An experimental analysis of the vortex-induced vibration (VIV) of a catenary flexible riser with length to diameter ratio of 158, placed within a log-law sheared oncoming flow, is presented in this work. The experiments were conducted in a water flume with a wide reduced velocity range of 8.1–25.8, using the non-intrusive high-speed cameras to capture the in-plane and out-of-plane responses simultaneously. Experimental results indicate that the dominant frequency varies both spatially and temporally, suggesting the mode competing in space and the mode switching in time. The co-existence of multiple frequencies becomes more significant at the response envelope troughs with a broader frequency band. Travelling waves are preferentially oriented from high- to low-velocity regions while the in-plane response exhibits the converse propagating direction. The mode transition is out-of-sync in the in- and out-of-plane, resulting in a complex interaction between the two directions. The out-of-plane dominant frequency always takes part in the in-plane response, and the in-plane response is preferentially dominated by the out-of-plane frequency at low reduced velocities until the reduced velocity is sufficient high.

在这项工作中，对放置在对数律剪切迎面流中的悬链柔性立管的长径比为158的涡激振动（VIV）进行了实验分析。实验是在水槽中进行的，该水槽的速度范围在8.1-25.8的宽范围内，使用非侵入式高速相机同时捕获平面内和平面外响应。实验结果表明，主频在空间和时间上均发生变化，表明模式在空间上竞争并且模式在时间上转换。在具有更宽频带的响应包络线谷处，多个频率的共存变得更加重要。行波优先从高速区域指向低速区域，而面内响应则显示相反的传播方向。模式转换在平面内和平面外是不同步的，从而导致两个方向之间的复杂交互。平面外主频始终参与平面内响应，并且平面内响应优先由平面外频率以较低的降低速度主导，直到降低的速度足够高为止。