# why continuity doesn't solve when p be fixedGradient in groovyBC?

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July 4, 2013, 16:09
why continuity doesn't solve when p be fixedGradient in groovyBC?
#1
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Ehsan
Join Date: Oct 2012
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I have set p in outlet be:
Code:
`(internalField(p)-50000)`
in a period of time in start of run.
but it seems continuity doesn't solve for that as can be seen in the attached image.why?
Attached Images
 cont.png (6.8 KB, 17 views)
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 July 6, 2013, 20:27 #2 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,702 Rep Power: 27 How come that you are not satisfied with 1e-18? I would say it was perfect from a continuity perspective. Kind regards, Niels

 July 7, 2013, 07:40 #3 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 18 hi Niels in first time steps its a straight line without fluctuations.I think maybe it be an issue. __________________ 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.

July 8, 2013, 15:07
#4
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Bernhard Gschaider
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Quote:
 Originally Posted by immortality hi Niels in first time steps its a straight line without fluctuations.I think maybe it be an issue.
No. For continuity error of 1e-18 to be a problem the system has to be really tiny. If your system is really that tiny the question is whether the continuum assumption is still valid (if it isn't then of course the question is whether the standard OF-solvers are still the right thing for you)
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 July 8, 2013, 15:25 #5 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 18 dear Bernhard.I don't want that residuals to be less than 1e-18 ar such thing. I focus on time 0 till around time 2e-5 that the continuity is a stright horizontal line.I ask why in this period (in figure) there are not any fluctuations in residuals.is it normal?how and why?! __________________ 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.

 July 8, 2013, 16:20 #6 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 18 I found out why its so! in first time steps the residuals are of order 0f 1e-22 or 1e-21 and are very low in compare with later times(2e-5 to next)(I don't know the exact reason) then they appear as a line without fliuctuations,in next time steps continuity errors are a bit higher but are low enough as dear Benhard and dear Niels told to say continuity is satisfied. __________________ 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.

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