Application of wake oscillators to two-dimensional vortex-induced vibrations of circular cylinders in oscillatory flows

Abstract

A nonlinear time-domain simulation model for predicting two-dimensional vortex-induced vibration (VIV) of a flexibly mounted circular cylinder in planar and oscillatory flow is presented. This model is based on the utilization of van der Pol wake oscillators, being unconventional since wake oscillators have typically been applied to steady flow VIV predictions. The time-varying relative flow-cylinder velocities and accelerations are accounted for in deriving the coupled hydrodynamic lift, drag and inertia forces leading to the cylinder cross-flow and in-line oscillations. The system fluid-structure interaction equations explicitly contain the time-dependent and hybrid trigonometric terms. Depending on the Keulegan-Carpenter number (KC) incorporating the flow maximum velocity and excitation frequency, the model calibration is performed, entailing a set of empirical coefficients and expressions as a function of KC and mass ratio. Parametric investigations in the case of varying KC, reduced flow velocity, cylinder-to-flow frequency ratio and mass ratio are carried out, capturing some qualitative features of oscillatory flow VIV and exploring the effects of system parameters on response prediction characteristics. The model dependence of hydrodynamic coefficients on the Reynolds number is studied. Discrepancies and limitations versus advantages of the present model with different feasible solution scenarios are illuminated to inform the implementation of wake oscillators as a computationally efficient prediction model for VIV in oscillatory flows.

Modelling of wake-induced vibrations of tandem cylinders with a nonlinear wake-deficit oscillator

“…For calibration, the Nelder-Mead simplex algorithm for an unconstrained optimisation embedded in the Matlab function 'fminsearch' is herein applied as in Opinel and Srinil (2020) to minimize an error function For fixed-free tandem cases in Fig. 7a, numerical and experimental results agree that A2/D response builds up as Ur > 0 and attends a resonance peak of A2/D  0.8 at Ur  5, in all d cases.…”

“…A phenomenological modelling of VIV of a single circular cylinder subject to a steady cross flow based on a wake oscillator has been considerably implemented and applied to both rigid and long flexible structures (Facchinetti et al, 2004;Gabbai and Benaroya, 2005;Gao et al, 2019;Opinel and Srinil, 2020;Srinil, 2010Srinil, , 2011Srinil et al, 2018;Srinil and Zanganeh, 2012;Violette et al, 2007;Srinil, 2014, 2016).…”

Bending and low‐frequency vortex shedding of flexible cylinders in laminar shear flow

“…As an example on the opposite, microscopic, side: at the intracellular level, the cytoskeleton interacts with the flow of cytosol, the liquid inside cells, at scales of tens to hundreds of nanometers. In between these eight to ten orders of magnitude there is a rich collection of phenomena that involve FSI: deformation of red blood cells in hemodynamics, 1,2 flow-plant interactions in biomechanics, 3,4 vortex-induced vibrations of cylinders in cross flow, 5 and flight of insects and birds and airplanes 6,7 to name just a few.…”

“…Many systems that involve vortex-induced vibrations are examples of the latter. 5 The present article deals with detailed numerical simulations of FSI at an intermediate length scale of the order of millimeters. It is inspired by experimental work on soft hair beds by Alvarado et al 10 in which they show nonlinear behavior as a direct consequence of linear elastic cylinders ("hairs") bending under the influence of a laminar shear flow.…”

“…In other cases, FSI results in a strong interference between structural and fluid flow time scales. Many systems that involve vortex‐induced vibrations are examples of the latter 5 …”