I turned off the overlapping domain decomposition (ghost cells) for a
simple problem and the sequence
MergeBlocks->CleantoGrid->ExtractSurface->Clip
shows just the physical boundary of the problem (clipped open so you
can see inside). Also volume visualization and streamline calculation
works with no processor boundary artifacts.
From what I understand, there are no filters in paraview or
abstractions in the XDMF data model at this time that will allow
paraview to read in overlapping blocks and really make use of the
ghost cells correctly. For now truncating our output to only "owned"
elements will solve our problems. Thanks again for the help.
Chris
On Mar 30, 2009, at 2:06 PM, Chris Kees wrote:
Thanks for the help. I also tried suggestions from Paul, Ken, and
Berk, but it does seem that I'm stuck right now unless I provide
ParaView with more information. Since streamlines are computed
correctly on the current multiblock mesh I just generated the mesh
on a single processor and used ExtractSurface->Clip on that mesh to
visualize the geometry around the streamlines from the multiblock
grid.
On the first method: Each of my UnstructuredGrids in the Multiblock
Grid is a subdomain in an overlapping decomposition of the domain.
Each of the subdomains has several elements of overlap (the layer of
ghost cells is more than one element thick). Presumably the
streamline generation works now on the multiblock grid because the
overlap is loaded into ParaView. Is there a way I can just set a
cell-centered attributed to identify the ghost cells so that surface
extraction and volume visualization will work too? Currently volume
visualization of the multiblock grid shows only a single subdomain
and volume visualization after MergeBlocks shows the whole domain
but with overlap regions being more opaque.
On your other method, we have both the external boundary mesh and a
pre-mesh polygonal representation of the boundaries available in the
simulator. You are suggesting that I just dump one of those to a
valid ParaView format as well, is that correct?
Chris
On Mar 30, 2009, at 9:14 AM, Jean Favre wrote:
Chris Kees wrote:
So far I've tried MergeBlocks->ExtractSurface->FeatureEdges->Clip
and
various permutations that I've seen in previous posts and the wiki,
but I always end up with the surfaces on the interior of the tank
as
if it still sees each subdomain as a closed surface.
In fact, it seems to me that ParaView does the best it can. Your
unstructured mesh is partitioned in 512 pieces and [presumably],
you did
not specify ghost-cells at the partition boundaries. Without
ghost-cells, ParaView has no information to help decide whether an
outside face looks towards the outside world, or to another
partition. I
don't think any combination of filters would help you. Removing
duplicate points may only remove duplicate fake boundaries, but these
fake boundaries must be removed all together.
I use two methods to achieve what you want. Ghost-cells, or another
multi-piece object containing the different boundary types (solid,
symmetries, inflow, outflow, etc) stored as vtkPolyData. These are
read
in from the models on disk.
Jean --
Swiss National Supercomputing Center
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