Study On The Influence Of Wave Loading On The Bearing Capacity Of SPM Gravity Anchor

With the development of marine energy in full swing,the oil extracted from the ocean is transported to the land by tankers.The tankers are fixed by single point mooring(SPM)systems and the gravity anchor is the primary anchoring form of the single point mooring system.At present,the researches on gravity anchor are all based on static analysis,without considering the impact of wave loading.However,the wave-induced dynamic response of the seabed that around the gravity anchor has an impact on the structural safety.In order to ensure the safety of gravity anchor in engineering,this paper takes Dar Es Salaam harbor as an example and do numerical simulation of gravity anchor that under wave loading based on the elastoplastic incremental finite element method.Then the horizontal bearing capacity of the gravity anchor and the variation of the pore pressure and plastic strain of the surrounding soil were analyzed.The research focuses on the following aspects:1.In order to ensure the accuracy of finite element method,the anchor-seabed model was established,and the results of the simulation were compared with the previous indoor model test results to verify the reliability of finite element method.It is concluded that the numerical simulation results of the gravity anchor are about 2.3% larger than the measured values of the indoor model test.Therefore,the simulation results are credible within the tolerance range.2.By analyzing the marine environment where the SPM gravity anchor is located in,the dynamic response of the single point mooring system that under wave loading is studied,and the anchor-seabed model that under wave loading is established in ABAQUS.Then the displacement characteristics of the model and the variation law of horizontal bearing capacity of gravity anchor that under wave loading were analyzed.The results show that the displacement of the gravity anchor will increase under cyclic loading which makes it easier to destabilize,and the impact of cyclic loading on horizontal displacement of gravity anchor is greater than that on vertical displacement.The horizontal bearing capacity of gravity anchor will decrease under cyclic loading,and the drop values of different soil vary greatly.3.The change law of the seabed's excess pore water pressure and plastic strain can be obtained from the simulation results of the model that under wave loading.It shows that the accumulative excess pore pressure ratio at different locations of the seabed increases with the circulation times,but the variation degree at different points on the same path is different.Thechange of the excess pore pressure at the corner position is most significant.The wave-induced accumulative plastic strain occurs in the soil that around the gravity anchor,and the accumulation of excess pore water pressure and plastic strain in the seabed is the main reason for the decline of anchor's bearing capacity.4.The finite element simulation on the gravity anchor with shear keys that under wave load were carried out,and the results were compared with the flat bottom gravity anchor to analyze the influence of shear keys on the dynamic response of soil and bearing capacity of the anchor.It can be seen that the shear key will reduce the influence of cyclic loading on the horizontal bearing capacity of the gravity anchor,and it will also affects the accumulation of excess pore pressure and plastic strain in the seabed that around the anchor.