Fatigue analysis of steel catenary riser at the touch-down point based on linear hysteretic riser-soil interaction model

• We proposed a useful riser-soil interaction model considered the depth of trench.
• Higher mudline shear strength and shear strength gradient result in lower fatigue life at TDP.
• Soil suction has a great influence on TDP's fatigue damage.
• Trench development would increase the fatigue life of SCR at TDP.

The fatigue life of a steel catenary riser (SCR) at the touch-down point (TDP) is substantially affected by its interaction with the seabed. In order to broaden the understanding of seabed effects on TDP's fatigue performance and provide more accurate fatigue life prediction in the SCRs design, the effects of the seabed characteristics on fatigue damage of the SCRs at the TDP have been studied in this paper. In this study, a new element at touch-down zone (TDZ) is created to simulate the riser-soil interaction based on the proposed linear hysteretic riser-soil interaction model. A conventional twin-pontoon semi-submersible with a particular riser geometry in the South China Sea, is adopted to evaluate how the fatigue damage was affected by the seabed characteristics. The results based on this study indicate that: ① Larger mudline shear strength and shear strength gradient corresponding to stiffer seabed lead to shorter fatigue life. ② The seabed suction effect could not be neglected in the SCRs design, since its effect on the TDP's fatigue damage is obvious and the greater suction force causes more fatigue damage. ③The deeper the trench, the less TDP's fatigue damage will be. Therefore the development of trench is in favor of longer fatigue life of the riser.