ABSTRACT

Torpedo anchor is a promising novel offshore anchor foundation for deep-water floating facilities due to its efficient and economical installation. The pullout resistance of torpedo anchor is thus key for the stability of mooring system. The pullout performance of torpedo anchor is highly dependent on the loading angle, anchor embedment depth, seabed soil and the mooring line connected due to the complex interaction of mooring line, anchor and seabed soil. However, most of the existing studies focused only on the pullout capacity of torpedo anchor under vertical or inclined loading, there is a lack of deep understanding on the effect of anchor line on pullout capacity. Given that the anchor pullout response is important for the mooring system failure and the mooring line-soil interaction is largely involved in the anchor continuous pullout, the current study focuses on the pullout performance of torpedo anchor in clay with investigating the effect of the interaction mechanisms of mooring line and soil. Three dimensions large deformation finite element (LDFE) analyses using Coupled Eulerian-Lagrangian (CEL) method in ABAQUS were conducted to investigate the effect of mooring line on pullout performance of torpedo anchor. The model considers the failure of the mooring line and anchor under different motion angles at drag point of mooring line. It is found that the state of mooring line affects largely the anchor loading angle and anchor posture and thus the anchor capacity in mooring. It is more reasonable to evaluate the anchor capacity considering practical line angle at padeye and anchor inclination with considering the line effect.

INTRODUCTION

A dynamically installed anchor is a promising novel offshore anchor foundation for deepwater floating facilities due to its economic installation and high capacity. Torpedo anchor is one of the main types of dynamically installed anchor, which has been used in the Campos Basin and the North Sea (Brandão et al., 2006; Lieng et al. 2010). It is a torpedo-shaped anchor that is dropped at a preassigned height above seabed and penetrates into seabed with the depth of up to 3 times anchor length under its self-weight. The mooring line is connected to the padeye at anchor top to transfer loadings from floating structures to anchor. The pullout resistance of torpedo anchor is thus key for the stability of mooring system.

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