I am not getting sir, 

actually same problem I am started with 1e-5 ..after few iteration its giving nan problem, so I am started to initiate the problem with the 1e-6 time step size ..after some iteration, I can change to 2e-6 or 3e-6 like that, but my question is before changing the time step size 2e-6 or 3e-6  from 1e-6 what condition i need to look through consoile