Experimental Investigation on Vortex Induced Vibration of a Rigidly Coupled Twin-Tube Model

The objective of this experimental study is to reveal the features of vortex-induced vibration (VIV) for a tandem rigidly coupled twin-tube model. A series of self-oscillation model tests were carried out under uniform flow with a range of reduced velocity from 3 to 20, and Reynolds numbers from 2 × 103 to 1.5 × 104. The spacing ratio, defined as the center-to-center distance divided by the cylinder’s diameter, varied within a range of 1.5–5. The cross-flow VIV response amplitudes and frequencies of the twin-tube model were studied under different spacing ratio compared with a single-tube model. The results reveal that the VIV response amplitude of the twin-tube structure follows a different trend from that of conventional single-tube structures or two free cylinders. The response characteristic of the twin-tube model shows a separated VIV-galloping at the spacing of 1.5D. The most suitable spacing ratio for a submerged floating tunnel (SFT) is 1.5, as it exhibits the lowest response amplitude. The spacing ratio has a significant influence on the response amplitude and frequency, 3D is a transition spacing of the vortex shedding modes, an amplitude modulation phenomenon is observed at the spacing ratio of 3. When the spacing ratio is larger than 4, the response tends to be similar.