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

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 January 12, 2013, 04:55 what do global and cumulative terms in continuity refer to exactly? #1 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 Sponsored Links 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?

 January 13, 2013, 06:17 #2 Senior Member   Fumiya Nozaki Join Date: Jun 2010 Location: Yokohama, Japan Posts: 217 Blog Entries: 1 Rep Power: 11 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 kiddmax and vbnhfylbh like this.

 January 16, 2013, 10:15 #3 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 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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