This paper discusses several new technologies for mooring floating marine energy converter (MEC) devices, such as wave energy generators, tidal current turbines and floating wind turbines.The principal mooring component is a special nylon fiber rope which provides cyclic tension fatigue endurance much superior to that of conventional nylon ropes. The nylon fiber is treated with a new proprietary coating which has excellent wet yarn abrasion properties. The parallel-subrope type rope construction further reduces internal abrasion.Extensive laboratory testing was carried out on this new nylon rope design. Cyclic tension fatigue tests were conducted at mean loads and load amplitudes typical of actual service conditions and at higher mean loads and amplitudes. These tests demonstrate that the special nylon rope has essentially the same, desirable stretch characteristics as conventional nylon rope and has much better endurance performance.The mooring connection to the floating MEC device consists of a high-modulus fiber rope pendant which passes through a low-friction bell-mouth nylon fairlead on the MEC device. This eliminates the use of heavy, unreliable chain in this critical connection.A unique bag anchor system would be used on sand, clay, rock and other sea beds in which conventional drag embedment anchors and driven piles are impractical. The bag anchor consists of a large abrasion resistant carcass with lifting straps and top closure. The bag is transported to site in a collapsed form and is filled with local sand or aggregate to provide ballast weight. Several or many such bags are enclosed within a fiber rope net for deployment and are grouped together for connection to the mooring line.The paper will be of particular interest to designers of moorings for MEC systems in shallow water and severe wave environments. It will also be of interest for other mooring applications.

SummaryThis paper brings together two experiences from TTI (Tension Technology International) and the UoE (University of Exeter) and aims to quantify the damage that could be experienced by fibre mooring lines during the transit and commissioning phase of Marine Renewable Energy (MRE) devices.1. While deploying a new prototype of anchoring system for a MRE device, UoE experienced the failure of a new polyester mooring line during transit to site (90 minute duration). A thorough visual inspection supported by Scanning Electron Macroscopy (SEM) analysis and tensile test have established the physical conditions of the fibre rope before its failure.2. Wear testing led by TTI has investigated and established a relation between the degree of abrasion sustained and the residual strength of Dyneema ® fibre ropes. The ropes were submitted to friction forces via cycling over a roller and a fairlead with different abrasive surfaces (from 7.6 to 254.3μm). Negligible wear occurred with the low roughness surfaces and very high wear at the higher roughness surfaces.The load experienced by the polyester line during the deployment of the anchoring system was simulated with the software OrcaFlex TM . Dynamic modelling using representative conditions indicates that the polyester mooring line was loaded between 3 and 20% of its Minimum Breaking Load (MBL) which is well below the design load of the rope. IntroductionTo date there are only a few MRE designs which have achieved a pre-commercial development status. Experience in deploying such devices and specific guidance are missing. The approach of designers is thus conservative and based on the offshore oil and gas industry and anecdotal evidence [4].The use of synthetic fibre ropes for mooring systems has seen a sudden rise in marine applications over the last two decades [5] albeit mainly for deep water mooring [6]. Experience and feedback from the use of polyester ropes for MRE device moorings is still limited in terms of publications produced. This paper focuses on the commissioning phases of MRE devices, with a specific focus on the deployment of a novel anchoring system. Handling, lifting and rigging of mooring lines could result in damage during transport or installation as discussed in [7] and [8]. The strength of a rope will inevitably degrade from mishandling. Several research programs have been carried out to investigate the abrasion and twisting damage by rope manufacturers for towing systems. For example incorrect handling during transport could cause significant damage to the rope due to abrasion and the application of sudden high loads is one of the most severe conditions that a rope can experience [9].Certification standards and specific test methods have been developed to test the abrasion resistance of yarns [10] - [11]. The abrasion mechanism was described in [12] as a sequence of fibre peeling induced by surface shear forces. However the abrasion resistance of a fibre rope is not determined by standards and knowledge is only based on empirical test data.The exte...

Offshore foundations are typically designed to resist mooring loads coming from a single direction. This paper provides some insights into the geotechnical challenges associated with anchor sharing (i.e. where mooring loads are coming from multiple directions to one anchor) for Offshore Renewable Energy (ORE) applications. Firstly, the multidirectional mooring load conditions on shared anchors are characterised for cases with one, two and three mooring lines connections. Secondly, multi-directional loadings applied on a caisson foundation in a geotechnical centrifuge facility showed large capacity reduction and large displacement of the foundation at large loading angle. Thirdly, multi-directional simple shear tests have showed that volumetric contraction increases as the degree of shear stress reversal increases. Lastly, the results from the soil element tests are brought into discussion with the physical modelling results to identify the foundation’s response to multi-directional loading.

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