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

FFT in FLUENT

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

Like Tree1Likes
  • 1 Post By samad87

Reply
 
LinkBack Thread Tools Display Modes
Old   March 23, 2008, 23:25
Default FFT in FLUENT
  #1
Thanathat
Guest
 
Posts: n/a
Dear All In the first sorry for my bad English. I have a problem about FFT in Fluent. I create a "point" in my fluid domain and need to collected the data for FFT ( Running by LES and use surface monitors , report type : mass flow rate , report of : Pressure , Static pressure )after I open the files all of my data show "0" all points. Can every body help me for this case.
  Reply With Quote

Old   March 24, 2008, 01:37
Default Re: FFT in FLUENT
  #2
Sham
Guest
 
Posts: n/a
You need to change the scale I think. If you are after the peak freq., change the scale of x-axis from 0 to 1.

Could you also tell me do you get a good results with LES? What approach do you take for LES modelling?

Sham.
  Reply With Quote

Old   March 24, 2008, 04:50
Default Re: FFT in FLUENT
  #3
Thanathat
Guest
 
Posts: n/a
Thank your for your help , do you mean the scale in surface monitor plot or where ???.
  Reply With Quote

Old   March 24, 2008, 05:13
Default Re: FFT in FLUENT
  #4
Sham
Guest
 
Posts: n/a
scale in FFT graph
  Reply With Quote

Old   March 24, 2008, 05:18
Default Re: FFT in FLUENT
  #5
Thanathat
Guest
 
Posts: n/a
I found this error

Warning :Read_Signal: FFT can handle a costant sampling interval only! Jump in sampling interval at number 30 is more than 1 percen ! what does it mean ???
  Reply With Quote

Old   March 27, 2008, 08:08
Default Re: FFT in FLUENT
  #6
Renato Pacheco
Guest
 
Posts: n/a
it means that your interval is very small. try increasing it, then u probably get your plot right.
  Reply With Quote

Old   March 31, 2008, 09:38
Default Re: FFT in FLUENT
  #7
Thanathat
Guest
 
Posts: n/a
You mean Data sampling for time statistics ( sampling interval)or where ??
  Reply With Quote

Old   March 31, 2008, 11:08
Default Re: FFT in FLUENT
  #8
Renato Pacheco
Guest
 
Posts: n/a
i mean when u go to axes, then u can select the interval of plotting. i had the same problem, and when i increased this interval of ploting(the range), it worked.
  Reply With Quote

Old   August 14, 2009, 15:02
Default FFT warning
  #9
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 174
Rep Power: 9
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
While taking FFT of a signal in Fluent I get the following warning

Warning: Unknown x-function in Process_and_Plot_Signal function.

Can anybody tell me what does it mean?
Shamoon Jamshed is offline   Reply With Quote

Old   August 15, 2009, 07:16
Default
  #10
New Member
 
abdul samad
Join Date: Aug 2009
Posts: 14
Rep Power: 8
samad87 is on a distinguished road
doesn't matter....ths s no error
seucj likes this.
samad87 is offline   Reply With Quote

Old   August 15, 2009, 07:18
Default
  #11
New Member
 
abdul samad
Join Date: Aug 2009
Posts: 14
Rep Power: 8
samad87 is on a distinguished road
u r doing fft for sound amplitude or wt?
samad87 is offline   Reply With Quote

Old   August 15, 2009, 08:04
Default
  #12
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 174
Rep Power: 9
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
no just simple FFT with ideal gas and transonic flow and density based solver.
the problem is that I am getting very low value of Power Spectral Density on y axis (e-09) is it ok?
Shamoon Jamshed is offline   Reply With Quote

Old   August 15, 2009, 08:21
Default
  #13
New Member
 
abdul samad
Join Date: Aug 2009
Posts: 14
Rep Power: 8
samad87 is on a distinguished road
these values are pretty lesser........
perhaps if u can expalin ur case in detail...........i may help
samad87 is offline   Reply With Quote

Old   August 15, 2009, 09:21
Default
  #14
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 174
Rep Power: 9
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
I am simulating unsteady flow over Ariane 5 rocket. The solver is density based explicit and time formulation is explicit as well. I think in this case the number of samples=no of iterations. I want to simulate till 1 m sec. When I get the FFT in between about 2e-04 second this situation arose which I just discussed. I am using URANS (with k omega model). for SA model I dont remember bt y axis but it gave me another warning that differnce in sample 1000 (I hope its 1000 iter because I increased CFL no there) is less than 1 %.
Hope its clear now
Shamoon Jamshed is offline   Reply With Quote

Old   November 2, 2009, 01:54
Default
  #15
New Member
 
Morteza
Join Date: Nov 2009
Posts: 9
Rep Power: 8
neo_mor is on a distinguished road
Quote:
Originally Posted by Sham
;149391
You need to change the scale I think. If you are after the peak freq., change the scale of x-axis from 0 to 1.

Could you also tell me do you get a good results with LES? What approach do you take for LES modelling?

Sham.
Hello my freind.
i guess u should use first K-epsilon model until ur residuals converges ,after that by inputting the:"solve/initialize/init-flow-statistics" in the text command.then u can choose the LES model.
good luck
neo_mor is offline   Reply With Quote

Old   May 10, 2014, 07:32
Default
  #16
New Member
 
Charles Odijie
Join Date: May 2014
Posts: 1
Rep Power: 0
Charles Lancaster is on a distinguished road
I am new here, I registered few mins ago. I need help with reading FFT files. Non of the files that were saved during d calculation will loading into d fft. I'm trying to Plot d graphs on 'power spectral density, frequency and strouhal number. After d simulation, I clicked Plots/FFT/Set-up/Load Input files.... no file appeared. I scrolled down to All Files, and some file showed up, saved in .dat and .cas. When I tried to load one of d files, this error appeared: 'error reading file.

What should I do?? I need help please.
Charles Lancaster is offline   Reply With Quote

Old   October 24, 2014, 10:46
Default
  #17
Member
 
kabilan.B
Join Date: Jul 2010
Location: chennai
Posts: 79
Rep Power: 8
kabilan is on a distinguished road
how to define les model in fluent 6.3.
thank you
kabilan is offline   Reply With Quote

Old   October 24, 2014, 14:07
Default
  #18
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 174
Rep Power: 9
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
for les model you need to check on unsteady and the model should be 3D.
Shamoon Jamshed is offline   Reply With Quote

Old   October 25, 2014, 09:03
Default
  #19
Member
 
kabilan.B
Join Date: Jul 2010
Location: chennai
Posts: 79
Rep Power: 8
kabilan is on a distinguished road
thank you sir..
kabilan is offline   Reply With Quote

Reply

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
Fluent in Linux vs. Fluent in Windows Melih FLUENT 6 November 16, 2014 10:39
Fluent/Unix vs. Fluent/Windows sjjaber FLUENT 10 January 5, 2005 17:58
Running FLUENT 6.0 sims. on FLUENT 6.1 ozgur FLUENT 2 April 2, 2004 13:23


All times are GMT -4. The time now is 19:50.