Numerical Simulation Of The Penetration Depth Of Dynamic Penetration Anchors In Clay

With the exploration of oil and gas moving from continental shelf to deep water, the floating and semi-submersible platform is more suitable for deep sea than the traditional gravity platform. When the floating and semi-submersible platform is in an operating state, it needs mooring systerm to position in a certain range. Dynamic penetration anchor (DPA) is a newly developed mooring anchor to provide mooring capacity for mooring systems. Owing to its anvantages of convenient for transportation and installtion, cost-effective and high bearing capacity, DPA has been widely deployed in offshore engineering. As DPA is a kind of mooring anchor installed through self-weight to penetrate into the seabed, its uplift capacity largely relies on its penetration depth. It is not long since DPA is developed, so there are still some dificiencies in the current research on its penetration depth. This thesis employed finite element analysis (FEA) to investigate the scale of parameters of the differential equations for DPA's motion response and improve the prediction formula for DPA's penetration depth. Then, the influence of strain-rate effect on the embedment depth of DPA was investigated through the differential equation for DPA's motion response on the basis of the summary of the previous study about stain effect parameters. Thus, this research is helpful to further understand the factors that affect DPA's penetration depth, and provide technical support and theoretical guidance for the design and installation of DPA.The first part of the thesis studied the bearing capacity factor of rectangular footing with various aspect ratio and embedment ratio in clay through small strain finite element ananysis. The finite element analysis model of this thesis was validated by comparing the limit bearing capacity of the rectangular footing in shallow embedment ratio with the previous study. Then, the bearing capacity of rectangular footing with high embedment depth up to 150 was investgiated. The result of the study shows that the bearing capacity factors of rectangular footing increase with increasing embedment ratios and there are no critical embedment depths observed where the bearing capacity factor reached its limit. Based on the obtained bearing capacity factors, a relatively simple formula is proposed. The proposed formula can provide a good prediction of the bearing capacity factor of footings with various aspect ratios and embedment ratios in uniform clay, including thin plate footings and high embedment depths.The second part of the thesis summarized the previous study about the scales of strain-rate parameters, and then the differential equation for DPA's motion response was employed to investigate the influence of strain-rate effect on the penetration depth of DPA. The results indicate that the penetration depth of DPA would drastically decrease due to the strain-rate effect. This finding sets a clear direction for future research. The reference strain-rate ratio with high values of strain-rate parameters have significant effect on the embedment depth of dynamically anchors. According to the results of the study in chapter 2, the penetration depth of DPA will decreases when the bearing capacity of rectangular footings is chosen to represent the end bearing force acted on the fins of DPA instead of the classical solution of strip foundation's bearing capacity factor 7.5.The third part of the thesis adopted Coupled Eulerian-Lagrangian (CEL) method to simulate the continuous penetration of torpedo anchor in rate-dependent clay. By analyzing the end bearing resistance and frictional resistance acted on the torpedo anchor during its penetration process, the relationship between the shear strain-rate effect of clay and the end bearing force and frictional resistance acted on the torpedo anchor was analyzed.