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 Musa August 21, 2012 20:48

invalid lvalue in assignment

Dear Friends,
I am trying to program a custom drag function but I am getting an invalid lvalue assignment in line 17.Kindly help me and give Suggestions. The line in question is in bold.

#include "udf.h"

#define pi 4.atan(1.)
#define diam2 4.06e-4

{
real x_vel_g,x_vel_s,y_vel_g,y_vel_s,abs_v,slip_x,slip_ y,
rho_g,rho_s,mu_g,reyp,vof_g,vof_s,vof_m,taup,k_g_s ;
vof_m = 0.644;

/* find the threads for the gas(primary)*/
/* and solids(secondary phases) */

/* find phase velocities and properties*/

/* compute slip*/
abs_v = sqrt(slip_x*slip_x + slip_y*slip_y);

/* compute reynolds number*/
reyp = rho_g*abs_v*diam2/mu_g;

/* compute particle relaxation time*/
taup = rho_s*vof_s/k_g_s
vof_g = C_VOF(cell,thread_g);/* gas vol frac */
vof_s = C_VOF(cell,thread_s);/* solid vol frac*/

k_g_s = 18.*mu_g*vof_s*(1.+ 0.1*pow(reyp,0.75))/diam2/diam2/pow(1.-(vof_s/vof_m),2.5*vof_m);
return k_g_s;
}