Numerical study on the performance of a novel gravity installed anchor with ring fins in clay

Abstract

A novel gravity installed anchor with ring fins (RGIA) is proposed in the present work, which combines features of the conventional gravity installed anchor (GIA) and the drag embedment plate anchor, with two soft shanks attached to the anchor body. A systematic study on the performance of the RGIA in clay is performed by large deformation finite element analyses using the coupled Eulerian-Lagrangian technique (CEL), with emphasis on the initial penetration, the behaviors of keying, diving and pulling out, the optimization of the shackle point, and the effect of loading rates on the maximum embedment loss (MEL). The initial penetration of the anchor is simulated under various impact velocities, from which the maximum initial embedment depth in the seabed is acquired. Two factors of the shackle point, en and eh, are defined and the detailed criteria for optimizing the shackle point are put forward. A series of analytical cases are designed to thoroughly explore the effects of the shackle point on the performance of the RGIA in clay, focusing on the keying and diving behaviors and the pullout capacity. The formulas for calculating the diving angle and the MEL are then constructed with high precision, by taking into account the effect of the shackle point, and can be utilized to optimize the position of the shackle point. Comprehensive drag effects under multiple factors, especially the high loading rate, on the performance of the RGIA in clay are quantitatively investigated by performing six groups of cases, from which the effects of drag velocity, initial embedment depth, gradient of shear strength of clay, and cable parameters can be known. The formula for calculating the MEL of the RGIA in clay is also constructed with high precision by taking into account comprehensive drag effects. The numerical study demonstrates that, compared with the OMNI-Max anchor, the RGIA achieves deeper initial penetration depth during installation, requires shallower initial penetration depth that ensures subsequent keying and diving, and possesses stronger ability of resisting dynamic loading with high loading rates.