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[ICEM] Problem with ICEM generated Mesh

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Old   May 8, 2009, 23:36
Exclamation Problem with ICEM generated Mesh
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George Thomas
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Hi,

I'm having a problem with the ICEM generated mesh for the geometry. Could anyone advise me how to fix it.

The geometry is:

A compression cylinder.

A series of inlets and exits in the domain on either sides, both are added with interfaces so that the cylinder domain can move wrt the inlets and exists.

The mesh is : Tetra in ICEM. Quad Dominant, very fine.

Only for two openings on the same side the mesh shows not good enough. The interface on those ports(I call it) are having a number of primitives compared to a single one on the rest of the ports. What could be the problem with these two meshes of the port?

Plz see the attachment (thumbnails).

Thank you,

George
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File Type: jpg ICEM Mesh George.jpg (32.2 KB, 67 views)
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Old   May 9, 2009, 21:56
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Simon Pereira
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I am happy to help, but can't understand your problem from this post. Please try again?
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Old   May 9, 2009, 23:52
Exclamation The mesh problem - In detail
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George Thomas
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Hi Simon,


The ICEM Mesh:


  • Mesh requirements : Finer mesh, with capabilities to undergo high levels of deformation without crashing and least errors
  • I played around with Hexagonal, Tetra, Sweep...meshes in CFX. Inconsistent results obtained with them pushed me to use ICEM
  • Mesh type : Tetra/Mixed
  • Mesh method : Robust (Octree)
  • Rest of the settings : Left as default
Now the problem is; as you can see in the attachment figure, the mesh for two ports among the other ports is not looking good after meshing using ICEM. I do not know how to say it, but I'm not quiet sure if that mesh if correct
  • The zoomed-in figure attachment clearly shows this trouble with the 2 ports. It looks more or less like cracks on a wall.
  • Once I meshed and later imported the mesh for analysis, the interface of the said mesh showed around 5 primitive faces while for the other normal meshess on the port the number of primitive face was only 1
  • I tried meshing it again and again, and the problem persisted.
  • Do you know why this is happening? What could be the most probable reason for this problem?
Expecting a quick reply for this query

Thank you

George
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Old   May 11, 2009, 13:26
Default Check it in ICEM CFD
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Your image is in CFX Pre (I guess), not ICEM CFD (which would have all the diagnostics you would need to check the problem). The Octree Patch Independent Tetra mesher can handle pretty much anything… So I am guessing you have a problem with material points (leakage) or normals…

From the image, it looks like the central cylinder and the surrounding inlet and outlet blocks are each a separate volume (separated by surfaces).

My first guess is that this is a surface normal thing… CFX may be interpreting the different directions as different surface regions. In ICEM CFD you could right click on shells and display the normals (or normals by color) to check this out. By default, normals point out from a volume, but in some cases (such as when there is a volume on both sides) you may need to help it out. This was recently improved in 12.1 (not yet released) specifically for problems with prism normals on membranes like this, I think it will point based on which volume mesh has the lower id number. Under mesh editing, you can adjust normals to make them consistent. Since you have multiple edges, you may need to do a more manual approach to reverse the normals.

If that is not it, check the material points, Make sure you have material points in each region and that they are in the region, not sitting on the wall. They can all be the same material but I would probably put a different material in the central cylinder so that it can be easily selected later. ICEM CFD will create material points if you forget to, but if your geometry has a problem (such as if those particular blocks were not perfectly closed) something may go wrong, so I usually just create them manually.
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