Inlet Velocity Profile BC - Floating Point exception during solution initialization

Janshi · March 12, 2012, 05:51

Hello,

I´ve 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]

I´ve defined a vector field function in this form:

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

Then I´ve 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 I´ve to use if i want to raise x to the power of y?

Edit: Okay I think I´ve 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 won´t work with any decimal digit. For example try to use 1.5 or 2.4 for the exponent, it won´t 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.

March 12, 2012, 05:51	Inlet Velocity Profile BC - Floating Point exception during solution initialization	#1
Janshi New Member Join Date: Aug 2010 Posts: 11 Rep Power: 16	Hello, I´ve 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] I´ve defined a vector field function in this form: Function Name: Velocity Profile Definition: [30 pow(($$Position[2]/15),0.22), 0 , 0] Then I´ve 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

March 14, 2012, 09:44		#2
ryancoe Member Ryan Coe Join Date: Jun 2010 Location: Albuquerque, NM Posts: 98 Rep Power: 16	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. __________________ Ryan

March 14, 2012, 11:14		#4
ryancoe Member Ryan Coe Join Date: Jun 2010 Location: Albuquerque, NM Posts: 98 Rep Power: 16	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...? __________________ Ryan

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March 14, 2012, 10:47		#3
Janshi New Member Join Date: Aug 2010 Posts: 11 Rep Power: 16	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 I´ve to use if i want to raise x to the power of y? Edit: Okay I think I´ve 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?

March 14, 2012, 11:21		#5
Janshi New Member Join Date: Aug 2010 Posts: 11 Rep Power: 16	Actually it won´t work with any decimal digit. For example try to use 1.5 or 2.4 for the exponent, it won´t 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.