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-   -   what do global and cumulative terms in continuity refer to exactly? (https://www.cfd-online.com/Forums/openfoam-solving/111663-what-do-global-cumulative-terms-continuity-refer-exactly.html)

 immortality January 12, 2013 04:55

what do global and cumulative terms in continuity refer to exactly?

at results there are 3 types of residuals of continuity equation.whats the definition of them and difference?if cumulative and or global be negative whats wrong in the problem?

 fumiya January 13, 2013 06:17

For the solvers of incompressible fluid, take a look at the
src/finiteVolume/cfdTools/incompressible/continuityErrs.H:

Code:

volScalarField contErr(fvc::div(phi));

scalar sumLocalContErr = runTime.deltaTValue()*
mag(contErr)().weightedAverage(mesh.V()).value();

scalar globalContErr = runTime.deltaTValue()*
contErr.weightedAverage(mesh.V()).value();
cumulativeContErr += globalContErr;

Info<< "time step continuity errors : sum local = " << sumLocalContErr
<< ", global = " << globalContErr
<< ", cumulative = " << cumulativeContErr
<< endl;

From the above definitions, the difference between the local and global
continuity error is whether the magnitude of divergence is taken or not.
The "local" error is a measure of the continuity of each cell and the
"global" error represents the continuity in the whole computational domain.
If the global error converges to zero, I think the negative value is of no matter.

I have no idea about the importance of considering the cumulative error.

Fumiya

 immortality January 16, 2013 10:15

thanks fumiya
I cant grasp how the total continuity is calculated.my case is compressible.
What does mean cumulative continuity error?
Any hint is accepted here!

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