Hello, I am trying to calculate the platform moment of inertia for OC3 Spar in python, the definition file for OC3 spar does not contain enough information to provide the parameters needed to calculate the moment of inertia, so I considered the data in this paperDesign optimization of the OC3 phase IV floating spar-buoy, based on global limit states, based on the specific parameters for OC3 spar given in this paper, I calculated and got very close to the OC3 definition of the pitch and roll moment of inertia, 4.34904183e9, 4.22923e9 in the OC3 definition file, the same as COG and total mass,but the yaw moment of inertia is much worse, I calculated 9.30108155e7, while 1.6423e8 in the definition file, I don’t think that there is something wrong with my own calculations, considering that the yaw moment of inertia formula is very simple.

I noticed in the thread “Yaw stiffness for Spar - #4 by Krishnaveni.Balakris” that the mooring seems to introduce an additional yaw stiffness to the platform.

1. Does this affect the yaw inertia of the platform? If so, how is it factored into the yaw inertia?

2. if not, is there any other component of the platform’s yaw inertia to consider?

Thank you in advance for your kind answers,

Dear @Zhiyan.Dong,

Regarding (1), I would not expect the yaw stiffness of the mooring system to have any effect on the yaw inertia.

Regarding (2), I can’t think of anything specifically, but the OC3-Hywind specifications report does not provide enough detail on the structural properties of the spar to calculate its inertias from first principles. You’ll have to make your own assumptions about the structural properties for your own purposes.

Best regards,

Dear jason

Thank you very much for your reply! I recently read another paper https://www.mdpi.com/1996-1073/13/8/1974and it too came to very similar conclusions as I did that the yaw inertia of spar floats is difficult to verify due to the lack of more accurate geometry, while pitch and pitch inertia can be verified!

Best regards