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

Derivative

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 25, 2014, 04:50
Default Derivative
  #1
Member
 
Mansoor Saleem
Join Date: Jun 2014
Posts: 31
Rep Power: 3
Saleeman1234 is on a distinguished road
Hello
Good Morning

I want to define derivative in my expressions, I have seen in the post of 2011, Singer1812 has suggested someone to use TRANS_LOOP as an alternative of derivative. I want to introduce Density in this way.

Is anyone here who has any idea how to use this how we introduce the Old Variable??

Thank you so much.
Saleeman1234 is offline   Reply With Quote

Old   August 25, 2014, 06:49
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,954
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
If you just need the time derivative then use the time derivative modifier. This is described in the reference manual.

There are several thread son the forum which describe how to use the TRANS_LOOP approach, do a search to find them.
ghorrocks is offline   Reply With Quote

Old   August 25, 2014, 06:52
Smile
  #3
Member
 
Mansoor Saleem
Join Date: Jun 2014
Posts: 31
Rep Power: 3
Saleeman1234 is on a distinguished road
Thank you so much ghorrocks

I will try
Saleeman1234 is offline   Reply With Quote

Old   August 25, 2014, 08:17
Default
  #4
Member
 
Mansoor Saleem
Join Date: Jun 2014
Posts: 31
Rep Power: 3
Saleeman1234 is on a distinguished road
Hello Ghorrocks

If I want to introduce an expression like this

CEL = Density at time 0 - Density of current time step

is it possible to introduce in this way. I think for 2nd value we can use the simple variable Density but for first variable how can we introduce time reference?

Thank you so much
Saleeman1234 is offline   Reply With Quote

Old   August 25, 2014, 08:37
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,954
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
If you want to reference it against the density at time zero I see two options:
* If your time zero density can be calculated then you can simply calculate it when you need it. Then you do not need to store it.
* The TRANS_LOOP trick only gives you the variables value at the last time step. If you want to store the first time step value then you will have to write a fortran routine to do this.
ghorrocks is offline   Reply With Quote

Old   August 25, 2014, 09:23
Default
  #6
Member
 
Mansoor Saleem
Join Date: Jun 2014
Posts: 31
Rep Power: 3
Saleeman1234 is on a distinguished road
Thank you ghorrocks

I am using the 1st option but I dont have any idea of User Fortran, Can you please recommend some tutorial or example because from user Guide its really difficult to understand.
Saleeman1234 is offline   Reply With Quote

Reply

Tags
trans_loop

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Derivative of a scalar or a variable through UDF fevi84 Fluent UDF and Scheme Programming 7 February 3, 2015 22:39
Derivative in CFD-Post fevi84 ANSYS 0 August 2, 2012 16:29
discontinuous second derivative new_at_this Main CFD Forum 9 April 28, 2012 16:55
scalar and its derivative sucker Main CFD Forum 1 April 15, 2008 13:28
Second derivative with cfx 5.7.1 Alessandro CFX 10 April 21, 2006 10:31


All times are GMT -4. The time now is 21:33.