[wanis]

hi all,
really i would be appreciate if u help me because i am not familiar with c++ and coding to change this udf to 3 degree of freedom in x,y and z.

/************************************************** **********
* 1-degree of freedom equation of motion (X direction)
* compiled UDF
************************************************** **********/
#include "udf.h"
static real v_prev = 0.0;
DEFINE_CG_MOTION(piston,dt,vel,omega,time,dtime)
{
Thread *t;
face_t f;
real NV_VEC(A);
real force, dv;
/* reset velocities */
NV_S(vel, =, 0.0);
NV_S(omega, =, 0.0);
if (!Data_Valid_P())
return;
/* get the thread pointer for which this motion is defined */
t = DT_THREAD(dt);
/* compute pressure force on body by looping through all faces */
force = 0.0;
begin_f_loop(f,t)
{
F_AREA(A,f,t);
force += F_P(f,t) * NV_MAG(A);
}
end_f_loop(f,t)
/* compute change in velocity, that is, dv = F * dt / mass velocity update using explicit Euler formula */
dv = dtime * force / 50.0;
v_prev += dv;
Message ("time = %f, x_vel = %f, force = %f\n", time, v_prev,
force);
/* set x-component of velocity */
vel[0] = v_prev;
}

Thanks in advance

[`e`]

This user-defined function (UDF) uses vector macros (including NV_VEC and NV_S) which should generally scale well for 3-D. Could you explain your problem in detail, including what this UDF currently does and what you're hoping to achieve by modifying it?

[wanis]

Originally Posted by `e`

This user-defined function (UDF) uses vector macros (including NV_VEC and NV_S) which should generally scale well for 3-D. Could you explain your problem in detail, including what this UDF currently does and what you're hoping to achieve by modifying it?

Thank you `e`, I am doing simulation of 3D moving of an object, i have tried to compile this UDF and then the motion of the object was restricted in one dimension which is stated in definition of UDF in X-direction, therefore i would like to see the movement also in other direction Y and Z. is there any way to modify it? really i don't know how and i am still studying about it and no progress achieved.

[`e`]

The UDF is currently modifying the velocity in the x-direction with this code segment:

/* set x-component of velocity */
vel[0] = v_prev;

You could change the direction which this velocity is applied to, for example in the y-direction:

/* set y-component of velocity */
vel[1] = v_prev;

Furthermore, if you wanted to apply the same speed in all three directions then:

/* set x-, y- and z-components of velocity (all equal in magnitude) */
vel[0] = v_prev;
vel[1] = v_prev;
vel[2] = v_prev;

If you'd like a different speed in each direction then modify the components accordingly. It appears the code calculates the pressure force on the body to find the resulting change in velocity. A piston is restricted to one direction which was why I asked you to describe your problem in further detail.

[wanis]

Really thank you `e` and I appreciate it, now it's more clear to me and i will see how to use another equations to define y, z components.