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ThinkQuick July 24, 2012 02:26

UDF for 2d translational motion
Hi all,

I am relatively new to ANSYS Fluent and am trying to impose a simple UDF to move a disturbance through a fluid. I only require the disturbance to move in the x direction with a constant velocity.

Could anyone please point me in the right direction about how to write this UDF?


Marion July 25, 2012 05:26

Profiles instead
This is a udf for X-velocity (3D)

DEFINE_CG_MOTION(velo_needle, dt, cg_vel, cg_omega, time, dtime)

cg_vel[0] = -0.6;
/* x-velocity*/
cg_vel[1] = 0.0;
cg_vel[2] = 0.0;
NV_S (cg_omega, =, 0.0);
/* no angular motion */
/* Messages in Fluent TUI */

" \n");
"velocity \n");
" \n");

However, Fluent support advised me to use profiles files for this kind of motion (i.e. non force driven motions)... It's easier since you do not have to compile your udf or have to keep the files together, etc.

Since I discovered the use of profiles for transient motions my life has changed :D


ThinkQuick July 25, 2012 21:49


Originally Posted by eng_s_sadeghi (Post 373393)
May you please send me a sample paper to know what exactly you want to model? Please take a look at my website and feel free to email me for any questions.

Hi Saeed, I have emailed you.

'Fluent support advised me to use profiles files for this kind of motion'

Thanks for the reply. Do you have any resources on using profiles to specify translation?

Its pretty frustrating it seems like a relatively simply problem to move an object at a constant velocity in one dimension however the simulation is becoming difficult and cumbersome.

Marion July 26, 2012 07:43

Have you tried the udf I gave you yesterday and it is not working? Maybe you have an issue with compiling udfs?
For the profile files, there is a section about this in the user guide, but here is a copy of a recent reply I posted on this forum:

For the profile:
you have to write it like this and save it as
disp_needle 2 10 0
time x
0.00000E+00 0.00000E+00
1.00000E-06 -1.20000E-07
2.00000E-06 -2.40000E-07
3.00000E-06 -3.60000E-07
4.00000E-06 -4.80000E-07
5.00000E-06 -6.00000E-07
6.00000E-06 -7.20000E-07
7.00000E-06 -8.40000E-07
8.00000E-06 -9.60000E-07
9.00000E-06 -1.08000E-06

*disp_needle--> name of the profile
*2 --> number of columns
*10 --> number of points
*0 --> for periodicity - 0=not periodic and 1=periodic

once you've created this file, within Fluent TUI you type
(make sure everything is in your working directory)

and then in the fluent dynamic mesh panel, choose disp_needle in the drop down list under "profile/udf".

As it is displacement vs. time the 1st column has to be time. the 2nd column can be displacement (x,y,z) velocity (v_x, v_y, v_z) , etc...

I hope this helps,


XthianGA May 9, 2013 21:27

Simple UDF motion
1 Attachment(s)
Like Carlos, I'm trying to impose a simple UDF for moving a body through a fluid. I require only your body moving in the X direction with a constant speed, this movement is caused by fluid entering the duct. Carlos, you could help in achieving this UDF, or guide in performing the same.

I leave a picture

Like you I would like to learn the use of profiles for transient motions :).
Thanks !!

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