Steady current induced vibration of near-bed piggyback pipelines: Configuration effects on VIV suppression

• Physical modeling for steady current induced vibration of piggyback pipelines.
• Main influential factors for VIV response of near-bed piggyback pipelines.
• Comparison of VIV of piggyback pipelines with that of a single pipeline.
• Optimal configuration for VIV suppression of piggyback pipelines.

A series of experiments on steady current induced vibration of piggyback pipelines close to a plane seabed were conducted with a hydro-elastic facility in a conventional water flume. The effects of the mass-damping parameter, the diameter ratio, the gap-to-diameter ratio, the spacing-to-diameter ratio and the position angle on the VIV response were studied. The VIV suppression for the piggyback pipeline system by the small pipe was investigated based on the analysis of the vibration amplitude and the critical reduced velocity for the onset of VIV. Comparison with the prediction with the modified Griffin plot by Govardhan and Williamson (2006) [10] shows that the peak vibration amplitude of near-wall piggyback pipelines is smaller than that for a wall-free single pipe. The configuration parameters of piggyback pipelines have significant effects on the VIV suppression. For the configuration of the small pipe above the main pipe (θ = 90°), the minimum peak amplitude and the maximum critical reduced velocity occur at the spacing-to-diameter ratio of G/D ≈ 0.25, indicating that VIV is suppressed most effectively by the small pipe at this value of G/D. For a constant value of G/D = 0.25, both the minimum peak amplitude and the maximum critical reduced velocity occur at the position angle of θ ≈ 120°.