Sloshing tank natural frequencies in Fluent
 

I want find sloshing frequencies of a rectangular tank half filled with water. I came to know that I have to do FFT in Fluent to get natural frequencies. But for that I need to input some time sequence data. What is that data ? (amplitude vs time ?). Should I need to perform transient analysis for getting that data? Where can I find "time sequence data" after performing transient analysis?
Can I perform any transient analysis or it should be only periodic? Is there any problem if I do analysis for constant acceleration in X direction.

Please, someone clear my doubts :confused: