VIV of a Composite Riser at Moderate Reynolds Number Using CFD

Abstract

The vibratory response of a long slender riser, made of composite materials and subject to an ocean current, is examined for a range of conditions. A major focus of this study is the performance of composite materials when used for risers. The influence of the number of modes of vibration is studied, as is the influence of the mass ratio and the value of the damping coefficient. The flow past the riser is represented by a shear flow, ranging from Re=8000 at the lower end of the riser to Re=10,000 at the upper end of the riser. The riser vibration is treated as a coupled fluid-flow/vibration problem. The fluid-flow equations are represented by a large eddy simulation model for the wake turbulence present in the flow. Strip theory is used to represent different forcing locations along the length of the riser. Since the composite riser has a material damping that is frequency dependent (it decreases with increasing frequency), its response is different from, say, a steel riser with a constant material damping. The composite riser, with variable damping, has a larger rms displacement than a riser with constant damping, primarily because of the smaller mass ratio. The vibration amplitude is found to increase with an increase in the number of modes.

Modeling and simulation of vortex induced vibration on the subsea riser/pipeline (GRP pipe)

“…Another paper presented vortex-induced vibration of composite riser using CFD by T. Rakshit et al [7]. This study has revealed some interesting features regarding VIV of a composite riser.…”

Review of Composite Marine Risers for Deep-Water Applications: Design, Development and Mechanics

“…In addition to studying the mechanical properties of composite materials in sea water, there are effects from fatigue, load distributions, global responses and performances of the full-length composite riser. However, the CPR tube, its stress joint, steel tension joint and other standard joints face global functional and environmental conditions [98,[143][144][145][146]266]. The effects of functional loadings have also been studied in comparative studies presented on both steel and composite risers, including vortex-induced vibrations (VIVs) and resonances on the CPR [11,55,[199][200][201][202]246].…”

Comparative Study of Vortex-Induced Vibration of FRP Composite Risers with Large Length to Diameter Ratio Under Different Environmental Situations

“…Besides the research of mechanical properties of FRP composite materials in seawater, the responses and performances, including load distributions, fatigue, and vortex-induced vibrations (VIVs) of composite risers under environmental and functional loads have also been investigated [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The improvement of composite risers in performance over a pure metallic mandrel had been proved through a scaled-down test [23].…”

“…In terms of the VIV of composite risers, it is found that the fundamental frequency of a composite riser with the same boundary condition and geometry was higher than that of a steel riser [18] since the composite riser was much lighter and the value was relatively small [13,14]. The structural damping and tension variations were also significant to the VIV of composite risers [13], i.e., higher tension and damping could reduce VIV-induced fatigue [13,17]. A. F. Omar et al [18] found that the maximum VIV stresses of a composite riser were much smaller than those of a steel riser, indicating the better fatigue lives of composite risers.…”