Numerical studies on passive suppression of one and two degrees-of-freedom vortex-induced vibrations using a rotative non-linear vibration absorber

Abstract

This paper presents a numerical investigation on the use of a rotative non-linear vibration absorber (NVA) as a passive suppressor for the vortex-induced vibrations phenomenon (VIV). The structural model consists of rigid cylinders mounted on elastic supports and the hydrodynamic loads are calculated using phenomenological models. The NVA is defined as a rigid bar, fitted with a tip-mass and hinged to the cylinder. Energy is dissipated by means of a linear dashpot linked to the bar.Two major groups are studied, the first one being that in which the cylinder is constrained to oscillate in the cross-wise direction (1-dof VIV). The second group, herein named 2-dof VIV, refers to the condition in which simultaneous oscillations in the cross-wise and in-line directions are allowed.Characteristic oscillation amplitude curves are obtained as functions of reduced velocities covering the lock-in for different values of the control parameters that define the NVA (namely, its mass, radius and dashpot constant). In addition, quantitative and qualitative aspects of cylinder and suppressor responses are explored in the form of colormaps defined in the space of control parameters for three specific reduced velocities.The systematic study shows that the mass parameter of the NVA has more influence on the VIV suppression for both 1-dof VIV and 2-dof VIV. In general, the suppression has proved to be greater in the 1-dof VIV case.