how to define velocity for particle (DPM) at the inlet face
 

Hi,
Dear All, I want to define velocity for particle at the inlet face of the DPM model. the z-velocity is assumed to increase from 0 m/s to 1.085 m/s in 2 min (such as 2s to 4s). I read the UDF help, and found : DEFINE_DPM_BC, but I have no idea to use it ,the examples are too hard to understand. What I know now is:

#include "udf.h"
DEFINE_DPM_BC(z-velocity,p,t,f,f_normal,dim)
{
real time,vz;
time = CURRENT_TIME;
if (time>=2&&time<=4)
vz = (time-2)*1.085/2;
else
vz = 1.085;
?:confused:
}
but I do not know how to return, bros, can you help me?
thanks in advance.

Maybe the DEFINE_DPM_INJECTION_INIT macro is uesful for you.