Fibre Rope Mooring

The main elements can be listed as follows: 1. Research enabling a detailed design of a mooring system based on a combination of polyester ropes, clump weights, buoyancy elements and chains for the OO Star floaters, two water depth (150m and 800m) and two climates (North Sea and tropical). 2. Research based as above for a taut leg system using nylon ropes. Important issues here are long term properties of nylon ropes considering its life time and maintenance and the qualification and testing of the nylon ropes which have been in progress for some time without much disclosed information. Other issues which also need to be addressed are related to seafloor contact and effect of protective coating. 3. Research based on 'Honeymooring' system of polyester ropes with shared rope and anchor, which was patented by SEMAR. 4. Nylon rope test by DNV Bergen.

The outcome of the project will be 3 different mooring systems, with different degrees of maturity and novelty. The first system is based on previous work, resulting in a system that can be utilized in commercial wind farms in the near future. The two other systems are ready after two and three years, respectively, and have a higher degree of novelty and cost reduction potentials. The companies involved in the project will gain knowledge about these particular systems, products will be matured, and the industry as a whole will be able to offer more effective mooring systems to commercial floating wind farm developers. A materials data base and improved simulation tool will improve the future engineering of mooring systems. Nylon rope property test were performed at DNV Berger. the test data were used to establish the material data base and improved simulation tool. Switching to fiber ropes is one way of obtaining significant cost reductions on the mooring system. This can help opening a vast market for floating wind farms, benefiting not only the companies involved in this project, but the whole offshore industry.

The Fiber Rope Mooring project (FIRM) aims to develop innovative mooring systems for floating wind farms based on fiber ropes, together with new and more efficient methods for installation, condition monitoring, maintenance and decommissioning. Compared to catenary chain systems, earlier research shows a cost reduction potential around 50%. The main deliverables are (i) a polyester rope mooring system with clump weights and buoyancy elements, (ii) a nylon rope taut leg system, possibly with shared anchors, and (iii) an innovative mooring system developed in this project. A diverse group of research institutes, engineering companies, rope manufacturers and offshore equipment suppliers also perform supporting work packages on rope properties database, rope property testing, simulation tool development with advanced material models, condition monitoring and maintenance, anchors and soil/structure interaction and power cable aspects. The main R&D challenges are related to the material properties of fiber ropes. The force-elongation properties have contributions from instant-elastic-, visco-elastic-, construction-, and visco-plastic-stretch. Obtaining material data that describe these aspects and modelling this behavior when computing the loads will be addressed by compiling and obtaining data by experiments and implementing advanced material models in the aero-servo-hydro-elastic simulation tool 3dfloat.