Analysis Of Mechanical Performance Of Unbonded Flexible Riser With Limited Bend Based On Improved Friction

In recent years,as marine oil and gas exploration and production have more developed into deep water,the more complicated marine environment in deep water has made the design,installation and application of flexible risers more difficult.At present,most marine risers use steel pipes,but the steel pipes have problems such as poor corrosion resistance,heavy weight,and high installation costs.Unbonded flexible risers have the advantages of good flexibility,low laying costs and other advantages,and can withstand larger Axial load allows larger bending deformation,so it is more and more widely used in the process of deep-sea oil and gas resource exploration.Therefore,the mechanical analysis of unbonded flexible pipes is particularly important.Based on the theory of thick-walled cylinders,this paper firstly analyzes the constitutive relationship of unbonded flexible riser under axisymmetric load and bending load,and establishes the stiffness matrix of each layer.Then,considering the frictional slip state between the flexible riser layers,a new type of static-dynamic friction exponential attenuation friction model is proposed,a simplified finite element model of the flexible composite riser section is established,and it is verified based on literature data and the model is analyzed.Friction energy consumption curve under combined working conditions.Finally,based on the finite element software Orca Flex,the overall mechanical model of the unbonded flexible riser under complex environmental loads is established,and the mechanical response of the flexible riser under the restraint of the bend arrester and the hydrodynamic load is calculated.Optimize the design of the anti-bending device to obtain the optimal size of the anti-bending device,which provides a theoretical analysis basis for the design and evaluation of the anti-bending device and the unbonded flexible riser.The research results show that in the local mechanical analysis of the unbonded flexible riser,the new friction model proposed in this paper is closer to the experimental value than the traditional Coulomb friction model.The magnitude and direction of the load under the axisymmetric combined working condition.It will affect the energy value of frictional energy consumption and the energy consumption rate.Internal and external pressure loads and the winding angle of the spiral strip of the tensile armor layer will have a nonlinear effect on the tensile stiffness and torsional stiffness of the unbonded flexible riser.In the overall analysis part,it can be concluded that the restraint effect of the anti-bending device has almost no effect on the bending moment,effective tension,and von Mises stress of the unbonded flexible riser,but the curvature of the end of the flexible riser is greatly reduced.The optimized design of the anti-bending device shows that the optimal size of the anti-bending device under the action of this case is 170 mm in the fixed end diameter and 2.5 m in the length of the anti-bending device.