Dear Yingyi,
Unless the airfoils are symmetric (zero camber), the aerodynamic twist angles are zero, the blade-pitch angles are 90 degrees, and the rotor is not rotating, the rotor will be aerodynamically asymmetric. The structural twist could also induce asymmetry in the rotor.
I can’t really comment on why the yaw angle differs from the wind direction, but I would guess the difference results from the rotor asymmetry.
Best regards,
Dear Jason,
I am trying to duplicate the single-point mooring system concept on the OC3 Hywind spar. All the FAST original files remain unchanged, except the mooring file. In the revised mooring file, a single fairlead point is set to allow all the mooring lines connected to it.
Then I did a free decay test in yaw. Turning off the generator DOF and CompAero, and setting the environmental condition to still wave and still air, I expected the yaw free-decay motion would remain at the initial value and would not vary with time. However, to my surprise, the yaw motion is a damped free decay motion as if the single-point mooring system provided some yaw restoring moments, which is physically not true, see the attached graph.
I’ve carried out an exactly similar test for the OC4 semi-submersible as described in the previous old posts, the results are as expected and completely different to the OC3 spar, see the Figure 3 of the following paper: Applied Sciences | Free Full-Text | Response Characteristics of the DeepCwind Floating Wind Turbine Moored by a Single-Point Mooring System. The setting files are downloadable from the link: https://archive.iii.kyushu-u.ac.jp/public/vEIQwtfI3qyvITNJF7f1O-CDZxeWKf7a7JWQKKjU9lib
I changed every possible setting in the OC3 spar case that I could think over, but all these attempts failed.
I just enclose the setting files of the OC3 spar case for your reference (downloadable from: 九州大学 職員専用ファイル共有システム（Proself） Web Publication). If you could take a look and help find out the reason, that will be very much helpful. Many thanks.
For your reference, I’ve
Best Regards,
Yingyi
Dear @Yingyi.Liu,
My guess is that you did not zero out the (6,6) element of the AddCLin matrix in HydroDyn, which was used to model the yaw stiffness associated with the delta mooring line connection to the OC3-Hywind spar, which was not directly considered in the mooring model.
Best regards,
Dear @Jason.Jonkman,
Exactly, you are right. I forgot the delta mooring. Now it works successfully. Thank you.
Best regards,
Yingyi
How can I find the pretension? Why don’t I want the same tension at 0 seconds when there is no wind or waves?
Dear @Cuizhi.Zhu,
A answers your similar question about mooring pretension in another forum post: How can I find the pretension of the mooring system after openfast is calulated？. I’m not sure I understand your second question.
Best regards,
