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    A review on vortex-induced vibrations in confined flows
    (Pergamon-Elsevier Science Ltd, 2023) Duranay, Aytekin; Demirhan, Alkin Erdal; Dobrucali, Erinc; Kinaci, Omer Kemal
    The response of structures to Vortex-induced vibrations (VIV) is heavily influenced by the type of confinement of the surrounding bodies. The vortex patterns and motion responses are highly dependent on factors such as the finite aspect ratio, tip effects, characteristics of 3D flow, proximity to a bottom boundary layer, and piercing cylinders or proximity to a free surface. The response of these bodies in confined waters is significantly altered, which can be investigated in terms of the fluctuating lift, drag, amplitude, frequency, Strouhal number, and the phase difference between oscillations and vortex shedding. A physical explanation of these ingredients and a way out for the corresponding problems have been discussed in the literature individually or given as a review of certain parts. In the present review, we have aimed to compile all the ingredients of the confinement types on VIV including the physical meaning and effects on the structures. The paper is structured as follows: in the first part the introduction is given, in the second part physical explanation of VIV in confined flows is discussed, and in the third part the ingredients of confinement are divided into three main categories. The main categories are separated as finiteness or aspect ratio effect on VIV regarding end conditions - tip effects - free end, free surface effect, and effect of bottom or proximity of plane. Finally, some important points of these VIV studies are underlined.
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    Circular cylinders exposed to vortex-induced vibrations in restricted waters: VIV response from the bottom to the free surface
    (Elsevier Sci Ltd, 2025) Duranay, Aytekin; Demirhan, Alkin Erdal; Dobrucali, Erinc; Kinaci, Omer Kemal
    In this paper, we present a comprehensive experimental investigation into the effect of bottom and free surface boundaries on vortex-induced vibrations (VIV) of a freely oscillating circular cylinder. Effects of the boundaries were examined under varying gap ratios between the cylinder and these boundaries at a low mass ratio of m(r)=0.827, only in the cross-flow direction, in the Reynolds number range of 1.210(4) <= Re <= 910(4). The gap ratios, varied from -0.75 to 2, correspond to an approximate Froude number (Fr) of around 0.50. We have examined the VIV response of this cylinder through thirteen tests conducted in various stages: near the bottom boundary, at a sufficient distance from all boundaries, close to the free water surface, and partially submerged. The findings show that as the cylinder approaches the free surface, the synchronization range gradually narrows, and the amplitude response diminishes. Within these cases, frequencies deviate from the general trend nearby the end of the synchronization range. Upon the cylinder's upper surface contacting or penetrating the free surface, the VIV synchronization starts at a higher non-dimensional velocity. In the cases of piercing cylinders, a wide synchronization range was observed where the submergence of the body was only around 25 %. The cylinders piercing the free surface showcase a distinctive frequency pattern, revealing a nearly-constant trend despite the escalating flow velocity within the synchronization range. Lower amplitude and broader range of synchronization were observed in the experiments close to the bottom boundary. As the cylinder moves further from the bottom, the boundary effect vanishes and the amplitudes get higher.