Time step continuity error (cumulative very high ~ 0.89)

chandra shekhar pant · February 12, 2021, 10:34

Hello Foamers,

I am trying to run a simpleFOAM solver for a 2D aerofoil, I have a strange output regarding the Time step continuity error, which says:

Code:

time step continuity errors : sum local = 1.57644e-08, global = -5.51118e-10, cumulative = 0.895961

Even though the local error and global error seems fine but the cumulative looks very off, could anyone please comment on the issue? Thanks in advance.

Tobermory · February 13, 2021, 10:50

Well, the cumulative error is the running total of the global error from each time step:

https://www.openfoam.com/documentati...uityError.html

so at some point in your earlier time steps you must have some iterations where the global continuity error was large. Perhaps seek this out and find out why? Otherwise, since this is steady state and the "problems" are in the past - perhaps you shouldn't care? If the solution is well converged now (we can't tell this from the single log file line that youposted), then everything is fine and it doesn't matter that you had a rocky road to get there (albeit future simulations might be smoother/easier if you figure out what the problem was).

chandra shekhar pant · March 2, 2021, 07:02

Many thanks Tobermory for your help and elaborated explanation. I highly appreciate that.

February 12, 2021, 10:34	Time step continuity error (cumulative very high ~ 0.89)	#1
chandra shekhar pant Senior Member chandra shekhar pant Join Date: Oct 2010 Posts: 220 Rep Power: 16	Hello Foamers, I am trying to run a simpleFOAM solver for a 2D aerofoil, I have a strange output regarding the Time step continuity error, which says: Code: time step continuity errors : sum local = 1.57644e-08, global = -5.51118e-10, cumulative = 0.895961 Even though the local error and global error seems fine but the cumulative looks very off, could anyone please comment on the issue? Thanks in advance.

February 13, 2021, 10:50		#2
Tobermory Senior Member Join Date: Apr 2020 Location: UK Posts: 666 Rep Power: 14	Well, the cumulative error is the running total of the global error from each time step: https://www.openfoam.com/documentati...uityError.html so at some point in your earlier time steps you must have some iterations where the global continuity error was large. Perhaps seek this out and find out why? Otherwise, since this is steady state and the "problems" are in the past - perhaps you shouldn't care? If the solution is well converged now (we can't tell this from the single log file line that youposted), then everything is fine and it doesn't matter that you had a rocky road to get there (albeit future simulations might be smoother/easier if you figure out what the problem was). chandra shekhar pant and hogsonik like this.

March 2, 2021, 07:02		#3
chandra shekhar pant Senior Member chandra shekhar pant Join Date: Oct 2010 Posts: 220 Rep Power: 16	Many thanks Tobermory for your help and elaborated explanation. I highly appreciate that. Tobermory likes this.

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