Wake structures and vortex-induced vibrations of a long flexible cylinder—Part 1: Dynamic response

Results showing the dynamic response of a vertical long flexible cylinder vibrating at low mode numbers are presented in this paper. The model had an external diameter of 16 mm and a total length of 1.5 m giving an aspect ratio of about 94, with Reynolds numbers between 1200 and 12 000. Only the lower 40% of its length was exposed to the water current in the flume and applied top tensions varied from 15 to 110 N giving fundamental natural frequencies in the range from 3.0 to 7.1 Hz. Reduced velocities based on the fundamental natural frequency up to 16 were reached. The mass ratio was 1.8 and the combined mass–damping parameter about 0.05. Cross-flow and in-line amplitudes, x–y trajectories and phase synchronisation, dominant frequencies and modal amplitudes are reported. Cross-flow amplitudes up to 0.7 diameters and in-line amplitudes over 0.2 were observed with dominant frequencies given by a Strouhal number of 0.16.