深海气液混输立管涡激振动及疲劳损伤分析

发布时间：2018-11-10 16:10

【摘要】：深海气液混输立管处于复杂的深海环境中,受到波浪、海流等环境载荷和立管顶端张紧力、自重和浮力等载荷共同作用,其力学性能分析较为复杂。当海流经过立管(细长结构物)时,会在两侧产生漩涡。当漩涡的释放频率与立管本身的固有频率接近时,立管会发生耦合共振,其振动幅值急剧加大。长此以往,立管会发生疲劳损伤,危害石油平台的生产安全。本文先介绍了立管力学性能分析时使用的线性波浪理论、斯托克斯波浪理论和Morison方程。选取合适的波浪理论和流体动力学系数,计算Morison方程可得到立管单位高度的波浪力。得到立管的载荷后,可通过直接积分法对立管的运动控制方程求解,分析立管的响应特性。应用ABAQUS有限元分析软件比较、分析了立管在不同的边界条件下的立管模态响应。在此基础上,分析了立管的环境变量和自身物理参数对立管固有频率的影响。立管的干模态和湿模态在阶数较低时,两者的频率相差较大;不过随着模态数的增加,其差距越来越小。立管的固有频率随着立管长度、壁厚和外径的增大而减少,随着顶张力的增大而增大。在第三类边界条件的基础上,通过改变海流流速,研究了立管的“失谐”和“锁定”现象。在ABAQUS的分析基础上,通过FLUENT研究了立管的圆柱绕流现象。并比较立管在裸管和带螺旋侧板两种方式下的立管振动特性,结果表明安装螺旋侧板后,立管临界流速变大,在一定程度上抑制立管的涡激振动。最后,根据ABAQUS动力分析中得到的应力时程曲线,判断立管是否处于安全状态。通过雨流计数法和不同S-N曲线可以计算立管的疲劳寿命,发现立管顶端处的截面为最危险截面。应用不同的S-N曲线计算疲劳损伤,DNV规范的D类曲线最为严格。
[Abstract]:Deep-sea gas-liquid mixed riser is in a complex deep-sea environment, subjected to waves, currents and other environmental loads and the top of the pipe tensioning, gravity and buoyancy loads, the mechanical properties of the analysis is more complex. As the current passes through the riser (slender structure), a whirlpool occurs on both sides. When the vortex release frequency is close to the natural frequency of the riser itself, the riser will have coupling resonance and its vibration amplitude will increase sharply. In the long run, the riser will have fatigue damage, endangering the production safety of oil platform. In this paper, the linear wave theory, Stokes wave theory and Morison equation are introduced. The wave force per unit height of riser can be obtained by calculating Morison equation with appropriate wave theory and hydrodynamic coefficient. After the load of riser is obtained, the response characteristics of riser can be analyzed by solving the motion control equation of riser by direct integration method. The modal responses of risers under different boundary conditions are analyzed by using ABAQUS finite element analysis software. On this basis, the influence of environmental variables and physical parameters of riser on the natural frequency of riser is analyzed. The frequency difference between dry mode and wet mode of riser is larger when the order is lower, but with the increase of the number of modes, the difference becomes smaller and smaller. The natural frequency of riser decreases with the increase of riser length, wall thickness and outer diameter, and increases with the increase of top tension. On the basis of the third kind of boundary conditions, the phenomenon of "detuning" and "locking" of risers is studied by changing the current velocity. Based on the analysis of ABAQUS, the flow around a cylinder of riser is studied by FLUENT. The vibration characteristics of riser in bare tube and with spiral side plate are compared. The results show that the critical velocity of riser increases after the installation of spiral side plate, which to some extent inhibits the vortex-induced vibration of riser. Finally, according to the stress time history curve obtained from ABAQUS dynamic analysis, the safety of riser is judged. The fatigue life of riser can be calculated by rain flow counting method and different S-N curves. It is found that the section at the top of riser is the most dangerous section. Using different S-N curves to calculate fatigue damage, the class D curve of DNV code is the strictest.
【学位授予单位】：中国计量大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P756.2

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