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

Time averaging in Fluent

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

Like Tree5Likes

Reply
 
LinkBack Thread Tools Display Modes
Old   May 12, 2012, 18:50
Default Time averaging in Fluent
  #1
New Member
 
Benjamin Yesu
Join Date: May 2012
Posts: 4
Rep Power: 5
Benjie29 is on a distinguished road
Users,
I have case and data files saved after ever 5s. I also enable data sampling statistics in the iterate panel. How do I get it? Any advice will be much appreciated.
Benjie29 is offline   Reply With Quote

Old   May 12, 2012, 22:51
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 605
Rep Power: 12
LuckyTran is on a distinguished road
Quote:
Originally Posted by Benjie29 View Post
Users,
I have case and data files saved after ever 5s. I also enable data sampling statistics in the iterate panel. How do I get it? Any advice will be much appreciated.
Did you enable data sampling before you started solving?

The data is stored in new variable names with either Mean or Rms at the end.

For example the instantaneous x-velocity, average x-velocity, and rms x-velocity are named, respectively:
X Velocity
X Velocity Mean
X Velocity Rms

any other variable that has statistics will also follow a similar nomenclature for the new variable names.
maysmech and mm.abdollahzadeh like this.
LuckyTran is offline   Reply With Quote

Old   May 13, 2012, 07:13
Default
  #3
Senior Member
 
Join Date: Jun 2011
Posts: 108
Rep Power: 6
mali28 is on a distinguished road
Quote:
Originally Posted by Benjie29 View Post
Users,
I have case and data files saved after ever 5s. I also enable data sampling statistics in the iterate panel. How do I get it? Any advice will be much appreciated.
This article explains how to get time average of simulation variable in transient simulation.
http://cape-forum.com/index.php/topic,1074.0.html
mali28 is offline   Reply With Quote

Old   May 13, 2012, 10:44
Default Time averagin followup
  #4
New Member
 
Benjamin Yesu
Join Date: May 2012
Posts: 4
Rep Power: 5
Benjie29 is on a distinguished road
Thanks Tran and Mali.
Mali,
I used the UDF from the link. Where are the average values stored. I checked the UDS panel is post processing they show all zeros for the 12 scalars. The documentation provided with the .scm does not mention where the user is supposed to look for the averages. Also i think there is one step missing. One has to hook the execute on demand fuction in Define on Demand panel or else fluent complains "avg" chip exec not found.
Your calrifications in this matter will be of great help.
Benjie29 is offline   Reply With Quote

Old   May 13, 2012, 16:37
Default
  #5
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 605
Rep Power: 12
LuckyTran is on a distinguished road
Quote:
Originally Posted by mali28 View Post
This article explains how to get time average of simulation variable in transient simulation.
http://cape-forum.com/index.php/topic,1074.0.html
You don't need this complicated UDF for time-averaged statistics since Fluent supports data sampling for time statistics in the newer versions

You can always access the results at each time step directly by reading the saved data file. You can access the time-averaged data (so far) up to any time step by accessing the data variables I mentioned earlier with the corresponding Mean of Rms. Other than loading the proper data or finding the right variable name, the rest is straightforward, just do what you usually do to manipulate/plot data.

You can use the UDF you want, but I don't think it's worth the hassle for a few button clicks.
joy2000 and DungPham like this.
LuckyTran is offline   Reply With Quote

Old   May 13, 2012, 17:35
Default
  #6
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 531
Blog Entries: 14
Rep Power: 17
sbaffini will become famous soon enough
I would definitely not follow what mentioned in the link. First, as you have the ability to let Fluent activate its statistics (and these are available at least from Fluent 6) you also have the way to retrieve them, which is very simple: go under contours, unsteady statistics and you're done.

These variables are also accessible by UDF (a little bit more cumbersome than usual)

However, let us suppose you don't have this statistics feature. I would not certainly save all the cas and dat i want to average. Instead it is much more convenient to have running averages, variances and covariances defined as UDM and update them at each time step

Edit: LuckyTran explined much better what i wanted to say. It's just that i started the reply more than a hour ago and then i got stucked in something else.

Last edited by sbaffini; May 13, 2012 at 17:38. Reason: See the post
sbaffini is offline   Reply With Quote

Old   May 14, 2012, 07:00
Default
  #7
New Member
 
Benjamin Yesu
Join Date: May 2012
Posts: 4
Rep Power: 5
Benjie29 is on a distinguished road
Thanks for your replies.
Benjie29 is offline   Reply With Quote

Old   March 25, 2013, 13:37
Default
  #8
Member
 
Join Date: Jul 2011
Posts: 92
Rep Power: 6
haze_1986 is on a distinguished road
May I clarify, what is the unit for the sampling interval? is it Hz (/s) or per time step size or something else? Please advise, thanks.
haze_1986 is offline   Reply With Quote

Old   March 27, 2013, 11:59
Default
  #9
Senior Member
 
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 11
oj.bulmer will become famous soon enough
It is per "so many timesteps" or "so many seconds" and you can specify value, how much.

OJ
oj.bulmer is offline   Reply With Quote

Old   March 27, 2013, 12:13
Default
  #10
Member
 
Join Date: Jul 2011
Posts: 92
Rep Power: 6
haze_1986 is on a distinguished road
Quote:
Originally Posted by oj.bulmer View Post
It is per "so many timesteps" or "so many seconds" and you can specify value, how much.

OJ
Yes that was my question, is it once every "so many timesteps" or once every "so many seconds"

i.e. my time step size is 0.1s, I want to sample once every second. Should I input 1 or 10 in the sampling interval?
haze_1986 is offline   Reply With Quote

Old   March 28, 2013, 11:01
Default
  #11
Senior Member
 
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 11
oj.bulmer will become famous soon enough
Time sampled option suggests the seconds for which the data is sampled. If you divide this time by timestep, it will give you the number of datasets used for creating statistics.

Documentation is elaborate on this.

OJ
oj.bulmer is offline   Reply With Quote

Old   March 28, 2013, 11:06
Default
  #12
Member
 
Join Date: Jul 2011
Posts: 92
Rep Power: 6
haze_1986 is on a distinguished road
Quote:
Originally Posted by oj.bulmer View Post
Time sampled option suggests the seconds for which the data is sampled. If you divide this time by timestep, it will give you the number of datasets used for creating statistics.

Documentation is elaborate on this.

OJ
Please share the documentation as I am unable to find an elaborate explanation on this topic, thanks.
haze_1986 is offline   Reply With Quote

Old   March 28, 2013, 11:13
Default
  #13
Senior Member
 
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 11
oj.bulmer will become famous soon enough
https://www.sharcnet.ca/Software/Flu...me_inputs.html
oj.bulmer is offline   Reply With Quote

Old   March 28, 2013, 11:35
Default
  #14
Member
 
Join Date: Jul 2011
Posts: 92
Rep Power: 6
haze_1986 is on a distinguished road
Quote:
Originally Posted by oj.bulmer View Post
I did not read anywhere that specifically mentions what exactly the sampling interval means. Whether it refers to the seconds or the timesteps.

You can set the Sampling Interval such that Data Sampling for Time Statistics can be performed at the specified frequency.

Here it mentioned frequency, isn't it supposed to be number of dataset created per second?
haze_1986 is offline   Reply With Quote

Old   March 28, 2013, 12:21
Default
  #15
Senior Member
 
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 11
oj.bulmer will become famous soon enough
Oh, I see your confusion now.

Sampling interval is no. of timesteps after which transient statistics is recorded for averaging. So if your time step size is 0.1 and you want to create time averaged data using results after every 1 sec, you should specify the value as 10 (1 sec/0.1 sec).

Sampled time is the total time for which the sampling will happen. So if your sampling time is 10 sec. the total datasets recorded for your time averaging is 10/1=10.

OJ
haze_1986 likes this.
oj.bulmer is offline   Reply With Quote

Old   April 27, 2013, 02:30
Default
  #16
New Member
 
Yang-Jianfeng
Join Date: Apr 2013
Posts: 1
Rep Power: 0
yjf11230301 is on a distinguished road
Thank you!
Solution Initialization Reset Statistics
Note that you can also reset the flow statistics after you have gathered some data for time statistics. If you perform, say, 10 time steps with the Data Sampling for Time Statistics option enabled, check the results, and then continue the calculation for 10 more time steps, the time statistics will include the data gathered in the first 10 time steps unless you reinitialize the flow statistics.
yjf11230301 is offline   Reply With Quote

Old   June 16, 2013, 13:09
Default
  #17
New Member
 
rsaha's Avatar
 
Join Date: Jan 2012
Posts: 8
Rep Power: 5
rsaha is on a distinguished road
Quote:
Originally Posted by yjf11230301 View Post
Thank you!
Solution Initialization Reset Statistics
Note that you can also reset the flow statistics after you have gathered some data for time statistics. If you perform, say, 10 time steps with the Data Sampling for Time Statistics option enabled, check the results, and then continue the calculation for 10 more time steps, the time statistics will include the data gathered in the first 10 time steps unless you reinitialize the flow statistics.
If I want to include the data generated in both first and second 10 time steps to be considered for time averaging, do I have to reinitialize the statistics after the second 10 time steps are done? So here the word 'reinitialize' means updating huh?
rsaha is offline   Reply With Quote

Old   June 16, 2013, 13:19
Default
  #18
Senior Member
 
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 11
oj.bulmer will become famous soon enough
No, if you do not reset statistics, you will have timeaveraged data for all 20 seconds. If you reset it, you will have data for last 10 seconds, ie, since you reset it.

OJ
oj.bulmer is offline   Reply With Quote

Old   June 16, 2013, 13:33
Default
  #19
New Member
 
rsaha's Avatar
 
Join Date: Jan 2012
Posts: 8
Rep Power: 5
rsaha is on a distinguished road
Yes that is what I thought. But the above sentence confused me by saying that, unless I reinitialize it will include the result only for the first 10 time steps.

Thanks for your clarification.
rsaha is offline   Reply With Quote

Old   June 11, 2014, 07:23
Default
  #20
New Member
 
Join Date: Sep 2011
Posts: 11
Rep Power: 5
djing is on a distinguished road
Quote:
Originally Posted by mali28 View Post
This article explains how to get time average of simulation variable in transient simulation.
http://cape-forum.com/index.php/topic,1074.0.html
hi , i can't download this UDF if you can do it please give me an example . thanks
djing 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
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20
Orifice Plate with a fully developed flow - Problems with convergence jonmec OpenFOAM Running, Solving & CFD 3 July 28, 2011 05:24
Convergence moving mesh lr103476 OpenFOAM Running, Solving & CFD 30 November 19, 2007 15:09
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07


All times are GMT -4. The time now is 16:25.