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Processor Affinity to Enhance Speed

Posted September 11, 2012 at 11:09 by Hisham (Notes for OpenFOAM!)
Updated September 12, 2012 at 10:02 by Hisham

To enhance the speed of running a solver one can use a "hard" assignment of the job to a specific core. This reduces the work needed to switch jobs between cores and enhances the speed. It is really neat if you need to do some other work on the workstation while the run is going on in the background.

# apt-get install schedtool
$ schedtool -a 5 10640
This command assigns job 10640...
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under-relaxation factors -> level of residuals

Posted August 27, 2012 at 09:27 by kira

more helpful info on under-relaxation factors:

Originally Posted by LuckyTran View Post
No magic here, that's what's supposed to happen. Unless your solution is diverging, do not bother with the under-relaxation factors. If it is diverging, do as you did, lower the factors until you can a stable solution, and then raise them again if possible. If not, then it is a hint that there is an inherent stability issues in the problem you are trying to solve or perhaps one of your modeling parameters is incorrect.

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what is under relaxation factor?

Posted August 27, 2012 at 09:23 by kira

something to keep in mind:
Originally Posted by Phil
Each of the variables(mass,mom,density) represents an equation the solver is trying to solve. Each iteration the values obtained for the variables should get closer and closer together - converge. FOR SIMPLE PROBLEMS ESPECIALLY COLD FLOWS WITHOUT COMBUSTION YOU SHOULD SIMPLY KEEP THE RELAXATION FACTORS AT DEFAULT.

Sometimes for many many reasons the solution can become unstable so a relaxation factor is used - takes part of value from previous iteration
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Useful Threads

Posted August 10, 2012 at 13:50 by lakeat (Daniel Wei's CFD Blog: (
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2D unstructured mesher in F90

Posted August 9, 2012 at 08:23 by truffaldino

This is 2D unstructured mesher.

tri_mesh.f90 is a mesher and the rest are input files

Example 1: Cavity flow driven by upper cavity wall

file: cavity_bc.txt

Example 2: flow past NACA 0012 airfoil

files: NACA0012_bc.txt - airfoil
wt_bc.txt - wind tunnel
wake_bc.txt -wake

Description of the program is placed in the header of tri_mesh.f90
Attached Files
File Type: f tri_mesh.f (100.5 KB, 209 views)
File Type: txt cavity_bc.txt (65 Bytes, 110 views)
File Type: txt NACA0012_bc.txt (16.6 KB, 130 views)
File Type: txt wt_bc.txt (184 Bytes, 113 views)
File Type: txt wake_bc.txt (5.5 KB, 220 views)
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