Numerical Analysis Of Torpedo Anchor Bearing Characteristics Under Static Load And Cyclic Load

Due to the reduction of land and offshore oil and gas resources,more deep-sea oil and gas resources will be exploited in the future.For this reason,it is urgent to develop a new mooring system suitable for floating oil production platforms.The torpedo anchor is penetrated by self-gravity,the installation cost is low,and it is very suitable for use in the deep sea environment.Regarding the installation and working characteristics of torpedo anchors,in recent years,scholars at home and abroad have carried out a lot of research and achieved certain results.Under normal working conditions,torpedo anchors not only bear static loads,but are also subjected to dynamic loads caused by tides and waves.This paper analyzes and calculates the bearing capacity characteristics of T-98 torpedo anchors under static and cyclic loads through small deformation numerical calculations,and discusses the various factors and laws that affect the bearing capacity.The main work includes the following aspects:(1)Based on the ABAQUS software,a three-dimensional numerical calculation model of T-98 torpedo anchors in different types of soil was established,and the pullout bearing capacity was calculated.The calculation results are compared with the API method and the test results of other scholars,and the correctness of the established model is verified.(2)Under static load,the bearing capacity characteristics and failure modes of torpedo anchors in clay are studied.Firstly,the influence of factors such as the drawing angle,soil properties,buried depth,length diameter ratio and other factors on the pull-out bearing capacity of torpedo anchors is analyzed.The results show that when the pullout angle α=90°,the bearing capacity is the minimum,and with the decrease of α,the bearing capacity gradually increases,and reaches the maximum value at α=30°～45°.When the pullout angle continues to decrease,the bearing capacity decreases.The bearing capacity of torpedo anchor is significantly affected by soil strength or buried depth.;the same other conditions,compared with the torpedo anchor without anchor wing,the bearing capacity of the four-anchored torpedo anchor is significantly improved when drawn in different directions;for the torpedo anchor without anchor wing,when the buried depth and soil strength are constant,the higher length diameter ratio of the torpedo anchor,the greater the bearing capacity.Then,based on the calculation results and the test datas of other scholars,the V-H envelope of torpedo anchor bearing capacity is established.Based on the multiple regression analysis of the numerical results,the calculation formula of pullout bearing capacity of T-98 torpedo anchor in any direction in cohesive soil seabed is established.Finally,the failure modes of torpedo anchors under different directions are analyzed:under horizontal load,the failure mechanism is rotation around the anchor body and instability:under horizontal load,the failure mechanism is that the torpedo anchor rotates around a certain point of the anchor body and becomes unstable;under vertical load,the failure mechanism is vertical shear failure;under inclined load,the failure mechanism is the coupling of the first two.(3)Under cyclic loading,the influence of cyclic load parameters and soil strain softening parameters on the bearing capacity of torpedo anchors are mainly discussed.When the average load FM,load amplitude FA,and number of cycles N are small,the cumulative displacement of the torpedo anchor during cyclic loading is small.As the average load FM,load amplitude FA,and number of cycles N increase,the strain softening of surrounding soil is gradually obvious,the cumulative displacement increases,and the bearing capacity decreases until failure When the sensitivity of the soil St is small,the accumulation of displacement is small,with the increase of the sensitivity of the soil St,the strain softening of surrounding soil is gradually obvious,the cumulative displacement increases until failure;When the soil ductility ξ95 is large,the displacement accumulation is smaller,with the decrease of the soil ductility ξ45,the strain softening of the surrounding soil is gradually obvious,the accumulation displacement increases,and the bearing capacity gradually decreases until failure.