A Study of the Effects that Change the Vibration Mode of Riser VIV

为了弄清隔水管振动模态的动态变化现象，采用长模型进行了大规模试验。为了研究振动模态变化对隔水管涡激振动运动的影响，进行了一系列顶部张力周期性变化的实验。动态张力变化下的涡激振动幅值小于静态条件下的涡激振动幅值。另外，模态过渡周期较长时，振幅的减小幅度大于周期较短时。推测立管模型的振动较小，是因为振动模态在涡激振动充分发展之前就发生了振动模态转移。

To clarify the phenomena of dynamic variation of the riser's vibration mode, a large-scale experiment using a long model was carried out. In order to investigate an influence of the change of vibration mode on the riser VIV motion, a series of experiments were conducted with the periodic variation of top tension. VIV amplitude under dynamic tension variation is smaller than that under static condition. Additionally reduction of amplitude in case of relatively long mode-transition period is larger than that with short period. It is speculated that vibration of riser model is small because vibration mode shifted before VIV with certain mode is fully-developed.