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The dynamic stiffness of polyester rope presents a complex mechanical performance, and the search for an appropriate calculation method to simulate this property is important. Distorted simulation results eventually yield inaccurate line tension and vessel offset predictions, with the inaccuracy of vessel offset being particularly large. This paper proposes a flexible calculation method for the dynamic behavior of polyester rope based on the dynamic stiffness model. A real-time varying stiffness model of polyester rope is employed to simulate tension response through rope strain monitoring. Consequently, a simulation program is developed, and related case studies are conducted to explore the differences between the proposed method and analytical procedure of the DNV standard. Orcaflex is used to simulate the results of the latter procedure for comparison. Results show the convenience and straightforwardness of the procedure in the selection of an approximate dynamic stiffness model for polyester rope, which leads to an engineering-oriented approach. However, the proposed method is related to line property, which can directly reflect the dynamic behavior of polyester rope. Thus, a flexible calculation method may provide a reference for the simulation of the dynamic response of polyester mooring systems. [ABSTRACT FROM AUTHOR]

Owing to the particularity of a polyester fiber material, the polyester mooring undergoes large axial tensile deformation over long-term use. Large axial tensile deformation significantly impacts the dynamic response of the mooring system. In addition, the degrees of large axial tension caused by different elastic moduli are also different, and the force on the mooring line is also different. Therefore, it is of great significance to study the influence of elastic modulus on the dynamic results of the mooring systems under large axial tension. Conventional numerical software fails to consider the axial tension deformation of the mooring. Based on the theory of slender rods, this paper derives the formula for large axial tension using the method of overall coordinates and overall slope coordinates and provides the calculation programs. Considering a polyester mooring system as an example, the calculation program and numerical software are used to calculate and compare the static and dynamic analyses to verify the reliability of the calculation program. To make the force change of the mooring obvious, the elastic moduli of three different orders of magnitude are compared and analyzed, and the dynamic response results after large axial tension are compared. This study concludes that the change in the elastic modulus of the polyester mooring changes the result of the vertex tension by generating an axial tension. The smaller the elastic modulus, the larger the forced oscillation motion amplitude of the top point of the mooring line, the more obvious the axial tension phenomenon, and the smaller the force on the top of the polyester mooring. [ABSTRACT FROM AUTHOR]

In order to improve the safety properties of an offloading system with side-by-side (SBS) mooring in which the FPSO is moored by a yoke system in the field of BZ25-1, it is necessary to analyze those properties. According to the experience of similar projects, tow strategies of different offloading arrangements were discussed by using the 3-D radiation/diffraction theory and quasi-static time domain method to assess their respective safety properties. Through the safety assessment analysis of different arrangement comparisons, various ways to improve the safety properties of offloading systems with side-by-side mooring were verified by analyzing the tension in the mooring lines and the fender deflection. Through comparison it can be concluded that by enlarging the key factors properly, including the size of the fenders and the hawsers as well as the number of hawsers, a better safety performance can be achieved. [ABSTRACT FROM AUTHOR]