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

为了弄清立管振动模式的动态变化现象，利用长模型进行了大型实验。为了研究振型变化对立管涡激运动的影响，利用顶部张力的周期性变化进行了一系列实验。动态张力变化下的VIV幅值小于静态下的VIV幅值。另外，在模式转换周期较长的情况下，振幅的减小比在较短周期的情况下要大。推测立管模型的振动较小，是因为振型在涡激振型充分发展之前发生了位移。

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.