VIV of tensioned flexible cylinder under bidirectionally sheared flow

Background

The measured results demonstrate that there exists flow field with bidirectionally sheared flow distribution in South China Sea. VIV characteristic of slender structures under such flow field is unclear, which challenges the design of risers in the South China Sea.

Previous VIV experiments almost focus on the flow field in unidirectional distribution by towing or mechanical control. How to realize the simulation of bidirectionally sheared flow in the laboratory?

Contribution

We designed the laboratory apparatus for simulating bidirectionally sheared flow for the first time. The core component of the experimental setup is a gear structure that rotates due to the frictional force of the timing belt, generating a bidirectionally sheared flow field.

I led the first VIV experiment of a flexible riser under bidirectionally sheared flow, and designed the laboratory apparatus for simulating bidirectionally sheared flow and was responsible for carrying out the experiments. This experiment includes bare/straked and single/tandem cylinder systems under bidirectionally sheared and linearly sheared flows.

For the first time, the Strouhal number of vortex-induced vibration under bidirectionally sheared flow was proposed, which provides frequency model in VIV prediction.

The experiment data is being ongoing analyzed.

Reference

1. Fu, X., Fu, S.*, Ren, H., Xie, W., Xu, Y., Zhang, M., Liu, Z., & Meng, S. (2022). Experimental investigation of vortex-induced vibration of a flexible pipe in bidirectionally sheared flow. Journal of Fluids and Structures, 114, 103722.
2. Fu, X., Zhang, M.*, Fu, S., Zhao, B., Ren, H., & Xu, Y. (2022). On the study of vortex-induced vibration of a straked pipe in bidirectionally sheared flow. Ocean Engineering, 266, 112945.

VIV of free-hanging cylinder under 6-DOF motion

Background

Due to the increasing focus of temperature difference energy, more and more studies for water-intake riser, always simplified as a free-hanging cylinder, are conducted. Previous researches on water-intake riser VIV usually limited to the VIV response under background currents. However, the water-intake riser is also driven by the top vessel motion which will induce a spatial-temporal varying background flow. The study of VIV of water intake pipe considering the coupling effect of background current and top vessel motion has not been carried out yet.

Contribution

I participated in the design and manufacture of a six-degree-of-freedom (6-DOF) motion simulator. We realized the laboratory simulation of the coupling of irregular vessel motion and background currents in towing tank for the first time. We have conducted the most complete experiments about free-hanging cylinder VIV.

The experiment was completed recently, and the experimental data are being analyzed.