Dear Anuj,
HydroDyn expects hydrodynamic input data derived from WAMIT. If you are not using WAMIT, I suggest you reformat your data according to the WAMIT format (including nondimensionalization) before inputting them to HydroDyn. Information on the WAMIT format is available from Chapter 4 of the WAMIT User’s Guide, available publicly from here: wamit.com/manual6.4/Chap4.pdf. HydroDyn needs data from the *.1, *.3, and *.hst WAMIT output files.
The reason why the vertical center of gravity (VCG) and radii of gyration are set to zero in WAMIT is described in the forum topic found here: About WAMIT model for 5MW OC3 Hywind.
Best regards,