for FPSO service piping, how to input inertial accelerations such as Surge acc., Sway acc. and Heave acc. into software? Thanks

Accelerations can be input using the uniform load option in the piping input.
To use G loads instead of force/length units, you must activate the switch called "Uniform Load in Gs". This is found in the Special Execution Options screen in the piping input.
To access it, you can either use the guillotine-looking toolbar button, or the "Kaux" menu in version 4.50, or the "Environment" menu in 5.00.
You will need to set up your load cases manually in the load case editor, as CAESAR doesn't know what kind of loads these are.