Analysis Of Mechanical Behavior And Optimization Of Tensile Armor Of Flexible Riser

Flexible riser with high rigidity,good corrosion resistance and strong resistance to fatigue has been widely used in deepwater exploitation and development for oil and gas.In general,increasing depth of water,the layout of the flexible riser is often arranged in the form of lazy wave to reduce the impact of rocking on the seabed.However,in this form,the flexible riser will produce a large tension which will lead to tensile fracture.At the same time,the flexible float will also produce large bending deformation.And the two failures generally occur on the tensile armor of flexible riser.Therefore,it is of great significance to study the mechanical properties of tensile armor under loads.In this paper,the mechanical response of tensile armor of flexible riser under tensile and bending loads is calculated respectively by theoretical modeling and finite element numerical analysis.Specific contents are as follows:(1)Considering top of the flexible riser as the fixed end,it is established under tensile load.Using the Lagrange multiplier method,and assuming that the deflected angle of central axis which is far away from the end is not affected by the fixed end.Then setting the strain energy function as minimum,equation of deviated angle is deduced.Accordingly,axial stress and local bending stress of dangerous points in the spiral steel belt is available.(2)Considering distributed buoy linked on the floating section of flexible riser,it's produced bending load by the net buoyancy.Both ends of floating section are seen as simply supported.Based on flexural differential equations for the simple beam and the deformation coordination equation,bending moment,displacement and rotation equations of cross section of flexible riser can be calculated.Through the energy method,the bending stiffness of the tensile armor is calculated in different stage.In order to ensure that the flexible riser has enough bending capacity,the reasonable range of the net buoyancy of the float is determined.In the end,the stress of the cross section of the spiral steel belt is calculated.(3)Using ABAQUS to establish a simplified model of flexible riser,it is calculated under tensile or bending load to get tensile stiffness or bending stiffness in eight kinds of working conditions.And researching on the relationship of tensile stiffness or bending stiffness with different internal pressure,external pressure and so on.Finally optimize the design of aspect ratio and winding angle of spiral steel belt of tensile armor.