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Warning #007

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Old   March 18, 2005, 23:14
Default Warning #007
  #1
Shazlan
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Hi,

I keep on getting this warning:

MAXIMUM COURANT NUMBER = 1.722E+00 AT CELL 300178 MEAN COURANT NUMBER = 2.945E-03 *** WARNING #007*** SETTING T AT CELL 27614 FROM 5.189E+01 TO 5.400E+01 *** WARNING #007*** SETTING T AT CELL 80748 FROM 4.762E+01 TO 5.400E+01 *** WARNING #007*** SETTING T AT CELL 121808 FROM 5.312E+01 TO 5.400E+01 3 CELLS WITH T BELOW LOWER LIMIT

what do they mean and how to eliminate them? or maybe, are they merely warnings that needs no attention?

also, how to determine the smallest time step required for the (transient) analysis do not diverged? i have been doin via trial and error method but this is expensive time-wise. is there a way to find this out? or maybe to ask star-cd to calculate it itself?

many thanks!
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Old   March 21, 2005, 07:05
Default Re: Warning #007
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4xF
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When you are running a compressible simulation (which I believe is the case here) & the time step is large, you can overshoot and undershoot the temperature range. There is a lower limit in the code which is set by default to 54K, so that when the temperature goes below, the code sets its to the default lowest value. You can increase this default value by defining the right REAL constant. I cannot remember which is it. Something like 142 or 143. Check it out...
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Old   March 24, 2005, 04:31
Default Re: Warning #007
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Shazlan
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Ok. but is this warning a critical one? i mean, do i really need to look at the model setup or i can simply ignore the warning?
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Old   March 24, 2005, 05:49
Default Re: Warning #007
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4xF
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This one can be critical, because the density is calculated accordingly to the temperature. You may end up with negative densities. This can happen when you have locally very high velocities, hence temperature can be dropping very fast. You can increase the lower temperature limit (it should be the real constant 143 or 142, when switch 90 is on, if I recall it correctly) to recover more physical values (because 54K is quite low).

Hope this helps...
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