Mitigation of Vortex-Induced Vibration of Cylinders Using Cactus-Shaped Cross Sections in Subcritical Flow

Abstract

Flexible cylinders, such as marine risers, often experience sustained vortex-induced vibrations (VIVs). Installing helical strakes on a riser is the most widely used technique to mitigate VIVs. This study was inspired by the giant Saguaro Cacti which can withstand strong wind with a shallow root system. In this study, numerical simulations of flow past a stationary cylinder of a cactus-shaped cross-section in a two-dimensional flow field at a subcritical Reynolds number of 3900 were performed. Results show that cylinders of a cactus-shaped cross-section have a lower lift coefficient without increasing drag compared to those of a circular cylinder. VIV experiments on a single flexible pipe as well as on a set of two tandem-arranged flexible pipes were conducted at different reduced velocities to investigate the effects of the streamwise spacing and wake of the cactus-like body shape on VIV mitigation. Experimental results show that the cactus-like body shape can mitigate VIV responses of the cylinder at upstream position with no cost of increased drag; however, similar to helical strakes, the efficiency of VIV mitigation for the cylinder at downstream position is reduced. Although the cactus-like body shapes tested in this study were not optimized for oscillation suppression, still this study suggests that modification of the cross-sectional shape to a well-designed cactus-like shape has potentials to be used as an alternative technology to mitigate VIV of marine risers.

Experimental Investigation and Numerical Modeling of Two-Phase Flow Development and Flow-Induced Vibration of a Multi-Plane Subsea Jumper

“…(a) (b) Existing studies on the vibration of subsea pipelines mainly focus on in-line planar pipelines and the corresponding vortex-induced vibrations caused by the oscillatory lift force generated by the vortex shedding [17][18][19][20][21][22]. With the development of deepwater oil and gas exploitation technology, the pressure and flow rate in the pipeline gradually increase.…”

“…Studies on multi-planar jumpers were rare, and only a few numerical analyses on internal flow characteristics such as slug flow were carried out by Wang, et al [30], Dai, et al [31], Lu, et al [32], and Song, et al [33]. Nair, et al [34] analyzed the vibration fatigue response of a multi-plane jumper structure for an internal Existing studies on the vibration of subsea pipelines mainly focus on in-line planar pipelines and the corresponding vortex-induced vibrations caused by the oscillatory lift force generated by the vortex shedding [17][18][19][20][21][22]. With the development of deepwater oil and gas exploitation technology, the pressure and flow rate in the pipeline gradually increase.…”