Key Techniques in Simulating Comprehensive Anchor Behaviors by Large Deformation Finite Element Analysis

With the application of innovative anchor concepts and advanced technologies in deepwater moorings, anchor behaviors in the seabed are becoming more complicated, such as 360-degree rotation of the anchor arm, gravity installation of anchors with high soil strain rate, and keying and diving (or penetration) of anchors. As a very important component of the installation or mooring system, anchor line connects the anchor and the anchor handling vessel (AHV) or floating moored platform. With moving of the AHV or platform, anchor line produces a space movement, and forms a reverse catenary shape and even a three-dimensional profile in the soil. Numerical analysis on the behaviors of anchor lines and deepwater anchors requires techniques that can deal with large strains and deformations of the soil, track changes in soil strength due to soil deformation, strain rate and strain softening effects, appropriately describe anchor-soil friction, and construct structures with connector elements to conform to their characteristics. Being an effective tool of large deformation finite element analysis, the coupled Eulerian-Lagrangian (CEL) method is advantageous in handling geotechnical problems with large deformations, where a traditional Lagrangian analysis is coupled with an Eulerian phase of material advection. This paper gives an overview of several key techniques in the CEL analysis of comprehensive behaviors of deepwater anchors, including construction of the embedded anchor line and the anchor line in the water, installation of gravity installed anchors (GIAs), keying or diving of drag anchors and GIAs, and implementation of the omni-directional arm of GIAs. Numerical probe tests and comparative studies are also presented to examine the robustness and accuracy of the proposed techniques. The aim of this paper is to provide a numerical framework to analyze the comprehensive behaviors of anchor lines and deepwater anchors.