[iceman53y]

Hi,

I have this UDF where I am trying to move a cylinder at a certain frequency.
But the cylinder moves to the right and comes back to its original position. I want it to oscillate about its origin. I want it to move right and left from its origin position.

What do I change in this UDF. Please help.

/* Moving Grid problem - CG movement of a cylinder */
#include "udf.h"
static real velx = 0.0;
DEFINE_CG_MOTION(cylinder, dt, vel, omega, time, dtime)
{
NV_S(vel, =, 0.0);
NV_S(omega, =, 0.0);

velx = 0.005 * sin(3.1415927 * time / 5.);
vel[0] = velx;
}

[blackmask]

Note that what you want is

x = A*sin(b*t);
where A, b denote the amplitude and frequency of the motion, respectively. Therefore, the velocity should be

u = dx/dt = b*A*cos(b*t);


i.e., change the sin() in your code to cos().

[moh_zain]

vel is for linear motion and you need omeg

[iceman53y]

Working perfectly now.

Thanks!

[iceman53y]

Hello again,

My intention is to move this cylinder at a certain frequency, i.e. 8Hz

When I consider the equation in the form of

u = dx/dt = b*A*cos(b*t);

Is this representing:

x = A sin (wt)
v = Aw cos (wt)

And w would be 2*pi*f
And A would be the amplitude.

Please let me know if i'm doing this right.

Also where does fluent get the t from? is is from the timestamp value that I put in?

Thanks

[moh_zain]

yes you right in the equation and t from time-step also right