Numerical Investigation Of Holding Capacity Of Torpedo Anchor In Clay

With the increasing demand for oil and natural gas resources,the exploration and development of offshore oil and gas resources are constantly shifting to the deep sea,and the production platforms are also changing from fixed platforms to floating ones.The floating mining platform is connected to the anchorage structure in the seabed through the mooring system.In order to ensure the normal operation in the relatively fixed ocean area,the deep-water anchorage structure is required to provide sufficient pull-out bearing capacity.Torpedo anchor is a new type of deep-water anchorage structure which can be installed by self-weight.It does not need to provide additional energy and has the advantages of simple and rapid installation,low cost and large bearing capacity.It is considered as the most promising deep-water anchorage structure and has been applied in many deep-sea areas.Due to the short time of torpedo anchor,the current research on the bearing capacity of torpedo anchor is not comprehensive and systematic.Accurate evaluation of the bearing capacity of torpedo anchors is the prerequisite to ensure the safety and stability of Marine floating facilities.Therefore,it is of great engineering significance to study the bearing capacity of torpedo anchors.In this paper,the penetration and pullout process of torpedo anchors are analyzed by means of theoretical analysis,and the holding capacity of torpedo anchors under inclined drawing is studied by CEL method.Because of the special installation of torpedo anchor,the penetration depth should be calculated in order to accurately evaluate the holding capacity of torpedo anchor.In this paper,the mechanical analysis of torpedo anchor penetration process is carried out,and the differential equation of torpedo anchor penetration process is established.Then,based on API method,the holding capacity of torpedo anchor is calculated,and the influence of impact velocity,density of torpedo anchor,strain rate parameters,reference shear strain rate,soil sensitivity and undrained shear strength of soil on penetration depth and holding capacity of torpedo anchor is analyzed,and relevant conclusions are obtained.The Tresca model built into ABAQUS software was extended to reflect the strain softening effect.Coupled Eulerian-Lagrangian(CEL)method was used to establish the finite element analysis model of torpedo anchor drawing process,and the validity of the model was verified through field tests.The holding capacity of anchor under different tilt angle of drawing was analyzed through numerical simulation,and normalized V-H envelope of the torpedo holding capacity was established.This paper studied the influence of the undrained shear strength of soil,the penetration depth of the anchor,friction coefficient,the torpedo anchor slenderness ratio and tilt of the torpedo anchor on the holding capacity of the anchor.Results indicate that the undrained shear strength of soil,the torpedo penetration depth of the anchor,the coefficient of friction between the torpedo anchor and soil and the torpedo anchor slenderness ratio does not affect the shape of the normalized of the V-H envelope,you could use the same set of fitting parameters describe the relationship between the component of the ultimate holding capacity of torpedo anchor under different conditions,and the tilt of the torpedo anchor will affect the shape of the normalized V-H envelope.Finally,the design and calculation process of a torpedo anchor is given based on the research results.