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The load-elongation properties of polyester ropes are often modelled through a static-dynamic model with parameters based on different proposed test procedures, which may not be sufficient for the mooring analysis since the stretch response to tension of fiber ropes is nonlinear. In the Syrope Joint Industry Project, a new procedure for tension vs. stretch testing of polyester ropes for mooring applications was developed. The test allows for determining parameters in a rope model, which was developed in the JIP, where the length and dynamic stiffness of the rope are given by the actual mean tension and the previous highest mean tension in each mooring line. Test results from this new procedure have been compared with results from the test procedures provided in API, ABS and ISO documents. All tests were performed on samples from the same sub-rope. Differences and similarities between the different test procedures and analysis methods have been investigated.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA spring-dashpot model is proposed to represent the change-in-length properties of polyester fiber rope. The model comprises four units arranged in series -a dashpot representting long-term creep, a spring-ratchet unit representing construction stretch, a spring-dashpot unit representing response to slow loading, and a spring representing response to fast loading. The change-inlength characteristics of the rope under any sequence of loading can be described using the model.The spring-dashpot model is not intended to be used directly for design analysis of mooring systems. Instead, the model is intended to represent fundamental changein-length characteristics of the rope. These characteristics can be presented in tables, graphs or equations which can then be used in calculations or computer simulations of mooring system response.The characteristics of the model's four units and thus the fundamental change-in-length properties of the rope can be determined by a series of short tests which need only be performed once for a particular rope design. Once these fundamental properties are determined, they can then be used without further testing to calculate the change-in-length performance of that rope in response to various installation, operational, and extreme-event (e.g. loop current or hurricane) sequences.These fundamental properties can be used in preliminary design, final design, and in-service analyses. If deemed necessary, the properties can be confirmed after the rope design has been selected by conducting additional tests on a prototype rope using the actual (expected) loading sequence. This approach will avoid time-consuming and costly testing of alternate rope designs during preliminary design.The model concept, the test method, and the calculation procedure are now being developed and verified as part of a JIP. The model is being tested on components of large polyester ropes typically used in deepwater mooring lines. The test method and calculation procedure will be documented as a DNV Offshore Standard.This paper will be of interest to mooring system designers, platform operators, rope manufactures and users, and regulatory agencies.

The objective of the Syrope JIP has been to improve the methods for safe and reliable design of fibre rope mooring systems. Normal, conservative, design practice for polyester rope mooring systems is to use an upper and a lower bound axial stiffness of the polyester. The use of a more advanced, but still manageable design practice allows for a more optimized design. Only polyester lines have been covered by the work, but the principles are assumed to have a general validity. Extensive testing on change-in-length behavior has been performed on subropes. Testing has covered recommended test procedures from different standards and recommended practices and more realistic load sequences. Based on test results a conceptual model for the behavior of polyester ropes has been developed. The mean length of a rope depends on the preceding highest mean tension in the rope and the actual tension, including its mean value. The response to wave-frequency and low-frequency loads is described by a dynamic stiffness which increases with the mean load in the line. Recommended change-in-length testing of subropes is described, and principles for analysis of such tests for identification of parameters in the model are presented. Finally, guidance for use of the model in mooring system analyses is given.

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 a multi-step test procedure to measure these six properties. The tests need only be performed once for a particular rope design. The measured properties are generally independent of the rope size and strength. Thus they can be applied to any rope of the same fiber material and construction. The measured properties are not unique to the loading history used during testing. Thus they can be used to predict the rope performance under any tension condition and history. The calculation procedures are described in the companion paper "Use of Six Change-in-Length Properties (6 CILP) in Designing Fiber Rope Mooring Systems." This paper briefly describes the test program which was conducted to develop the test methods. It describes how the change-in-length properties are calculated from the test results. It also presents the properties which were determined for a particular type of polyester rope.The paper will be of interest to makers and users of polyester and other synthetic fiber ropes. It will be of particular interest to designers of deepwater mooring systems. 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 The JIP was sponsored by a group of owners and operators of moored deepwater platforms, listed in the Acknowledgments at the end of this paper. The change-in-length properties were discussed in several earlier papers. 3, 4, 5 Use of the properties in mooring system design is described in a companion paper. 6 The objective of the JIP was to develop a universal test method to determine the change-in-length properties of fiber rope. The results should be usable for any mooring system design scenario. The method should adequately predict: installation length, dynamic stiffness, extreme force and extreme length. The method should be simple and of short duration.