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Old   January 28, 2012, 20:55
Default How to generate this kind of mesh?
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Hi, everyone.

I saw some mesh posted by Simon and I think I need this kind of mesh right now. Can anyone tell me the steps to generate this kind of mesh?


Thanks in advance

It seems that he built prism layer on hexa elements.
I had tried 2d surface blocking and generated hexa surface mesh, but when I tried to generate prism layer, some of hexa mesh turned in to triangles.
I tried use Octree to fill the volume first and then generate prism layer, all the hexa elements became tris.
I don't know how Simon build this mesh, it looks pretty good
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Old   January 30, 2012, 04:43
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1. Create 2D blocking for all geometry.
2. 2D to 3D, with options > "Multizone Fill" and O-grid around a fuselage and wing, "Fill type" Advanced.
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Old   January 30, 2012, 13:13
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not working .
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Old   January 30, 2012, 14:30
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Quote:
Originally Posted by Ludvik View Post
1. Create 2D blocking for all geometry.
2. 2D to 3D, with options > "Multizone Fill" and O-grid around a fuselage and wing, "Fill type" Advanced.
It's not working.... From help, the "fill" option seems generates volume inside the closed surface blocks.
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Old   January 30, 2012, 18:35
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I will put together a tutorial for this as soon as I can (yes, I know I have been promising it for a while), hopefully this quarter. It can actually be done in about 5 minutes, but it takes longer if I need to explain it all. ;^) And for some reason, putting together a 15 minute demo seems to take all day.

Simon
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Old   January 30, 2012, 20:55
Default PSYMN - You are absolute help
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That would be the great help to us.
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Old   January 31, 2012, 03:45
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Quote:
Originally Posted by PSYMN View Post
I will put together a tutorial for this as soon as I can (yes, I know I have been promising it for a while), hopefully this quarter. It can actually be done in about 5 minutes, but it takes longer if I need to explain it all. ;^) And for some reason, putting together a 15 minute demo seems to take all day.

Simon
Hi, Simon, would you please just give me a quick general guide line to generate this type of mesh ? Thanks!
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Old   February 2, 2012, 08:07
Smile MultiZone meshing
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Hello,
If it serves for stressing further more, I have been looking for this MultiZone solution for ages (more than 3 years). I am dying to see the solution!
Why MultiZone approach (and maybe other bottom-Up features) is not so well documented?, appears a superb feature.
Best regards
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Old   February 2, 2012, 11:46
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The general guideline would be to tell you how it works...

The first step is to Create a "2D surface Blocking"

Multizone starts by looking at your geometry. You need to have topology built because it uses that to understand what surfaces are attached to what. If it finds a surface patch with 4 corners, it can map it. If it finds a patch with more or less corners, it can pave it. The topology info is used to connect all these blocks together correctly. If you set a tolerance or have dormant curves, it can merge patches together.

After auto blocking all those patches (just a few seconds), it takes the mesh parameters from the curves (so you should set sizes to take advantage of this).

You can then adjust this surface blocking in preparation for the second step. In addition to adjusting the topology to what ever you want, you should make sure that your perimeter is closed (no single edges).

The second step is a 2D to 3D "Fill".

If you set this to sweep, it looks for rings of mapped blocks which could indicate the sweep direction. It can imprint, etc. to automatically handle multi source and target as well as multi direction sweep.

If the model just needs a regular fill... it uses code similar to the hexa dominant fill... But instead of filling a quad dominant mesh with hexas, it it fills the surface blocking with volume blocks.

You can run Ogrid to insert a boundary layer and it works just like with regular blocking.

If you are doing external aero, then the sweep or Hexa block fill are not likely to give you a good mesh. You should use the unstructured fill. This basically fills the volume with one of the unstructured fill options (like tetra), but then you can insert an OGrid to give a nice hexa boundary layer around the aircraft...

All of this is done on the ICEM CFD hexa framework, so you can adjust verticies or edge distributions, etc. You can also change block types, etc.
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Old   February 2, 2012, 15:42
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Quote:
Originally Posted by PSYMN View Post
The general guideline would be to tell you how it works...

The first step is to Create a "2D surface Blocking"

Multizone starts by looking at your geometry. You need to have topology built because it uses that to understand what surfaces are attached to what. If it finds a surface patch with 4 corners, it can map it. If it finds a patch with more or less corners, it can pave it. The topology info is used to connect all these blocks together correctly. If you set a tolerance or have dormant curves, it can merge patches together.

After auto blocking all those patches (just a few seconds), it takes the mesh parameters from the curves (so you should set sizes to take advantage of this).

You can then adjust this surface blocking in preparation for the second step. In addition to adjusting the topology to what ever you want, you should make sure that your perimeter is closed (no single edges).

The second step is a 2D to 3D "Fill".

If you set this to sweep, it looks for rings of mapped blocks which could indicate the sweep direction. It can imprint, etc. to automatically handle multi source and target as well as multi direction sweep.

If the model just needs a regular fill... it uses code similar to the hexa dominant fill... But instead of filling a quad dominant mesh with hexas, it it fills the surface blocking with volume blocks.

You can run Ogrid to insert a boundary layer and it works just like with regular blocking.

If you are doing external aero, then the sweep or Hexa block fill are not likely to give you a good mesh. You should use the unstructured fill. This basically fills the volume with one of the unstructured fill options (like tetra), but then you can insert an OGrid to give a nice hexa boundary layer around the aircraft...

All of this is done on the ICEM CFD hexa framework, so you can adjust verticies or edge distributions, etc. You can also change block types, etc.
Thanks Simon, I can do it on very simple geometry now...
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Old   February 2, 2012, 15:59
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I got stucked in periodic conditions

Last edited by mingersai; February 4, 2012 at 02:12.
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Old   February 2, 2012, 23:25
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It is working now, but I am getting fully hexa mesh, how to convert the outer blocks into tetra type. I have also tried edit block command.
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Old   February 3, 2012, 02:51
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Quote:
Originally Posted by Far View Post
It is working now, but I am getting fully hexa mesh, how to convert the outer blocks into tetra type. I have also tried edit block command.
maybe your domain is not enclosed?

How to generate full hexa with this though...? I can't find where to choos...
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Old   February 3, 2012, 03:03
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I found this have problem on the tip of the airfoil with sharp trailing edge or similar shapes. When I tried to do 2d to 3d fill, it automatically deletes some surfaces...



Also there's some periodic issue... I set periodic in mesh tab, then 2d surface initialization, Edit block=>periodic vertices, I made all the vertices on the periodic surface periodic. the surface is tri-paved surface. It seems that all the nodes are matched, but the elements on the surface are not, the block faces are not periodic. I think it's because type of block face is "free". How to make free surface periodic?

I had similar problem before when I tried to generate surface mesh then use Delaunay under mesh tab. Only octree give respect to periodic set up. The surface mesh generation seem ignored the periodic set up.



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Old   February 3, 2012, 06:01
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Quote:
Originally Posted by Far View Post
It is working now, but I am getting fully hexa mesh, how to convert the outer blocks into tetra type. I have also tried edit block command.

Blocking -> Edit Block -> Convert Block Type

That should work !
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Old   February 8, 2012, 05:36
Default WOW this works!
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PSYMN, Thank you so much!
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Old   February 8, 2012, 05:42
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Mingersai,
Did you check the periodic faces by ploting them on the faces options?, sometimes the collapsed node have to be marked as "periodic" to make the face periodic (I remember they were marked in red color)
cheers!
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Old   February 8, 2012, 13:13
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Quote:
Originally Posted by chor View Post
Mingersai,
Did you check the periodic faces by ploting them on the faces options?, sometimes the collapsed node have to be marked as "periodic" to make the face periodic (I remember they were marked in red color)
cheers!
Hi chor

I had contacted customer support and got negative answer
the periodic is designed for Octree method and mapped type face blocks

They suggested me some tricky ways to deal with free type face, I'm still trying to make it work.

My application is to fluent and it seems that fluent could define non-conformal periodic faces.

I'll try either way..

cheers~~
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Old   February 11, 2012, 01:38
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mingersay,
yep in Fluent there is no problem defining periodic faces that are not conformal. I have use it many times.
cheers
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Old   February 27, 2012, 22:57
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Simon when you will going to post the tutorial for generating this kind of mesh because the beginners like me are still waiting for it. I now it will take your time to prepare tutorial but it will help a lot people. Thanks
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