Dear Satish,
I’m not an expert on the file formatting requirements associated with WaveMod = 6, so, I can’t really comment if what you’ve done is correct. Are you getting any errors or warnings when running OpenFAST? What wave elevation do you see? What wave kinematics are being output from HydroDyn?
If you feel there is still a bug, I would post your complete set of input and output files to on the OpenFAST issues page on github: github.com/OpenFAST/openfast/issues/118.
Best regards,