When structural damping enhances flow-induced vibrations

This work uncovers a counterintuitive effect of structural damping on vortex-induced vibrations (VIV). The influence of structural damping is examined numerically in the canonical problem usually considered to study these vibrations driven by flow-body synchronisation, i.e. a circular cylinder free to oscillate within a uniform cross-current, for Reynolds numbers up to 160 160 $160$ , based on the body diameter and inflow velocity. For rectilinear VIV without structural restoring force, the peak-amplitude responses, which develop for low structure to displaced fluid mass ratios, are always attenuated by damping, as previously reported. Yet, the lower-amplitude responses occurring for higher mass ratios exhibit a contrasting trend: they are amplified by damping. The amplification can be substantial and leads to vibrations that become significant compared with the peak-amplitude responses. It is observed over the entire Reynolds number range of VIV, and is even accompanied by an extension of this range in the subcritical region, relative to the threshold of 47 47 $47$ that marks the onset of flow unsteadiness for a fixed body. The enhancement of VIV by structural damping is interpreted in light of the distribution of fluid–structure energy transfer in the amplitude–frequency domain. Such an enhancement is a counterintuitive but general phenomenon, which is shown to persist along curvilinear trajectories and when a structural restoring force is added to the system.