Numerical Analysis Of Torpedo Anchoring Process Based On Material Point Method

With the increasing demand for oil and natural gas development in deep and ultradeep water,the cost of construction,installation and use of deep-water mooring foundations increases with the water depth,and the development of low-cost,hightensile-strength anchoring foundations is urgent.The torpedo anchor is a new type of deep water anchoring mooring foundation that penetrates by its own gravity.It has the advantages of simple and fast installation,low cost,and high pull-out bearing capacity.It is of theoretical significance and practical value to study its penetration process and bearing capacity for the development of deep water resources in China.There are relatively little analysis of factors influencing penetration and the conventional numerical simulation research methods are limited because the high-speed penetration of torpedo anchor in the soil will cause a significantly high strain rate and extreme deformation.The main works and results of this papers are shown as follows:(1)By the unconfined-undrained shear compression test,the influence of different deformation rates on the mechanical properties of clay soil was studied,and the effects of different deformation rates on the deformation characteristics and undrained shear strength of saturated clay soil with different water content were analyzed.The results show that the stress-strain curve is a hardening type,the higher the water content,the lower the strength of the soil.Under the same water content,the higher the shear rate,the higher the elastic modulus,the higher the undrained shear strength,the strain rate increased by 10 times,and the undrained shear strength of kaolin increased by an average of 33.2%.(2)It is found that the impact energy is positively correlated with the penetration depth,by the anchor drop model test.The material point method algorithm program is used to simulate the anchor drop test,and the results verify that the material point method is reliable to study the torpedo anchor penetration process.(3)Penetration process and influencing factors of torpedo anchor were analyzed by material point method.The material point method was used to simulate the in-situ penetration test of the wingless torpedo anchor and the torpedo anchor movement mechanics,soils resistance Mises stress and equivalent plastic strain of soils,The analysis of the influencing factors of the deformation law of the foundation soil and the range of plastic deformation zone and penetration depth are obtained.The results show that the penetrating plastic zone is a semi-elliptical range with the buried depth of the foundation at the 15 D position under the anchor tip as the long axis and 8D as the short axis.The vertical displacement of the anchor tip is mainly downward,and the vertical displacement of the anchor side is mainly upward.The closer to the anchor,the greater the vertical displacement.The impact velocity is approximately linearly related to the penetration depth.For every 10 m/s increase in impact velocity,the penetration depth increases by an average of 1.08 times the anchor length.The undrained shear strength of soil is inversely related to the penetration depth.(4)Study on the uplifting bearing capacity of torpedo anchors and its influencing factors.The material point method was used to simulate the in-situ bearing capacity test of the wingless torpedo anchor.The results verified the reliability of the material point method in the study of the vertical pull-out bearing capacity,and the deformation and plastic zone of soils during the uplift process were obtained.The influencing factors of the deformation law of the foundation soil during the uplifting process,the range of the plastic deformation zone and the vertical uplifting bearing capacity are obtained.The analysis results show that the vertical displacement of the foundation soil during the uplifting of the anchor is mainly upward,and the deformation of the foundation soil near the tail of the anchor is greater than the foundation soil near the anchor side;the area of significant plastic deformation of the uplift of the anchor is the initial burial depth of the anchor tip 5 The burial depth of the foundation at the location of ?6 times the anchor diameter is the apex,and the isosceles triangle with the anchor surface at the base surface 12 times the anchor diameter as the base.The analysis results of the factors affecting the vertical pull-out bearing capacity of torpedo anchors show that,within the test range,the buried depth,soil strength and the vertical pull-out bearing capacity are positively correlated.