Vortex-induced vibration of a flexible pipe under oscillatory sheared flow

A vortex -induced vibration (VIV) test of a tensioned flexible pipe in oscillatory sheared flow was performed in an ocean basin. The model was 28.41 mm in diameter and 3.88 m in length. The test was performed on a rotating test rig to simulate oscillatory sheared flow conditions. One end of the test pipe is fixed, and one end is forced to harmonically oscillate to simulate oscillatory sheared flows with various combinations of amplitudes and periods, Keulegan-Carpenter (KC) numbers from 25 to 160, and five kinds of reduced velocities Vr from 6 to 14. Fiber Bragg grating strain sensors were arranged along the test pipe to measure bending strains, and the modal analysis approach was used to determine the VIV response. The VIV response in the cross -flow direction is investigated. The results show that VIV under oscillatory sheared flow exhibits amplitude modulation and hysteresis phenomena. Compared with oscillatory uniform flow -induced VIV, the Strouhal number is smaller in oscillatory sheared flow -induced VIVs. The VIV developing process in oscillatory sheared flow is analyzed, and critical KC is proposed to describe the occurrence of modulated VIV under oscillatory sheared flow.