CFX Solver Control, Max iteration

adilsyyed · May 15, 2012, 11:43

I am doing a steady state analysis.
I have given maximum iterations in solution control to be 10000 with physical timescale of 5 sec.
The solver gives me result in 55 iterations, and does not go for the whole 10000 iterations.
Why?
And before this, in the very same analysis, I just specified maximum iterations to be 1000 with 2 sec physical timescale, and the solver go up to complete 1000 iterations.

evcelica · May 15, 2012, 12:10

Did you reach your convergence criteria? That would also stop the run.

k.vafiadis · May 15, 2012, 13:06

Check what's the convergence criteria: RMS or MAX Residual Target. Also, check the way you define your Timescale.

adilsyyed · May 15, 2012, 13:32

Quote:

Originally Posted by k.vafiadis

Check what's the convergence criteria: RMS or MAX Residual Target. Also, check the way you define your Timescale.

RMS, RMS target 0.0001

And what do you mean by he way I define your Timescale?

k.vafiadis · May 16, 2012, 04:32

A reasonable physical time scale value selection is important for good and faster convergence.
So for time scale 2sec and RMS target 10^-4 the solver needed 10000 (or more?) iterations to converge.
But with time scale 5sec and RMS 10^-4 the solver converged (converged to your RMS target) with only 55 iterations.
According to CFX Solver Modeling Guide (Chapter 14), physical time scales that are too large are characterized by bouncy convergence or results that do not converge. Time scales that are too small are characterized by very slow, steady convergence.

May 15, 2012, 11:43	CFX Solver Control, Max iteration	#1
adilsyyed Member Adil Syyed Join Date: May 2012 Posts: 49 Rep Power: 13	I am doing a steady state analysis. I have given maximum iterations in solution control to be 10000 with physical timescale of 5 sec. The solver gives me result in 55 iterations, and does not go for the whole 10000 iterations. Why? And before this, in the very same analysis, I just specified maximum iterations to be 1000 with 2 sec physical timescale, and the solver go up to complete 1000 iterations.

May 15, 2012, 13:06		#3
k.vafiadis New Member Kyriakos Vafiadis Join Date: Feb 2011 Location: Kozani, Greece Posts: 29 Rep Power: 15	Check what's the convergence criteria: RMS or MAX Residual Target. Also, check the way you define your Timescale. __________________ -- Kyriakos Vafiadis Mechanical Engineer, PhD candidate

May 16, 2012, 04:32		#5
k.vafiadis New Member Kyriakos Vafiadis Join Date: Feb 2011 Location: Kozani, Greece Posts: 29 Rep Power: 15	A reasonable physical time scale value selection is important for good and faster convergence. So for time scale 2sec and RMS target 10^-4 the solver needed 10000 (or more?) iterations to converge. But with time scale 5sec and RMS 10^-4 the solver converged (converged to your RMS target) with only 55 iterations. According to CFX Solver Modeling Guide (Chapter 14), physical time scales that are too large are characterized by bouncy convergence or results that do not converge. Time scales that are too small are characterized by very slow, steady convergence. adilsyyed likes this. __________________ -- Kyriakos Vafiadis Mechanical Engineer, PhD candidate

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May 15, 2012, 12:10		#2
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	Did you reach your convergence criteria? That would also stop the run.