Hi,
Ok, after reviewing it, I am going to impose a constraint of the form :
u(0,y) = u(1,y) + lambda and v(0,y) = v(1,y) (lambda is the total
compression of my square). If I'm not mistaken, that is what Jean-Paul was
advicing.
I have to example, one is a 1D-beam on a linear elastic foundation. The
only degree of freedom is the vertical displacement. So everything is in
one dimension. I want to impose the constraint y(0) = y(1) (only vertical
displacement y allowed).
Here is the declaration of my FESystem :
fe(FE_Q<dim>(parameters.poly_degree), dim)
This needs to be changed to Hermitian cubic elements, but this is another
topic. My triangulation is :
Triangulation<dim> triangulation;
with dim = 1. I then construct it, refine it, and mark the "faces". But
what are the faces in 1D?
GridGenerator::hyper_cube(triangulation, 0.0, 1.0);
triangulation.refine_global(std::max (1U,
parameters.global_refinement));
const double length = GridTools::volume(triangulation);
std::cout << "Grid:\n\t Length: " << length << std::endl;
// We mark the sides of the beam in order to apply the boundary
conditions after
typename Triangulation<dim>::active_cell_iterator cell =
triangulation.begin_active(), endc = triangulation.end();
for (; cell != endc; ++cell)
for (unsigned int f = 0; f < GeometryInfo<dim>::faces_per_cell; ++f)
if (cell->face(f)->at_boundary())
{
const Point<dim> face_center = cell->face(f)->center();
if (face_center[0] == 0) //Left
cell->face(f)->set_boundary_id (1);
else if (face_center[0] == 1) //Right
cell->face(f)->set_boundary_id (2);
else //No way
cell->face(f)->set_boundary_id (3);
// Is this working in 1D ?
}
Then I make my sparsity pattern and all the like, and begin my timesteps,
and so on, my Newton-Raphson iterations. The function make_constraints is
as follows :
template <int dim>
void Solid<dim>::make_constraints(const int &it_nr)
{
// Since the constraints are different at different Newton iterations,
we
// need to clear the constraints matrix and completely rebuild
// it. However, after the first iteration, the constraints remain the
same
// and we can simply skip the rebuilding step if we do not clear it.
if (it_nr > 1)
return;
constraints.clear();
std::vector<GridTools::PeriodicFacePair<typename
DoFHandler<dim>::cell_iterator> >
periodicity_vector;
const int direction = 0;
GridTools::collect_periodic_faces(dof_handler_ref, 1, 2, direction,
periodicity_vector);
const FEValuesExtractors::Scalar y_displacement(0);
//DoFTools::make_periodicity_constraints<DoFHandler<dim> >
// (periodicity_vector, constraints/*,
fe.component_mask(y_displacement)*/);
DoFTools::make_periodicity_constraints (dof_handler_ref,1,2, direction,
constraints,
fe.component_mask(y_displacement));
constraints.close();
}
On Wednesday, June 1, 2016 at 11:55:31 AM UTC-5, Daniel Arndt wrote:
>
> It is quite difficult to say what is going wrong without seeing the code.
> You probably want to check first if you really want to impose that kind of
> boundary conditions and follow Jean-Paul's advice.
>
> If the problem persists, it would be really helpful if you can give us a
> minimal compiling code that reproduces the problem.
>
> Best,
> Daniel
>
> Am Mittwoch, 1. Juni 2016 18:05:32 UTC+2 schrieb Bastien Lauras:
>>
>> Hi Daniel,
>>
>> So, I'm modelling a unit square, with an incompressible neo-hookean
>> material. The formulation is (for the density of energy) : c_1 * (I_1 - 3)
>> - p (I_3 - 1) where c_1 = mu / 2, p is a lagrangian parameter, and I_1 and
>> I_3 are the first and third invariant of C = F^T * F.
>> For me to see that my periodic boundary conditions are not applied, I put
>> a non-uniform mu aver the material (graded material). In the example
>> attached, I blocked the horizontal displacement (x_displacement) over left
>> and right faces, and blocked vertical displacement (y_displacement) over
>> the bottom face. And I (try to) apply a periodic boundary condition for the
>> vertical displacement over left and right faces.
>> Attached is the output given to me after the first timestep (all
>> timesteps are the same since I'm not applying any displacement nor force
>> constraint).
>>
>> We can obviously see that vertical displacement is not the same on the
>> left and right faces. Any idea of where it could come from?
>>
>> Many thanks!
>> Best,
>>
>> Bastien
>>
>>
>> On Wednesday, June 1, 2016 at 5:43:48 AM UTC-5, Daniel Arndt wrote:
>>>
>>> Bastian,
>>>
>>> can you provide us with a minimal example that shows your problem? What
>>> you are trying to do should be possible even if it might not be the right
>>> thing to do in your situation.
>>>
>>> Best,
>>> Daniel
>>>
>>> Am Mittwoch, 1. Juni 2016 02:10:36 UTC+2 schrieb Bastien Lauras:
>>>>
>>>> Hi,
>>>>
>>>> I am working on a 2D square, a incompressible neo-hookean material.
>>>> I've used step 44 and modified it to work on a two field formulation (
>>>> *u* and p).
>>>> I am trying to implement periodic boundary conditions for the vertical
>>>> displacement on lateral faces (right and left).
>>>> My left face has boundary indicator 1, and my right face has boundary
>>>> indicator 3.
>>>>
>>>> In the make_constraints function, I've added, after constraints.clear()
>>>> :
>>>>
>>>> DoFTools::make_hanging_node_constraints (dof_handler_ref,
>>>> constraints); // I have local refinement in my code
>>>>
>>>> std::vector<GridTools::PeriodicFacePair<typename
>>>> DoFHandler<dim>::cell_iterator> >
>>>> periodicity_vector;
>>>>
>>>> const unsigned int direction = 0; // I've tried 0 and 1, I didn't
>>>> understan what it really was
>>>>
>>>> GridTools::collect_periodic_faces(dof_handler_ref, 1, 3,
>>>> direction,
>>>> periodicity_vector);
>>>>
>>>> const FEValuesExtractors::Scalar x_displacement(0);
>>>> const FEValuesExtractors::Scalar y_displacement(1);
>>>>
>>>> DoFTools::make_periodicity_constraints<DoFHandler<dim> >
>>>> (periodicity_vector, constraints,
>>>> fe.component_mask(y_displacement));
>>>>
>>>>
>>>> And then I apply Dirichlet boundary conditions on face 1 and 3 on the
>>>> horizontal displacement (x_displacement).
>>>> I've also added the command :
>>>>
>>>> DoFTools::make_hanging_node_constraints (dof_handler_ref, constraints);
>>>>
>>>> before making my sparsity pattern.
>>>> My triangulation is not a parallel::distributed one. I'm working on
>>>> multithreads with the workstream::run of step 44.
>>>>
>>>>
>>>> The problem is that my periodic boundary conditions are not enforced.
>>>> The make_periodicity_constraints command does not change the number of
>>>> constrained degrees of freedom (that I compute using a loop over the DOFs
>>>> and calling constraints.is_constrained(i)).
>>>> And moreover, I can see on my outputs that there is definitely no
>>>> periodicity on my vertical displacement.
>>>>
>>>> Where can the problem come from?
>>>>
>>>> Thanks a lot for your help beforehand!
>>>>
>>>> Bastien Lauras
>>>>
>>>>
>>>
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