# low local continuity while high global continuity

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 June 15, 2013, 10:19 low local continuity while high global continuity #1 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,186 Rep Power: 16 what does low local continuity residual(1e-5)but high global(1e-18)mean? Code: ```DILUPBiCG: Solving for Ux, Initial residual = 0.0004256482273, Final residual = 3.42419877e-17, No Iterations 4 DILUPBiCG: Solving for Uy, Initial residual = 0.0008584110976, Final residual = 1.699508551e-16, No Iterations 4 DILUPBiCG: Solving for e, Initial residual = 0.0004690168561, Final residual = 4.48278334e-17, No Iterations 4 DILUPBiCG: Solving for p, Initial residual = 0.0004642938087, Final residual = 8.887120082e-17, No Iterations 4 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 4.223753118e-06, global = -9.485719823e-18, cumulative = -4.473784803e-05 DILUPBiCG: Solving for p, Initial residual = 3.306483671e-07, Final residual = 6.449921349e-17, No Iterations 3 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 4.21218922e-06, global = -9.149711212e-18, cumulative = -4.473784803e-05 DILUPBiCG: Solving for omega, Initial residual = 0.0003045968168, Final residual = 4.305610069e-16, No Iterations 4 DILUPBiCG: Solving for k, Initial residual = 0.0008443110421, Final residual = 9.851206562e-18, No Iterations 5``` what does it indicate for? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

June 16, 2013, 09:12
#2
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Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
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Hi Ehsan,

Quote:
 low local continuity residual(1e-5)but high global(1e-18)
Uhm... isn't it the other way around? Low global and high local?

Quote:
 OK, from what I could figure out, the following code is needed:#include "initContinuityErrs.H" //this is to be placed before the "while" loop #include "compressibleContinuityErrs.H" //this is found in the "pEqn.H" file, after including "rhoEqn.H" The two files are located at OpenFOAM's "src/finiteVolume/lnInclude/" folder.
Have a look into the file "\$FOAM_SRC/finiteVolume/lnInclude/compressibleContinuityErrs.H" to see how it's calculated.

Best regards,
Bruno

 June 16, 2013, 09:32 #3 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,186 Rep Power: 16 Hi Bruno I meant the accuracy.local has low accuracy.maybe wasn't careful enough! rhoCentralFoam hasn't any difficulty in relation to continuity.both local and global continuity residuals are low enough,these results are from sonicFoam. __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

 June 16, 2013, 12:25 #4 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 8,312 Blog Entries: 34 Rep Power: 84 rhoCentralFoam does things in a very different way, at least from what I've vaguely read about it. If I'm not mistaken, it tends to smooth out the values (because it's "central", it takes into account more values from it's sides and the previous times?), which would be why the continuity would be well preserved. But sonicFoam doesn't have this feature that rhoCentralFoam has got, which is probably why you're seeing larger continuity issues. Try reducing the "deltaT", to see if it has any effect. If it doesn't, then "fvSchemes" and the mesh itself should perhaps be the ones to blame? immortality likes this. __________________ OpenFOAM: Frequently Asked Questions | Useful links for building and using Forum: How to ask for help | Posting code and output with [CODE] My to-do list and when I'll be able to come to the forum: http://wyldckat.github.io And please: Read this before sending private messages to me

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