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what reasons may make fluctuations in residuals?

1 Attachment(s)
Hi everybody,

what reasons may make fluctuations in residuals?
residuals are attached.

I work with a modified viscoelasticFluidFoam solver that combined whit buoyantBoussinesqSimpleFoam.

thanks
Mostafa

 nikesh March 7, 2013 09:13

Such a small fluctuation in residuals is not a problem. You should take care to see whether ur residual reaches below the convergence tolerance or not! Generally we would set the convergence tolerance to be 10^-5 or 10^-6 or less which depends on user.
In your case, the residuals are not decreasing. They are fluctuating around a mean value and that mean value is of the order 10^-3 for the p-residual and 10^-1 for Uy-residual. As we can see, these are pretty high values. We want our residuals to be as small as possible, thats the general concept.

Quote:
 Originally Posted by nikesh (Post 412285) Such a small fluctuation in residuals is not a problem. You should take care to see whether ur residual reaches below the convergence tolerance or not! Generally we would set the convergence tolerance to be 10^-5 or 10^-6 or less which depends on user. In your case, the residuals are not decreasing. They are fluctuating around a mean value and that mean value is of the order 10^-3 for the p-residual and 10^-1 for Uy-residual. As we can see, these are pretty high values. We want our residuals to be as small as possible, thats the general concept.
I meant that what might cause this problem????!?

 nikesh March 7, 2013 10:11

There could be numerous reasons for your residuals to be so high. We can't point out one reason for sure. However, you might want to recheck your boundary conditions and schemes used and also the mesh criteria first.