Structural Design And Strength Analysis Of Bonded Non-Metallic Marine Flexible Riser

Marine flexible riser,as a tool for deep sea oil exploitation in various countries,has many advantages such as good flexibility,corrosion resistance,light weight and convenient installation.It has gradually replaced the traditional steel pipeline,and become a main trend of marine engineering development in the future.The research of marine flexible riser started late in China.Foreign countries implement strict technical secrecy and patent protection to export flexible riser products.As a result,the marine flexible riser products used in China's deep-sea development depend entirely on import.This not only increases the production cost,but also seriously affects the development process of deep-sea oil exploitation in China.To this end,it is urgent to develop the marine flexible riser made in China,which will become an important direction of marine engineering development in the future.In this paper,a typical bonded non-metallic marine flexible riser—thermoplastic glass fiber reinforced flexible riser is studied from the perspectives of preparation process of key technology,cross-section structure design,mechanical properties and overall strength under extreme sea conditions.The specific research is summarized as follows:(1)Two key technological preparation processes of glass fiber reinforced flexible riser,that is,filament winding process of reinforcing layer and three-layer co-extrusion process of inner lining layer,are studied.The key equipment and some problems in the two processes are briefly introduced and analyzed.(2)According to the basic technical design index of the marine flexible riser used in 500-meter deep sea,the ABAQUS finite element software is used to design two winding schemes of single spiral angle winding and multi-angle winding for the section structure of reinforcement layer of glass fiber reinforced flexible riser by referring to DNV-RP-F119 standard.Moreover,a flexible riser with a single spiral angle winding structure satisfying the strength requirement is designed.The minimum winding thickness is 11.4mm,and the winding angle is±60°.The reinforcement structure of the flexible riser with multi-angle winding structure is as below:compression resistance layer 4mm(winding angle90°),resistance tensile layer 3.6mm(winding angle ±30°),and supplementary strength winding layer 4mm(winding angle±55°).(3)The ABAQUS finite element software is used to calculate the tensile,bending and torsional rigidity of the two flexible riser with different reinforcement layer winding structures through the material mechanics formula.The results show that the rigidity values of the flexible riser with multi-angle winding structure are 129074744N,512.36KN.m2 and 750000N.m2,which are greater than those of the flexible riser with single angle winding structure:119593220N?459.5KN.m2?600000N.m2.In addition,the minimum bending radiuses of the two flexible riser models with and without internal pressure are calculated.The calculation results show that the minimum bending radiuses of the flexible riser with single angle winding without internal pressure and with internal pressure are 3.79m and 8.57m,respectively,which are smaller than those of the flexible riser with multiple angle winding structure:3.87m and 9.23m.(4)In view of the overall strength of glass fiber reinforced flexible riser under extreme sea condition,the multi-angle winding flexible riser with good mechanical properties is studied.In this paper,the strength analysis method from whole to part is adopted,and the whole statics analysis is carried out by using the professional marine software Orcaflex.It is determined that the dangerous area of the flexible riser is the top suspension area with the largest tensile tension and the bottom contact area with the largest bending moment.Moreover,for these two dangerous areas,the typical near and distant positions are conducted with dynamic analysis under the combined actions of once-in-a-century current and once-in-a-decade wave,once-in-a-decade current and once-in-a-century wave.The maximum tensile tension and bending moment of the dangerous section are extracted and used as the boundary conditions for subsequent local strength checking analysis.Finally,the local flexible riser model is conducted with strength checking analysis.The results demonstrate that the designed multi-angle winding flexible riser can meet the strength requirements in these two extreme sea conditions.