Meshing question

[Ross]

I have come across a couple of issues:

1- Non-uniform Mesh

Any idea how to get the elements at the tow edges to shrink down to the same size as the other elements in the tow?

Mesh with Problem Areas Circled



2- Problem Elements in Large Model

There are elements in this model which seem to have problems with their z coordinates.

Wide View of Mesh


Closeup View of Problem


I haven't done much investigation into this, but I wanted to point it out. I would imagine that it is related to the size of the model (which in this case is rather large at about a million nodes, 3 quarter million elements). I made this model using the textile wizard. The plotting is done using our in-house plotter, so there is a small chance that the problem lies in the way I am converting from XML to our plotter's input format, but it would seem odd that an issue with that code would appear as systematic as this problem does. Let me know if you have any idea as to why the mesh is doing this and if there is anything I can do to help you figure it out.

[Martin]

Hi Ross,

1) I'm afraid this is an artefact of the meshing procedure, 2D projected mesh is created first using "Triangle" (http://www.cs.cmu.edu/~quake/triangle.html). Then that mesh is used as the basis for the 3D volume mesh. The larger spacing in the regions you have circled are due to the mesh created by Triangle. Aside from it not looking pretty, does this actually cause problems running simulations?

2) I have seen issues like this appearing before and I thought I had fixed it (several times in fact, this bug just seems to keep on cropping up, perhaps I should invest in some stronger pesticide). I will look into, sorry about that. Actually if you told me what parameters you use to create this model and the mesh that would help me replicate the problem.

[Ross]

1-
We are concerned that this non-uniformity in the size could result in problems, particularly around the edges of the tows which will most likely need higher refinement for accurate results. We are not certain that the non-uniformity will cause problems, we are just concerned.

2-
I unfortunately did not save the model that created the problem, but I was able to recreate the problem in the following way:

Using the wizard, generate a 2-D composite with the following attributes:

# Warps: 4
# Wefts: 4
Yarn Spacing: 1
Yarn Width: 0.95
Fabric Thickness: 0.5
and select to refine model.


Then, configure the fabric in the following way:
R R B B
B R R B
B B R R
R B B R

after that is done, generate the mesh with the following script:

Code: Select all

meshfilepath = 'C:\\PathToMeshFile\\'
meshfilename = 'MeshFileName.vtu'
mesher = CMesher()
mesher.SetSeed(0.05)
mesher.SetMergeTolerance(0.001)
mesher.SetQuadratic(True)
mesher.CreateMesh(r'2DWeave(W:4,H:4)')
mesher.SaveVolumeMeshToVTK(meshfilepath+meshfilename)

For me, this results in a number of errors in the mesh along the edges of some of the yarns similar to the ones I saw earlier. Let me know if you need any other information.

[Martin]

Ok thanks for the instructions, I've managed to reproduce the problem. I will try and get this fixed ASAP.

PS: Happy new year!

[Martin]

I believe I've now fixed the bug where the mesh at the edges of the yarns where getting messed up. Its uploaded to the SVN, I need to do some more testing to make sure it's stable. But for now it seems to work on the case you described.