CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

negative grid volumes when adapting

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 19, 2005, 09:24
Default negative grid volumes when adapting
  #1
Dave
Guest
 
Posts: n/a
Problem: negative volumes appearing when trying to adapt or smooth an originally sound grid.

A ship is modelled using 'utility tmerge' to combine 3 parts of the domain:

1. A rectangular block containing the ship geometry as a gap (subtracted volumes). This has been meshed and appears to be sound.

2. An 'inner cylinder' less the rectangular shape in part 1 above. This has been meshed and appears to be sound.

3. An 'outer rectangular block' less the inner cylinder in part 2. This has been meshed and appears to be sound.

All three grids were combined using 'utility tmerge -3d', ensuring correct positioning and alignment. This method allows for rotation of part 2 to model wind-over-ship at different angles, and has been successfully implemented on a different ship previously.

The four 'interface' boundaries defined in Gambit were used to create two grid interfaces in Fluent. The complete combined grid was checked in Fluent and reported no errors and no negative volumes.

A calculation ran without errors or divergence until convergence.

However, after running, any attempt to adapt the grid or smooth it immediately results in 'non-positive' volumes which appear to correspond to the size of the grid interface boundaries, i.e. quite large. Progression of the solution is impossible, any attempt to continue iterations after the adaption fails at the first iteration, with the following error message:

Error: divergence detected in AMG solver: x-momentum Error Object: ()

The whole process was started again (for a different wind angle) in Gambit but the eventual result was identical. Initial grid was good but any adaption led to negative volumes.

As mentioned, the same process was used in the past successfully, so the reason for these errors is unclear. Any help or suggestions would be gratefully received. Thanks.
  Reply With Quote

Old   August 20, 2005, 13:47
Default Re: negative grid volumes when adapting
  #2
razvan
Guest
 
Posts: n/a
I think you should consider deleting the grid interfaces before the adaption process is started, than make the adaption (which should still work considering the fact that deleting an interface does not change any solution values stored in the cells adiacent to the interface boundary). After obtaining the desired result, recreate the interface with the new grid boundaries.

I bet this would work.

Best whishes, Razvan
  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
Mapping results from CFD grid to structural grid of a free-form surface mbecker OpenFOAM Running, Solving & CFD 1 October 18, 2013 10:16
Why doesn't coarsening occur during grid adapting? A. S. FLUENT 2 July 11, 2011 17:00
trailing edge negative volumes Nick R ANSYS Meshing & Geometry 2 February 2, 2011 03:05
Mesh orientation and negative volumes Nick R CFX 3 January 10, 2011 17:34
Negative volumes Christie FLUENT 2 March 29, 2007 08:46


All times are GMT -4. The time now is 23:35.