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

Convergence in (diffn only)coupled problems(FIDAP)

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 27, 2000, 00:47
Default Convergence in (diffn only)coupled problems(FIDAP)
  #1
Mulla
Guest
 
Posts: n/a
I am a chemical engineer trying to model a set of coupled equations. To ensure that I am on the safe side of the computation, I had devised some simple test problems for which I obtained the analytical solutions myself and wanted to check with the FIDAP results. TO my surprise, I found that the solutions varied as widely as the acceleration factors I have used. (a point to be noted is that the "Fully coupled solver" failed completely and diverged. I use the USRSRC subroutine and hence the segregated solver)

IS there a disciplined way to approach this problem ? The test problem is simple and since I know the analytical solution I am trying to verify the FIDAP results against the analytical solution. But, how will I be convinced that the bigger version of the test problem, which I will have to encounter soon, will have dependable results ?

If anybody can thrwo some light on the usage of "SOLUTION" command in FIDAP and the "velconv" and "resconv" arguements, I will be more than grateful.

Thx
  Reply With Quote

Old   August 27, 2000, 01:11
Default Re: Convergence in (diffn only)coupled problems(FI
  #2
John C. Chien
Guest
 
Posts: n/a
(1). The only reason why the forum is here is because some users have some problems. (2). Nobody guarantee a solution when you are using a commercial code. They all provide no warranty page somewhere. (3). One way to do is to ask the vendor to provide good sample cases, and see whether you can repeat those cases. (4). The chances of getting a good solution would be higher if both of you and the vendor can obtain the same solution to a sample problem. (5). It is useless to design your test cases to check out the code. Unless the vendor happened to include your cases in the code in the code development phase. (6). There have been some discussions on the proper ways to use a commercial code in this forum. Use search to locate the old messages.
  Reply With Quote

Old   August 27, 2000, 08:08
Default Re: Convergence in (diffn only)coupled problems(FI
  #3
Ahmed Hassaneen
Guest
 
Posts: n/a
The Segregated solver is less accurate than the fully coupled but it is much more stable and very sensitive to the RELAXATION FACTORS and number of GRIDS.To get a converged solution from the fully coupled solver (N.R) you should start with (S.S) solver for 5 iterations or so and then switch to N.R or Q.N.
  Reply With Quote

Old   August 27, 2000, 14:10
Default Re: Convergence in (diffn only)coupled problems(FI
  #4
Mulla
Guest
 
Posts: n/a
Ahmed:

thx a lot for your suggestion. I shall implement your suggestion and 'll discuss the outcome here.
  Reply With Quote

Old   August 28, 2000, 02:34
Default Re: Convergence in (diffn only)coupled problems(FI
  #5
Ahmed Hassaneen
Guest
 
Posts: n/a
There is also one more thing. You should put the VELC and RESC at least 0.0001 to get the converged solution (Segregated solver) at higher # of iterations (at least 500 or so) for the solution to be more accurate.
  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
Convergence Centurion2011 FLUENT 24 May 9, 2015 08:02
Force can not converge colopolo CFX 13 October 4, 2011 22:03
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
Defect correction and convergence ganesh Main CFD Forum 4 June 30, 2006 14:20
Convergence problems Chetan FLUENT 3 April 15, 2004 19:13


All times are GMT -4. The time now is 01:58.