CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > STAR-CCM+

When to stop a simulation

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   March 15, 2011, 15:36
Default When to stop a simulation
  #1
New Member
 
Join Date: Mar 2011
Posts: 2
Rep Power: 0
Astropower is on a distinguished road
Hello All;
I'm new to this forum.
I'm using Star-CCM to simulate a tube having a hot spot in the middle of it. water flow inside this tube as a coolant.
I'm asking about the stopping criteria.
Residuals seem to saturate after about 300 iterations, and I can achieve temperatures of hot water and the hot spot on the tube.
When I increase to iterations (with very saturated residuals still) to say 5000, temperature of the hot spot on the tube seem to increase noticeably.

So, how to judge the adequacy of the number of iterations, and which one is correct : the results with few (300) iterations or that with 5000 iterations

Thanks
Astropower is offline   Reply With Quote

Old   March 16, 2011, 04:18
Default
  #2
New Member
 
Matthias Fitl
Join Date: Mar 2009
Location: Austria
Posts: 12
Rep Power: 8
MFitl is on a distinguished road
Hi

Quote:
Originally Posted by Astropower View Post
[...]
I'm asking about the stopping criteria.
Residuals seem to saturate after about 300 iterations,
[...]

So, how to judge the adequacy of the number of iterations, and which one is correct : the results with few (300) iterations or that with 5000 iterations

Thanks
In a steady state case like this I do look at the convergence of results I am interested in, in this case mass flow, temperature of outflow, heat transfer coeffcient and heat flux of the hot spot.
As the residuals are normalized on the first five (or ten) iterations the value for judging is limited.

In a transient case the residuals should return to a similar value at the last inner iteration.

Best regards,
Matthias
MFitl is offline   Reply With Quote

Old   April 5, 2011, 07:51
Default
  #3
New Member
 
Join Date: Feb 2011
Posts: 7
Rep Power: 6
mmaukii is on a distinguished road
You can judge more easily on residuals if you turn the normalization of them of so you can see them in SI units.
mmaukii is offline   Reply With Quote

Old   April 17, 2011, 08:39
Default
  #4
New Member
 
Martin
Join Date: Nov 2010
Posts: 23
Rep Power: 6
screech1987 is on a distinguished road
I find doing a separate report for a maximum and minimum (Temperature) Scalar witin the flow region, then creating a monitor and plot (which can combine the two in one graph) very useful.

Also a summation of all mass flows at boundaries is good, as should be near enough zero when converged. But to note that this type of report does very quickly reach 'convergence' for simple flows.
screech1987 is offline   Reply With Quote

Old   April 19, 2011, 06:45
Default
  #5
Senior Member
 
Join Date: Jun 2009
Posts: 100
Rep Power: 8
alastormoody11 is on a distinguished road
I think Mathias' idea is better, you should judge the convergence of a simulation, if its not converging according to conventional criterion through the use of data you desire to obtain by the means of the simulation.

You can set up a monitor for the temperature(vs iteration) and then setup an asymptotic limit with the value equal to the acceptable deviation for you.

I definitely would not recommend turning off the normalization becuase more often than not it leads humungous changes in the magnitude of the residuals and you are lost as to what should be used as the cutoff for the unnormalized residuals.
alastormoody11 is offline   Reply With Quote

Reply

Tags
stopping criteria

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Solar Radiation in OpenFOAM plainstyle OpenFOAM Running, Solving & CFD 15 July 8, 2014 04:43
velocity profile export from a simulation onto another sudhirlv STAR-CCM+ 1 September 12, 2010 18:57
Solver STOP with a variable Roland R CFX 3 March 10, 2010 19:38
How stop simulation if convergence is not reached? Andreas FLUENT 0 October 16, 2007 12:35
strange simulation error Ralf Schmidt FLUENT 2 May 4, 2007 13:02


All times are GMT -4. The time now is 18:02.