The influence of load history on synthetic rope response

Abstract

Although used for the station-keeping of offshore equipment for several decades, synthetic ropes have only recently been used for marine renewable energy (MRE) devices. The fundamental mooring load differences between these two applications necessitate the detailed quantification of mooring component performance. Of particular importance for lifecycle analysis, installation and maintenance operations is the evolution of synthetic component performance over time due to load history and fatigue mechanisms. Changes to the stiffness and damping properties of these materials will affect the global response of the device if the mooring system and device responses are closely coupled. To address these uncertainties, tension experiments have been conducted on Nylon parallel-stranded rope samples at IFREMER as part of a MERiFIC (Marine Energy in Far Peripheral and Island Communities) consortium. Measurements are reported from tests involving three new samples subjected to a mixed creep/relaxation and harmonic loading regime. Different initial bedding-in levels are used to investigate the influence of load history on the immediate quasi-static and dynamic properties of the rope. For the load regimes studied, it is found that the rope condition with respect to the load-strain characteristic has a strong influence on the performance of the line.