The cyclic contact of the SCR with the seabed soil causes progressive remoulding and degradation of the seabed soil stiffness. This process results in gradual embedment of the SCR into the seabed and developing a trench several diameters deep underneath the riser. The oscillating SCR tries to progressively achieve an equilibrium between the trench geometrical profile and the seabed soil stiffness evolution in the touchdown zone through a complex process. Several studies have used different trench modeling approaches to investigate the trench effect on fatigue. However, contradictory observations have been reported with no coherent agreement on the beneficial or detrimental effect of the trench on fatigue. In this study, the significance of trench geometry in fatigue damage evaluation was investigated against the seabed stiffness degradation effect. It was observed that the geometrical riser profile dominates the effect of seabed stiffness degradation on many occasions. This strengthened the probability of the case dependency of the peak damage accumulation and its significant dependence on the direction of the low-frequency vessel excursions.
Hodjat Shiri and Rahim Shoghi
Keywords: Steel catenary risers, Riser-seabed interaction, Touchdown point, Trench profile, Fatigue response
Publisher: DFI