RE: [deal.II] Computing the solution gradient at the quadrature point on a face

Michael Li Mon, 02 Aug 2021 09:04:01 -0700

Hi Jean-Paul,

Thank you for your hints.

I initialized a local variable solution_grads_u_face_total with fe_face_values_ref[u_fe].get_function_gradients to get the gradient of displacement at the quadrature point on the face (see codes below). But the gradient acquired is not sensible and the resultant deformation is totally wrong.

void assemble_neumann_contribution_one_cell(…)

{

…………….

const FEValuesExtractors::Vector &u_fe = data.solid->u_fe;

std::vector<Tensor<2, dim,NumberType> > solution_grads_u_face_total(data.solid->qf_face.size());

scratch.fe_face_values_ref.reinit(cell, face);

scratch.fe_face_values_ref[u_fe].get_function_gradients(scratch.solution_total,

solution_grads_u_face_total);

for (unsigned int face = 0; face < GeometryInfo<dim>::faces_per_cell; ++face)

{

for (unsigned int f_q_point = 0; f_q_point < n_q_points_f; ++f_q_point)

{

const Tensor<2,dim,NumberType> &grad_u = solution_grads_u_face_total[f_q_point];

const Tensor<2,dim,NumberType> F = Physics::Elasticity::Kinematics::F(grad_u);

………….

}

………..

}

………..

}

Can you tell me what’s wrong with the code above?

Thank you!

Michael

From: Jean-Paul Pelteret
Sent: Sunday, August 1, 2021 1:46 PM
To: dealii@googlegroups.com
Subject: Re: [deal.II] Computing the solution gradient at the quadrature point on a face

Hi Michael,

The problem here is that “scratch.solution_grads_u_total” is initialised with the cell FEValues, and so has n_cell_quadrature_points entries. You need to pass "scratch.fe_face_values_ref[u_fe].get_function_gradients(scratch.solution_total, scratch.solution_grads_u_total);” something that has size n_face_quadrature_points. That’s what this error is informing you.

As a side note, Physics::Transformations::nansons_formula() can compute the transformation of the normal vector + area change for you, should you like the traction direction to follow the moving boundary surface as well.

Best,

Jean-Paul

On 1. Aug 2021, at 20:05, Michael Lee <lianxi...@gmail.com> wrote:

fe_face_values.get_function_gradients returns a rank 2 tensor as the solution is the displacement vector.

Let me be more specific. In the code gallery " Quasi-Static Finite-Strain Compressible Elasticity (The deal.II Library: The 'Quasi-Static Finite-Strain Compressible Elasticity' code gallery program (dealii.org) ). It does not consider the follower force as described in the documentation: "
// We specify the traction in reference configuration.
                // For this problem, a defined total vertical force is applied
                // in the reference configuration.
                // The direction of the applied traction is assumed not to
                // evolve with the deformation of the domain."

So I made a modification to consider the effect of the deformed area on the traction as follows according to the formula da/dA = J sqrt(N C^-1 N) .

void
    assemble_neumann_contribution_one_cell(const typename DoFHandler<dim>::active_cell_iterator &cell,
                                           ScratchData_ASM &scratch,
                                           PerTaskData_ASM &data)
    {
      // Aliases for data referenced from the Solid class
      const unsigned int &n_q_points_f = data.solid->n_q_points_f;
      const unsigned int &dofs_per_cell = data.solid->dofs_per_cell;
      const Time &time = data.solid->time;
      const FESystem<dim> &fe = data.solid->fe;
      const unsigned int &u_dof = data.solid->u_dof;
      const FEValuesExtractors::Vector &u_fe = data.solid->u_fe;

// Next we assemble the Neumann contribution. We first check to see it the
      // cell face exists on a boundary on which a traction is applied and add
      // the contribution if this is the case.
      for (unsigned int face = 0; face < GeometryInfo<dim>::faces_per_cell; ++face)
        if (cell->face(face)->at_boundary() == true
            && cell->face(face)->boundary_id() == 11)
          {
            scratch.fe_face_values_ref.reinit(cell, face);
            scratch.fe_face_values_ref[u_fe].get_function_gradients(scratch.solution_total,
                                                                    scratch.solution_grads_u_total);

            for (unsigned int f_q_point = 0; f_q_point < n_q_points_f; ++f_q_point)
              {
// Note that the contributions to the right hand side vector we
                // compute here only exist in the displacement components of the
                // vector.
                const double time_ramp = (time.current() / time.end());
                const double magnitude  = 0.5*1.95*1000*0.32*0.32*time_ramp; // (Total force) / (RHS surface area)
                Tensor<1,dim> dir;
                dir[0] = 1.0;
                Tensor<1,dim> face_normal = scratch.fe_face_values_ref.normal_vector(f_q_point);

                const Tensor<2,dim,NumberType> &grad_u = scratch.solution_grads_u_total[f_q_point];
                const Tensor<2,dim,NumberType> F = Physics::Elasticity::Kinematics::F(grad_u);
                const SymmetricTensor<2,dim,NumberType> C = Physics::Elasticity::Kinematics::C(F);
                const SymmetricTensor<2,dim,NumberType> C_inv = invert(C);
                const Tensor<1, dim> traction  = magnitude*dir;

                for (unsigned int i = 0; i < dofs_per_cell; ++i)
                  {
                    const unsigned int i_group = fe.system_to_base_index(i).first.first;

                    if (i_group == u_dof)
                      {
                        const unsigned int component_i =
                          fe.system_to_component_index(i).first;
                        const double Ni =
                          scratch.fe_face_values_ref.shape_value(i, f_q_point);
                        const double JxW = scratch.fe_face_values_ref.JxW(f_q_point);

                        data.cell_rhs(i) += (Ni * traction[component_i])
                                            * sqrt(face_normal * C_inv * face_normal)
                                            * JxW;
                      }
                  }
              }
          }
    }

The errors I got are as follows:
If I set the parameters as:   set Polynomial degree = 2     set Quadrature order = 2
An error occurred in line <645> of file </home/michael/dealii-9.2.0/source/fe/fe_values.cc> in function
void dealii::FEValuesViews::internal::do_function_derivatives(const dealii::ArrayView<Number>&, const dealii::Table<2, dealii::Tensor<order, spacedim> >&, const std::vector<typename dealii::FEValuesViews::Vector<dim, spacedim>::ShapeFunctionData>&, std::vector<typename dealii::ProductType<Number, dealii::Tensor<(order + 1), spacedim> >::type>&) [with int order = 1; int dim = 3; int spacedim = 3; Number = double; typename dealii::FEValuesViews::Vector<dim, spacedim>::ShapeFunctionData = dealii::FEValuesViews::Vector<3, 3>::ShapeFunctionData; typename dealii::ProductType<Number, dealii::Tensor<(order + 1), spacedim> >::type = dealii::Tensor<2, 3, double>]
The violated condition was:
static_cast<typename ::dealii::internal::argument_type<void( typename std::common_type<decltype(derivatives.size()), decltype(n_quadrature_points)>::type)>::type>(derivatives.size()) == static_cast<typename ::dealii::internal::argument_type<void( typename std::common_type<decltype(derivatives.size()), decltype(n_quadrature_points)>::type)>::type>(n_quadrature_points)
Additional information:
  Dimension 8 not equal to 4.

If I use set Polynomial degree = 2     set Quadrature order = 1
An error occurred in line <335> of file </home/michael/dealii-9.2.0/source/lac/sparse_direct.cc> in function
void dealii::SparseDirectUMFPACK::factorize(const Matrix&) [with Matrix = dealii::SparseMatrix<double>]
The violated condition was:
status == UMFPACK_OK
Additional information:
UMFPACK routine umfpack_dl_numeric returned error status 1.

On Sunday, August 1, 2021 at 12:08:37 AM UTC-6 peterr...@gmail.com wrote:
The return type should be `Tensor<2,dim,NumberType>` shouldn't it?

Hope this helps. If not, could describe how the code does not work? It it not compiling? Is the result wrong?

PM
On Sunday, 1 August 2021 at 04:09:45 UTC+2 lian...@gmail.com wrote:
Dear All,

I want to do a surface integration which needs to evaluate the gradients of the solution on the face. The following code does not work

  fe_face_values.get_function_gradients(solution, solution_grads);
  for (unsigned int f_q_point = 0; f_q_point < n_q_points_f; ++f_q_point)
              {
const Tensor<2,dim,NumberType> &grad_u = solution_grads[f_q_point];
  ...
  }

Can anybody give a hint on that?

Thanks,
Michael

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RE: [deal.II] Computing the solution gradient at the quadrature point on a face

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