深海采矿系统中悬臂式立管涡激振动分析

不同于传统的海洋立管, 深海采矿系统中的垂直提升管道可以被视为一个底部无约束的柔性悬臂式立管, 工作过程中同样面临涡激振动和柔性变形问题. 本文采用一种无网格离散涡方法和有限元耦合的准三维时域求解数值模型, 系统性地研究了不同流速下悬臂式立管的涡激振动问题. 结果表明: 悬臂式立管的横向振动模态阶数随折合速度增加而增大, 在一定折合速度范围内主导振动模态保持不变; 当主导模态转变时, 对应的横向振幅会发生突降, 但是当新的高阶模态被激发后, 立管振幅随来流速度增加而再次逐渐增大; 在相同的振动模态下, 立管底部位移均方根值随折合速度线性增加, 主导振动频率在模态转变时会出现跳跃现象; 特别地, 本文讨论了三阶主导模态下悬臂式立管的振动响应, 无约束的立管底部呈现出较大的振动能量, 且振幅的驻波特征随折合速度增加而逐渐增强; 本文比较了两端铰支立管与悬臂式立管的涡激振动响应特征, 两者在振幅和主导振动频率两方面均表现出了相同的变化趋势. 

ANALYSIS OF VORTEX-INDUCED VIBRATION FOR A CANTILEVER RISER IN A DEEP-SEA MINING SYSTEM

Different from the traditional marine riser, the vertical lifting pipeline in the deep-sea mining system can be regarded as a flexible cantilever riser with an unconstrained bottom end. Likewise, problems in terms of vortex-induced vibrations (VIVs) and flexible deformations can be encountered during operation. In this paper, a quasi-three-dimensional time-domain numerical model coupled with the discrete vortex method (DVM) and finite element method (FEM) is employed in the time domain. Systematic simulations have been carried out to investigate the VIVs of a cantilever riser under different current speeds. The results indicate that, for a cantilever riser, the transverse vibration mode number rises with increasing the reduced velocity. In a certain range of reduced velocities, the dominant vibration modes remain unchanged. When the modal transition occurs, the corresponding vibration amplitudes can abruptly drop. However, when the new high-order mode is excited, vibration amplitudes of the riser again gradually increase with increasing the incoming velocities. In the same vibration mode, the root-mean-squared values for the bottom displacements of the riser linearly rise with the reduced velocities. When vibration mode changes, a jump phenomenon for the dominant vibration frequencies can be observed. Especially, the present work discusses the vibration responses of the cantilever riser in the three-order dominant mode. It can be found that the unconstrained bottom end of the riser exhibits relatively large vibration energy. The standing wave characteristics of the vibration amplitudes gradually enhance with the increase of the reduced velocities. The VIV response characteristics of a two-ends hinged riser and a cantilever riser are compared in this investigation, both of which exhibit the same variation tendency in terms of amplitude and dominant vibration frequency.