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Old   March 7, 2005, 21:28
Default Divergence
  #1
Sham
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Hello,

When I try to iterate, thsi msg appears

"Error: divergence detected in AMG solver: pressure correction Error Object: ()"

Does anyone know what it means and how can I overcome this?

Sham.
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Old   March 8, 2005, 03:54
Default Re: Divergence
  #2
Melaku Habte
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Hi,

This error is usually related to the pressure correction factor ( under-relaxation factor). What causes it? Well many reasons: do u have any UDF, what is your model? transient/steady state? compressible/or not? especially if you have a floating operating pressure its very likely to happen. It can also come from your mesh size. So not much to say without knowing your particular model. But to have a short/general answer to it you can try to reduce the pressure under-relaxation factor from the menue - solve - controls - solution and reduce under-relaxation factor for pressure to a value roughly 0.2 - 0.3 or may be lower if it is during the initial period and then keep on increasing as the solution progresses. The default value is 0.3 but you can try to reduce and see if it helps. This is the most basic stuff to do. As I said there are many other reasons for it to happen. Fluent makes the pressure correction based on that factor. The higher the factor the bigger the change in pressure correction and the faster your solution converges IF EVERYTHING IS OK.

regds

Melaku Habte.
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Old   March 8, 2005, 04:09
Default Re: Divergence
  #3
Luca
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Try to use the coupled solver. Luca
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Old   March 8, 2005, 07:04
Default Re: Divergence
  #4
sawa
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Hi,

If you gonna change Under-relax, then consider the following: For the steady flow, the nearly optimem value for sum of under-relaxation of pressure and velocity is considered to be <=1.1( peric,pg205). But you can find optimum values for your case by changing these parametrs so that the sum equals to 1.1 (for one case i found it to be 0.6 and 0.4 for press and momentum). I am not sure about some guess of these values in unsteady case. May be somebody can help about that.

Good luck sawa
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