[vtkusers] Painting finite element meshes with information defined at quadrature points, not at nodal locations

[Kodanda]

Jeff Amelang <jeff.amelang <at> gmail.com> writes:

> 
> 
> Hello, 
> 
> I sincerely appreciate any time you take to answer.  In finite element 
calculations, you often end up with quantities (such as stresses) defined at 
integration points, not at the nodes.  I would like to, without any further 
interpolation or processing, hand 1) such an array of values at integration 
points and 2) a mesh to vtk and have it paint the cells by interpolating within 
each cell.  As an example, consider the attached picture (hopefully I can attach 
things here).  It contains two adjacent triangles, each with values of a field 
defined at 3 interior quadrature points.  I would provide the values of the 
field at the integration points within the cells and vtk would paint each cell 
by interpolating within that cell.  So, even though the values of the field 
within the left triangle are around 4 and 5, the left triangle would be painted 
with a value of around 3 on the left point and a value of around 6 on the right 
edge.  The right triangle would be painted with a value of around 4 on the left 
edge and a value of around 1 on the right edge.  The colors would not match on 
either side of the adjoining edge (just as if you were painting each triangle by 
a different CellData scalar, except it wouldn't be constant in each cell).  That 
really won't make sense if the attachment doesn't go through.  
> 
> 
> Please do not refer me to 
this: http://www.vtk.org/Wiki/VTK/VTK_integration_point_support or 
this: http://www.vtk.org/Wiki/File:VTK-Quadrature-Point-Design-Doc.pdf without 
giving me some sort of guidance on how the classes in those documents can be 
used to accomplish what I'm describing.  To my reading, the pdf is describing a 
way to get vtk to interpolate from fields defined at nodes to integration 
points.  That is not what I am looking for.  Nor do I need to interpolate from 
integration points to nodal values.  
> 
> I have fields defined at integration points and need to paint the mesh by 
those fields interpolated within each cell.  If the mesh were a 2d triangular 
mesh with N triangles, for a 3-point quadrature rule I would be providing 3N 
field values defined at the 3 quadrature points within each cell, the positions 
of the nodes of the mesh, and the connectivities to create the cells.  That's 
it.  
> 
> Please feel free to ask clarifying questions.  Again, I sincerely appreciate 
any time you take to answer.  Does vtk have support for this?
> jeff 
> 
> 
> 
> 
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Hello,

I am also facing the exact issue. I use abaqus and would like to postprocess the 
data using ParaView. Did you figure it out?

thanks,
Kodanda