Study On Mechanical Properties Of Deep-sea Unbonded Flexible Riser

Unbonded flexible riser is a kind of marine pipeline which can work in complex marine environment.As one of the important equipment for the development of offshore oil and gas resources,it has the advantages of low bending stiffness,strong corrosion resistance,light weight and corrosion resistance,which has attracted many attentions in academic research and engineering applications.The study of flexible riser conforms to the development trend of China ’s oil and gas exploration to the ocean.However,due to the complex structure of the pipe body,it is difficult to study and analyze the flexible riser.At present,numerical simulation is widely used in the current research of unbonded flexible risers.This paper will summarize the research status of flexible riser at home and abroad,and study it from two aspects : cross-section mechanical characteristics analysis and overall static analysis,It aims to provide reference for riser design.Based on the basic assumptions,For an 8-layer unbonded flexible riser,two numerical analysis models are established by different equivalent simplification methods.The theoretical model and numerical model are compared with the mechanical response analysis under various loads,and the results of the two are compared with the experimental results.The simplified model of numerical analysis established in this paper describes the mechanical properties of flexible riser under tension,torsion and bending loads.,Compared with the linear description of the mechanical properties of the riser by the theoretical model,the numerical model reflects the nonlinear characteristics of the flexible riser under axisymmetric load and the hysteresis effect under bending load,which is closer to the experimental results.This paper improves the computational efficiency of finite element analysis of flexible riser and has good applicability.Based on the configuration characteristics of the catenary layout of the flexible riser,the riser control equation considering the external load of the ocean and the internal fluid is derived from the catenary method,and the corresponding two-dimensional static numerical calculation model is established.The equation is discretized by the finite difference method,and the equation is solved by the iterative method.The calculation results are compared with the calculation results of the finite element software to verify the accuracy of the numerical solution.Through the solution of the numerical model,the relevant parameters of the flexible riser including riser configuration,rotation angle,bending moment,effective tension and so on are mastered.The overall static analysis software of flexible riser based on finite difference method is developed by using VB.NET language,and the user interface of pipe mechanics calculation is created,which improves the analysis efficiency of overall statics.