Research On Initial Penetration Of The Vertically Loaded Anchor

With the exploration for oil and gas reaching deeper waters,the use of floating production, storage and offloading (FPSO) facilities has increased,identifying a need for high-capacity anchoring systems. Vertically loaded anchor (VLA) has the advantages of low weight and high holding capacities, and it is installed in the same way with a drag anchor. A unique and patented system makes the anchor change from installation mode to vertical mode which results in an immediate 3.5 factor of increase in holding capacity. It is the lightest and smallest deep water anchor available on the market, and it has the business with great future.There are many studies about factors affecting the holding capacities of VLA, but the studies about the location and penetration are much less, and there is not a special method to calculate it by far. Based on the former studies and criterions, a FORTRAN program is compiled to analyze the effects on penetrations by depth of water, VLA type and soil character. As the results calculated, the initial penetration of VLA grows fast as the water grows deeper in the case of shallow water and changed little in deep water. In a certain depth of water, the initial penetration of VLA increases as the weight of VLA grows, and it is prominently deeper in the clays than that in the sand.The finite element program LS-DYNA is employed in the analyses. In the model of water penetrated, the ALE (Arbitrary Lagrangian-Eulerian) method is used to calculate it, and the curves of velocity-time and displacement-time history of the VLA are given. In the model of soil penetrated, the SPH method is used to calculate it, and the curves of velocity-time and displacement-time history of the VLA, and the propagations of strain are given. At last, conclusions are made by comparing the results of the two methods.