# CEL problem

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 March 5, 2010, 16:07 CEL problem #1 New Member   Join Date: Sep 2009 Posts: 5 Rep Power: 9 Hi, I need some help to define a moving function by the expression, the following is the function I created: (((0.8[cm])^2-(z-5[cm])^2)^0.5-((1.0-(z-5[cm])^2/(0.75[cm])^2)*(0.1[cm])^2)^0.5)*(t/tt)/0.4 When z=5.8[cm], which is supposed to be zero, while when I evaluate or run my simulation, an error shows up, as the following: The problem was: INVALID-EXPONENTIATION FURTHER INFORMATION The problem was encountered in executing the expression for: value The complete expression is: (((0.8[cm])^2-(z-5[cm])^2)^0.5-((1.0-(z-5[cm])^2/(0. The error occurs on sub-expression: ((0.8[cm])^2-(z-5[cm])^2)^0.5 BACKGROUND INFORMATION These values were set before reaching the current expression: Name = Expression = Value tt = 1 [s] = 1.00000 END OF DIAGNOSTIC OUTPUT FOR CFX EXPRESSION LANGUAGE Can Anyone point out how to solve it? I really appreciate! Thanks,

 March 5, 2010, 16:45 #2 Member   Join Date: Mar 2009 Posts: 49 Rep Power: 9 use /1[cm] to cancellate the unit

March 5, 2010, 17:10
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Quote:
 Originally Posted by John use /1[cm] to cancellate the unit
No, it not the units problem, the problem appears only when z=5.8cm, which should be zero.

 March 6, 2010, 05:55 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 I suspect you will need to put more brackets in it to ensure the order of operations is correct. I suspect it is evaluating something like 1.0-(z-5[cm])^{2/(0.75[cm])^2} (the curly brackets are my addition) and that is an invalid operation due to the units of the exponential operation.

 March 6, 2010, 10:57 #5 Member   Join Date: Mar 2009 Posts: 49 Rep Power: 9 ((1.0-(z-5[cm])^2/(0.75[cm])^2)*(0.1[cm])^2)^0.5 appears to be invalid, it is a (negative vlaue)^0.5 at higher Z value. Last edited by John; March 6, 2010 at 11:48.

 March 6, 2010, 12:39 #6 New Member   Join Date: Sep 2009 Posts: 5 Rep Power: 9 yes, thanks John, it seems there is one point in the plane I want to use the function exceed 5.8 for just a little, but it does influence, I just made some modification, it works now. thanks again for all.

 July 14, 2016, 05:15 #7 Member   Brett Join Date: May 2013 Posts: 64 Rep Power: 5 Ha! I've got one for ya. Input from CFX-5 The problem was: INVALID-EXPONENTIATION FURTHER INFORMATION This is from the static enthalpy at outlet, I haven't changed any pre set equations. It happens when I try to run the gas compressor performance macro.

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