About mooring line of OC4 5MW FOWT

[axxyyyyyyyy378]

Hi,

I have learned from some papers that for floating wind turbines like the OC4 5MW semi-FOWT when designing the catenary mooring lines, it is necessary to ensure that the part of the mooring line connected to the seabed anchor point is always in contact with the seabed while the floating wind turbine is moving. In order to avoid excessive tension in the z-direction at the anchor point, SO how long should the mooring line in contact with the seabed be? I have seen in some papers that 200m is appropriate, but I am not sure about this. Can you provide some suggestions? Thanks.

[RyanDavies19]

Hi @axxyyyyyyyy378, the total line length and amount resting on the seabed depends on the design of your system and the site conditions that your FOWT might experience. Generally we try to keep at least 20m of the line in contact with the seabed when the FOWT is at it's maximally displaced position.

[axxyyyyyyyy378]

Hi @RyanDavies19 , Thanks for your kind reply. I would like to know if there are any design standards or papers that can be referred to regarding the total length of the line and the part that lies on the seabed. I have not yet found a scientific basis.

[erickaloz]

Hi @axxyyyyyyyy378, the ABS FOWT Guide Ch. 8 Sec. 5 states that for a catenary mooring system with drag anchors, the mooring line length should be sufficiently long such that there is no angle between the mooring line and the sea floor in any design condition. In practice, we usually ensure about 20 m of chain on the seabed in any load case as a margin, but this is a design choice that is informed by how conservative our mooring design/loads analysis process is.

[axxyyyyyyyy378]

Hi @erickaloz , Thanks for getting back to me, and sorry for not replying sooner. I've been pondering another question and wanted to hear your advice. So, which of these parameters do you think would have a bigger impact on the safety of the seabed anchor points: the total tension at the anchor point, the component of tension along the z-axis at the anchor point, or the short-term fatigue load calculated from the tension at the anchor point?

[erickaloz]

Hi @axxyyyyyyyy378, I'm not sure I fully understand your question, but the z force component at the anchor point would have the largest impact on the safety of a drag embedment anchor because vertical loads on DEAs should be avoided.