normal vector of boundary faces

[Shahab Golshan]

Dear all,

I was looking for a function to obtain the normal vectors of boundary faces. Are there any functions in dealII which returns the normal vector of a face?

Thank you in advance.

Shahab

[navneet roshan]

Hi Shahab, 

  Please look at the following piece of code, it might be useful to you.

   unsigned int n_face_q_points = face_quadrature_formula.size();

   FEFaceValues<dim> fe_face_values (fe, face_quadrature_formula,
                                      update_values |  update_normal_vectors
                                      | update_JxW_values);

 

   typename DoFHandler<dim>::active_cell_iterator

    cell = dof_handler.begin_active(),
    endc = dof_handler.end();

 // iterate over cells
    for (; cell!=endc; ++cell)
      {

      // iterate over faces

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

         // query if the faces of the cell belong to the boundary id needed
          if (cell->face(face)->at_boundary() == true
              && cell->face(face)->boundary_id() == 2)
            {
              fe_face_values.reinit(cell, face);

              for (unsigned int f_q_point = 0; f_q_point <n_face_q_points;
                   ++f_q_point)
                {
                  const Tensor<1, dim> &Nv =
                   fe_face_values.normal_vector(f_q_point);

                }

        }    

}   

Best,

Navneet

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[Shahab Golshan]

That was very helpful, thank you Navneet.

Best,

Shahab

On Thu, Nov 28, 2019 at 3:26 AM Shahab Golshan <shahab....@gmail.com> wrote:

Dear all,

I was looking for a function to obtain the normal vectors of boundary faces. Are there any functions in dealII which returns the normal vector of a face?

Thank you in advance.

Shahab

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For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en
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[Shahab Golshan]

Thank you again for your help. I have another question. I want to find the projection of a point on a face (the point on a face that has the closest distance to the query point). I think the function: project_real_point_to_unit_point_on_face should do this task, but I'm not sure. Can someone help me on this?

On Thursday, November 28, 2019 at 12:57:43 AM UTC-5, navneet roshan wrote:

On Thu, Nov 28, 2019 at 3:26 AM Shahab Golshan <shahab....@gmail.com> wrote:

Dear all,

I was looking for a function to obtain the normal vectors of boundary faces. Are there any functions in dealII which returns the normal vector of a face?

Thank you in advance.

Shahab

--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en
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[Wolfgang Bangerth]

On 12/2/19 12:52 PM, Shahab Golshan wrote:
> Thank you again for your help. I have another question. I want to find the
> projection of a point on a face (the point on a face that has the closest
> distance to the query point). I think the function:
> project_real_point_to_unit_point_on_face should do this task, but I'm not
> sure. Can someone help me on this?

The function is going to give you a point in the reference coordinate system
of the face. If that's what you want, then that's the function you should
call. Have you tried?

As a general rule, it's often useful to start not using points in real space
and transforming them back into the coordinate systems of cells and faces
(which is very expensive), but by starting from points in the reference
coordinate systems and transforming them forward into real space (cheap). This
is, for example, how we define quadrature points. I don't know what you're
trying to do, but it might be worthwhile thinking about alternative ways to
achieve what you're looking for.

Best
W.

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/