*/ 0,
/*b_id*/ 1,
/*direction*/ 0,
constraints);
DoFTools::make_periodicity_constraints(dof_handler,
/*b_id*/ 2,
/*b_id*/ 3,
/*direction*/ 1,
constraints);
// This block add to the periodicity constraint the boundary
displacement
// in x direction for left and right faces and in y direction
for top and bottom faces
{
{
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(x_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();
for(unsigned int i = 0; i < nb_dofs_face_x; i++)
{
constraints.set_inhomogeneity(*dofs_x, (apply_dirichlet_bc ?
5e-2 : 0.0));
dofs_x++;
}
}
{
IndexSet selected_dofs_y;
std::set< types::boundary_id > boundary_ids_y=
std::set<types::boundary_id>();
boundary_ids_y.insert(2);
DoFTools::extract_boundary_dofs(dof_handler,
fe.component_mask(y_displacement),
selected_dofs_y,
boundary_ids_y);
unsigned int nb_dofs_face_y = selected_dofs_y.n_elements();
IndexSet::ElementIterator dofs_y = selected_dofs_y.begin();
for(unsigned int i = 0; i < nb_dofs_face_y; i++)
{
constraints.set_inhomogeneity(*dofs_y, (apply_dirichlet_bc ?
-5e-2: 0.0));
dofs_y++;
}
}
}
//and here I fix one displacement DoF in every direction ....
}
}
constraints.close();
}
//////////////////////////////////////////////////////
I printed the constraint matrix for a domain of just one 2D linear element
(4 node and 8 DoFs) as follows:
4,5___________6,7
| |
| |
| |
| |
0,1__________ 2,3
when I just apply delta_x:
0 6: 1
0: 0.05
1 7: 1
2 6: 1
3 7: 1
4 6: 1
4: 0.05
5 7: 1
when I just have delta_y:
0 6: 1
1 7: 1
1: -0.1
2 6: 1
3 7: 1
3: -0.05
4 6: 1
5 7: 1
As you can see, the inhomogenity applied on DoF 1 is ironically doubled and
that's why the corner element get distorted.
I was wondering why despite the identical code
for constraints.set_inhomogeneity for the x and y direction, I have this
problem.
Any hint would be appreciated,
Thanks,
Hamed
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