Different from the previous studies of the vortex-induced vibration (VIV) dominated by first mode of flexible pipe in an oscillatory flow, the features of a higher mode dominated are experimentally investigated in the ocean basin. The flexible pipe is forced to harmonically oscillate with different combinations of a period and amplitude. The design dominant mode consists of first and second modes under the maximum reduced velocity (V_R) of approximately 5.5 with a KC number ranging from 22 to 165. The VIV responses between only the excited first mode and the excited higher mode are compared and studied using displacement reconstruction and wavelet transform methods. The discrepancies of spatial and temporal response between smaller and larger KC numbers (KC = 56 and 121) are first observed. The strong alternate mode dominance and lock-in phenomena occur in the case of larger KC numbers, while they cannot be observed in the case of smaller KC numbers under higher modes. The VIV dominant frequency in the in-line (IL) direction is found to be always triple the oscillatory flow frequency and not twice that in the cross flow (CF) direction. The dominant frequency in the CF direction can be predicted by the Strouhal law, and the Strouhal number is approximately 0.18 under V_R = 5.5, which is not affected by the excited mode. Moreover, differences of response motion trajectory are also revealed in this paper. The present work improves the basic understanding of vessel motion induced VIV and provides helpful references for developing prediction methods of VIV in an oscillatory flow.

中文翻译：

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振荡流中高模态下挠性管涡激振动的实验研究

与先前的关于在振荡流中由挠性管的第一模式主导的涡激振动（VIV）的研究不同，在海盆中通过实验研究了由更高模式主导的涡旋振动。挠性管被迫以周期和振幅的不同组合谐波振荡。设计主导模式由最大降低速度（V _R）下的第一和第二模式组成大约5.5，KC值在22到165之间。使用位移重建和小波变换方法比较和研究了仅在激发的第一模式和激发的较高模式之间的VIV响应。首先观察到较小和较大的KC数（KC = 56和121）之间的时空响应差异。在较大的KC数情况下，会出现强的交替模式优势和锁定现象，而在较高的模式下，较小的KC数则无法观察到它们。发现沿串联（IL）方向的VIV主导频率始终是振荡流动频率的三倍，而不是沿交叉流动（CF）方向的两倍。CF方向上的主导频率可以通过Strouhal定律进行预测，在以下情况下，Strouhal数约为0.18V _R = 5.5，不受激励模式的影响。此外，本文还揭示了响应运动轨迹的差异。本工作提高了对血管运动诱发的VIV的基本理解，并为开发振荡流中的VIV预测方法提供了有用的参考。