Vortex-induced vibration on a low mass ratio cylinder with a nonlinear dissipative oscillator at moderate Reynolds number

Abstract

The vortex induced vibration (VIV) mitigation on a circular cylinder with low mass ratio (i.e. the ratio of structural to displaced fluid mass) parameter and moderate Reynolds numbers through a nonlinear energy sink (NES) is investigated numerically as basis for applications on dynamics of spar platform, marine tunnel or risers used in the ocean engineering industry. The Reynolds-Averaged-Navier–Stokes (RANS) equations and shear Stress transport (SST) k–ω turbulence model are used to calculate the flow field, while a fourth-order Runge–Kutta method is employed for evaluating the nonlinear structure dynamics of flow–cylinder–NES coupled system. The computational model includes an overset mesh solution which can avoid the negative volume grid problem as a dynamic mesh method is involved to deform the domain according to the motion of the fluid–structure interface. The numerical model is validated against experimental data of VIV of an isolated cylinder in uniform current. The study is aimed to investigate the effect of NES parameters, including mass, damping and nonlinear cubic stiffness, and various reduced velocities on the VIV response of the cylinder. The VIV amplitudes’ distribution along the various reduced velocities, trajectories of cylinder motion, hydrodynamic response, and temporal evolution of vortex shedding, are obtained by conducting numerical simulations. Subsequently, it is found that placing a NES with appropriate parameters inside the cylinder, can affect the distribution of the three-branch response and narrows the lock-in range. A good VIV amplitudes’ suppression can be achieved with a large NES mass, small nonlinear cubic stiffness, and the NES damping is higher in the critical range for this kind low mass ratio cylinder structures.