CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Differences solutions in Parallel and Serial

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 29, 2009, 09:13
Default I'm performing simulations wit
  #1
New Member
 
Antonio Attili
Join Date: Mar 2009
Location: Rome, Italy
Posts: 21
Rep Power: 8
wizard1301 is on a distinguished road
I'm performing simulations with the coodles solver, running the application both in serial and in parallel (on a single machine with several cores).
I' ve observed that the solution obtained with the parallel run (mpirun) is slightly different from the one obtained running the application on a single processor(I'm observing the time history of pressure, temperature,...in some points). Obviously the two simulations start from identical condition; the initial conditions for the parallel case has been obtained decomposing the solution of the serial case in a certain time instant.
Has someone observed the same behaviour?
wizard1301 is offline   Reply With Quote

Old   January 30, 2009, 03:28
Default There are several possible exp
  #2
Member
 
Martin Aunskjaer
Join Date: Mar 2009
Location: Denmark
Posts: 48
Rep Power: 8
aunola is on a distinguished road
There are several possible explanations. If floatTransfer is on you may sacrifice some accuracy due to round-off. Preconditioning of matrices does not always parallelize well. The IC preconditioning for instance relies on a scheme whereby matrix elements are visited in an order which cannot be replicated in a parallel run. I'm not sure if it makes sense for your case, but you can try diagonal preconditioning and see what happens - it does not have the samme parallelization problem as IC.
aunola is offline   Reply With Quote

Old   January 30, 2009, 06:38
Default Thank you for your answer Mart
  #3
New Member
 
Antonio Attili
Join Date: Mar 2009
Location: Rome, Italy
Posts: 21
Rep Power: 8
wizard1301 is on a distinguished road
Thank you for your answer Martin. I think that all the possible causes you proposed can be applied to my case.
I've also observed that for long time the differences tend to disappear, probably the main source of differences is related to the fieldDecomposition.
wizard1301 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
More DPM incompletes in parallel than in serial Paul FLUENT 0 December 16, 2008 10:27
Serial vs parallel different results luca OpenFOAM Bugs 2 December 3, 2008 11:12
Differences between serial and parallel runs carsten OpenFOAM Bugs 11 September 12, 2008 11:16
Serial run OK parallel one fails r2d2 OpenFOAM Running, Solving & CFD 2 November 16, 2005 13:44
parallel Vs. serial co2 FLUENT 1 December 31, 2003 03:19


All times are GMT -4. The time now is 16:44.