Response Characteristic Analysis And Fatigue Analysis Of A Lazy-Wave Riser With Multi-Buoy Sections

The demand for energy has been increasing steadily.With the rapid consumption of land oil and gas resources,deep-sea oil and gas development is becoming more and more important.As an important component of offshore oil and gas development,riser has gradually appeared a variety of configurations to cope with different sea conditions.In order to avoid the possible fatigue problem of SCR in deep sea,a lazy-wave riser is developed,which can reduce the fatigue damage of the riser by adding a float section in the middle.However,the lazy-wave riser with a single-buoy section also has problems.For example,its tension or bending moment is too large in some places.To solve these problems,the static / dynamic analysis and fatigue analysis of lazy-wave risers with multi-buoy sections are carried out.In this paper,the response characteristics and fatigue life of lazy-wave riser are studied by numerical analysis method.(1)The response characteristics of a lazy-wave riser in deep sea studied by using selfdesigned software.The Vector Form Intrinsic Finite Element(VFIFE)method is adopted to build a mathematical model to analyze the lazy-wave risers with multi-buoy sections using Fortran.We changed the number and buoyancy of the buoy sections,the distance between buoy sections,the current speed,and the position of the buoy sections and simulate the loss of the buoy sections.Then,we conducted static analysis and make analysis of impact.We also determined the hang-off point of vertical harmonic motion to simulate the real sea environment.Then,we analyzed the maximum bending moment and effective tension of the riser.Finally,we analyzed the velocity component of the entire riser.(2)Based on the self-made software,the vector finite element analysis of the deep-sea slow wave flexible riser with continuous buoyancy loss of the float section is carried out.The change of configuration of the lazy-wave risers and the effective tension at the top of riser are analyzed.The process of continuous loss of buoyancy in buoy sections of the lazywave risers which may appear in reality is simulated and analyzed.(3)Based on the commercial software OrcaFlex,this paper analyzes the lazy-wave risers with DBS,ballast section,multi-buoy section,clap and tether.And it also analyzes the fatigue life of the riser under different environmental loads(normal environmental load,extreme environmental load and irregular wave load),as well as the effective tension and bending moment at the maximum fatigue point.It provides a reference for the setting of deep-sea slow wave riser in reality.