monitoring of displacement during fall of a body
 

hi,

i am using the tutorial for the 2d falling box. i want to get the displacement monitoring for the box. is it possible to get a plot of it in fluent as we get for pressure ,velocity etc...


thanks for all the inputs.

deepti

I assume you can only do that with UDF. (is the tutorial running with an udf?)

yes,i am using the cg udf. isnt the udf meant for giving properties to the physicals phenomenon? can i include the kind of solution that i need to extract? is it possible to define a custom function? i tried doing it. but i couldnt incorporate the flow time variable.

thank you for the inputs.

i don't know this tutorial, but cg udf sounds like "center of gravity". It should be an 6dof motion, so I assume you can extract the displacement in a file.
just like in this udf (no 6dof motion):
*********
#include <stdio.h>
#include "udf.h"
#if !RP_NODE
# define UDF_FILENAME "udf_loc_velo"
# define UDF_DATA "data.dat"
/* read current location and velocity from file */
static void
read_loc_velo_file (real *loc, real *velo)
{
FILE *fp = fopen(UDF_FILENAME, "r");
if (fp != NULL)
{
float read_loc, read_velo;
fscanf (fp, "%e %e", &read_loc, &read_velo);
fclose (fp);
*loc = (real) read_loc;
*velo = (real) read_velo;
}
else
{
*loc = 0.0;
*velo = 0.0;
}
}
/* write current location and velocity in file */
static void
write_loc_velo_file (real loc, real velo)
{
FILE *fp = fopen(UDF_FILENAME, "w");
if (fp != NULL)
{
fprintf (fp, "%e %e", loc, velo);
fclose (fp);
}
else
Message ("\nWarning: cannot write %s file", UDF_FILENAME);
}

/* write current location and velocity in datafile */
static void
write_data_file (real time, real loc, real velo, real force)
{
FILE *fp = fopen(UDF_DATA, "a+");
fprintf (fp, "%e %e %e %e\n", time, loc, velo, force);
fclose (fp);

}

#endif /* !RP_NODE */

DEFINE_ON_DEMAND(reset_velocity)
{
#if !RP_NODE
real loc, velo;
read_loc_velo_file (&loc, &velo);
write_loc_velo_file (loc, 0.0);
Message ("\nUDF reset_velocity called:");
#endif
}
DEFINE_CG_MOTION(valve, dt, cg_vel, cg_omega, time, dtime)
{
#if !RP_NODE
Thread *t = DT_THREAD (dt);
face_t f;
real force, loc;
#endif
real velo;
/* reset velocities */
NV_S (cg_vel, =, 0.0);
NV_S (cg_omega, =, 0.0);
if (!Data_Valid_P ())
return;
#if !RP_NODE
/* compute force on piston wall */
force = 0.0;
begin_f_loop (f, t)
{
real *AA;
AA = F_AREA_CACHE (f, t);
force += F_P (f, t) * AA[0];
}
end_f_loop (f, t)
# if RP_2D
if (rp_axi)
force *= 2.0 * M_PI;
# endif
read_loc_velo_file (&loc, &velo);
/* add in spring force */
# define K_SPRING 253.18
{
real init_disp = 0.02791;
real s_force = K_SPRING * (loc + init_disp);
force = force - s_force;
}
/* compute change in velocity */
{
real dv = dtime * force / 0.0217;
velo += dv;
loc += velo * dtime;
}
Message ("\nUDF valve: time = %f, x_vel = %f, force = %f, loc(m)= %f\n",
time, velo, force, loc);
write_loc_velo_file (loc, velo);
write_data_file (time,loc,velo,force);
#endif /* !RP_NODE */
#if PARALLEL
host_to_node_real_1 (velo);
#endif
cg_vel[0] = velo;
}
DEFINE_CG_MOTION(moving_fluid, dt, cg_vel, cg_omega, time, dtime)
{
#if !RP_NODE
Thread *t = DT_THREAD (dt);
face_t f;
real force, loc;
#endif
real velo;
/* reset velocities */
NV_S (cg_vel, =, 0.0);
NV_S (cg_omega, =, 0.0);
if (!Data_Valid_P ())
return;

#if !RP_NODE
read_loc_velo_file (&loc, &velo);
#endif /* !RP_NODE */
#if PARALLEL
host_to_node_real_1 (velo);
#endif
cg_vel[0] = velo;
}

Fluent user guide (6DOF) :
Note that you can also keep track of an object's motion history using the text user interface and by entering yes for the motion-history? text interface command.
define -> models -> dynamic-mesh-controls-> six-dof-parameter->
motion-history?