As an update to this thread (please let me know if you think i should start
a new one):
I continued to find out why I wasn't getting the correct applied Dirichlet
values on the boundary for a code very similar to step-20, where the
Dirichlet condition is applied weakly using
for (unsigned int face_no=0;
face_no<GeometryInfo<dim>::faces_per_cell;
++face_no)
if (cell->at_boundary(face_no))
{
fe_face_values.reinit
<https://www.dealii.org/8.4.1/doxygen/deal.II/classFEFaceValues.html#af6e079ca7429d54433343d50bd334c3c>
(cell, face_no);
pressure_boundary_values
.value_list (fe_face_values.get_quadrature_points
<https://www.dealii.org/8.4.1/doxygen/deal.II/classFEValuesBase.html#a5f8732ebe2d3c6746f6de26a79cb1e45>
(),
boundary_values);
for (unsigned int q=0; q<n_face_q_points; ++q)
for (unsigned int i=0; i<dofs_per_cell; ++i)
local_rhs(i) += -(fe_face_values[velocities].value (i, q) *
fe_face_values.normal_vector
<https://www.dealii.org/8.4.1/doxygen/deal.II/classFEValuesBase.html#a130eea0fa89263d93b20521addc830c7>(q)
*
boundary_values[q] *
fe_face_values.JxW
<https://www.dealii.org/8.4.1/doxygen/deal.II/classFEValuesBase.html#ad097580a2f71878695096cc73b271b9d>
(q));
}
I then looked at step-20 - I used the exact code but solved directly
instead, giving me the same results as in the tutorial (for the errors etc).
Even in step-20, the boundary values aren't correct for most of the tests,
or rather, have a lot of error in itself.
For example, at the point (1,1) which is on the boundary, p = -1.1 with the
given test problem.
These are the values I obtained having run the code:
at lowest degree (0), refinement level (RL) 3, p=-0.941992, which is rather
far off the -1.1 value for the Dirichlet condition applied. even at RL6,
p=1.07976
I tried the next degree up (1), at RL3, p= -1.09984. eventually at RL6 for
this degree, we get -1.1.
Similarly, at degree 2, at RL3. p is still not accurate at p = -1.10004
How else can we imposed the Dirichlet condition (without having to use very
high refinement levels and degrees) on the boundary for this problem?
Earlier in the thread, I mention that the boundary value I have is
important as it is used in the next set of equations I solve after this
darcy-like system.
I'd appreciate any ideas or suggestions
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