An experiment study of a cylinder's two degree of freedom VIV trajectories

• An experiment study of a cylinder's one and two degree of freedom VIV was done.
• The in-line vibration frequency appeared to be “multi-frequency” phenomenon.
• The cylinder trajectory appeared to be various motion forms besides “8” shape.
• The study of motion trajectory evolution was done in this paper.

The paper reports the results of experiments on the vortex-induced vibration of a horizontal cylinder with two degrees of freedom and with the diameter of 5 cm, and length of 120 cm. It has been found that the vibration of the cylinder in in-line direction appeared to be “multi-frequency”. That is, under certain combinations of natural vibration frequency and reduced velocity, the in-line vibration frequency contained both the cross-flow vibration frequency and two times the cross-flow vibration frequency. Consequently, the trajectories of the cylinder were “egg” and “raindrop” shapes, which were significantly different from the traditional figure “8” and “new moon” shapes. In addition, the study found that the vibration trajectory in other forms moves towards a figure “8” shape as xxx increases. Also, it was found that the various forms of cylinder vortex vibration trajectories depended primarily on the combination of natural vibration frequency and reduced velocity.