CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > ANSYS Meshing & Geometry

[ICEM] Problem when I try to merge hexa & prism

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree2Likes
  • 2 Post By PSYMN

Reply
 
LinkBack Thread Tools Display Modes
Old   November 29, 2012, 05:28
Default Problem when I try to merge hexa & prism
  #1
New Member
 
Join Date: Jul 2012
Location: France
Posts: 19
Rep Power: 4
pipolaki is on a distinguished road
Good morning,

I want to build an hybrid mesh and I need to merge the nodes at the interface. The geometry composed with :
- an external environement in hexa ;
- a swirl injector in tetra + its boundary layer in prism.






I can merge the two volumes if the swirl injector is purelly made with tetra.
But when I try to merge the two volumes with the swirl injector composed with tetra and prism, I obtain the message "unable to remove prims node xxxx" and then ICEM is blocked.

Do you think if it's possible to merge hexa with prism ?

Thanks.

Last edited by pipolaki; November 29, 2012 at 13:44.
pipolaki is offline   Reply With Quote

Old   November 29, 2012, 11:13
Default
  #2
Super Moderator
 
diamondx's Avatar
 
Ghazlani M. Ali
Join Date: May 2011
Location: Canada
Posts: 1,218
Blog Entries: 23
Rep Power: 18
diamondx will become famous soon enough
Send a message via MSN to diamondx
that might not be possible. because prism is the result of height that you defined. hexa too. merging mesh only works between hexa and tetra (and not hexa/hexa), so it can be free
to change tetra and adapt it to hexa. In your case, you are asking him to change prism height... That is again based of how i understand the mecanism of prism and merging.
Someone can correct me if i'm wrong...
__________________
Regards,
New to ICEM CFD, try this document --> http://goo.gl/G2gkE
Ali
diamondx is offline   Reply With Quote

Old   November 29, 2012, 14:31
Default
  #3
New Member
 
Join Date: Jul 2012
Location: France
Posts: 19
Rep Power: 4
pipolaki is on a distinguished road
Before reading the answer of diamondx (thank you by the way), I found a "solution" to my problem.
Step 1 : I create the mesh of the swirl injector only with tetra.
Step 2 : I smooth it in order to have a correct quality.
Step 3 : I create the mesh of the external area with hexa.
Step 4 : I merge the two meshes.
Step 5 : I create the layer of prism in the swirl injector.

By this way, I obtained a layer of prism inside my tetra mesh which is correctly connected to the hexa mesh. I guess this is well known by the experienced users but if needed, I can develop this method and I could show you some images next monday.

Now, the problem is that, even if my initial tetra mesh is quiet correct, the prism layer creates a lots of bad elements I didn't have before (quality < 0.2, Min angle < 9...) Even with different smooth operations, it's impossible to obtain the quality I've had before adding the prism layer. It's very frustrating because I'm feeling I'm really close from the definitive mesh...
I tried a first series of smoothing operations with prism freezed.
Then I released the constraint on the prism and continued with the smoothing but I still have very bad elements. It looks like the smoothing operations were useless. It's strange.

Do you have any advice regarding the smooth process of such mesh in such geometry ?
pipolaki is offline   Reply With Quote

Old   November 30, 2012, 02:48
Default
  #4
Senior Member
 
AB
Join Date: Sep 2009
Location: France
Posts: 323
Rep Power: 12
BrolY will become famous soon enough
Quality of 0.01 for prism is good enough.
Check other threads about it in this forum.
BrolY is offline   Reply With Quote

Old   November 30, 2012, 05:03
Default
  #5
New Member
 
Join Date: Jul 2012
Location: France
Posts: 19
Rep Power: 4
pipolaki is on a distinguished road
Quote:
Originally Posted by BrolY View Post
Quality of 0.01 for prism is good enough.
Check other threads about it in this forum.
In fact, the problem is not the quality of the prism, it's the quality of some tetra elements.
pipolaki is offline   Reply With Quote

Old   November 30, 2012, 10:49
Default
  #6
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,650
Blog Entries: 1
Rep Power: 34
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
Correct, you can only merge meshes if one side is all tetra... It needs the flexibility of the tetra mesh make it work. Prisms are too restrictive. We are working on ways to improve this situation.

Prism quality looks worse than it is... No worries there either.

As for the poor tetras, run the smoother with the prisms and hexas frozen... see what it can do. It should fix most tetras. The tetras it can't fix are those that are stuck between close layers of prisms...

In that case, you may want to free up the prisms to be smoothed, but greatly reduce the "upto quality" number. So instead of trying to smooth just the tetras with an upto of 0.6, turn on prism smoothing and set the upto down to 0.1...

If the problem is just that your prism layers get too close together and there isn't room for the smoother to get any improvement, you could try regenerating the prisms with auto-reduction (an advanced option) on, or adjust the height or number of layers in that area.

Best regards,

Simon
Far and BrolY like this.
__________________
-----------------------------------------
Please help guide development at ANSYS by filling in these surveys

Public ANSYS ICEM CFD Users Survey

This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)...

CFD Online Users Survey
PSYMN is offline   Reply With Quote

Old   December 1, 2012, 05:24
Default
  #7
New Member
 
Join Date: Jul 2012
Location: France
Posts: 19
Rep Power: 4
pipolaki is on a distinguished road
Thanks for your answer Simon.
I will try your solution next Tuesday and I will inform you about the results asap.
Have a good week end.
pipolaki is offline   Reply With Quote

Old   December 4, 2012, 08:44
Default
  #8
New Member
 
Join Date: Jul 2012
Location: France
Posts: 19
Rep Power: 4
pipolaki is on a distinguished road
I followed the advices of Simon and here are the results for the quality of my mesh. It helps me to improve it. I have to mention that I also modified node by node some elements (Edit Mesh -> Move Node) in order to obtain these histogram. What's your opinion ?
I think the worst parameter is the MIN ANGLE because I still have a lots of element between 9 and 18...



On these quality histograms I mentionned the results with or without the surface elements. As you can see, some surface elements have a bad influence on some histograms but I think that surface element are irrelevant in the analysis of the mesh quality of a 3D mesh. Am I wrong ?

Last edited by pipolaki; December 4, 2012 at 12:57.
pipolaki is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[ANSYS Meshing] stuck element vs prism layer hadrien51 ANSYS Meshing & Geometry 5 January 23, 2012 13:02
[ICEM] yet another prism problem... prandtl ANSYS Meshing & Geometry 1 December 17, 2009 16:50
[ICEM] prism problem zkdkeen ANSYS Meshing & Geometry 5 December 2, 2009 20:54
ICEM5 Hexa output problem Pete CFX 9 September 16, 2004 18:33


All times are GMT -4. The time now is 11:31.