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[ICEM] merge meshes between hexa and prism

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Old   February 7, 2013, 00:00
Default merge meshes between hexa and prism
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I have a question confusing me for a while. Can ICEM merge hexa and prism meshes at an interface. For example, the mesh on the left side is triangular prism and on the right side is the hexahedral mesh. I always get some fail message when I try to merge these two type of meshes at an interface. Does anyone have the experience for it? Thanks!
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Old   February 7, 2013, 00:28
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No not possible. However you can create non-conformal interface in CFX/Fluent.
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Old   February 7, 2013, 10:29
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Thank you, Far. I also think about this solution. I am just worried about the convergence problem since at one side the domain will be defined as porous media.
Btw, do you know how to hexahedral meshes without using blocking function. Like in gambit, I can firstly create hexa meshes in the porous media domain, and then create tetra meshes. The interface can automatically create formal meshes. Do you have any idea?
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Old   February 7, 2013, 10:46
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Procedure in ICEM is different than any bottom-up approach whether it is Gambit or gridgen.

The solution is to mesh one domain with tetra and other with Hexa and merge them. It is to be noted pyramids will be there at interface.
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Old   February 7, 2013, 11:27
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Thank you for your reply. You helps me a lot to answer my questions.
If merge meshes is not functional for the mesh pair of prism and anyother, it will become a real problem in practice. Becaues this is the situation that I met quite often in my work. I will have to define interfaces in fluent anyway.

Thanks, far!
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Old   February 7, 2013, 11:30
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Why you dont try full hexa ?
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Old   February 7, 2013, 11:50
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prism+tetra merging with hexa... that's my dream

@FAR, i previously saw a thread where someone claimed he could do it but the quality was very bad... do you remember that thread ? i can't find it ...
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Old   February 7, 2013, 12:40
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Thanks for you guys' suggestions. I will try both solutions.
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Old   February 7, 2013, 13:00
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@Ali: In fact those were your words which I just wrote here " Prisms cannot be merged with Hexa due to stiffness of prism" Remember

The basic logic is " when we merge Hexa with tetra, it changes tetra mesh on that face and keep the Hexa as it is. While this is not possible with prisms. In other words prisms cannot redistribute themselves to conform with Hexas
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Old   February 7, 2013, 13:07
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yeah yeah i do remember, here is why i also remember:

That guy said he created the tetra without prism, then the hexa. he after that merged them. Until here everything everything can be done without affecting the quality.

then after the merge he generated the prism. (on the hexa+tetra). it is doable when you think about it, but i don't know about the reality...
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Old   February 7, 2013, 13:13
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that is simply not possible due to working style of ICEM.
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Old   May 13, 2013, 10:29
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Hi all,
I've read this post to try to deal with a problem. I'm surprised to read Farīs word about merge meshes because I made the "Merged Tetra-Hexa Mesh in a Hybrid Tube" tutorial and in that case is possible. I did it. And, now Iīm trying to do exactly the same between this two meshes.

I mean, Iīd thought to do in the same project, the first mesh, then save it, then close it, secondly, create the second mesh (picture 2), and then merge them. Exactly, the same procedure as the tutorial. So.. Is it not possible?

Thanks in advance!
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File Type: jpg 2.jpg (66.5 KB, 99 views)
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Old   May 14, 2013, 03:02
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Hi guys,
I have an other doubt. Itīs about merge meshes tool. In the same tutorial that I said yesterday, at beginning, give some advices. In the next-to-last is:

"The perimeters of all the interface parts must be associated to curves that are aligned (or even onthe same curve) on both sides of the interface."

So, when appears "aligned" it means that I canīt do this with geom I presented you yesterday? Because those curves are not aligned, even those curves are not parallels...

Iīm not sure about it and I donīt want to waste the time in something at the end is not possible. Anyone know about it?

Thank you guys!
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Old   May 20, 2013, 16:51
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Hello FJSJ and all,

I have been trying to battle with hybrid meshing the past few days myself. I've definitely been a little unhappy with the capabilities of ICEM vs. other hybrid meshing I've seen.

From what I can tell, you can easily do a hybrid tet+hex mesh if you have no inflation/prism layers. In this case, you can make the two meshes separately, load them both together (selecting merge rather than replace), and then use the merge mesh tool at the interface. I think this is something that has some tutorials on the customer portal and has also been discussed here.

Where it gets tricky is when prism layers are included. Like some of the above posts, I have not yet been able to merge meshes when the tet already includes prism layers. The one place I have had a little success though is by:
1) building the hex and tet (no prism)
2) loading both together and merging
3) adding a prism layer to both the tet and hex blocks

I believe this works as long as the total height of the prism layer is less than the first cell height in the hex mesh. I have only done this with really simple test geometries so far, but it seems to just replace a portion of the first hex cell and leave the rest unchanged. I just put a two node (1 element) o-grid right next to the surface I wanted the prism layer on, that way I easily make sure I had the right element size. One problem I see in the future for this method might be that, for complex geometry, it isn't always possible to really closely control the height of an ogrid. This might mean it either grows a lot compared to the desired first cell height (so you have a strange intermediate cell between prism and rest of mesh), or it might shrink and the prism layer may fail entirely.

If anyone tries any of this or has any success including inflation layers/prism layers in hybrid meshes, I'd really appreciate your thoughts.

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Old   May 21, 2013, 03:05
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thank you Scribby182,

I have been dealing with this problem too. I got the mesh that I suggested few days here. Yes, youīre right, Iīve made the approach you comment. And it worked. I have a conformal mesh between hexas and tetras by pyramids layer (pic.1). About your prism layer doubt.. I think I canīt help you, Iīve not tried prism layer yet. The only I can say you itīs about tutorials, Tetra/prism Mesh in a Fin Confituration or Tetra/Prism Mesh generation for a Helicopter....
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Old   October 25, 2013, 10:45
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Quote:
Originally Posted by scribby182 View Post
Hello FJSJ and all,

I have been trying to battle with hybrid meshing the past few days myself. I've definitely been a little unhappy with the capabilities of ICEM vs. other hybrid meshing I've seen.

From what I can tell, you can easily do a hybrid tet+hex mesh if you have no inflation/prism layers. In this case, you can make the two meshes separately, load them both together (selecting merge rather than replace), and then use the merge mesh tool at the interface. I think this is something that has some tutorials on the customer portal and has also been discussed here.

Where it gets tricky is when prism layers are included. Like some of the above posts, I have not yet been able to merge meshes when the tet already includes prism layers. The one place I have had a little success though is by:
1) building the hex and tet (no prism)
2) loading both together and merging
3) adding a prism layer to both the tet and hex blocks

I believe this works as long as the total height of the prism layer is less than the first cell height in the hex mesh. I have only done this with really simple test geometries so far, but it seems to just replace a portion of the first hex cell and leave the rest unchanged. I just put a two node (1 element) o-grid right next to the surface I wanted the prism layer on, that way I easily make sure I had the right element size. One problem I see in the future for this method might be that, for complex geometry, it isn't always possible to really closely control the height of an ogrid. This might mean it either grows a lot compared to the desired first cell height (so you have a strange intermediate cell between prism and rest of mesh), or it might shrink and the prism layer may fail entirely.

If anyone tries any of this or has any success including inflation layers/prism layers in hybrid meshes, I'd really appreciate your thoughts.

Scribby182
Hello Scribby182,
How did you manage to generate the prims on the hexa part? When i try to create the prims after merging the two parts i only obtain prims on the tetra part .
Thank you,
Peter
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Old   November 13, 2013, 07:44
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Hi PeterDaniel,

I have the same problem, it generates the prisms only on the tetra mesh even if the height of the prism layer is less than the height of the first cell in the hexa mesh.
I am wondering if someone actually managed to create a conformal interface between tetra-with-prism and hexa or you are bounded to use non conformal interface when you have prisms.
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Old   November 13, 2013, 11:44
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What do you think about interrupting generation of the prisms just before the interface in the unstructured domain? in this way the interface is only between tetra and hexa and should not be problematic to make it conformal.
what are the drawbacks of this approach in your opinion?

I will attach some screenshot shortly.
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Old   November 13, 2013, 12:17
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this illustrates, in a very rough example, what I meant in the previous post
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Old   November 13, 2013, 18:19
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Conforming hexas into prisms is doable, but not easy. If you are not familiar with ICEM, just stick with a non-conformal interface.

The trick is that you must build the tetra/prism zone bottom-up to be conformal. Firstly create conformal surface mesh in the unstructured region using PD or PI with respect line elements. Then inflate prisms off the surface with the Advanced Prism Param: "Using Quad Elements" enabled. Finally fill the rest of the void with Delaunay to connect the prisms, quads and whatever other tris are in your domain.

You can only do this using the Pre Inflation technique. "Using Quad Elements" will not work if there is already tetras/pyras in your domain.

Once again, if you did not understand these instructions, I would suggest using a non-conformal interface.

Good Luck,

Stu
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