Towing tank experiments on the vortex-induced vibrations of low mass ratio long flexible cylinders

A series of experiments describing the dynamic response resulting from vortex shedding excitation, on isolated long flexible cylinders with two different low mass ratios (mass to displaced fluid mass), are presented. The cylinder models had aspect ratios (length to diameter) of 158 and 187 and mass ratios of 1.1 and 2.7 respectively, both with very low damping ( < 1 % of critical). The models were towed to generate a stepped current in a 100 m long still water tank with a cross-section of 3.8×2.5 m, and curvatures were measured at 11 strain gauge stations distributed along the length of the models, resulting in an extensive data set. Reynolds numbers over 37 000 were reached and responding modes up to the fifth were observed, showing maximum amplitudes of more than 3 diameters in the model with the lowest mass ratio. Drag coefficients with values well over 3 were also measured.