Dear @Xu.Pengfei,
In FAST v7, the HydroDyn module inputs are included with the platform-related inputs in the platform file. To include seismic functionality for an offshore wind turbine atop a monopile, the model should be set up similar to the coupled springs model–e.g., see the platform file named NRELOffshrBsline5MW_Platform_Monopile_CS.dat and the associated tower file named NRELOffshrBsline5MW_Tower_Monopile_CS.dat that I shared in my Nov '18 post in the following forum topic: Simulating OC3 phase II coupled springs in FAST v7 - #2 by Jason.Jonkman. In that post, setting PtfmLdMod = 1 referenced a SUBROUTINE UserPtfmLd() that included an implementation of a coupled springs foundation. When running the seismic version of FAST v7, SUBROUTINE UserPtfmLd() includes the seismic functionality instead, which requires the addition of the seismic input file.
The standard version of FAST v7 is available here: https://www.nrel.gov/wind/nwtc/assets/downloads/FAST/FASTv7.02/FAST_v7.02.00d-bjj.exe. The version of FAST v7 with the seismic functionality should be available here: Seismic | Wind Research | NREL, but I’ve had to send the associated archive via WeTransfer as stated above.
Best regards,