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September 4, 2009, 05:57 
use equations

#1 
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Tuffy
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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:B6490 [K] )/1[K])*60[V] how much is the value? 60 V if? please, help me!!!! thanks, Ema 

September 4, 2009, 06:07 

#2 
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Tuffy
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i've also tried to implement the following expression:
volt= 60[V]*(1/(1+e^(5*(maxVal(Temperature)@REGION:B9790[K])/1[K]))) but my update failed... 

September 4, 2009, 06:28 

#3 
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George
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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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September 4, 2009, 06:54 

#4 
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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.


September 4, 2009, 07:59 

#5  
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George
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Quote:
step( (T  90 [K]) / 1[K] ) or step( (T/1[K]  90 )
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Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials 

September 4, 2009, 08:02 

#6 
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Tuffy
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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... 

September 4, 2009, 08:02 

#7 
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September 4, 2009, 08:08 

#8 
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George
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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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Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials 

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