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-   -   [ICEM] ICEM 14.0 basics (http://www.cfd-online.com/Forums/ansys-meshing/123868-icem-14-0-basics.html)

arunzz41 September 23, 2013 05:48

ICEM 14.0 basics
 
I'm new to this ICEM. I couldn't understand why we are using build diagnostic topology while meshing?? please reply.

siw September 23, 2013 08:24

As the Help Manual says:

Build Topology builds curves and points, which will help to diagnose the model for geometrical problems. The curves will autmotcially take on colors to show their association to adjacent surfaces.

This is required for the Octree mesh method to ensure a watertight model.

arunzz41 September 23, 2013 14:11

thank you for your reply. i'm learning ICEM. Now i'm in the starting level.

thank you for your support.


after applying build diagnostic topology. what is exactly happening. is it creates curves and points in the geometry??

PSYMN September 24, 2013 11:25

Build Diagnostic Topology It is not actually "required for Octree", but the filtering part of it helps. It is required for MultiZone and Patch Conforming because those are patch based methods that rely on the connectivity information (topology) to build a mesh.

Basically, build topology starts with the surface edges in your model. If you have no curves, it creates curves around all the edges of every surface. If you do have curves, it just keeps them and marks them as connected to that adjacent surface edge. Then it creates points at both ends of every curve. Again, if you already have points, it keeps them, and again, connectivity relationships are established. Also note, that if you have dormant curves and points, it will reuse those instead of creating new ones.

Note, it does not create surfaces or change the surfaces in any way other than to remove duplicates.

Then the tolerance comes into play. It checks every curve and point for other curves and points within that tolerance. "duplicate" curves, points and even surfaces are removed. If you started with an imported curve or point, the originals are kept (we assume they are better than the ones we created next to them, if you don't think so, then just delete these before running build topology).

Then things are colorized... If a curve is at the edge (within a tolerance) of 2 surfaces, it is colored yellow. If it is on the edge of only one, it is red. If more than 2 edges are represented by the curve, it is blue.

By the end of all this, connectivity information is built into the model. We now know that this surface is connected to that surface at that curve. This point is connecting those curves, etc. Meshers can use this information to create "loops" for connected meshes. Note, the loops can be created even if the geometry is not perfectly connected. The mesh size can span small gaps without a problem, as long as the loop topology is good.

Then the filter kicks in (if it is enabled). Curves that are between surfaces in the same part that meet at less than a specified angle are "filtered out". Actually, they are just made dormant so the connectivity information is preserved, but mesh nodes are not constrained to them. Similarly, points between curves in the same part that meet at less than a specified angle (tangentially) are filtered out. This part helps with Octree Tetra because these additional curves and points over-constrain the algorithm and result in lower quality meshes.

I think you can find a nicely detailed (more detailed than this) description in the help under "theory"...

arunzz41 September 24, 2013 14:16

Thank you for your reply.. Very useful comment. got the basic idea of topology. Thank you.


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