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-   -   [ICEM] Delaunay gone wrong. (http://www.cfd-online.com/Forums/ansys-meshing/97786-delaunay-gone-wrong.html)

federvo.mala February 24, 2012 21:33

Delaunay gone wrong.
 
2 Attachment(s)
Hello,

I am trying to replace my octree volume mesh (1st pic) with a bottom up mesh such as Delaunay.

But as you can see in the second picture, there is definiely something wrong with the generation of it.

SOME MORE DETAILS:

I do the octree mesh, smooth then go to Volume meshing parameters and click on DELAUNAY, Tgib:
Memory factor: 1
Spacing factor: 1.2

And also tick 'Fill holes in volume mesh'. I also tried a combination of the other options but does not change anything.

I keep the same dimensions for the volume body from previous tetra mesh.

Then go to compute mesh and finish.

Santos-Dumont March 3, 2012 06:13

I have the same problem. It randomly worked once but I couldn't figure out why...
I use Part by Part input (with geometry and boudaries included, all pre meshed), All Geometry and Existing Mesh. None worked...

Did you finally suceed ?

federvo.mala March 4, 2012 01:36

No it's still not working. What I have been doing is create the octree, smooth and etc, then delete the volume mesh and create a delaunay mesh by 'compute mesh' input. I don't know what's going on really......

federvo.mala March 4, 2012 01:44

Correction: I just tried right now and it worked, the geometry is slightly different though. So what I did was the same I said in the previous reply then I go to compute mesh and select delaunay and also select the volume part and compute.

But it almost double the elements, I thought there were going to be a lot less :S

Santos-Dumont March 4, 2012 07:21

So if I understand you create the Octree mesh, smooth it until it's ready to use then you compute a Delaunay mesh.

That is got to be a way to create Delaunay mesh from the surfaces meshes only. In the tutorials they do it without apparent trouble.

The thing is that Octree screws up my geometry and doesn't follow the curves, even with topology building and Patch Dependant mesh. The surface mesh is fine but after Octree meshing I got holes as you can see here :
http://imageshack.us/photo/my-images/577/10447806.jpg/
http://imageshack.us/photo/my-images/13/92755498.jpg/

During one try on the horizontal tail only I managed to do Delaunay from the surfaces only (without the Octree manipulation) and that was great because the geometry was respected.

federvo.mala March 4, 2012 20:52

Quote:

Originally Posted by Santos-Dumont (Post 347540)
So if I understand you create the Octree mesh, smooth it until it's ready to use then you compute a Delaunay mesh.

That is got to be a way to create Delaunay mesh from the surfaces meshes only. In the tutorials they do it without apparent trouble.

The thing is that Octree screws up my geometry and doesn't follow the curves, even with topology building and Patch Dependant mesh. The surface mesh is fine but after Octree meshing I got holes as you can see here :
http://imageshack.us/photo/my-images/577/10447806.jpg/
http://imageshack.us/photo/my-images/13/92755498.jpg/

During one try on the horizontal tail only I managed to do Delaunay from the surfaces only (without the Octree manipulation) and that was great because the geometry was respected.


I see, have you lowered your 'edge criterion' under 'Volume meshing Parameters'? If not try 0.02.

Have you run Build diagnostic tool let's say using a tolerance of 0.001?

stuart23 March 6, 2012 18:43

Quote:

Originally Posted by Santos-Dumont (Post 347540)
So if I understand you create the Octree mesh, smooth it until it's ready to use then you compute a Delaunay mesh.

That is got to be a way to create Delaunay mesh from the surfaces meshes only. In the tutorials they do it without apparent trouble.

The thing is that Octree screws up my geometry and doesn't follow the curves, even with topology building and Patch Dependant mesh. The surface mesh is fine but after Octree meshing I got holes as you can see here :
http://imageshack.us/photo/my-images/577/10447806.jpg/
http://imageshack.us/photo/my-images/13/92755498.jpg/

During one try on the horizontal tail only I managed to do Delaunay from the surfaces only (without the Octree manipulation) and that was great because the geometry was respected.

Hi Charles,
Octree Volume meshing is a top down process and will therefore "throw out" any surface mesh you have already created. To understand why this is the case you must first understand how the algorithms differ. Octree will take your fluid volume and divide it into 8 (oct!!!) sections by drawing three orthagonal planes through your geometry. It will then check if any of these 8 sections lie outside your fluid volume and dispose of that particular section if it does. It then takes these 8 sections and divides each section into another 8 sections giving a total of 8^2=64 sections and then disposes of non enclosed sections again. The algorithm recursively works to smaller and smaller elements until your sizing criterion are satisfied (like branches on a "tree"!!!). Once the sizing is correct, it will move nodes to the surfaces to more accurately represent them. This is why the octree process a) does not require a surface mesh, and b) does not follow curves like delauney because the mesher works from the volume and then merges nodes to the surfaces rather than meshing each curve, then surface and then volume (i.e. bottom up = Delauney)

Hope this clarifies :-)


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