
[Sponsors] 
March 17, 2014, 11:02 
FloEFD Residuals

#1 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,145
Rep Power: 32 
Hello,
As we used to work with typical residuals curves, we are a little bit lost with those % barcharts, So here are the questions: 1 if we choose convergencecriterior for goals as Automatic; how set FloEFD the limit for the convergence? 2 If we want to switch from automatic to manual; how big or how small should be the limit for having converged, credible and reliable solution? 3 During how many iterations should remain the "Delta" under the specific value untill FloEFD decides that the solution has converged? Thanks for the explanations
__________________
In memory of my friend Hervé: CFD engineer & freerider 

March 23, 2014, 10:49 

#2 
Senior Member
Boris Marovic
Join Date: Jul 2009
Posts: 464
Rep Power: 15 
Hi Maxime,
By %Charts you probably have all goals in the goal plot which will automatically use the normalized yaxis for the plot. If you use only similar parameter types when creating the goal plot you should get the absolute value as yaxis. You can also change the type of yaxis by rightclick into the graph and change it from normalized to absolute. You will see very large values and very small when looking at pressure in Pa and velocity in m/s as the one values are in the hundrests of thousands and the others are single digit numbers. That's the reason why it normalizes it. Otherwise you will only see flat lines at the bottom of the graph and at the very top. 1. These absolute values mentioned above show the absolute value of the parameter and you can see how much it fluctuates which is a more obvious indication for non numerical experts than residuals. 2. That depends on the acutal value of your goal. If you are looking at velocities around 23 m/s the criteria shouldn't be in the same order but much smaller. It wouldn't make sens to look for convergence with 1m/s fluctuations as it would be 3050% of the final value. I usually consider something around less than 5% as good convergence. Sometimes some values are set automatically very high but others need much longer to converge so that even thought the automatic setting is very high the acutal delta (right click on the top row of the table in the goal plot where the names are and activate "Delta" as a parameter column to display). The criterion might be 1m/s but the actual delta is at 0.0000012532 m/s or something like that and with that way below 1%. 3. The typical setting is half a travel which is good. If you can see the values are very good increasing and then flatteing to a converged value you can also say that is good enough but as long as they are fluctuating a lot I would let it run. I hope this helps, Boris 

March 24, 2014, 01:56 

#3  
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,145
Rep Power: 32 
Thank you Boris for your replies, 2 points more:
Quote:
We are talking now about "monitoring" goalsvalues. But is there a way to observe the real residuals from equations of continuity, NavierStokes, energy etc...
__________________
In memory of my friend Hervé: CFD engineer & freerider Last edited by mAx; March 28, 2014 at 01:26. 

March 27, 2014, 21:46 

#4 
Senior Member
Boris Marovic
Join Date: Jul 2009
Posts: 464
Rep Power: 15 
Yes, roughly that's what I do if the general delta value is not already small enough
If I'm not mistaken the residuals can be found in the *.stdout in small tables with the header in the table such as "Target res". But that's not very usefull to look for it in a nice way and I'm not 100% sure. Let me check and I will get back to you. Boris 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Tutorial of how to plot residuals !  wolle1982  OpenFOAM Running, Solving & CFD  132  May 20, 2016 09:28 
underrelaxation factors > level of residuals  Zigainer  FLUENT  17  February 6, 2016 01:12 
motorBike Residuals for SST komega... and mine  JR22  OpenFOAM Running, Solving & CFD  6  August 1, 2013 09:08 
judging convergence through residuals  MachZero  Main CFD Forum  7  December 25, 2012 13:18 
Convergence  scaled vs unscaled residuals  HS  FLUENT  1  November 7, 2005 06:45 