Abrasion testing of fibre rope on impermeable fabrics for wave energy converter systems

Abstract

The NetBuoy system is being developed as means of providing low cost buoyancy, typically for use in the wave energy converter (WEC) sector where many devices rely on large, heavy and expensive fabricated steel hulls/structures to absorb the incoming wave energy.The NetBuoy system is an elegant concept in that it utilises an air pressurised impermeable buoyant pod to provide structural rigidity, which is restrained by a synthetic fibre rope net. This provides a structure that is cheaper to produce than steel equivalents and has additional benefits in terms of ease of transport to site and maintenance. However, there are a number of considerations relating to the performance of the buoy and the containing net. It is important that the net does not damage the buoy (which might lead to loss of buoyancy) as wave action may cause relative movement between net and buoy. Equally, the net must retain integrity so that the buoy does not come free from its tether (creating a shipping hazard and loss of device).This paper describes a novel test method developed to investigate the performance of a range of impermeable elastomer membranes (buoy materials) when abraded against a polyester fibre rope. It discusses the methodology of the tests and provides results of testing on a number of elastomer membrane materials, considering both wear volumes and measurement of friction between the rope and the membrane material as a means of assessing performance. Of the five materials assessed, a clear ranking of abrasive resistance in the elastomers was found on test with EPDM and Neoprene being clearly better than all other materials. Natural rubber performed well, whilst Hypalon and Nitrile were found to be least resistant to abrasion from the rope. In all tests the rope was largely unaffected by the abrasion.