Hi Amit...
I'm pretty sure I just went with a sine wave and fed it into a cylindrical equation. I'm not sure right now how I got to the equation off the top of my head. I'd have to take a look at it again. Unfortunately I'm up against a wall at the moment with a really important task and I can't take the time right now to do the necessary digging. After PTC Live Global next week I will have more time (thankfully).
Take care...
-Brian