Video demonstrating 3D scour beneath a submerged pipeline in a steady current

It was filmed during Experiment 13 (far field Shields parameter \theta=0.126) from the study of Sui et al. (2021). Snapshots from this video were utilized to produce Figure 15 within the paper.

This video demonstrates three-dimensional scour beneath a submerged pipeline in a steady current from an experiment conducted in the Hydraulics Laboratory at the Technical University of Denmark, Department of Mechanical Engineering.

The video demonstrates clear differences in the amount of sand put into suspension during the primary (initial, rapid) and secondary (slower) stages of span migration during the 3D scour beneath a submerged pipeline. There is much more sediment put into suspension during the primary stage.

This visualization thus supports the contentions of Cheng et al. (2009), who asserted that the initial (rapid) stage of scour span migration is likely induced by a strong three-dimensional flow, driven through the relatively small (short and thin) initial scour hole by a relatively large pressure gradient associated with the contracted flow beneath the cylinder. Cheng et al. (2009) likewise stated that as the scour span progresses along the cylinder, and the local scour at mid-cylinder (i.e. the position of initialized scour, y = 0), reaches equilibrium, that the driving pressure gradient will become smaller, and the flow will locally become much more two-dimensional. They asserted that the slower secondary migration stage would hence coincide with the disappearance of the additional scouring mechanisms associated with the initial stage.

References

Cheng, L., Yeow, K., Zhang, Z. & Teng, B. (2009) Three-dimensional scour below offshore pipelines in steady currents. Coast. Eng. 56 (5-6), 577–590.

_{https://doi.org/10.1016/j.coastaleng.2008.12.004}

Sui, T., Staunstrup, L.H., Carstensen, C. & Fuhrman, D.R. (2021) Span shoulder migration in three-dimensional current-induced scour beneath submerged pipelines. Coast. Eng. 164, article no. 103776.
_{https://doi.org/10.1016/j.coastaleng.2020.103776}