A passive amplification of VIV through a semi-hollow cylinder for Reynolds number 200

Since the demonstration that the kinetic energy generated by vortex-induced vibrations (VIVs) can be converted into electricity, the amplification of VIV has been of significant interest. For this practical relevance, we present a passive method to amplify VIVs of a circular cylinder for Reynolds number 200. We employ an empty space inside a solid circular cylinder and place an orifice on the stagnation point to embody a concept of passive control, considering a potential combination with existing passive devices. We quantified the performance of the semi-hollow model via two-dimensional simulations for a range of reduced velocity 3$\le U_{red}\le $8, and these are compared to solid cylinder counterparts. We show that significant elevations of the transverse force and the dynamic response are achieved by the semi-hollow body under the synchronization condition as well as otherwise ones. In addition, the transverse net force acting on the inner surface of the semi-hollow cylinder is shown to be developed in time as a consequence of internal flow circulations, and this is asserted as a key role for the amplification.