POLYAMOOR

Durable and flexible polyamide moorings for offshore renewable energies

Context

Mooring systems used for floating wind turbines differ significantly from those used in the oil & gas sector due to elevated dynamics in shallow waters. The challenge is to be able to maintain a floater in an extreme environment by limiting the forces transmitted by the mooring lines as well as limiting the maximum offset of the floater to which the export cable is connected. One envisaged solution is to use nylon mooring lines capable of absorbing the involved forces but whose behaviour is highly non-linear and poorly understood in cases of long service life.

Objective

To characterise in detail the dynamic and long-term behaviour of nylon mooring lines in order to develop standards accordingly

Main achievements

Identification of a nylon cable configuration compatible with the lifetime of a floating wind farm (20-25 years)

Identification of a generic visco-elasto-plastic rheological scheme

Analytical formulations of the different rheological blocks adapted to nylon, then calibration and validation of these formulations by specific test sequences

Identification of a simple long-term creep law (period > 1 year)

Feasibility of an accelerated self-heating life prediction method

Main outputs

Database of small-scale stress and elongation for nylon behaviour characterisation
Database of stress and elongation for subcord fatigue tests
Analytical model of the visco-elasto-plastic behaviour of nylon and proprietary module of this behaviour law in the commercial software DeepLinesTM
Analytical formulation and test protocol for accelerated qualification of nylon by self-heating
Analytical formulation of long-term nylon creep
Update of the guidance note for the certification of synthetic lines used in offshore environments (BV NI432)

Fact sheet

Pitch vidéo

Webinaire

Rapports publics

Conclusion

POLYAMOOR has identified a behavioural law that closely reproduces the instantaneous behaviour of nylon. A long-term creep behaviour law has been identified. Creep at different loading rates and its effect on the behaviour law will be studied in the MONAMOOR project.

The service life objectives are achieved with a dedicated rope construction and the use of a specific polymer coating. The performance durability of this coating remains to be qualified. The results have led to the updating of a recommendation note for the certification of synthetic lines used in the offshore environment (BV NI432).