A large-eddy simulation study on the similarity between free vibrations of a flexible cylinder and forced vibrations of a rigid cylinder

Abstract

The strip theory in hydrodynamics has been widely used for predicting complex vortex induced vibrations (VIV) behind bluff bodies, but the question of how accurate such predictions are has not been addressed adequately before. In order to corroborate the application of strip theory in VIV, we present a comparative study between free mono-frequency vibrations of a long flexible cylinder in both uniform and linearly sheared flow and corresponding forced vibrations of a rigid cylinder with prescribed sinusoidal motions. We employ the entropy–viscosity large-eddy simulation (LES) to resolve the vortical flow and the coupled cylinder response, which we validate by companion experiments of the same configuration. We then extract from LES, at the same Reynolds number, the values of the sectional vibration amplitude, frequency, and phase angle (between inline and crossflow motions), and use them as input parameters for the forced vibration case, for which we perform two-dimensional simulations. We show here by systematic simulation studies that the hydrodynamic coefficients exhibit strong similarities between the two cases, and the forced vibration closely resembles the sectional near wake of the free vibration.