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

Divergence detected in AMG solver: pressure correction

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

Like Tree2Likes
  • 2 Post By mmentzos

Reply
 
LinkBack Thread Tools Display Modes
Old   January 22, 2010, 12:14
Default Divergence detected in AMG solver: pressure correction
  #1
New Member
 
Emily
Join Date: Jan 2010
Posts: 3
Rep Power: 7
emlejeen is on a distinguished road
I am having major issues with convergence of my solution. I am running a moving/deforming boundary UDF and cannot seem to get past a certain time step in the flow solution. I have now began a guess and check method to find the relaxation factors that best suit my needs. However, I cannot seem to find the correct parameters to successfully converge the solution. Ironically, the solution errors at the same time for every case I run and I always get the same error: "Error: divergence detected in AMG solver: pressure correction". I have tried to use two different solvers: the default with relaxation factors of 0.2, 0.8, 0.8, 0.1 for pressure, density, body forces, and momentum, respectively...and PISO with second order pressure and momentum (using the same relaxation factors as above). I have also decreased my pressure relaxation factor down to 0.5 and am still getting an error. As a last attempt, I re-ran all of my cases with the varying solvers and relaxation factors with a smaller time step (0.025s was used first then 0.01). I am willing to provide my UDF and case files is desired. Thank you.
emlejeen is offline   Reply With Quote

Old   January 22, 2010, 12:22
Default
  #2
Senior Member
 
Join Date: Nov 2009
Posts: 411
Rep Power: 10
DoHander is on a distinguished road
Try to run the same case at t=0 but using the steady solver, wait until convergence or until the residual is flat. Then switch to the unsteady solver - this will give you a good initial solution.

Do
DoHander is offline   Reply With Quote

Old   January 22, 2010, 13:59
Default
  #3
New Member
 
Emily
Join Date: Jan 2010
Posts: 3
Rep Power: 7
emlejeen is on a distinguished road
Quote:
Originally Posted by DoHander View Post
Try to run the same case at t=0 but using the steady solver, wait until convergence or until the residual is flat. Then switch to the unsteady solver - this will give you a good initial solution.

Do
I am using a dynamic mesh which cause fluid motion. If i used a steady state solver, the fluid remains static because the mesh does not move. I could, however, apply a steady flow rate to the inlet, but then my model would just continue to move and would never converge. I am using a closed bulb model, similar to a boiling flask. The inlet of my bulb acts like the outlet because there is only one point of entry. Hope this helps to clear up my methods.
emlejeen is offline   Reply With Quote

Old   January 26, 2010, 12:17
Default
  #4
New Member
 
Mike Mentzos
Join Date: Dec 2009
Posts: 4
Rep Power: 7
mmentzos is on a distinguished road
Check if
When you use PISO neighbor correction, under-relaxation factors of 1.0 or near 1.0 are recommended for all equations. If you use just the PISO skewness correction for highly-distorted meshes (without neighbor correction), set the under-relaxation factors for momentum and pressure so that they sum to 1 (e.g., 0.3 for pressure and 0.7 for momentum). If you use both PISO methods, follow the under-relaxation recommendations for PISO neighbor correction, above.
gfoam and acgnipper like this.
mmentzos is offline   Reply With Quote

Old   August 7, 2010, 06:45
Default pressure correction
  #5
Member
 
ahmad
Join Date: Jul 2010
Posts: 57
Rep Power: 7
almostafa67 is on a distinguished road
hi dear all...
i'm trying to simulate peristaltic pump,when i was iterating simulated case i this error message showed up:
Error: Divergence detected in AMG solver: pressure correction.
i tried a lot to get rid of it,decreased urf from 0.6 to 0.1,changed meshing,changed skewness correction,....
but this message again and again showed up!
dear all i will be thankful if u help me out
thank u in advance for any help provided.
almostafa67 is offline   Reply With Quote

Reply

Tags
amg, divergence, pressure correction, relaxation factor, solver

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
divergence detected in AMG solver selvaganesh FLUENT 5 February 5, 2014 04:55
Error: Divergence detected in AMG solver? frank FLUENT 7 July 21, 2012 13:29
Divergence in AMG solver :k Guillaume FLUENT 7 May 20, 2010 19:17
divergence detected in AMG solver-pressure correction sivaraja FLUENT 2 June 18, 2009 11:55
divergence of pressure solver CFT Fluent UDF and Scheme Programming 0 May 4, 2009 00:33


All times are GMT -4. The time now is 10:17.