Numerical prediction of potential 3-dimensional seabed trench profiles considering complex motions of mooring line

Seabed trenches near deep-sea anchors bring risks to the mooring system's safety. The prediction of 3-dimensional (3-D) trench profiles is a key task to reduce the risk. However, the trench width related to the trench wall collapse and lateral movement of the mooring line has not been well studied. This paper first proposes a 3-D mooring line-seabed dynamics model to consider the mooring line lateral movement in the soil. Then, a seabed trenching model to simplify 3-D trench profiles is developed based on the field data. By combining the above models, a novel method to predict 3-D trench profiles around embedded mooring lines is established by considering trench wall collapse and integrating dynamics of mooring line. Based on the verified method, both static and dynamic responses of mooring lines are investigated, then a series of parametric sensitivity studies are carried out. The simulation results reveal that dynamic movement of mooring lines at fairlead may result in remarkable seabed trenches, and lateral motion of mooring lines enlarges the disturbed zone near the mooring line touchdown area. The proposed method in this paper provides a reasonable assessment of the 3-D trench profiles and reduces risks in the operation of mooring systems.