Dear Sean,
Which inertias of the OC3-Hywind system are you referring to when you ask how they were calculated?
The tower yaw inertia can be calculated at each cross section as the sum of the TwFAIner and TwSSIner values from Table 2-1 in the OC3-Hywind specifications report.
Although this data is not in the OC3-Hywind specifications report, I have calculated the aggregate mass/inertia of the total system (platform + ballast + tower + nacelle + rotor)—not including the moorings—using MSC.ADAMS. (I have never computed the aggregate properties including the mooring system.) The output from MSC.ADAMS is given below. You can use these to derive the radii of gyrations that you want. The center of mass location, orientation, and inertias in this output are all relative to the coordinate system described in the OC3-Hywind report. This system originates at the tower centerline at still water level with “X” pointing downwind, “Y” pointing to the left when looking downwind, and “Z” pointing vertically upwards.
The aggregate mass relative to ._127_ADAMS.Ground_P.InertialFrameCS_M is:
Mass : 8.0660481545E+006 kg
Center of Mass :
Location : -1.3918125391E-002, 1.1132995542E-002, -78.001301464 (meter, meter, meter)
Orientation : 231.3122968126, 6.8230961454E-002, 88.6142095906 (deg)
Mass Inertia Tensor :
IXX : 6.8025977471E+010 kg-meter2
IYY : 6.8022535284E+010 kg-meter2
IZZ : 1.9157300092E+008 kg-meter2
IXY : 9.9135213851E+006 kg-meter2
IZX : -8.6878157798E+006 kg-meter2
IYZ : 6.965876724E+006 kg-meter2
These inertias are computed in a vacuum. While damping does not contribute to the inertia, added mass will. Figure 4-4 shows the added mass matrix as a function of the platforms oscillation frequency.
I hope that helps.
Best regards,