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-   -   Asymptotic stopping criterion is not working (http://www.cfd-online.com/Forums/star-ccm/112289-asymptotic-stopping-criterion-not-working.html)

rob50904 January 25, 2013 08:05

Asymptotic stopping criterion is not working
 
Hello,
I have a problem with the user defined asymptotic stopping criterion in StarCCM+ 7.06:

I'm calculating the resistance of a ship using free surface with VOF and DFBI (6DOF).

I created a stopping criterion from a force monitor. The plot of the force monitor is decreasingly oscillating. Using the asymptotic stopping criterion for the outer iterations I want to stop the calculations ones the oscillation is within a certain limit for a certain time.
In the stopping criterion I set number of samples to 10 and |Max-Min| to the desired oscillation limit.
My problem is that the criterion is never fulfilled, no matter how high I set the oscillation limit.

example: over a period of 10 timesteps my plotted force changes about 1N. So I would expect a criterion with 10samples and |Max-Min|=2N to immediately stop the calculation but that doesn't happen (the "criterion satisfied" checkbox is "false" all the time).

The Minimum and Maximum criteria work fine by the way!

Did anybody encounter the same problems? Might there be a bug in StarCCM+?

ryancoe January 27, 2013 11:13

I encountered this same issue a while ago. Like you I was confounded.

When I finally talked to a CD-adapco rep., he explained that the asymptotic limit is simply controlling the inner iterations (this makes sense when you look at the node structure in the GUI). When the limit is met, the simulation advances to the next time-step.

I agree that it would be nice to have an asymptotic limit to end the unsteady simulation. You could try to write a field function or macro like:

if: (asymptotic condition met)
then: set TimeLimit = (CurrentTimeLevel - 1s)

rob50904 January 28, 2013 09:25

Thanks!
I will try that.


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