Numerical investigations on load transfer of mooring line considering chain–seabed dynamic interaction

Abstract

Taut or semi-taut mooring lines are often used in deep-sea area to connect the floating structures to the anchors in the seabed. In previous studies, the quasi-static analysis method was adopted to assess the load transfer of the mooring line. However, the inertia effect of mooring line and chain–seabed dynamic interaction cannot be neglected in practice. In this paper, the soil strain rate effect was incorporated in the chain–seabed dynamic analyses, and the load transfer mechanism of mooring line was investigated based on the proposed model. The numerical model was firstly verified with the quasi-static analysis results and experimental data under dynamic condition, and then the contributions of different forces to the variations of line tension were evaluated. It is found that two factors (inertia force and soil resistance) have a great influence on the mooring line tension variation. The inertial effect is dominated under high-frequency condition, and the maximum line tension at the fairlead is larger than that under static condition. However, the tension at the pad-eye under dynamic condition always has a certain increase. The reason is that partial reverse soil resistance under dynamic condition increases the tension at the pad-eye.