Penetration Mechanism and Kinematic Behavior of Drag Anchors.pdf

1、With resource exploitation reaching deep and ultra-deep waters more often, largefloating structures such as the FPSO, Spar and SEMI combining with sufficientlyeffective and reliable mooring systems are becoming increasin

2、gly popular indeepwater offshore engineering. Because of better performances both in pulloutcapacity and deepwater installation, drag anchors, including the vertically loaded plateanchors, are increasingly applied and pl

3、ay a key role in deepwater mooring systems.The penetration mechanism and kinematic behavior of the drag anchor in seabed soilsis not only a complicated engineering problem, but also an interesting topic with lotsof scien

4、tific meanings. In this dissertation, some fundamental problems that areclosely related to the penetration mechanism and kinematic behavior of drag anchorsare systematically investigated by synthetically employing theore

5、tical andexperimental methods.
　　 Firstly, a contact measurement technique, which is based on the knowledge of themotion characteristic of the drag anchor in soils, is developed and applied inmeasuring the trajectory

6、 of the anchor models. This technique is easier to perform andhas little effect on the behavior of drag anchors in soils. The measurement precisionand applicability of the technique are verified through specially designe

7、d experiments.Being an important application, the measurement technique is adopted to detect themovement direction of the anchor with an arbitrary fluke section. The present workhas demonstrated that, through model tests

8、 and employing the developed technique,the movement direction of any type of drag anchor can be effectively and easilydetermined.
　　 Secondly, five fundamental problems closely relevant to the penetrationmechanism an

9、d kinematic behavior of drag anchors, including the effects of the initial orientation of the anchor, the effects of the shank angle, the relationship between the drag distance and the anchor displacement in soil, the re

10、lationship between the fluke orientation and the drag angle at the shackle, and the movement direction of the anchor, are investigated through model experiments. By systematically analyzing the kinematic parameters and t

11、rajectories of the anchor, further knowledge of the five fundamental problems, which is believed to be beneficial to improving ourunderstanding on the penetration mechanism and kinematic behavior of drag anchors.is clear

12、ly obtained.
　　 Thirdly, an analytical method that is capable of predicting the movement directionof the drag anchor with an arbitrary fluke section in both cohesive and noncohesivesoils is developed. The analytical

13、method is verified by experiments and applied topredicting the movement direction of the anchor with rectangular and wedge-shapedsections, and clear prediction results are obtained. Some important features of themovement

14、 direction are revealed, especially the step change of the movementdirection from the unstable to the stable penetration stages due to the anchor weight.The present work proves that the movement direction of the drag anc

15、hor with anarbitrary fluke section can be reasonably determined by the developed analyticalmethod.
　　 Finally, the interactional properties between the drag anchor and the installationline are theoretically and exper

16、imentally investigated. Based on the mechanicalmodels for the embedded line and the drag anchor, analytical expressions that canpredict the drag force at the shackle in both cohesive and noncohesive soils are derived. An

17、alytical methods that can predict not only the variational property but also the exact value of the drag angle at the shackle during penetration of the anchor are also developed. In order to examine the developed analyti

18、cal methods, experimental data are adopted to compare the predicted drag force and drag angle at the shackle. Meanwhile, a detailed parametric analysis is performed to explore the effects of different parameters on the d