HELP：error ：Floating point error: invalid number when i drag coefficient udf was used
 

Hi all,
I'm modeling gas-liquid two phase flow with eulerian model, at the beginning ,the simulation goes well,but when i load a drag coefficient, there is an error after about 50 steps calculation :
Floating point error: invalid number
Error Object: ()
I've tried to decrease the under relax factor, it seems not useful.what should i do?
Thank you for your answer in advance:)
zoesjtuer

Initiating the case with wrong conditions may lead to floating point error when the iterations start.

and also wrong boundary condition definition might cause the floating point error