Reliability and storm survival of Marine Energy Converters are critical to their commercial development and deployment. The Intelligent Active Mooring System (IAMS) is a novel device intended to minimise extreme and fatigue loading in mooring lines through a non-linear loadextension curve that is variable in operation to adjust to the prevailing metocean conditions. A static model of IAMS, validated by physical model tests at the Dynamic Marine Component test facility at the University of Exeter, is used in a dynamic simulation of the performance of IAMS as part of the mooring system of the South West Mooring Test Facility buoy. A 10 m length of IAMS can reduce the rms line tension in normal operating conditions by up to 21% and the peak line tension in storm conditions by up to 21% when compared to braided nylon mooring lines. Peak line tension reductions of over 50% can be achieved if a longer IAMS unit is used. The resulting mooring system can be optimised to give load reductions in a wide range of metocean conditions; while variable pre-tension could be used for tidal range compensation or to ease access for installation and maintenance. Dear Editors, I enclose a paper submission for your consideration, which I feel is appropriate for publication in Ocean Engineering.The outcomes relate primarily to the mooring of floating Marine Renewable Energy (MRE) devices, although the results could be applicable to any moored device. The work is based on physical and numerical modelling of a recently developed active mooring system component.The results show that the ability to alter the load-extension relationship of a mooring line in operation can lead to significant reductions in the peak and fatigue loads on the mooring system and hence on the moored device. The results show that the novel system gives a clear reduction in peak and rms loads on a representative device and that the benefits can be enhanced by altering the loadextension characteristics in response to the metocean conditions. As such I believe that the work can contribute to reducing the cost of energy from MRE devices by improving reliability and storm survival. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 conditions by up to 21% when compared to braided nylon mooring lines. Peak line tension reductions of over 50% can be achieved if a longer IAMS unit is used. The resulting mooring system can be optimised to give load reductions in a wide range of metocean conditions; while variable pre-tension could be used for tidal range compensation or to ease access for installation and maintenance.

Offshore renewable energy systems are generally required to operate in exposed offshore locations for long deployment periods at low cost. This requires innovative new mooring system solutions to go beyond the existing offshore industry designs. A number of novel mooring systems have recently been proposed which decouple mooring line compliance and minimum breaking load, offering multiple benefits to designers. Demonstrating reliability for such highly novel systems where standards do not yet exist is a common problem both for mooring systems specifically and in offshore renewable applications generally. A performance and reliability test method is proposed here and is applied to a novel mooring system, the Intelligent Active Mooring System. The line stiffness and damping properties of Intelligent Active Mooring System can be optimised to the prevailing metocean conditions without compromising minimum breaking load; the pre-tension is also adjustable for tidal range compensation or for service access. The article presents the results of a feasibility study for Intelligent Active Mooring System including detailed, large-scale physical performance tests that demonstrate load reductions under normal operating and extreme sea state conditions. The rationale and findings for an accelerated reliability test regime that quantifies the ultimate load capacity of the component and gives insight into the governing failure modes are also presented. The presented test approach provides assurance for the overall system integrity.