The tolerance criteria used to check for convergence
Moderators: silvia, selimgunay, Moderators

 Posts: 84
 Joined: Tue Nov 07, 2017 7:47 am
 Location: University of Central Florida
The tolerance criteria used to check for convergence
Hello Engineers,
Can anyone tell me what is the best value for the tolerance in:
test NormDispIncr $tol $iter <$pFlag> <$nType>
I assume the smaller value, the more accurate response I get but I might face convergence issues.
I modeled 9 story benchmark building, yielding material and I am using 1.0e4 as the tolerance. Is it accurate enough? how can I know that? or in general how I find the best value for the tolerance.
Can anyone tell me what is the best value for the tolerance in:
test NormDispIncr $tol $iter <$pFlag> <$nType>
I assume the smaller value, the more accurate response I get but I might face convergence issues.
I modeled 9 story benchmark building, yielding material and I am using 1.0e4 as the tolerance. Is it accurate enough? how can I know that? or in general how I find the best value for the tolerance.

 Posts: 879
 Joined: Mon Sep 09, 2013 8:50 pm
 Location: University of California, Berkeley
Re: The tolerance criteria used to check for convergence
1e4 seems to be a bit large. The best way is to use a smaller tolerance (e.g., 1e8) and if nonconvergence happens, try to overcome that using adaptive strategies (including increase of the tolerance only at the problematic time step). You can also consider using energyincr to start with as it considers both force and displacement
If your analysis was successfully completed with 1e4 tolerance, one rough way of checking if that is accurate enough, is to run it with smaller tolerances and compare the results
If your analysis was successfully completed with 1e4 tolerance, one rough way of checking if that is accurate enough, is to run it with smaller tolerances and compare the results

 Posts: 84
 Joined: Tue Nov 07, 2017 7:47 am
 Location: University of Central Florida
Re: The tolerance criteria used to check for convergence
Thanks selimgunay, I am using adaptive strategies you shared before but it seems it has to reduce the tolerance in almost every steps to converge....is this shows my model has some issues? I developed a new yielding material in C++ and I am using that in 9story building.....the new material works just fine in SDOF and I verified that with MATLAB. In my MDOF structure, eigen analysis is just fine and I get 5 first frequencies of the structure as I expected but in order to do the timehisotry analysis, if I use a very small tolerance and the adaptive strategies, it takes so long.....is this reasonable?

 Posts: 879
 Joined: Mon Sep 09, 2013 8:50 pm
 Location: University of California, Berkeley
Re: The tolerance criteria used to check for convergence
If the convergence issues start at low levels of inelasticity, that may indicate that there might be some issues with your material. But, overall if it takes long with many iterations, but if it gets completed with meaningful results, it should be okay