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Description

Title:Vortex-induced vibration of a linearly-sprung cylinder with nonlinear energy sinks
Author(s):Blanchard, Antoine
Director of Research:Bergman, Lawrence A.; Vakakis, Alexander F.
Doctoral Committee Chair(s):Bergman, Lawrence A.
Doctoral Committee Member(s):Pearlstein, Arne J.; Fischer, Paul F.; Balajewicz, Maciej
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Vortex-induced vibration
Nonlinear energy sink
Abstract:We investigate the effect of coupling an essentially nonlinear and dissipative attachment to a linearly-sprung circular cylinder undergoing rectilinear vortex-induced vibration (VIV) normal to the mean flow. The attachment is a nonlinear energy sink (NES). The essentially nonlinear coupling between the rectilinear motion of the cylinder and the motion of the NES allows for efficient, one-way transfer of kinetic energy from the former to the latter, where it is dissipated through a process known as targeted energy transfer. We use a spectral-element approach to compute the flow and the rigid-body quantities, and show that for values of the Reynolds number in the laminar regime (20 ≤ Re ≤ 350) and well into the turbulent regime (Re ≈ 10,000), the addition of an NES to a linearly-sprung cylinder undergoing transverse VIV gives rise to a variety of physical phenomena not seen otherwise. We consider two NES configurations, namely, a rotational NES and a translational NES. The former consists of a mass allowed to rotate about the cylinder axis, with its rotational motion being linearly damped. The latter consists of a mass allowed to translate in the direction of travel of the cylinder, with its rectilinear motion being restrained by a cubic spring and a linear viscous damper. We show that, in a range of Re values (20 ≤ Re ≤ 100) in which the flow is expected to be two-dimensional and laminar, a rotational NES leads to phenomena as diverse as passive VIV suppression, partial stabilization of the vortex street formed downstream of the cylinder, drag reduction, capture of the trajectory on underlying slow-invariant resonance manifolds, and coexistence of multiple long-time solutions. We also investigate the extent to which a rotational NES affects the linear stability of the steady, symmetric, motionless-cylinder solution, as well as the onset of three-dimensionality in the wake. We additionally present preliminary evidence that, in the turbulent regime, the rotational NES displays great potential for being used not only as a VIV suppression device, but also as an efficient hydrokinetic energy harvester. For a translational NES, at a value of the Reynolds number slightly above the fixed-cylinder Hopf bifurcation, we construct a reduced-order model (ROM) of the fluid–structure interaction based on a wake oscillator, asymptotic analysis of which predicts the existence of complete and partial VIV-suppression mechanisms, relaxation cycles, as well as Hopf and Shilnikov bifurcations. These outcomes are confirmed by numerical integration of the ROM and comparison against spectral-element computations of the full-order system.
Issue Date:2017-10-06
Type:Text
URI:http://hdl.handle.net/2142/99300
Rights Information:Copyright 2017 Antoine Blanchard
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12


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