One more thing:
you should loop over q point before loop over dof.
Léonhard YU <[email protected]> 于2024年6月8日周六 18:14写道：
> Dear all,
> I am working on impose constant pressure load on a plate's upper surface.
> The code is derived from step-18 and attached below. But I found that the
> diplacement is not right, and it varies when the number of face elements
> changes. I am thinking about something wrong with the loading but I do not
> have any idea. Thanks a lot if you can help me.
> The constant pressure is 1e-2 and the boundary_id for loading is
> bc_uppersurface. The codes attached below:
>
> for (const auto &cell : dof_handler.active_cell_iterators())
> if (cell->is_locally_owned())
> {
> cell_matrix = 0;
> cell_rhs = 0;
>
> fe_values.reinit(cell);
> for (unsigned int i = 0; i < dofs_per_cell; ++i)
> for (unsigned int j = 0; j < dofs_per_cell; ++j)
> for (unsigned int q_point = 0; q_point < n_q_points; ++q_point)
> {
> const SymmetricTensor<2, dim>
> eps_phi_i = get_strain(fe_values, i, q_point),
> eps_phi_j = get_strain(fe_values, j, q_point);
>
> cell_matrix(i, j) += (eps_phi_i * //
> stress_strain_tensor * //
> eps_phi_j //
> ) * //
> fe_values.JxW(q_point); //
> }
>
> // pressure load
> for (const auto &face : cell->face_iterators())
> {
> if (face->at_boundary() && (face->boundary_id() ==
> bc_uppersurface))
> {
> fe_face_values.reinit(cell, face);
> for (unsigned int i = 0; i < dofs_per_cell; ++i)
> {
> const unsigned int component_i =
> fe.system_to_component_index(i).first;
> for (unsigned int face_q_point = 0; face_q_point <
> face_n_q_point; ++face_q_point)
> {
> Tensor<1,dim> dir;
> dir = fe_face_values.normal_vector(face_q_point);
> Point<dim> point_dof =
> fe_face_values.quadrature_point(face_q_point);
> const double magnitude = 1e-2;
> const Tensor<1, dim> traction = -1.0 * magnitude * dir;
> cell_rhs(i) +=
> fe_face_values.shape_value(i, face_q_point) *
> traction[component_i] *
> fe_face_values.JxW(face_q_point);
> }
> }
> }
> }
> }
>
> Best Regards
>
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