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jellio March 5, 2010 16:07

CEL problem
 
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,

John March 5, 2010 16:45

use /1[cm] to cancellate the unit

jellio March 5, 2010 17:10

Quote:

Originally Posted by John (Post 248767)
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.

ghorrocks March 6, 2010 05:55

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.

John March 6, 2010 10:57

((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.

jellio March 6, 2010 12:39

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.


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