A Review of Fatigue Curves for Mooring Lines

2005 ◽  
Author(s):  
Ronaldo Rosa Rossi
Keyword(s):  
Production Systems ◽  
Steel Wire ◽  
Fatigue Curve ◽  
Breaking Load ◽  
Fatigue Tests ◽  
American Petroleum Institute ◽  
Mooring Lines ◽  
Wire Ropes ◽  
Oil Rig ◽  
Quality Chain

For mooring chains of offshore floating production units, API (American Petroleum Institute) recommends the use of its TxN fatigue curve considering the MBL (Minimum Breaking Load) of an ORQ (Oil Rig Quality) chain even if the chain has a higher grade. This curve has been used in mooring system design of offshore floating production units since the draft edition of API Recommended Practice for Design, Analysis and Maintenance of Catenary Mooring for Floating Production Systems in May 89 and several fatigue tests have been done by petroleum industries, chain manufacturers and research centers. Those fatigue tests show that the use of the MBL of an ORQ chain for higher grades is a conservative assumption. This paper will present an overview of the fatigue curves of materials for mooring lines: stud and studless chains, steel wire ropes and polyester fiber ropes. This overview is based on recent tests, rules and published papers.

TN X SN Fatigue Curves for KS Hook and Chain Using Finite Element Modelling

2006 ◽  
Author(s):  
Jose´ Carlos Lima de Almeida ◽  
Ronaldo Rosa Rossi ◽  
Ricardo Sobral
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Finite Element Modelling ◽  
Fatigue Curve ◽  
Breaking Load ◽  
Wire Rope ◽  
American Petroleum Institute ◽  
Oil Rig ◽  
Quality Chain

For mooring chains of offshore floating production units, API (American Petroleum Institute) recommends the use of its TxN fatigue curve considering the MBL (Minimum Breaking Load) of an ORQ (Oil Rig Quality) chain even if the chain has a higher grade. DNV (Det Norske Veritas) recommends the use of SxN fatigue curve where the stress is taken using the tension over the nominal area of the chain or wire rope. So it is easy to convert this SxN curve to a TxN curve or vice-versa. The geometry of the chain or wire rope and the material are implicit considered. To develop SxN curve for new accessories design it is necessary the using of FEM (Finite Elements Method) to obtain the distribution of stresses and strains and the stress concentration factor and the SxN curves of the material. The analysis of the tension and the stress concentration factor will be used to obtain the slope and intercept parameters of the fatigue curve. This paper will present the study developed for KS hook and how to obtain the fatigue curve for this accessory based on published papers, rules and recent tests.

scholarly journals Numerical Modelling for Synthetic Fibre Mooring Lines Taking Elongation and Contraction into Account

2021 ◽  
Vol 9 (4) ◽  
pp. 417
Author(s):  
Ivan Ćatipović ◽  
Neven Alujević ◽  
Smiljko Rudan ◽  
Vedran Slapničar
Keyword(s):  
Synthetic Fibre ◽  
Steel Wire ◽  
Three Dimensional ◽  
Weight Ratio ◽  
Coupled Model ◽  
Mooring Line ◽  
Outer Diameter ◽  
Mooring Lines ◽  
Wire Ropes ◽  
Coupled Dynamic Analysis

Synthetic fibre mooring lines are used as an alternative to traditional steel wire ropes due to their higher strength to weight ratio. Benefits are also found in relative ease of handling, and therefore the marine industry has largely accepted this type of mooring line. By rules and regulations, the design of mooring lines should be based on a coupled dynamic analysis of a particular mooring system and moored vessel. This approach incorporates damping and inertial forces (i.e., hydrodynamic reactions) acting directly on the mooring lines due to their motion through the seawater. On the basis of the outer diameter of the synthetic fibre rope, the Morison equation gives estimations of the mooring line hydrodynamic reactions. In comparison to the traditional steel wire ropes, the synthetic mooring lines usually have relatively larger elongations and consequently larger reductions of the outer diameter. Furthermore, the lower diameter certainly leads to reduced values of damping and added mass (of mooring lines) that should be considered in the coupled model. Therefore, the aim of this study was to develop a new numerical model that includes diameter changes and axial deformations when estimating the hydrodynamic reactions. The development of the model is carried out with a nonlinear finite element method for mooring lines with the assumption of large three-dimensional motions. The obtained results show the effectiveness of the newly developed model as a more accurate approach in calculation of hydrodynamic reactions.

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