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Error: 6199 Attempt to evaluate real square root of negative number.

Posted 19 nov. 2009, 14:57 UTC−5 4 Replies

Ozgur
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Hi all,

I get this error very often in fluid mechanics simulations. What are some of your best practices to handle this; what are the first things you would check?

Thanks,
Ozgur
4 Replies Last Post 27 sept. 2013, 19:48 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 2 decades ago 19 nov. 2009, 15:06 UTC−5
Hi Osgur,

for me the first thouth would be to turn on "complex numbers" in the solver section, but I expect that you have already done that, thereafter I do not really know where to look, apart that the error message details might give you some more clues.

I have heard that COMSOL will improve the merror messages exlanations in V4, there were already a few nice examples in the beta version

Good luck
Ivar
Hi Osgur, for me the first thouth would be to turn on "complex numbers" in the solver section, but I expect that you have already done that, thereafter I do not really know where to look, apart that the error message details might give you some more clues. I have heard that COMSOL will improve the merror messages exlanations in V4, there were already a few nice examples in the beta version Good luck Ivar
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 2 decades ago 21 nov. 2009, 04:59 UTC−5
Hi again

there is the other issue about possible complex results from solving "real" equations, if you have functions, you need to define their derivatives too, and you should also tell it to use only the real or imaginary part when the two are possible, mostly only one is "physical" and COMSOL cannot decide alone

and if you play with complex values in functions and equations you are aware of the "realdot" operator issue see Guide V3.5a p168+

and the PHASOR VARIABLE representations p182+
or THE IMPORTANCE OF A CORRECT JACOBIAN MATRIX p382,
or WORKING WITH COMPLEX-VALUED PROBLEMS p 383+ ....

Hope this can help you on your way
Ivar
Hi again there is the other issue about possible complex results from solving "real" equations, if you have functions, you need to define their derivatives too, and you should also tell it to use only the real or imaginary part when the two are possible, mostly only one is "physical" and COMSOL cannot decide alone and if you play with complex values in functions and equations you are aware of the "realdot" operator issue see Guide V3.5a p168+ and the PHASOR VARIABLE representations p182+ or THE IMPORTANCE OF A CORRECT JACOBIAN MATRIX p382, or WORKING WITH COMPLEX-VALUED PROBLEMS p 383+ .... Hope this can help you on your way Ivar
MAK Bulelzai
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Posted: 1 decade ago 30 nov. 2010, 19:06 UTC−5
I happen to have this error in NS equation simulations. Just putting OFF the cornor smoothing from the properties of physics menu would do.
Mak.
I happen to have this error in NS equation simulations. Just putting OFF the cornor smoothing from the properties of physics menu would do. Mak.
Siddhartha Gadiraju
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Posted: 1 decade ago 27 sept. 2013, 19:48 UTC−4
Where do we find this settings..???
Where do we find this settings..???

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