Hi. I wish to have a pulsating inlet B.C. of the form U = Uo + Um sin(wt) where Uo is the mean velocity and Um is some fraction of Uo. How do I write an UDF which computes the U at every new time step i.e. refreshing t = t + time_step at every time level. For this I recon that I will need the time_step which would depend upon the number of iterations required for convergence. Am I right?? Please help me if somebody has an idea.

There is a example in UDF document. I think it is you needed.