Dear Yifan,
Just a couple comments:
- The values of Kh(4,4) and Kh(5,5) are negative because they reflect the effects from hydrostatic pressure only. In addition to Kh (hydrostatic), and Km (mooring), you should also add the effect from body weight, i.e., Kw(4,4) = Kw(5,5) = -mgz, where m is the full-system mass, g is gravity, and z is the full-system center of mass location (negative valued), so Kw(4,4) and Kw(5,5) are positive. This topic has been discussed for the OC4-DeepCwind semisubmersible more in the following forum topic: The frequency component of flapwise.
- The nonzero (4,4) and (5,5) elements of AddCLin in the HydroDyn model of OC4-DeepCwind semisubmersible model are associated with the water ballast. But please be aware that in OpenFAST v2.6 and newer, AddCLin no longer needs to be specified in HydroDyn when adding ballast; this is because hydrostatics in the strip-theory solution are now computed at the displaced position/orientation of the floater.
Best regards,