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

3d & 3ddp

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 3, 2012, 04:19
Default 3d & 3ddp
  #1
New Member
 
Join Date: Feb 2012
Posts: 4
Rep Power: 5
pazhouhesh.m.j is on a distinguished road
Dears,

Would you please,tell me what is the difference between 3d & 3ddp in fluent?
The results i got from 3d & 3ddp are different,I mean the difference between them are large.So which results is reliable? or are the 3d results wrong?

Sincerely,
Pazhouhesh
pazhouhesh.m.j is offline   Reply With Quote

Old   April 3, 2012, 04:58
Default
  #2
New Member
 
karthik
Join Date: Oct 2010
Posts: 14
Rep Power: 6
kitrax is on a distinguished road
Hi,

3d results are single precision floating point numbers and 3ddp are double precision floating point numbers. You normally use double precision in a Fluent solver.

It works like this:
In single precision: This is a binary format that occupies 32 bits, has a precision of roughly 7 decimal places.

In double precision: occupies 64 bits, has a precision of 16 decimal places.

The main idea you have to take from this is that over a series of iterations, the errors in single precision (3d) could be significant, hence your 3ddp is the solution you should use

Hope this helps, if it does, increase my rep power B)

K
kitrax is offline   Reply With Quote

Old   April 3, 2012, 05:04
Default
  #3
New Member
 
Join Date: Feb 2012
Posts: 4
Rep Power: 5
pazhouhesh.m.j is on a distinguished road
Dear,

There is not any error in my problem (both 3d & 3ddp),only a big difference is in the results.So does it mean that ,3d of fluent does not work properly?

Sincerely,
Pazhouhesh
pazhouhesh.m.j is offline   Reply With Quote

Old   April 3, 2012, 05:34
Default
  #4
New Member
 
karthik
Join Date: Oct 2010
Posts: 14
Rep Power: 6
kitrax is on a distinguished road
Well depending on the number of iterations, I would think 3d is not suitable, if you have a very coarse mesh, I think 3d would be fine. Though for a fine mesh, the error of 3d is carried forward through each iteration therefore leading to a difference between 3d and 3ddp.

What you can do is run your system with a few iterations with each precision and compare the 2 numbers, though I would say if you have already done 3ddp just stick with it

Btw what are you studying?
kitrax is offline   Reply With Quote

Old   April 3, 2012, 10:29
Default
  #5
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 591
Rep Power: 11
LuckyTran is on a distinguished road
Quote:
Originally Posted by kitrax View Post
Well depending on the number of iterations, I would think 3d is not suitable, if you have a very coarse mesh, I think 3d would be fine. Though for a fine mesh, the error of 3d is carried forward through each iteration therefore leading to a difference between 3d and 3ddp.

What you can do is run your system with a few iterations with each precision and compare the 2 numbers, though I would say if you have already done 3ddp just stick with it

Btw what are you studying?
Just use double precision. There is no reason not to, it is standard nowadays. The difference between single precision and double precision should be hardly noticeable, but just use double precision. It is outright superior.

If the solution is converged, the number of iterations should not affect the accuracy of the single precision vs double precision in the sense of the error being carried forward (unless the simulation is transient). For steady state solver there is no difference, except in the machine precision. i.e. we define convergence based on the solution value and not on the number of iterations that have passed.
LuckyTran is offline   Reply With Quote

Old   November 11, 2012, 13:43
Default About double precision in piecewise polynomials
  #6
Member
 
Abhijeet Shrawage
Join Date: Feb 2012
Posts: 31
Rep Power: 5
ashrawage is on a distinguished road
Hello there,
I was just hoping you guys would know about how to increase the decimal places in the piecewise polynomial box where you enter the coefficients for your nth order equation for predicting material properties.
In my case i am using Double precision but for some reason the coeff. are getting rounded off and believe it or not; that reduction in the decimal places messes up my property prediction big time! (i plotted curves using MATLAB and saw the difference)
Please let me know how can I increase the decimal places in the piecewise polynomial boxes

thank you
Abhijeet


ashrawage is offline   Reply With Quote

Old   November 11, 2012, 13:44
Default Images
  #7
Member
 
Abhijeet Shrawage
Join Date: Feb 2012
Posts: 31
Rep Power: 5
ashrawage is on a distinguished road
I have attached the matlab vs fluent images for specific heat


Attached Images
File Type: jpg matlab.jpg (36.9 KB, 10 views)
File Type: jpg Fluent.jpg (35.8 KB, 9 views)
ashrawage 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
parallel mode failure in 3ddp but not in 2ddp ak6g08 FLUENT 1 September 22, 2009 06:56
parallel mode failure in 3ddp but not in 2ddp ak6g08 Fluent UDF and Scheme Programming 0 September 22, 2009 06:16
Parallel processing with 3ddp Error Kartik FLUENT 0 February 20, 2009 15:57
when use 3ddp? Txema FLUENT 3 February 21, 2007 17:11
about 3ddp &3d zwdi FLUENT 2 April 18, 2004 14:36


All times are GMT -4. The time now is 13:08.