CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

use equations

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 4, 2009, 06:57
Cool use equations
  #1
Ema
New Member
 
Tuffy
Join Date: Jun 2009
Posts: 28
Rep Power: 16
Ema is on a distinguished road
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
Ema is offline   Reply With Quote

Old   September 4, 2009, 07:07
Default
  #2
Ema
New Member
 
Tuffy
Join Date: Jun 2009
Posts: 28
Rep Power: 16
Ema is on a distinguished road
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...
Ema is offline   Reply With Quote

Old   September 4, 2009, 07:28
Default
  #3
Senior Member
 
ckleanth's Avatar
 
George
Join Date: Mar 2009
Location: Birmingham, UK
Posts: 257
Rep Power: 18
ckleanth is on a distinguished road
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"
__________________
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
ckleanth is offline   Reply With Quote

Old   September 4, 2009, 07:54
Default
  #4
Member
 
Join Date: Mar 2009
Posts: 44
Rep Power: 17
Timon is on a distinguished road
You don't need to define the unit [K] after your maxVal(Temperature)@.... statement, as the value returned already has unit.
Timon is offline   Reply With Quote

Old   September 4, 2009, 08:59
Default
  #5
Senior Member
 
ckleanth's Avatar
 
George
Join Date: Mar 2009
Location: Birmingham, UK
Posts: 257
Rep Power: 18
ckleanth is on a distinguished road
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 )
__________________
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
ckleanth is offline   Reply With Quote

Old   September 4, 2009, 09:02
Default
  #6
Ema
New Member
 
Tuffy
Join Date: Jun 2009
Posts: 28
Rep Power: 16
Ema is on a distinguished road
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...
Ema is offline   Reply With Quote

Old   September 4, 2009, 09:02
Default
  #7
Member
 
Join Date: Mar 2009
Posts: 44
Rep Power: 17
Timon is on a distinguished road
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...
Timon is offline   Reply With Quote

Old   September 4, 2009, 09:08
Default
  #8
Senior Member
 
ckleanth's Avatar
 
George
Join Date: Mar 2009
Location: Birmingham, UK
Posts: 257
Rep Power: 18
ckleanth is on a distinguished road
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
__________________
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
ckleanth is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Guide: Writing Equations in LaTeX on the CFD Online Forums pete Site Help, Feedback & Discussions 27 May 19, 2022 04:19
Maths problem when deriving conservation of energy equations. Demonwolf Main CFD Forum 1 June 15, 2009 15:21
Equations Andres Bernal Ortiz CFX 1 January 6, 2007 12:56
? fluctuating equations for homogenous shear turb. ff_fan Main CFD Forum 1 September 20, 2002 08:39
Euler equations? Jan Ramboer Main CFD Forum 2 August 19, 1999 02:58


All times are GMT -4. The time now is 10:51.