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Old   July 6, 2012, 05:54
Default Hybrid mesh
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Hello community,
since 2 weeks Im fighting with my problem and now I came to a point, where I dont know what to do, so I ask you and hope for your help:
I have to create a geometry ( I want to create a cone ) which contains/ is made of structured mesh. Here a pic:cone.jpg
After it is created I need a tetra-mesh around it, so it looks like this when I create it:cone2.jpg
So in the next step is merge it and smooth it, it looks not really good but this is what it looks like:cone3.jpg
So the quality is not that good but this is where the problem starts; I need hexa layers around my geometry and those merged with tetra and hexa mesh, something like this:cone4.jpg
But this is not merged. If I merge the tetra mesh before making the layers I cant make them afterwards with the prism layers option. and if I create them first, like in the last pic I also cant merge them with my geometry, because the computer crashes.
Can anyone help me with this:
- I need to know how to make better hexa mesh and also control the ratio ( so it gets bigger from cone to the walls and it is small around my geometry)
- how can I merge the hexa and tetra mesh and have those tetra layers around it.
I googled, searched through this and other forums but still nothing, that could help me.

best regards

Last edited by lostinicem; July 31, 2012 at 05:01.
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Old   July 6, 2012, 08:31
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for a good merging size elements matters, did you take a look at this thread:
Mesh unable to follow curved geometry
if you have the possibility to mesh it all in hexa, will you do that? hexa is much better than tetra, because of size and computation errors i found.
If you don't mind, you are welcome to share you project with us... we can dig more into the problem
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Old   July 7, 2012, 03:07
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Hi lostinicem,
Just a small note.. I just found out that, if you use fluent you dont have to merge the meshes.
You just have to define the "interface" in "mesh interfaces" in fluent and it will run normally. Even the size of the structured and unstructured elements at the interface does not matter..
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Old   July 7, 2012, 03:14
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in that case you have write the both meshes separately and then use read and append commands to combine them.
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Old   July 7, 2012, 03:19
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Far,
I dont think thats required. in case of fluent, after both meshes exist under the mesh tree in ICEM (ie both structured and unstructured mesh exists at the interface), you just have to take the output as usual into .msh type. then define the interface separately in fluent..
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Old   July 7, 2012, 07:35
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you mean using the interface command without appending the meshes. loading the meshe earlier in one shot ?? i didn't know that...
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Old   July 9, 2012, 04:27
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uh sorry to watch here late!
@diamondx: i saw that thread and actually this was my first choice to make this kind of steps, but it didnt worked out; i can see now why, i guess my tetra-mesh was too large, because i couldnt merge it, like in your picture.

@anan; also thanks for this hint, Ill try it when mesh is finished

all in all thanks for the answers; I just thought i could also work here with those layers/layer-option, so it would make easier with other geometries; because in tutorials you can see alot of those meshes, but I cant handle to create it ....

@diamondx regarding my problem: there is conical geometry, which is in a flow that includes also the temperature. my problem is to generate some structured-mesh-layers around the cone, to have a better quality of what is happening there. the rest is tetra-mesh/tri-mesh (unstructured mesh), because its not that interesting for us and since making it as a whole as structured, would cost too much calculating time. and if I take only unstrucutred mesh, it seems its not accurate enough. but you can correct me on my opinions here, since Im new to this kind of problems and maybe I misunderstood something.

best regards

Last edited by lostinicem; July 31, 2012 at 05:02.
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Old   July 16, 2012, 05:51
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by the way Im trying now to create a cone around cone and to control the structured mesh with this; but it seems like I cant adopt the idea from cube, because if I split here blocks at the end the mesh of the bigger cone looks pretty strange.
I guess I need to play with the settings of associatins ...

anyone got any hints?
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Old   July 16, 2012, 06:05
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sorry for tripple post ...
here some pics: before i make volume mesh ( so if I have only surface mesh) ;it looks ok:conenovolumemesh.jpg

and after I create the volume mesh:conewithvolumemesh.jpg
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Old   July 16, 2012, 06:07
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Quote:
Originally Posted by lostinicem View Post
my problem is to generate some tetra-layers around the cone, to have a better quality of what is happening there. the rest is hexa-mesh, because its not that interesting for us and since making it as a whole tetra would cost too much calculating time. and if I take only hexa mesh, it seems its not accurate enough.




why do you need tetra layers? i really don't understand.


i think you confuse tetra with hexa!? you need a hex mesh with hex layers and tetra around the body!? and you want to match the hex layer with tetra

sorry, but i don't understand your issue
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Old   July 17, 2012, 04:59
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@energy, thanks for your attention! maybe this is why nobody answers I edited my post:
yes, its about cone which has structured mesh-layers around it and after those layers there is tetra mesh
so I thought, maybe if I create around one geometry same but bigger geometry, I can influence those structured mesh layers. but blocking seems not be right here, because the volume mesh gets messed up ... and so Im looking for new ideas..

and here what Ive got till now, its a square form around cone:att1.jpg

and at the walls:att2.jpg

Last edited by lostinicem; July 17, 2012 at 10:26. Reason: pics attached
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Old   July 31, 2012, 04:44
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I managed to create the mesh of the cone ,finally, how I wanted, but the problem now is merging the mesh:mergeproblems.jpg

after creating surface and body, it doesnt want to merge hexa and tetra mesh. if I create normal geometry and dont do alot about it, the merging is no problem, but as soon as I create this kind of cone its says: there is currently only 1 region.
does anyone knows whats the cause of this problem????
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Old   July 31, 2012, 04:53
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can you put a screen shot of the "mesh tree" which is available on the left hand side of the window.. please expand it completely before taking the photo..
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Old   July 31, 2012, 05:08
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this one ?
mesh-tree.jpg
Attached Images
File Type: jpg enabled.jpg (94.3 KB, 23 views)
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Old   July 31, 2012, 05:19
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Yeah..
1. did you try using the merge option in edit mesh tab along with interface as the required surface.. Pls upload your block and tetin files..
2. try taking the output directly without merging.
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Old   July 31, 2012, 05:31
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1) yes I tried this; actually this is the only option I know
2) I am not sure what do you mean..

btw here are all the files I could attach ...:project6.atr.zip
tell me if something is missing =)
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Old   July 31, 2012, 06:05
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i am able to merge it at the interface cone but with some errors.. i dont get the "there is only one region " error..
2. Convert to .msh directly without "merging". In case of fluent you can directly tell the existence of this interface in fluent itself. It will be able to solve without a problem..
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Old   July 31, 2012, 07:19
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to your second point: ah yes you suggested it already and its good idea for fluent; but the problem is, that I need it for openfoam; though it would be also great to know how to merge it anyway.
for the one region error: I also dont get this, but it seems, that if I do ogrid blocking, icem does something while these steps; the regions are seen as one or made as one; because if its normal block, there are no problems with merging

but nevetheless: thank you for your help !!



EDIT: so I noticed now; the merge function doesnt work, because I put on the down surface a circle ( edge ) to associate it with the surface of the down part of cone, so I can control the ratio and size of the middle part of the mesh. because if I remove it and try to merge it afterwards it works, nevetheless it looks crippled ...

Last edited by lostinicem; August 1, 2012 at 04:23.
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Old   August 3, 2012, 04:04
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so found the error!! if its interesting for someone:
if the error occurs with "you have only 1 region" be sure to check whether on your surface are 2 mesh types ( recalculate or make again unstructure-mesh again)
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