following tutorial 18, I try to evaluate the stress at an arbitrary
point. I guess that is not such an unusual case so some of you might
stumbled upon it already.
I found FETools::compute_projection_from_quadrature_points, but that
only gets the stresses to the vertex points, but how do interpolate back
to the arbitrary point?
Do you need the stress only at a single point for which you have already
identified the cell, or at a large number of cells?
In the former case, I would suggest you use the function you mention to
get a finite element representation of the point values on the
quadrature points and then evaluate it in a way that's similar to what
we do in the VectorTools::point_value function, see its implementation
in include/deal.II/vectors.templates.h.
In the latter case, I would construct a DoFHandler, apply
FETools::compute_projection_from_quadrature_points on every cell to
construct a global representation of the data on the quadrature points
(you'll have to use a discontinuous element for that) and the use the
FEFieldFunction class to access arbitrary point values or gradients.
Best
W.
(As a sidenote, the FETools::compute_projection_from_quadrature_points
function does not bring the stresses back to the vertices, but in fact
to the nodes of a finite element field. There may be many more nodes
than vertices if you use the function with a higher order element.)
------------------------------------------------------------------------
Wolfgang Bangerth email: [email protected]
www: http://www.math.tamu.edu/~bangerth/
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