Hello YJ L,

You said you want to convert a 20 g amplitude, 5 ms duration signal into a Response input spectrum, but when I look at the plot of your data, the triagular pulse has a magnitude of 74.556 m/s^2 (7.6 g) and a duration of 0.0121 s. So which is it?

Software tools outside of Ansys are available to convert a time-history into a Shock Response Spectrum. I use the free, Stand-Alone Executable Version of Vibrationdata because it doesn’t require a copy of matlab to be installed. If you have matlab installed, there is a larger toolkit that is also free. Look for the relevant links on this page: https://vibrationdata.wordpress.com/

Conversion of time-history data requires you to choose the Q factor that defines the damping in your structure. If you know the critical damping ratio for your structure, Zeta, then Q = 1/(2Zeta). For example, if your structure has a critical damping ratio of 2%, then Q = 25. You add damping to the excitation because the Modal analysis provides undamped modes. What is the Q factor for your structure?

What is the frequency range you want to study for your structure? I suspect the sampling frequency used in the representation of this triangular pulse is too low as it is only 909 Hz (sampling delta t = 0.0011 s).

By sampling the triangular pulse at 10,000 Hz, the Shock Response Spectrum can be calculated above 1000 Hz.