Analysis Of The Mechanical Property For Deep-sea Flexible Riser

As the exploitation of the oil-gas resource advances into deeper waters and harsherenviroment, the flexible risers are becoming more and more widely used to serve as theessential channel to connect the offshore rigs and the well-heads. The main advantage offlexible risers is that they are compliant and highly deformable in bending, but also quitestiff in tension, which enables them to undergo large deformations induced by currents,waves, vortex-induced vibrations and the motion of floating vessels. However, due to theircomplex structure, the design and analysis of flexible risers is quite complex and difficult.Based on the demands above, the mechanical property of fleible risers is investigatedin this thesis. Some key problems involved in the design and analysis are analyzed. Themain contents and contributions of this thesis can be summarized as follows:1、A comprehensive review on the analysis of flexible risers is carried out. Firstly, thestructure of the flexible riser is introduced, and the structure characteristic and the functionof each component are explained. Then, the global analysis and cross-section mechanicalproperty analysis in the flexible riser design procedure is introduced, and the researchprogress for the two prolems is discussed systematically;2、Based on the equilibrium equation, the compatibility equation and the constitutiveequation, the analytical model that can accurately predict the axisymmetric response of theflexible riser is deduced. Meanwhile, a nonlinear numerical model, which can provide anaccurate prediction of the tension behavior, is established. Based on the analytical modeland the numerical model, the structural response of the flexible riser under tension, torsion, internal pressure and outer pressure is studied. The results are compared with theexperimental data and a good agreement is shown.3、According the sliding condition of the tensile layer, the bending response of theflexible pile is divided into three states, bounded state, part-sliding state and full-slidingstate. And the model that can predict bending moment and bending stiffness is derived foreach state based on the energy method. Besides, the numerical analysis of two flexible risersis conducted to analysis its response under bending load. Based on the analytical model andnumerical model, the structural response of the flexible riser under bending load is studied.The results are compared with the experimental data and a good agreement is shown.4、Based on the numerical software Ocraflex, the global analysis of the SCR and lazywave flxible riser is conducted. The structural response of the two layout configuration iscompared. Besides, the sensitive analysis of the length of the buoyancy catenary, thebuoyancy factor and the starting location of the buoyancy catenary on the globle response ofthe lazy wave flxible riser is performed.5、The calculation procedure for fatigue analysis of the flexible riser is introduced.Firstly, the globle response of an example flexible riser under desgin load cases is obtaind toget the cratical fatigue point and its load time serise. Then the fatigue stress of the tensilearmors is calculated by Bflex. Finally, the fatigue life is detemineted based on SN curve.