Hello sri lankan,
There is no standard function to calculate the velocity in DIAdem.
Assuming you have acceleration data (which is what you typically have in crash test), all you need to do is calculate the integral of the acceleration to get the velocity. The Integration function is part of the Basic Math palette in DIAdem.
This is the line to use in a Script:
Call ChnIntegrate("[1]/Time","[1]/Acceleration","/Integrated")
Otmar D. Foehner