CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Fluent UDF and Scheme Programming (
-   -   incorrect cg motion UDF sdof_properties (

M.Magdy March 25, 2013 20:50

incorrect cg motion UDF sdof_properties
I'm trying to simulate the movement of floating body in sea.
I'm using a udf for wall movement :
#include "udf.h"
DEFINE_CG_MOTION(wave, dt, cg_vel, cg_omega, time, dtime)
cg_vel[0] = ((4)*(sin((63)*(time))));
cg_vel[1] = 0.0;
cg_vel[2] = 0.0;

cg_omega[0] = 0.0;
cg_omega[1] = 0.0;
cg_omega[2] = 0.0;


and another one for the floating body six_dof_property:

/************************************************** *****
SDOF property compiled UDF with external forces/moments
************************************************** *****/
#include "udf.h"

DEFINE_SDOF_PROPERTIES(sdof_properties, prop, dt, time, dtime)
prop[SDOF_MASS] = 85167.33;
prop[SDOF_IXX] = 174112.84;
prop[SDOF_IYY] = 28237716.54;
prop[SDOF_IZZ] = 28237716.54;

printf ("\n updated 6DOF properties");

when i check the "six DOF" option in dynamic mesh the wall doesn't move and this message appears:
Unable to read motion history

while if i unchecked it an error appears -
but the waves are generated correctly-:
incorrect cg motion UDF sdof_properties::libudf on zone 6 (assuming no motion)

So if anyone could tell me whether I should -in my case- check the box beside "six DOF" in dynamic mesh options or not.
knowing that :
  • when i check it -----------> no waves are generated (the wall doesn't move)
  • when i uncheck it ---------> waves are generated but the floating body make no motion


vasava March 26, 2013 03:02

Hello Again

I think that you must have something else in your UDF that describes the motion/position of other faces/boundaries in your domain. While you have moving/dynamic face/boundary the motion of mesh attached to this face affects the meshes attached to other faces/boundaries.

I suggest you have a close look at the tutorial titled 'Using a UDF to Control the Dynamic Mesh of a Flexible Oscillating Membrane'.

All times are GMT -4. The time now is 11:42.