Precisely predicting the fatigue life of taut-wire mooring systems has become an interesting and important problem for scientists and engineers since there are still difficulties in the inspection and maintenance of mooring lines in a rough sea environment especially in deep waters. In this paper, a comprehensive fatigue analysis is performed for a polyester taut-wire mooring system of an FPSO based on the time domain dynamic theory, rainflow cycle counting method and linear damage accumulation rule of Palmgren-Miner. Three influential factors in the fatigue analysis including the pre-tension, dynamic stiffness and T-N curve are investigated in detail. Two polyester T-N curves, one is from the DNV-OS-E301 and the other is from the API-RP-2SM, are adopted in the calculation. The fatigue analysis of the mooring system after one-line failure is also carried out. The calculation results indicate that the fatigue life is significantly affected by the T-N curve. The fatigue life decreases with increasing pre-tension, and is largely reduced if taking into account the dynamic stiffness caused by cyclic loading. The analysis also proves that one-line failure has remarkable effects on the fatigue lives of other mooring lines. The present parametric and comparative study is believed to be meaningful to further understanding of the taut-wire mooring system for deepwater applications.

Solid particle erosion in piping systems is a serious concern of integrity management in the oil and gas production, which has been widely predicted by the numerical simulation method. In the present work, every step of the comprehensive procedure is verified when applied to predicting the bend erosion for gas flow, and improvements are made by comparing different computational models. Firstly, five turbulent models are implemented to model the flow field in a 90 degree bend for gas flow and examined by the static pressure and velocity profile measured in experiments. Secondly, the particle velocities calculated by fully coupling and one-way coupling are compared with experimental data. Finally, based on the knowledge of flow modeling and particle tracking, four classic erosion equations are introduced to calculate the penetration rates in a 90 degree bend. By comparing with the experimental data available in the literature, it indicates that the k–ε model is the most accurate and effective turbulent model for gas pipe flow; the fully coupling makes the simulation of particle motion closer to measured data; and the Grant and Tabakoff equation presents better performance than other equations.

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