Dear All,
I tried looking at the forum, but couldn’t find an answer. I have a question regarding the mooring line properties of the OC-3 hywind spar. In the report ‘Definition of the Floating System for Phase IV of OC3’ you state that each of the multisegment lines is replaced with an equivalent homogeneous line, with properties derived as the weighted-average values of the mass, weight, and stiffness.
My question is what kind of mooring line can I compare these values with? I’m for instance looking for a minimum breaking load for these lines. I modeled the hywind spar in Ansys AQWA and I want to check If I stay within the industry safety factor of 1.67.
I’m awaiting your reply.
With Regards,
Joeri Haaker
Dear Joeri,
I don’t think I can really answer your question. When the OC3-Hywind specification document was originally published (nrel.gov/docs/fy10osti/47535.pdf), I was able to obtain information from Statoil regarding the specifications of the delta (“crowfoot”) connection, multi-segmented lines, and clump weight; however, at the time, Statoil requested that I not redistribute those details to the entire OC3 group. I’ve recently heard from others that they were able to obtain information regarding the mooring line details when they contacted Statoil. I suggest that you reach out to Statoil.
Best regards,
Dear Jason,
That is unfortunate to hear, do you maybe have a name I can contact? If not, I’ll try trough their website.
With Regards,
Joeri Haaker
Dear Joeri,
The contact I was working with for the OC3-Hywind development no longer works for Statoil. I’m not sure who to recommend now, but I would start with those you know from Statoil.
Best regards,
Dear Jason,
As a student from Delft, I unfortunately don’t know many people at Statoil, but I just sent them an email through their website. I’m hoping that they can provide me with the information I seek.
Thank you for you help.
Best regards,
Joeri Haaker
Dear Jason,
I have one final question about the properties of the uniform line. In the report ‘Definition of the Floating System for Phase IV of OC3’ you mention a
Equivalent Mooring Line Extensional Stiffness of 384,243,000 N.
How is this defined? A stiffness is normally defined with the unit N/m. Is this value the cross sectional area x the modulus of elasticity or is it something else?
Best Regards,
Joeri Haaker
Dear Joeri,
Yes, the extensional stiffness of the mooring line is defined within the cross section, as the area times the modulus of elasticity.
Best regards,
Dear Jason,
I had a discussion with my thesis supervisor about using the term ‘Stiffness’ in this case. But I already concluded that the most likely explanation would be that this extensional stiffness is defined as the area x the modulus of elasticity. But he does not agree on calling it stiffness in this case.
Thank you for your reply.
Best regards,
Joeri Haaker
Hi Jason,
I’m trying to derive the mooring line mass per length (m) and axial stiffness (EA) as a function of the mooring diameter (d).
- Is the mooring line a studded chain? A = 2*(pid^2)/4, then I can obtain E = 384243000/(2pid^2/4) = 3.0200e10 N/m^2 with d=0.09,
Hence EA(d) = 3.0200e+10 * 2pi*d^2/4 = 4.7438e10 * d^2
- m = rho2(pid^2)/4, plugging values of m = 77.7066kg/m and d = 0.09: rho =6107.4kg/m^3 (which doesn’t look like steel?)
Thus m(d) = 6107.4 2(pid^2/4) = 9.5934e3 * d^2
Please which of these do I need to change to obtain valid expressions for EA(d) and m(d)?
Looking forward to hearing from you.
Regards
Salem
Dear Salem,
Details such as the material type, material density, and material modulus of elasticity have not been specified for the OC3-Hywind spar. This model was based on information provided by StatoilHydro (now Equinor), but not all details where provided and not all details can be made public. Beyond the information provided in the OC3-Hywind specifications report and corresponding FAST / OpenFAST models, you’ll have you to make your own assumptions for your own purposes.
Best regards,
Dear Jason
Many thanks for your response. Will do.
BR
Salem