浮式平台对深水立管振动的影响及共振研究

The Influence of Floating Platform on Deep-water Riser Vibration and Resonance

建立了考虑内部流体作用的深水立管振动数学模型,研究了输送流体密度以及浮式平台的升沉运动对立管固有频率的影响。研究结果表明,立管的各阶固有频率均随立管内部流体密度的变化而有规律地变化;当浮式平台做由定周期正弦函数控制的升沉运动时,立管的各阶固有频率将围绕各自的稳态固有频率上、下波动,其波动范围随平台升沉幅值的增大而增大;当浮式平台做定幅值变频率的升沉运动时,立管的各阶固有频率随平台频率的增大而剧烈波动;当平台以定频率0.698 1 rad/s和变幅值（0~5 m）运动时,输气立管只在第4阶与平台共振,输油立管则可以在第4、5、6、7和8阶与平台共振;当平台以定幅值1.69 m和变频率（大于0）运动时,总能找到立管与之共振的频率;由于共振频域随阶数的增加而变宽,所以平台做高频升沉运动时,立管发生高阶共振的概率较大。

A deep-water riser vibration mathematical model considering the effect of the internal fluid is built to study the fluid density and floating platform heave motion effects on the natural frequency of riser. The results show that each order natural frequencies of the riser change with the variation of the fluid density in riser. When the floating platform heaves in sinusoidal mode with fixed period, every order natural frequencies of riser will fluctuate around its own steady-state natural frequency and the fluctuation ranges increase with the increase of platform heave amplitude. As the platform heaves with fixed amplitude, the natural frequency of each order fluctuates intensely with the increase of platform frequency. Given the platform frequency of 0. 698 1 rad/s and amplitude of 0 - 5 m, the gas riser only resonates with platform in the fourth order, while the oil riser can resonate with the platform in the 4, 5, 6, 7 and 8 order. When the platform heaves with fixed amplitude of 1.69 m and variable frequencies （ greater than 0）, frequencies could always be found to make the riser resonate with the platform. As the resonance frequency domain widens with the increase of the order, the probability of higher-order resonance of riser increases when the platform heaves in high-frequency.