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-   -   Inlet Velocity Profile BC - Floating Point exception during solution initialization (http://www.cfd-online.com/Forums/star-ccm/98464-inlet-velocity-profile-bc-floating-point-exception-during-solution-initialization.html)

Janshi March 12, 2012 05:51

Inlet Velocity Profile BC - Floating Point exception during solution initialization
 
Hello,

Ive encountered a very weird problem during the implementation of a field function to describe an inlet velocity problem. I wish to use a velocity profil as inlet bc in this form: v = [k(zref)*(z/zref)^n , 0 , 0]

Ive defined a vector field function in this form:

Function Name: Velocity Profile
Definition: [30 * pow(($$Position[2]/15),0.22), 0 , 0]

Then Ive defined a local coordinate system for my simulation case, called cartesian 1. For the initial conditions and the inlet bc i selected for the velocity nodes for the coordinate System "Laboratory->Cartesian 1" and for the method "Field Function" and so on...
Once I try to initialize the simulation I get following error:

"Error

A floating point exception has occured: floating point exception [invalid operation]. The specific cause cannot be identified. "

Can anyone imagine what the problem could be?

Best regards

ryancoe March 14, 2012 09:44

That's tough...

Have you experimented with simplifying your field function ( to something like [$$Position[2], 0 , 0] ) and see if that resolves the issue. I know that doesn't fix your problem, but it may help you to track down the bug.

Janshi March 14, 2012 10:47

Thanks for your answer and your tip ryan.
Okay now things becomes really strange. The simplified vectorfunction [$$Position[2], 0 , 0] operates also a more complicated function like [30*($$Position[2]/15), 0, 0] operates too. It does not work with an exponential syntax like pow(($$Position[2]/15),0.22)...

I am I correct that the expression pow($x,$y) is the syntax Ive to use if i want to raise x to the power of y? :confused:


Edit: Okay I think Ive isolated the problem:

It seems that CCM+ does not accept decimal digits for the exponent n in the expression pow($x,n)...
So in my case the exponent n=0.22 is not accepted by CCM+. I checked it with n=1,5 ; 2,5 and so, same errors. When I change the exponent to 1, 2, 3 and so on, no problem occures and he intializes the solution correctly without errors.
Anyone knows the reason for this and how I can fix it?

ryancoe March 14, 2012 11:14

huh! this was so weird I just had to mess with it myself...

From my experimenting, it looks like pow doesn't accept entries to raise a number to a value less than 1. Is this what you see?

Not sure why that would be the case (you should send an email to the CD-adapco support poeple). Maybe as a work around you could create a table and use that to set you boundary values instead...?

Janshi March 14, 2012 11:21

Actually it wont work with any decimal digit. For example try to use 1.5 or 2.4 for the exponent, it wont work either.

I will contact the CD-Adapco support. The idea with the table as a workaround is good idea, thanks for your help Ryan.


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