A study on the proximity interference and synchronization between two side-by-side flexible cylinders

In this paper, we present the results of a study of the effects of proximity interference on the hydro-elastic responses of two pre-tensioned flexible cylinders in side-by-side arrangement subjected to uniform cross-flow (CF). Two flexible cylinders of the same size, properties, and pretensions were tested with two different vertical separation distances. It was found that at a small center-to-center separation distance (2.75 diameters), the upper cylinder showed no upper branch in the first CF lock-in region. With the increase in the initial vertical separation, both cylinders exhibited amplitude responses similar to the isolated cylinder. At this small separation distance, the upper cylinder showed a CF frequency response (higher values) quite distinct from both the lower cylinder and the single cylinder. For the reduced velocity range of 1.82≤Ur≤5.1, strong phase synchronization was detected. Anti-phase synchronization was even detected within the region of the collapsed classical vortex-induced vibration (VIV) amplitude response. It was also found that even for a separation of 5.5 diameters, the wakes of the cylinders were strongly synchronized within the region of high cylinder vibration amplitudes (2.91≤Ur≤5.1). From the analysis of the synchronization, no synchronization was built up for very small amplitudes for the large separation case, in contrast to the small separation case. The mean drag and the fluctuating components of the drag and lift forces of both cylinders showed quite different behaviors.