CFD Online Discussion Forums - UDF to change angular velocity after every timestep based on the previous value

Hello,
I am trying to run a simulation where the angular velocity of a dynamic mesh zone changes every time step based on this equation of motion where moment_z is the moment on the two aerofoils defined as one wall.

omega_prev + = ((1/I) * (moment_z - (alpha * omega_prev)))
When I set up the dynamic mesh with the udf, the initialisation returns an "All compute processes received SIGFPE." error. I am not sure what the cause of this error is. Could someone more knowledgeable please help me solve this?

This is the UDF I am using:

Code:

#include "udf.h"

real current_dt;

real omega_old;

real omega_new;

real moment_z;

static I = 0.0275; /* Moment of inertia */

static alpha = 0.00626;

static real omega_prev = 0.0;

DEFINE_CG_MOTION (rotational_motion1, dt, vel, omega, time, dtime)

{

#if !RP_HOST

current_dt = RP_Get_Integer("time-step");

if (current_dt ==1)

omega_prev = -128;

else

omega_prev = omega[2];

Message("Omega_old1 is %g",omega_prev);

Domain *d =Get_Domain(1);

Thread *t_object = Lookup_Thread(d, 2);

real moment [ND_ND], cg[ND_ND], force [ND_ND];

Compute_Force_And_Moment(d, t_object, cg, force, moment, TRUE);

moment_z= moment [2]; 

/* Equation of motion */

omega_prev += ((1/I) * (moment_z - (alpha * omega_prev)));

Message("Omega_new1 is %g",omega_prev);

omega[2] = omega_prev;

#endif

}

Thank you!