Choosing convergence criteria on monitor point

Torque_Converter · June 3, 2012, 00:00

I am monitoring torque in a rotating component. The torque value I am expecting is between 1000-2000 N*m, depending on rotational velocity. I would need to find the value within 25 N*m. What should I use to determine when this happens, as it seems there will always be a slight change if i let it go on forever. Would something like a change of less than .01% over 20 iterations likely be sufficient for what I'm looking for?

ghorrocks · June 3, 2012, 06:59

You are looking for quiet accurate results (2.5 on torque) so you are going to have to be very careful with accuracy to achieve this. I think you are going to have to be a bit more clever than that to achieve your target accuracy reliably.

I would have a look at the key reference text on CFD accuracy "Computational Fluid Dynamics" by Roache. Things like the link on this FAQ are a good summary http://www.cfd-online.com/Wiki/Ansys...publishable.3F

A thought on your specific case of judging convegernce: If you let your case converge for a while you may find that the torque returned is following a relationship like error=1/x^n or error=e^-nx or something. If you can pick what path it is taking for convergence you can get a far more accurate torque number than you simple tolerance approach. Note that this is a similar approach as Richardson extrapolation is to mesh refinement studies.

June 3, 2012, 00:00	Choosing convergence criteria on monitor point	#1
Torque_Converter Member Join Date: Jan 2012 Location: Edmonton, CA Posts: 87 Rep Power: 14	I am monitoring torque in a rotating component. The torque value I am expecting is between 1000-2000 Nm, depending on rotational velocity. I would need to find the value within 25 Nm. What should I use to determine when this happens, as it seems there will always be a slight change if i let it go on forever. Would something like a change of less than .01% over 20 iterations likely be sufficient for what I'm looking for?

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June 3, 2012, 06:59		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	You are looking for quiet accurate results (2.5 on torque) so you are going to have to be very careful with accuracy to achieve this. I think you are going to have to be a bit more clever than that to achieve your target accuracy reliably. I would have a look at the key reference text on CFD accuracy "Computational Fluid Dynamics" by Roache. Things like the link on this FAQ are a good summary http://www.cfd-online.com/Wiki/Ansys...publishable.3F A thought on your specific case of judging convegernce: If you let your case converge for a while you may find that the torque returned is following a relationship like error=1/x^n or error=e^-nx or something. If you can pick what path it is taking for convergence you can get a far more accurate torque number than you simple tolerance approach. Note that this is a similar approach as Richardson extrapolation is to mesh refinement studies.