[fatihaea]

Hi,

I´m trying to simulate the flow over a circular cylinder that is free to vibrate in both the direction, I´m using this UDF :

#include "udf.h"

DEFINE_SDOF_PROPERTIES(stage, prop, dt, time, dtime)
{
Thread *t;
Domain *d = Get_Domain(1);
real cg[3], vel[3]; // Arrays to store center of gravity position and velocity
real mass = 0.03575;
real f = 10.25;
real wn = 2 * M_PI * f;
real z = 0; // Introduce a small damping factor
real k = 148.28;
real c = 2 * mass * wn * z;

// Thread pointer for which this motion is defined
t = DT_THREAD(dt);

// Set SDOF properties
prop[SDOF_MASS] = mass;
prop[SDOF_ZERO_TRANS_Z] = TRUE;
prop[SDOF_ZERO_ROT_X] = TRUE;
prop[SDOF_ZERO_ROT_Y] = TRUE;
prop[SDOF_ZERO_ROT_Z] = TRUE;

// Get center of gravity position and velocity
cg[0] = DT_CG(dt)[0]; // x-direction
cg[1] = DT_CG(dt)[1]; // y-direction
cg[2] = DT_CG(dt)[2]; // z-direction

vel[0] = DT_VEL_CG(dt)[0]; // x-direction
vel[1] = DT_VEL_CG(dt)[1]; // y-direction
vel[2] = DT_VEL_CG(dt)[2]; // z-direction

// Calculate loads in y direction with damping
prop[SDOF_LOAD_F_X] = -k * cg[0];
prop[SDOF_LOAD_F_Y] = -k * cg[1];
// Open file for appending
FILE *fout = fopen("motion_x_direction01.txt", "a");
if (fout == NULL) {
Message("Error opening file.\n");
return;
}

// Write data into file
fprintf(fout, "%g %g %g %g %g\n", time, cg[0], cg[1], vel[0], vel[1]);

// Close file
if (fclose(fout) != 0) {
Message("Error closing file.\n");
}
}
The UDF is compiled and loaded correctly and it seems to be working, however, the results of displacement I´m getting are much smaller than the reference values, Does anyone have any idea why this is occurring?