Learning Forum

[Milne Ando]

G'day,

I followed the user guide to assign a dummy UDF to the prism inflation layer which surrounds the "system coupling" face of a moving body. But console shows a warning:

Warning: incorrect cg motion UDF dummy_motion::libudf on zone 10 (assuming no motion)

How should I fix it? or ignoring it is okay?

hope someone can help me, thank you.

[Rahul]

Hi,

May i know, whether you have compiled/interpreted UDF to add it in Fluent?

[Milne Ando]

hi,

I right clicked user defined function and clicked complied, then added dummyUDF.c (as the pic shows). After clicking build, it showed a window, then I just clicked OK but I didn't fully understand this part. Hope you can tell me which step was wrong. Thank you.

[Rahul]

Note that UDFs that are defined using DEFINE_CG_MOTION can ONLY be executed as compiled UDFs.
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v194/flu_udf/flu_udf_sec_define_cg_motion.html?q=DEFINE_CG_MOTION

[Milne Ando]

hi,

the dummy UDF is written in p.3323 as follows:

#include "udf.h"

DEFINE_GRID_MOTION(dummy_motion, domain, dt, time, dtime)

{

    return;

}

hmm, should I substitute DEFINE_GRID_MOTION with DEFINE_CG_MOTION? (I have no idea)

[Rahul]

Are you doing it in transient solver? If not, please turn on the transient solver.

[Milne Ando]

yes, I want to conduct a two-way coupling simulation and always turn on transient. Well, is there anyone meet the same problem? or maybe the user guide is wrong? maybe prism layer should not be assgined to rigid body but user-defined ?

[Rahul]

Could you please share the images of the settings provided?

[Milne Ando]

hi,

do you mean settings provided by the user guide? Here:

[Rahul]

Hi ,
I mean settings provided by you in your simulation (In Fluent).

[Milne Ando]

hi,

I think I found the answer. Initially I didn't check the Six DOF box in the Options panel; I just noticed that and checked it then also checked On and Passive in the Dynamic Mesh Zones window. Finally warning message didn't pop up!

[Rahul]

Hi,

Good to hear that. You have ensure that On is enabled in the Six DOF group box in the Motion Attributes tab, to ensure that the six DOF solver is being used. 

Note that the Passive option in the Six DOF group box is used when you do not want the forces and moments on the zone to be taken into consideration.

[Milne Ando]

hi,

I met a confused situation 'cause I just tried another setting as the pic shows, if Six DOF is checked in the Options panel while On isn't checked in the Dynamic Mesh Zones window, the console won't pop up warning neither. Well, maybe just keep On unchecked since the zone motion described by UDF doesn't need six DOF solver, right? And the prism layer hugs the body surface which is assigned to system coupling, so its motion may be covered by system copling at the same time, I guess.

[Rahul]

Please refer a video Ansys Fluent: Using the Six Degrees of Freedom (Six DOF) Solver - YouTube to setup case with six-DOF.