TWO-DEGREE-OF-FREEDOM FLOW-INDUCED VIBRATIONS OF A CIRCULAR CYLINDER WITH A HIGH MOMENT OF INERTIA RATIO

Two degree-of-freedom vortex-induced vibrations of a moderate mass and high moment of inertia ratio pivoted cylinder were investigated experimentally. The experiments were performed at a constant Reynolds number of 2100 for a range of reduced velocities from 3.4 to 11.25. The results show that, in addition to the reduced velocity, the transverse damping ratio has a significant effect on the amplitudes of response. The cylinder tip is observed to trace orbital trajectories, which is shown to be attributed to the frequencies of oscillations in both directions locking onto the natural frequency in the synchronization region. The results indicate that a phase angle between the streamwise and transverse oscillations governs the direction and orientation of the orbiting motion. Flow visualization results show that, at a given reduced velocity and transverse damping ratio, near-wake development changes along the cylinder span. The observed shedding patterns are shown to differ from those expected at the corresponding experimental parameters for one-degree-of-freedom uniform amplitude cylinder vibrations.