Convergence issue?

dinesh · July 15, 2013, 13:01

I am solving one transient problem.when I give a time step of 0.005s solution is converging on each iteration. But when i give 0.006 it does not converge. i am giving max itr/time step as 50. What does this indicate? what happens when solution is converging at each step or after just 1 step. Will i get the correct results if i keep my time step as 0.005s as my solution is converging.

plz sugggest.....

blackmask · July 15, 2013, 21:22

Convergence criterion is the source of debate. If the solution converged at the first iteration, it means that either you do not know which is the first iteration for each time step in fluent, or your convergence criterion is too tender.

vasava · July 22, 2013, 09:49

That means that 50 iterations are not enough to find a solution for time step of 0.006 s. Also even if your one solution converges with in 50 iterations does not necessarily imply that your other solutions will converge within same number of iterations.

Remember that even if you give 1000 or 1 million as maximum number of iterations/time-step fluent will stop calculating as soon as it reaches a good solutions. So be generous while declaring number of iterations/time-step .

July 15, 2013, 13:01	Convergence issue?	#1
dinesh Member Vjoess Join Date: Oct 2012 Posts: 54 Rep Power: 14	I am solving one transient problem.when I give a time step of 0.005s solution is converging on each iteration. But when i give 0.006 it does not converge. i am giving max itr/time step as 50. What does this indicate? what happens when solution is converging at each step or after just 1 step. Will i get the correct results if i keep my time step as 0.005s as my solution is converging. plz sugggest.....

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July 15, 2013, 21:22		#2
blackmask Senior Member Join Date: Aug 2011 Posts: 421 Blog Entries: 1 Rep Power: 22	Convergence criterion is the source of debate. If the solution converged at the first iteration, it means that either you do not know which is the first iteration for each time step in fluent, or your convergence criterion is too tender.

July 22, 2013, 09:49		#3
vasava Senior Member Paritosh Vasava Join Date: Oct 2012 Location: Lappeenranta, Finland Posts: 732 Rep Power: 23	That means that 50 iterations are not enough to find a solution for time step of 0.006 s. Also even if your one solution converges with in 50 iterations does not necessarily imply that your other solutions will converge within same number of iterations. Remember that even if you give 1000 or 1 million as maximum number of iterations/time-step fluent will stop calculating as soon as it reaches a good solutions. So be generous while declaring number of iterations/time-step .