Mooring system for a different water depth

Wind & Water Computer-Aided Engineering Software Tools
#1

Dear all,
I am writing you to ask some advice about the mooring system of the OC4 floating platform.
My desire is to run FAST with this support platform, for a water depth different from the default one (200 m).
How can I change then the mooring system (depth is 55 m for my case)?

I was thinking to keep the mooring line mass and structural properties (axial stiffness, diameter, mass per unit length), and then to find the anchor position and line unstretched length which give the same vertical force and line angle at the fairlead, that the system has for a depth of 200 m, at rest (in absence of waves and wind).

Honestly, I am not sure whether this approach is correct or not.

I am looking forward to receive your suggestions and opinions.

All the best,

#2

Dear Michele,

I’m not sure that the change you propose would work because the pretension of a catenary mooring system is dictated by the weight of mooring system hanging in the water, which would change if you kept the mooring properties identical, changing only the line lengths, water depth, and anchor positions.

My guess is for a such a drastic change in water depth a complete redesign of the mooring system would be warranted–that is, selection of mooring line cross sections, lengths, and anchor positions to obtain the desired response characteristics and stay within the load envelope.

Best regards,