CREEM2020

CREEM2020

Vortex-Induced Vibration Model of Rigid Cylinders With 2 Degrees of Freedom Near A Fixed Wall Based On Wake Oscillator

Submission Author: Rafael Feher , SP
Co-Authors: Rafael Feher, Juan Pablo Julca Avila
Presenter: Rafael Feher

doi://10.26678/ABCM.CREEM2020.CRE2020-0089

 

Abstract

When an offshore structure is placed near a boundary, such as the seabed, the vortex shedding from the downstream side of this structure may be not fully developed, affecting the motion of the structure. In the present work, a new wake oscillator model to predict Vortex-Induced Vibrations (VIV) of a rigid cylinder with 2 Degrees of Freedom (2-DOF) initially placed near a fixed wall is proposed. To account for the effects of the fixed wall on the motion of the cylinder, two empirical coefficients, beta and eta, are coupled to the wake oscillator equation. Gap ratios, defined as the ratio between the distance of the fixed wall to the cylinder, e, and the diameter of the cylinder, D, varying from 0.75 to 2 were simulated on a cylinder exposed to a fluid flow with Reynolds number varying from 6500$ to $20000. The empirical coefficients were calibrated using experimental data. After the calibration, using polynomial regression, the equations to calculate each empirical coefficient as function of the gap ratio were generated. The results of cross-flow reduced amplitude, mean drag coefficient and cross-flow reduced frequency for each gap ratio are presented in function of the reduced velocity and shows to be in good agreement with experimental data.

Keywords

vortex induced vibrations, wake oscillator, fluid-structure interaction, Two Degrees of Freedom Vibrations

 

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