The influence of internal solitary wave on semi-submersible platform system including mooring line failure

Abstract

As a primary catastrophic factor, an internal solitary wave (ISW) is typically characterized by a large amplitude and a long duration, which can cause severe damage to deep-sea platforms due to large drift or the rupture of mooring lines. In this paper, a secondary development of ANSYS AQWA was performed to study the dynamic response of the platform system under the combined action of surface wave load and ISW load. Then, mooring line failure under the ISW was analysed, and the differences between the simultaneous and progressive failure of the two mooring lines were compared. Numerical simulation results showed that under the action of the ISW, the movements of the platform and the tensions of mooring lines markedly increased. The low-frequency slow-drift motion under the combined action of the ISW and a regular wave was less than that under the action of the ISW. Mooring line failure worsened the movement of the platform and the mooring line section tension under the ISW. However, the transient responses of the platform caused by the progressive failure of two mooring lines were less than those caused by the simultaneous failure.