Hello,
you're right. I didn't notice that some of the elements have
negative volumes. Thank you very much.
Martin Vymazal
Quoting "Moreland, Kenneth" <[email protected]>:
After taking a look at your mesh, I see that the problem is that you
have some degenerate tetrahedra. That is, there are tetrahedra
where all 4 vertices are in a plane. In this case the tetrahedron
is self-intersecting and the gradient is ill-defined (over
constrained I believe), which is why the linear solver is failing to
compute it. You can find the degenerate tetrahedra by running the
Mesh Quality filter to compute the volume of the tetrahedra and look
for any resulting "Quality" that is not strictly greater than 0.
So, you can do one of two things. The first is to ignore the
errors. I don't think that any of the degenerate cells are part of
the surface (although I can't be sure), and since the end game is to
compute values on the surface it might not effect anything.
The second thing you can do is to fix the mesh. The best thing to
do is to go back to whatever created the original mesh, fix it, and
rerun the simulation. There is a reasonable chance that these
degenerate tetrahedra also had a negative impact on the simulation
results. If that's not practical, you can use the volume computed
by the Mesh Quality filter and the Threshold filter to remove any
tetrahedra that don't have a strictly positive volume. That will
mess up the connectivity of the mesh though.
-Ken
On 9/22/10 9:30 AM, "Martin Vymazal" <[email protected]> wrote:
Hello Ken,
I computed the x-velocity component using a calculator filter. Then
I applied the 'Gradient of Unstructured Data Set' filter to the output
of the previous filter. This is the place where the computation fails.
I sent you the data in a private email.
Best regards,
Martin Vymazal
Quoting "Moreland, Kenneth" <[email protected]>:
More information please.
How are you extracting the x-component of the velocity? What filter
are you running to compute the gradient? Would it be possible to
post some example data that exhibits the problem so that we can
replicate it?
-Ken
On 9/22/10 7:12 AM, "Martin Vymazal" <[email protected]> wrote:
Dear ParaView developers,
I'm trying to compute gradient of my x-component of velocity on a
grid of tetrahedra which has 55244 DOF. ParaView fails to compute the
gradients with the following error message:
Generic Warning: In
/home/kitware/Dashboard/MyTests/ParaView-3-8/ParaView-3.8/ParaView/VTK/Common/vtkMath.cxx,
line
1338
Unable to factor linear system
The mesh does not have degenerate/ugly elements, but it has some sharp
edges (in the inlet/outlet area). Is this a problem? If not, is there
a way of avoiding the error?
Thank you very much.
Martin Vymazal
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