The different types of vortex-induced vibration and galloping interference and distinguish them through forced motion

This study investigates the interference mechanism between vortex-induced vibration (VIV) and galloping at low mass ratios through numerical simulations of three prismatic sections at a Reynolds number of 200. Three distinct modes of VIV-galloping interference are identified, exhibiting characteristic variations in the vibration amplitude vs reduced velocity relationship across different mass ratios: (i) in the VIV-dominant mode, galloping is suppressed below a critical mass ratio; (ii) the galloping-dominant mode demonstrates increasing galloping amplitude with decreasing mass ratio at a given reduced velocity, with no observable critical mass ratio; (iii) the reattachment-suppressed mode involves boundary layer separation followed by reattachment, which weakly suppresses galloping, consequently, increased damping thereby reinstates galloping vibrations. The three modes exhibit different numbers of inflection points in their respective force coefficient vs angle of attack curves under quasi-steady theory. However, quasi-steady theory is limited in quantifying the influence of mass ratio, necessitating the adoption of the forced motion method incorporating energy transfer for further analysis. Results demonstrate that the single-frequency forced motion method accurately predicts the free vibration response at high mass ratios. However, it fails to adequately represent the pronounced vibration effects induced by significant vortex shedding on the prism at low mass ratios. Incorporating the amplitude component at the vortex shedding frequency enables effective characterization of the distinct VIV-galloping interference behaviors observed under low mass ratio conditions.