Synthetic rope responses in the context of load history: The influence of aging

Abstract

In order to design marine renewable energy mooring systems which are both economical and durable it is necessary to establish the lifecycle performance of individual components. In parallel with numerical tool development, physical component testing utilising realistic load cases is pivotal in achieving a greater understanding of performance variations including the contribution of degradation mechanisms. Building upon previous experimental tests conducted by the authors, tension-tension tests were conducted on a sample used in rst part of the study and samples extracted from a mooring line which was deployed for 18 months with the South West Mooring Test Facility. In agreement with the rst part of the study it was found that sample axial stiness and damping are inuenced by load history and instantaneous strain. The increased compliance, lower load bearing capacity and reduced tension-tension fatigue performance of aged specimens are symptomatic of bre-on-bre abrasion damage sustained in service. Visual inspections of the rope and yarns including scanning electron microscope analysis of bres revealed that abrasion wear was accelerated by debris found within the rope structure, highlighting the importance of preventing particle ingress. Datasets are provided to facilitate the development of rope and mooring system simulation tools.

Synthetic mooring ropes for marine renewable energy applications

“…Yarn-on-yarn cyclic tests are also conducted to determine the eectiveness of friction-reducing marine nishes [63,10] using the equipment shown in Figure 6d). In addition, experimental studies such as those conducted by Derombise et al [64] and Weller et al [65] have investigated the long-term behaviour of seawater-aged bres, focusing on aramid and nylon respectively. In Ref.…”

“…Comparative dynamic tensiontension rope and accelerated yarn-on-yarn tests were conducted on new and aged samples in Ref. [65] to investigate the eect of aging on component performance and durability.…”

“…Hence, the standard practice of applying thousands of harmonic load cycles to samples in order to determine material properties or to inform fatigue life calculations is debatable for MRE applications in which device responses and mooring loads are highly irregular (of varying amplitude, phase and mean load). An alternative approach could be the application of load cases based on measurements recorded in-service [68,18,65]. Certication guidance such as [44,3] species the use of non-linear load-extension characteristics in mooring system analyses.…”

“…Tension-tension fatigue is an eect caused by wear occurring due to friction between adjacent bres during repeated load cycling [77,65]. The ingress of particles of grit, debris and marine species into the rope structure will accelerate wear from bre-on-bre friction and even bre cutting may occur if hard-shelled species (e.g.…”

Numerical model validation for mooring systems: Method and application for wave energy converters

“…The drag and inertia coefficients for the mooring lines were taken from DNV standards 174 [14] for the nylon lines and from the Orcaflex™ manual [15] for the chains. The axial stiffness of three samples extracted 175 from the used model rope was quantified using tension testing equipment at Ifremer [16]. The yarns demonstrated axial 176 stiffness values between 10.0 and 12.6 kN when subjected to scaled (by N/Tex) loading using a 25 s oscillation period.…”