Durability of Polyester Ropes Used as Deepwater Mooring Lines

This paper discusses recent advances in understanding how the length of a fiber rope changes under various tension conditions and histories. The change-in-length characteristics of polyester rope can be completely represented by six properties: original stiffness, static stiffness, dynamic stiffness, construction strain, polymer strain, and working strain. This is called the 6 CILP method.This paper describes how to use the 6 CILP method to calculate fiber rope deepwater platform mooring system performance parameters, such as moored platform offset, highest mooring line load, and line length at end of service. The test method for these properties is discussed in the companion paper "Testing Polyester Fiber Rope for Six Change-in-Length Properties (6 CILP)."Using the 6 CILP method, the stretch of the mooring line and thus its overall length can be calculated at a given time and at a given tension. The spring rate of the mooring line can be calculated under various conditions, for example, before and during cycling. The peak and trough tensions and the maximum platform offsets can be calculated under various conditions, for example, during an extreme storm event. The properties can thus be used to analyze the performance of the fiber rope design in any mooring system and in any environment.The paper will be of interest to all designers of fiber rope systems. It will be of particular interest to deepwater mooring system designers. INTRODUCTIONThis paper presents the results of tests conducted on a polyester rope in the DNV industry-sponsored JIP "Improving Fiber Mooring Design Practices". 1, 2 Further information on that JIP, including the test method for determining the six change-in-length properties (6 CILP) and the actual properties for a particular polyester rope, are given in the companion paper. 3 The six properties were discussed in detail in several earlier papers. 4, 5, 6This paper describes how to use the 6 CILP method to calculate important mooring system performance parameters. The lengths of mooring lines are calculated both during and immediately after installation. The maximum and minimum mooring line tensions experienced during maximum storm-induced platform offset are calculated. These can also be used to calculate fatigue of mooring line components. The mooring line length at the end of service life is also calculated.

show abstract

A Study on Creep Effect of Synthetic Fiber Rope Mooring System on Motion Response of Vessel and Tension of Mooring Line

Park¹,

Lee²,

Kang³

2017

Journal of the Society of Naval Architects of Korea

View full text Add to dashboard Cite

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Growing demand and rapid development of the synthetic fiber rope in mooring system have taken place since it has been used in deep water platform lately. Unlike a chain mooring, synthetic fiber rope composed of lightweight materials such as Polyester(polyethylene terephthalate), HMPE(high modulus polyethylene) and Aramid(aromatic polyamide). Non-linear stiffness and another failure mode are distinct characteristics of synthetic fiber rope when compared to mooring chain. When these ropes are exposed to environmental load for a long time, the length of rope will be increased permanently. This is called 'the creep phenomenon'. Due to the phenomenon, The initial characteristics of mooring systems would be changed because the length and stiffness of the rope have been changed as time goes on. The changed characteristics of fiber rope cause different mooring tension and vessel offset compared to the initial design condition. Commercial mooring analysis software that widely used in industries is unable to take into account this phenomenon automatically. Even though the American Petroleum Institute (API) or other classification rules present some standard or criteria with respect to length and stiffness of a mooring line, simulation guide considers the mechanical properties that is not mentioned in such rules. In this paper, the effect of creep phenomenon in the fiber rope mooring system under specific environment condition is investigated. Desiged mooring system for a Mobile Offshore Drilling Unit(MODU) with HMPE rope which has the highest creep is analyzed in a time domain in order to investigate the effects creep phenomenon to vessel offset and mooring tension. We have developed a new procedure to an analysis of mooring system reflecting the creep phenomenon and it is validated through a time domain simulation using non-linear mooring analysis software, OrcaFlex. The result shows that the creep phenomenon should be considered in analysis procedure because it affects the length and stiffness of synthetic fiber rope in case of high water temperature and permanent mooring system.

show abstract

Durability of Polyester Ropes Used as Deepwater Mooring Lines

Cited by 3 publications

References 4 publications

Research on the Viscoelasticity of Polyester Mooring Lines Using the Absolute Nodal Coordinate Formulation

Research on the Viscoelasticity of Polyester Mooring Lines Using the Absolute Nodal Coordinate Formulation

Use of six change-in-length properties (6 CILP) in designing fiber rope mooring systems

A Study on Creep Effect of Synthetic Fiber Rope Mooring System on Motion Response of Vessel and Tension of Mooring Line

Contact Info

Product

Resources

About