How to determine time step size and Max. iterations per time step.

Aashi171185 · January 6, 2019, 14:20

hello every one i want to ask about the thumb rules for setting the time step size and how to set the maximum number of iteration.
like i am doing multi phase analysis how i decide about setting the time step size and maximum number of coefficient loops.
Plz reply

ghorrocks · January 6, 2019, 18:53

The recommendation for most simulations is:

Convergence settings:
Min coeff loops = 1
Max coeff loops = 10
Residual and/or imbalance convergence criteria determined by sensitivity analysis

Time step settings:
Adaptive time stepping, homing in on 3-5 coeff loops per time step.
Min time step small enough you never reach it
Max time step can be used to stop excessively large time steps if you need to

This way the solver finds its own time step, and the time step size it finds is always in the acceptable from a sensitivity analysis. At least I have never seen an example when it is not.

Aashi171185 · January 6, 2019, 19:54

Thanks for reply sir and your kind consideration. sir how can i perform the sensitivity analysis

ghorrocks · January 7, 2019, 06:43

Sensitivity Analysis: See post #17 on this thread for time step size Sloshing simulation using ansys cfx vof method

January 6, 2019, 18:53		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The recommendation for most simulations is: Convergence settings: Min coeff loops = 1 Max coeff loops = 10 Residual and/or imbalance convergence criteria determined by sensitivity analysis Time step settings: Adaptive time stepping, homing in on 3-5 coeff loops per time step. Min time step small enough you never reach it Max time step can be used to stop excessively large time steps if you need to This way the solver finds its own time step, and the time step size it finds is always in the acceptable from a sensitivity analysis. At least I have never seen an example when it is not. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

January 7, 2019, 06:43		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Sensitivity Analysis: See post #17 on this thread for time step size Sloshing simulation using ansys cfx vof method __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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January 6, 2019, 14:20	How to determine time step size and Max. iterations per time step.	#1
Aashi171185 Member Aashi Join Date: Dec 2018 Posts: 43 Rep Power: 7	hello every one i want to ask about the thumb rules for setting the time step size and how to set the maximum number of iteration. like i am doing multi phase analysis how i decide about setting the time step size and maximum number of coefficient loops. Plz reply

January 6, 2019, 19:54		#3
Aashi171185 Member Aashi Join Date: Dec 2018 Posts: 43 Rep Power: 7	Thanks for reply sir and your kind consideration. sir how can i perform the sensitivity analysis