Study of the trajectory performance on the vortex-induced vibration response of a flexible riser

Laboratory tests were conducted on a flexible cylinder in order to further improve the understanding of the response performance of the vortex-induced vibration (VIV). The experiment was carried on in a towing tank and the relative current was simulated by towing the flexible riser in one direction. Based on the modal superposition method, the VIV displacements were obtained from the measured strain. Before the experiment, the trajectory performances of the VIV on a rigid riser were studied by the numerical method. Furthermore, the motion trajectories of the single-mode and multi-modes VIV on a flexible riser were discussed using the experiment method. The analysis results indicate that the motion trajectory for the flexible riser at a low velocity displays a typical type-eight figure, which is very similar to that for a rigid cylinder. However, with the increased velocity, the motion trajectory for the flexible riser becomes chaotic, which is induced by the multi-mode VIV responses.