Research On Prediction Method Of The Kinematic Trajectory For Drag Anchors

With the exploration for oil and gas reaching deeper waters and the use of FPSO (floating production, storage and offloading) facilities increasing, more and more research focus on high-capacity anchoring systems. New types of drag-in plate anchors have become a kind of mooring foundation applying for the deep water mooring system in the international offshore engineering at present. The anchors reach the ideal state when they subject to a vertical load, which means that the orientation of the mooring force is normal with the anchor plate. In their normal loading mode, they act like embedded plate in seabed with high pull-out capacity. This high pull-out capacity mostly relay on the loading position of the anchor in the seabed including the orientation and embedment depth. Essentially speaking, to estimate the trajectory of the drag anchor accurately is the precondition and base of assessing the ultimate pull-out capacity.New types of drag-in plate anchors have larger area compared with conventional drag anchors, and they subject to vertical loads in the working state. However, there are no substantial differences in the installation procedure and embed mechanism. So the academic acheivements of conventional drag anchors embedment research can be also applied for the new type drag anchors to a great extent.In this dissertation, a reliable measurement system of sensing devices is designed to get the dynamics parameters accurately for the model test. Firstly, the moving model excluding the influence of the soil pressure on the anchor chain is put forward according to the moving process of the anchor in the soil, which means that the anchor performs circle motion around the terminal point of the anchor chain taking the length of the drag line as the radius. Secondly, the inverse catenary equation considering the influence of the soil pressure to the anchor chain is educed, considering the assumption of small anchor chain angle. Lastly, the concept of"equivalent length"is put forward to revising the ideal state to get the trajectory equation. Then the anchor kinematic trajectory equation will be analyzed by changing the parameters.