Dynamic Response And Fatigue Analysis Of Ultra-deep Water Multi-purpose Flexible Riser

With the depletion of oil and gas in land and shallow sea,people pay attention to the exploration and development of deep sea oil and gas resources.Marine riser is one of the key equipments in deep-sea oil and gas development.Traditional steel riser is difficult to meet the requirements of deep-sea oil and gas development.Compared with traditional steel riser,flexible riser has many advantages,such as strong fatigue resistance,low thermal conductivity and good corrosion resistance.At present,the thermoplastic composite flexible riser is mainly monopolized by foreign companies,the basic theory and key technology research is less.The mechanical properties,dynamic response and fatigue analysis of thermoplastic composite flexible risers are studied in this paper.In this paper,with PEEK carbon fiber as the research object,using the Composite Layup to simulate Enhancement layer in ABAQUS finite element analysis software.The mechanical properties of enhancement layer under internal pressure,external pressure,tension and bending were analyzed.The mechanical properties of riser enhancement layer under external pressure and tension are analyzed,and the sensitivity analysis of winding angle and number of winding layers to the strength of flexible riser is explored.In this paper,in the analysis of mechanical properties of flexible risers,the calculation of 196 models under single working conditions and 49 models under combined working conditions has been completed.Based on the theory of equivalent section,the equivalent simplification of PE composite flexible riser is carried out.On the basis of model simplification,considering the working marine environment and extreme marine environment,the dynamic analysis of the simplified flexible riser model is carried out by using OrcaFlex software.First,the static analysis of the flexible riser is carried out.And then the dynamic response of the simplified flexible riser model under the action of floating platform motion,fluid flow in riser,wave current and wind is calculated.Based on the Fatigue Analysis module in the finite element analysis software OrcaFlex.Analysis of wave working conditions in different action directions,the fatigue damage to the simplified flexible riser model is obtained according to the wave-period probability distribution of the working sea area,and the fatigue life of the flexible riser is calculated.The calculation results of mechanical properties of flexible riser show that,the number of winding layers and the winding angle has a significant effect on the mechanical properties of the flexible riser,and the combination of the mechanical properties of the flexible riser under different working conditions is given.The equivalent elastic parameters of 12 in PE flexible riser section are obtained by using the parameters in the flexibility matrix.In the overall dynamic response analysis,the maximum effective tension of flexible riser under catenary layout and slow-wave layout appears at the suspension point,and the maximum bending curvature of the flexible riser appears near the contact point under catenary layout.The maximum bending curvature of flexible riser appears at the float section under slow wave layout.Influence of fluid density in riser on the linear distribution of flexible riser integral model.The dynamic response to the flexible riser in the working marine environment and the extreme marine environment is calculated,and the effective tension,bending curvature and maximum stress of the flexible riser are obtained.The fatigue calculation results of flexible riser show that,the maximum damage is obtained at the touchdown part of the flexible riser.The fatigue life of the flexible riser is obtained,and the life of the flexible riser is the shortest at the touchdown part of the flexible riser.