FDPSO立管涡激振动响应分析

INFLUENCE OF HEAVE MOTION ON VORTEX-INDUCED VIBRATIONS OF FDPSO RISERS

基于FDPSO的概念设计原理,建立了立管系统的力学模型,运动方程的张力作用项中考虑了立管的自重和FDPSO垂荡运动的影响,流的作用力简化为涡漩串作用产生的周期性升力和阻尼力两部分。应用Galerkin法和4阶龙格库塔法求解上述非线性运动方程,重点分析了FDPSO垂荡运动对涡激振动的影响。数值结果表明:当垂荡运动频率引发的参数共振和涡激谐振共同发生时,立管有最大振幅的稳定响应;深海条件下,立管高阶振型响应在总位移中占有一定比重,对总弯矩及剪力分布有重要影响;而垂荡运动的振幅改变对立管的涡激振动影响不大。

Based on the conceptional design of FDPSO,the mechanical model and partial differential governing equation of risers are presented.Riser＇s top tension is variable with time because of FDPSO heave motion and it aslo changes with axial considered gravity.The fluid force expression includes both the votex-shedding effect and fluid damping force.The nonlinearly equation is solved through numerical method.The dynamic analysis is done to research the influence of parametric excitation to vortex-induced vibrations rooted from FDPSO heave motion.The comparison of the results of three special working cases reflects that risers have large response under the combined action of ＂lock in＂ and parametric resonance;the higher modes response have quite a little proportion in total displacement especially in the bending moment and shearing force;the amplitude of heave motion has little effect on the vibrations.