transient convergence criteria
 

Hi,
I'm working on a periodic simulation and I'd like to set up a temporal convergence criteria. It would be something like
if variable(t+T)=variable(t) then stop simulation

In the swak4foam library there are tools to stop a simulation if a criteria is reached, something like (in controlDict) :

My question is,how to access the data on a specified patch at a specified time ?

Regards,

Florian

Abusing that functionObject would be hardcore. But have a look at writeAndEndSwakExpression in the simpleSwakFunctionObjects-library. That might be EXACTLY what you're looking for (stops the run if a logical expression evaluates to "true" - either everywhere ("and") or somewhere ("or"))

Thank you for writeAndEndSwakExpression, I didn't know this one. I'm still wondering how to access data at a specified time. oldTime only works for one timeStep in the past...
Any idea ?

Regards,

Florian

Yep. Delayed variable

Thank you very much, a mix of delayedVariables and writeAndEndSwakExpression works perfectly !
Regards,
Florian.

Thank YOU. Without you I wouldn't have thought that delayed variables can be used for convergence-checking

Can you post the code? Might be useful for people in the future.

Even better: Adding it under http://openfoamwiki.net/index.php/Co...Usage_examples would make sure that people don't have to search threads for it

I guess I can compete for the ugliest way of doing things but it does work (so far).
Test case : one intlet with a sinusoidal pressure, 2 free outlets.

What it looks like :
http://uppix.net/VXLVj8l.png
With : blue = p(inlet), pink = 5% threshold, red and green : convergence criteria on both outlets.

I was wondering : how can I add the period as a parameter ?


Florian

Nice. Just one problem: you're testing for the maximum. So if on outlet1 the same maximum is on a different location it still might be judged as "converged". One possibility would be to use as valueType patch on outlet1 and instead of max(mag(U)) use mag(U). instead wrap the max around the expression maxU1. That way you'd get convergence if the values on the outlet are really the same. But this only works for one patch at once (to treat the outlet2 similarly AT THE SAME TIME) is a little bit more tricky

With "period" you mean the delay of the delayedVariables? This value can currently only be a fixed value. But if you want to set the values consistently then you can set a dictionary entry
and make all delays use that

Hi ! I'm aware of this this limitation and wand to create 2 functions like this, for each outlets :
and then get the results to be evaluated in the function writeAndEndSwakExpression but I still have problems to exchange data from a function to another.

Thank you !

Florian

If you're on outlet1 you don't have to write UA1fter{patch'outlet1}. UA1fter is sufficient.

Hi everyone,

I am not understanding well the use of this wonderful tool.

I would like to stop my (steady) simulation when Residuals are below a given threshold (let's say 1e-4) and outlet velocity remains unchanged with iterations, so, I have included this in my controDict file:
velocity_outlet
{
type patchExpression;
accumulations (
average
);
patches (
out
);
expression "mag(U)";
verbose true;
outputControl timeStep;
outputInterval 1;
}

This computes averaged outlet velocity as I desired.

But now I am not sure how to compare old and present values. I would like to:

if
|uaveraged(iteration n)-uaveraged(iteration n-1)|<0.1
and
Residuals<1e-4
then
STOP

Based on the code I have seen here, I have tried something like this( forget about the Residuals in this first try)


stopIfCrit {
type writeAndEndSwakExpression;
valueType internalField;
logicalExpression "(tol < threshold)";

logicalAccumulation and;
variables (
"UA1fter=velocity_outlet;" //delayed criteria on outlet1
"Ub41=velocity_outlet;"

"tol=mag(UA1fter-Ub41);"

"threshold=0.5;"

"test=((tol < threshold) )? 1 : 0;"
);
delayedVariables (
{
name UA1fter;
delay 1;
storeInterval 1;
startupValue "1";
}

{
name test;
delay 1;
storeInterval 1;
startupValue "0";
}
);
verbose true;
outputControlMode timestep;
outputInterval 1;
}

But nothing happens. It seems that I am not telling OpenFOAM when it has to stop .This definition I have tried looks so weird:

"UA1fter=velocity_outlet;" //delayed criteria on outlet1
"Ub41=velocity_outlet;"

Does anybody know how I have to proceed to compare a computed value in the previous iteration with this value in the current iteration?


Thanks in advance!:)

Hi,
you can look at the variables values that are stored during the simulation to check if they are what you expect (in the swak4Foam folder at each timeStep).
You can use the [CODE ] [/CODE ] bracket to make the code readable.

Hi Hiroshiman,

The values of:

velocity_outlet
{
type patchExpression;
accumulations (
average
);
patches (
out
);
expression "mag(U)";
verbose true;
outputControl timeStep;
outputInterval 1;
}

are written in postProcessing folder (no swak4foam folder in my case)

The problem is I don't know how to use this values to stop my simulation when differences between consecutive iterations is small.

Some more help will be much aprecciated.