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Old   September 4, 2009, 05:57
Cool use equations
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Ema
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Hi everyone!
I must use an equation in CFX to set a condition about the voltage.
The idea is to create something like this:
if the temperature is lower than 90 use a voltage of 60 V. If not decrease the voltage until the temperature is not lower than 90.
do you know exactly which is the meaning of the following equation?
step((maxVal(Temperature)@REGION:B64-90 [K] )/1[K])*60[V]
how much is the value? 60 V if?
please, help me!!!!
thanks,
Ema
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Old   September 4, 2009, 06:07
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i've also tried to implement the following expression:
volt= 60[V]*(1/(1+e^(5*(maxVal(Temperature)@REGION:B97-90[K])/1[K]))) but my update failed...
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Old   September 4, 2009, 06:28
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your equation doesnt make any sence

step function returns 0 or 1 and your conditions should be non dimensional (thats why you divide the temperature by 1/[K] )

if you multiply by 60[V] then your expression has value either 0*60[V] or 1*60[V]

if you want to to create some feedback control search in the cfx manual for "Example: Feedback to Control Inlet Temperature"
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Old   September 4, 2009, 06:54
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You don't need to define the unit [K] after your maxVal(Temperature)@.... statement, as the value returned already has unit.
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Old   September 4, 2009, 07:59
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Quote:
Originally Posted by Timon View Post
You don't need to define the unit [K] after your maxVal(Temperature)@.... statement, as the value returned already has unit.
the units are for the 90[K]. the step function can look something like:
step( (T - 90 [K]) / 1[K] ) or
step( (T/1[K] - 90 )
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Old   September 4, 2009, 08:02
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exactly. Otherwise CFX will say you that the values are not correct.
What about my equation? why no sense at all? i was thinking to implement like a sigm function to multiply with the voltage...
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Old   September 4, 2009, 08:02
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Quote:
Originally Posted by ckleanth View Post
the units are for the 90[K]. the step function can look something like:
step( (T - 90 [K]) / 1[K] ) or
step( (T/1[K] - 90 )
True, disregard my previous post...
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Old   September 4, 2009, 08:08
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Quote:
Originally Posted by Ema View Post
What about my equation? why no sense at all? i was thinking to implement like a sigm function to multiply with the voltage...
well you said you wanted to do some feedback. I replied that if you want to to create some feedback control search in the cfx manual for "Example: Feedback to Control Inlet Temperature". your equations as it stands dont do that
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