Nylon ropes for mooring of floating wind turbines

NYMOOR contributes to the implementation of safe, sustainable, and cost effective offshore floating wind energy. Floating wind turbines are kept in place by mooring systems, and the goal of NYMOOR is to enable design and use of nylon ropes in moorings. Nylon ropes are both flexible and elastic, and these properties reduce dynamic tensile line loads in wind and waves and by that reduce the amount of material needed in moorings. Steel chain is a standard component in mooring lines, and their limited availability has been identified as a constrain to the required development of offshore wind energy. Application of nylon ropes has the potential to solve this problem by reducing the need of heavy chains. However, there is no experience with use of this material in permanent moorings. Of concern is the long-term endurance and behaviour of nylon in the ocean environment. NYMOOR will provide knowledge on the long-term properties and failure mechanisms of nylon moorings. Time, load, humidity, and temperature dependent mechanical properties of nylon ropes will be found through development and use of new laboratory testing equipment and procedures, and mathematical models developed in the project. The results will be applied to study the effect of using nylon ropes in novel mooring solutions and the design opportunities this brings. The project applies an interdisciplinary approach combining experimental research, material science, numerical structural analysis, and structural reliability analysis. The first two disciplines are used to investigate, model and identify the nylon rope complex properties, which will be used to determine structural loadings and probabilities of failure. NYMOOR will strengthen the competitiveness of Norwegian companies by enabling them to enter the fast-growing market first with an innovative and cost-efficient product. Results from NYMOOR will contribute to reduce financial risks, accelerate innovation and reduce development time for wind farms.

The goal of NYMOOR is to enable design and use of nylon mooring systems for floating wind turbines (FTWs) with high durability in ocean environments. Availability of steel chain for mooring lines has been identified as a constrain to the required development of offshore wind energy. Application of flexible nylon mooring ropes has the potential to solve this problem, but there is no experience with their use in permanent moorings. Of particular concern is the long-term endurance and behaviour of nylon, while design analysis methods require new models for the mechanical properties of nylon ropes. NYMOOR will provide knowledge on possible long-term degradation and failure mechanisms of nylon moorings. Time, load, humidity, and temperature dependent mechanical properties of nylon ropes will be found using new tensile testing equipment and procedures, and mathematical models developed in the project. This is based on the hypothesis that mechanical properties of ropes can be established based on limited sub-rope testing, extensive yarn testing and mathematical/numerical methods. These results will be used to establish numerical models for load history dependent stiffness and elongation of nylon ropes, which will be applied in design analysis tools. Results will be applied to study the effect of using nylon ropes in novel mooring solutions and the design opportunities this brings. Finally, methods for determining the long-term reliability and behaviour of nylon ropes, including variations in mechanical properties and statistical models of mooring line loads, will be developed and applied in case studies. An interdisciplinary approach combines experimental research, material science, numerical structural analysis and structural reliability. The first two disciplines are used to investigate, model and identify the nylon rope complex properties, which are combined with last two disciplines to determine structural loadings and probabilities of failure.