The vortex induced vibration of slender cylindrical structures is common in offshore structures and marine applications such as risers, towing cables, etc. The VIV response of such slender elements in steady uniform current has been investigated in the past using numerical and experimental studies. Though few numerical studies exist for varying current (sheared flow), experimental studies are limited. Hence, the experimental studies are an essential part of VIV investigation, especially for sheared flow.
The experiments were conducted using a specially fabricated circular steel tank of diameter 2.4 m with a central hinge to rotate the pipe horizontally in a water pool of depth 0.7 m. Shear current is simulated by rotating the pipe about the hinge. A pipe of diameter 25 mm (= D) and length 1 m (= L) was fixed at one end of the rotating cable support, and the other end was passed over a pulley inside a rotating cylinder. The rotating cylinder is provided with a pulley at the top to tension the pipe. A shear current with a maximum velocity of 1.3 m/s and a minimum velocity of 0.1 m/s is generated using the set up. The VIV response of the pipe was measured using electrical resistance-type strain gauges pasted along the length. The measured axial strain was used to obtain transverse displacements, which was used to determine the response frequency, amplitudes, and forces. The Strouhal number was calculated. The VIV response and the fluid force coefficients obtained from the experiments were compared with Shear7 results.