Analysis and prediction of vortex-induced vibrations of variable-tension vertical risers in linearly sheared currents

Abstract

Many studies have tackled the problem of vortex-induced vibrations (VIV) of a vertical riser with a constant tension and placed in uniform currents. In this study, attention is focused on the cross-flow VIV modelling, time-domain analysis and prediction of variable-tension vertical risers in linearly sheared currents. The partial-differential equation governing the riser transverse motion is based on a flexural tensioned-beam model with typical pinned-pinned supports. The hydrodynamic excitation model describing the modulation of lift force is based on a distributed van der Pol wake oscillator whose nonlinear equation is also partial-differential due to the implementation of a diffusion term. The variation of empirical wake coefficients with system parameters and the water depth-dependent Reynolds number is introduced. Based on the assumed Fourier mode shape functions obtained by accounting for the effect of nonuniform tension, the Galerkin technique is utilized to construct a low-dimensional multi-mode model governing the coupled fluid-riser interaction system due to VIV. Numerical simulations in the case of varying sheared flow profiles are carried out to systematically evaluate riser nonlinear dynamics and highlight the influence of fluid-structure parameters along with associated VIV aspects. In particular, the effects of shear and tensioned-beam (tension versus bending) parameters are underlined. Some comparisons with published experimental results and observations are qualitatively and quantitatively discussed. Overall parametric analysis and prediction results may be worthwhile for being a new benchmark against future experimental testing and/or numerical results predicted by an alternative model and methodology.

Self-similar vortex-induced vibrations of a hanging string

“…Similarly, spatial variations of the cable's tension (for example due to gravity and/or free end conditions) is expected to impact the structure's dynamics, in particular by localizing vibrations in regions with lower tension. This second configuration has so far received little attention [15,16]. The present paper thus discusses an experimental investigation of the VIV of a hanging string, where gravity-induced tension does vary from bottom to the top.…”

Methods of setting depth range with credibility of conductor for deepwater drilling based on probability statistics

“…Among them, the setting depth of conductor in deepwater drilling directly affects the mechanical stability of subsea wellhead. If the depth design is relatively shallower, it will lead to instability of subsea wellhead; on the contrary, if the design depth is deeper, although it can ensure the security of subsea wellhead, it will result in a waste of resources, and may cause the conductor can not be to the specified depth [15][16][17]. Through investigation of currently used methods of setting depth of conductor for deepwater drilling [9][10][11][12], we found that the calculated value is a single value, while there are many uncertainties in the parameters of subsea shallow strata in deepwater drilling.…”

A practical approach to predicting cross-flow and in-line VIV response for deepwater risers

“…Chang and Isherwood [7] developed a time domain VIV prediction code using wake-oscillator model and vortex tracking model. Srinil [8] simulated Tognarelli's laboratory test model [9] using wake-oscillator model by assuming the riser response frequency locked in the Strouhal frequency associated with the maximum current velocity. Cheng et al [10,11] carried out lots of validation works using different riser models.…”