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Pete September 15, 2004 23:10

ICEM5 Hexa output problem

I have created a hexa mesh for my geometry in ICEM 5. Someone told me that I need to convert it to unstructured mesh (under "pre-mesh") before I can output the mesh to the pre. I wonder why do we need to do that. Is the mesh still structured after the conversion? I will be using CFX5.7 fro my problem.

Also, in tutorial, there's a section about scaling the O grid. I wonder when the scaling is needed. No explanation in the tutorial. All the tutorials ended without showing how to output the file to pre.

Please help me if you can. Thanks. Pete

guruprasad September 16, 2004 00:33

Re: ICEM5 Hexa output problem
I use ICEM CFD 4.3 & we save the unstructured one, as it will be Multy block structured mesh.. and as whole Unstructured one so we have to save this mesh as unstructured & then go to the Pre...

& for the scaling of O-grid: If you would like to "shorten" or "Lengthen" all the edges of the O-grid in one go, you can use this option of "rescaling".

hope this will help you! -guru.

deLuther September 16, 2004 00:43

Re: ICEM5 Hexa output problem
For CFX 5.7 you need unstructured mesh. So do not bother about it. Rescale O-grid useful if your O-grid after creation not placed as you want, so you can use rescale. Alternatively you can use set edge length.

Pete September 16, 2004 00:49

Re: ICEM5 Hexa output problem
Thank you for your help. CFX is not able to solve problem with multi-block structured mesh because the solver is an unstructured code. Is that what you mean here? Should I classify the mesh as unstructured when I have converted it from structured to unstructured? I really want to use structured mesh in my problem. Any way that I can use the original multi-block structured grid that I created in ICEM5 without having to convert it?

Thanks, Pete

Pete September 16, 2004 00:56

Re: ICEM5 Hexa output problem
In this case, I will lose the advantage of having structured mesh, right? :( I spend a lot of time to create this structured mesh and really don't want to see that happen. Always think that solver with structured mesh is more accurate than the unstructured one. Thanks for your help.

deLuther September 16, 2004 01:07

Re: ICEM5 Hexa output problem
Yes you right exactly that i mean. Why you need structured mesh if CFX 5.7 use unstructured? If you need structured you should use CFX-4 or TascFlow... For structured you can use, in worst case, old ICEM interface.

Pete September 16, 2004 01:30

Re: ICEM5 Hexa output problem
tetra unstructured mesh didn't give me good result in the previous test case. That's the reason I went for structured mesh. How come the structured code is not being supported anymore? Will unstructured code give the same amount of accuracy as the one for structured code? Thank you for your comment again.

Charles September 16, 2004 02:23

Re: ICEM5 Hexa output problem
I suspect that the difference in accuracy has more to do with the shape and distribution of your grid cells than with the question of structured or unstructured solver. So using a well-built "structured" hex mesh with an unstructured solver is a good approach from a grid quality point of view.

deLuther September 16, 2004 02:25

Re: ICEM5 Hexa output problem
...Now I`m really understood your question. Unstructured not means tetra, you can have unstructured hexa mesh. Difference is in threatment of nodal indexes. CFX-5 just not need structured multiblock mesh.

James Date September 16, 2004 18:33

Re: ICEM5 Hexa output problem

Without a doubt unstructered Hexa will produce far better results than unstructered tetra when i comes to resolving shear flows such as that found in the boundary layer. I tend to use hexa where possible, then prism then tetra.


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