Mechanical Properties Analysis And Optimization Of Composite Tensile Armour For Flexible Risers

The development and utilization of offshore oil and gas resources is the main trend of the development of the petroleum industry.Non-bonded flexible risers are the most widely used risers in offshore oil and gas field development,but the weight,corrosion resistance and fatigue resistance of risers have become the main factors restricting their wide application in deepwater oilfield development.Replacing the carbon steel material of the tensile armor layer in the non-bonded flexible riser with composite materials can effectively solve the above problems.In this thesis,the time-domain viscoelastic response and frequency-domain viscoelastic response of an unbonded flexible riser with composite tensile armour under axisymmetric loads are mainly studied.The main parameters affecting the mechanical properties of the composite tensile armor layer are also analyzed.Some optimization suggestions for riser material,riser structure,and external monitoring procedures are presented.Firstly,for the non-bonded flexible riser with composite tensile armour,on the basis of the original partial equilibrium equation,based on the stiffness constitutive of fiberreinforced composites,the equilibrium of the flexible riser with composite tensile armour is established.Then,considering that non-metallic materials will have certain viscoelastic characteristics,based on the principle of elasticity-viscoelasticity correspondence,the viscoelastic properties of non-metallic materials in the non-bonded flexible riser in the time domain and frequency domain are expressed by Prony series.Based on the elastic-viscoelastic correspondence principle,the viscoelastic balance equations in time domain and frequency domain were established.The viscoelastic constitutive equation of nonmetallic materials in the unbonded flexible riser was substituted into the balance equation in time domain and frequency domain,and the viscoelastic response in time domain and frequency domain of the unbonded flexible riser under axisymmetric load was obtained by the program calculation.In this thesis,considering the complexity and randomness of external load,the structural response generated when external load is random load is further studied based on the calculation model in frequency domain.It is found that with the increase of time,the time domain calculation results tend to the frequency domain calculation results,the higher the external load frequency,the greater the tensile stiffness and radial stiffness;The larger the spiral angle of the tensile armour layer,the smaller the tensile stiffness,the larger the loss factor and radial stiffness.The results show that calculating the structural response of the flexible riser in time domain and frequency domain can well predict the variation trend of the structural state and stress state of the riser during service,which provides a theoretical basis for the design and engineering application of the flexible riser.