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Ocean Engineering

An Engineering SDOF Model for Transverse VIV Response of a Cylinder in Uniform Steady Flow

[+] Author and Article Information
Gautam Chaudhury

 Intecsea, 1500 JFK Boulevard, Houston, TX 77032gautam.chaudhury@intecsea.com

J. Offshore Mech. Arct. Eng 133(3), 031106 (Mar 31, 2011) (6 pages) doi:10.1115/1.4001958 History: Received May 13, 2009; Revised April 21, 2010; Published March 31, 2011; Online March 31, 2011

A new model for fluid structure interaction during vortex shedding process and associated vortex induced vibration (VIV) of a cylinder in transverse direction is proposed. The present work is based on restrained inline motion. Nevertheless, the model can be further extended to include inline interaction. This is not the scope of the present work. The model predicts the control of shedding frequency by reduced velocity and collapsing it to structure natural frequency. It captures the self-exciting and self-limiting nature of VIV excitations and adequately describes the transverse force and motions experienced by an oscillating cylinder in steady flow with lift, added mass, and damping. Thus, steady state responses obtained from the model represent the unique nature of VIV found in the laboratory over a range of reduced velocities of practical importance. The model will benefit future extension to include interaction due to inline motion such that a better VIV prediction could be obtained for free cylinder vibration.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical sample of calibrated lift coefficients as a function of motion amplitude

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Figure 2

Shedding frequency control by reduced velocity due to self excitation. Frequency ratio is defined as (fs/fn), as developed in Eq. 9.

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Figure 3

Computed phase angles showing 180 deg phase shift at Uref=5 (Eq. 14). Reduced lift model only contains the structural damping whereas Hyd-Damping model includes total damping. Increased damping causes more separation.

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Figure 4

Variation of lift coefficient with reduced velocity. Reduced Lift coefficients are from Cl versus A/D relation obtained iteratively during analysis. Hyd-Damping Model-coefficients are back calculated, showing the same trend as the reduced lift model.

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Figure 5

Back calculated lift coefficients showing hysteretic amplitude variation (1)

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Figure 13

Comparison of VIV responses, based on with and without self excitation, and the associated consequence in underestimation of fatigue damage for not including the self-excitation. Particularly important is at the low end of the reduced velocity, probability of which is generally more due to higher probability of lower current velocity.

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Figure 12

VIV results showing the effect of using Reynolds number based on Strouhal number and associated Urf=1/St, instead of fixed Urf=5.0

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Figure 11

Time domain results using Reynolds number based Cd showing negligible amount of beating in response amplitudes

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Figure 10

Comparison of motion amplitudes between calculation and experiments (20) for mass damping (21)(4⋅M⋅ξ/(π⋅σ⋅D2)=0.122)

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Figure 9

Comparison of motion amplitudes between calculation and experiments (19) for mass damping (21)(4⋅M.ξ/(π⋅σ⋅D2)=0.013)

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Figure 8

Sensitivity of actual value of mass and damping. All results are for same mass-damping (21)(4⋅M⋅ξ/(π⋅σ⋅D2)=0.122). Series 2 and 3 are for high mass low damping. Series 4 and 5 are for low mass high damping. Model type has negligible effect.

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Figure 6

Mass-damping parameter and maximum amplitude response relationship. For high mass-damping, maximum amplitude occurs at reduced velocity close to reference (Ur=Urf=5) and for low mass-damping, it occurs higher Ur values (Ur>Urf). Mass-damping definition used(1)=4⋅π⋅M⋅ξ/(σ⋅D2).

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Figure 7

Motion response for very low mass damping (4⋅π⋅M⋅ξ/(σ⋅D2)=0.0294). It shows some differences between the two types of models. Note that at higher mass damping there is negligible difference

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