A nonlinear model of vortex-induced forces on an oscillating cylinder in a fluid flow

TL;DR

This paper develops a nonlinear polynomial state-space model to accurately predict vortex-induced forces on an oscillating cylinder in fluid flow, capturing complex vortex shedding and synchronization phenomena.

Contribution

It introduces a nonlinear modeling approach that leverages nonlinear distortion analysis to improve accuracy and reduce parameters in vortex-induced force prediction models.

Findings

Model accurately simulates force time series across frequency-amplitude ranges.

Nonlinear analysis distinguishes odd and even nonlinear behaviors.

Model outperforms generic approaches in accuracy and parameter efficiency.

Abstract

A nonlinear model relating the imposed motion of a circular cylinder, submerged in a fluid flow, to the transverse force coefficient is presented. The nonlinear fluid system, featuring vortex shedding patterns, limit cycle oscillations and synchronisation, is studied both for swept sine and multisine excitation. A nonparametric nonlinear distortion analysis (FAST) is used to distinguish odd from even nonlinear behaviour. The information which is obtained from the nonlinear analysis is explicitly used in constructing a nonlinear model of the polynomial nonlinear state-space (PNLSS) type. The latter results in a reduction of the number of parameters and an increased accuracy compared to the generic modelling approach where typically no such information of the nonlinearity is used. The obtained model is able to accurately simulate time series of the transverse force coefficient over a wide range of the frequency-amplitude plane of imposed cylinder motion.