Abstract
In this article, a vortex-induced vibration prediction model of a flexible riser conveying two-phase flow, including geometric and hydrodynamic nonlinearity, is established. A van der Pol wake oscillator is utilized to characterize the fluctuating lift forces. The finite element method is chosen to solve the coupled nonlinear fluid–structure interaction equations. The natural frequencies of the flexible riser are calculated to validate the method through comparisons with results from the literature. The modal analyses show that geometric nonlinearity has a significant effect on the natural frequency, and the critical internal velocity is reduced than those in linear analyses. The impacts of the gas volume fraction as functions of cross-flow velocity on the synchronization region, the displacement amplitudes, and the maximum stresses and frequency spectra have been investigated. The results show that an increase in the gas fraction results in the linear increase in natural frequencies and a wider synchronization region, and an increase in liquid flow rate led to the slight decrease in displacement amplitude and maximum stress within a small flow range.
Highlights
Offshore oil and gas exploration and production have attracted researcher’s interest in the marine fluidconveying riser, such as transporting oil, natural gas, and other resources, due to the action of the severe ocean environment loads
A vortex-induced vibration (VIV) prediction model with a combination of both CF and axial (AX) motions for a flexible pipe transporting two-phase flow, including top tension and nonlinear hydrodynamic forces, is established in section ‘‘Mathematical models.’’ The validation of model and method are discussed in section ‘‘Model validation.’’ The frequency analyses and nonlinear dynamic responses are investigated in section ‘‘Parametric investigations and discussions.’’ In section ‘‘Conclusion,’’ some conclusions and suggestions are summarized
A VIV model with a combination of both CF and AX motions of a flexible riser conveying two-phase has been established and solved by finite element method (FEM) to investigate the effect of gas fraction and liquid flow rate on the displacement and stress of a riser
Summary
Offshore oil and gas exploration and production have attracted researcher’s interest in the marine fluidconveying riser, such as transporting oil, natural gas, and other resources, due to the action of the severe ocean environment loads. For the VIV prediction models of flexible cylinders, some excitations of flexible fluid-conveying risers, such as pulsating fluid and base excitations, were discussed in the literature.[15,16,17,18] Srinil[19] constructed a CF VIV prediction model for variable-tension vertical risers under linear shear current, and numerical predictions are good coincidence with some published experimental and computational results These models ignored the effect of geometric and hydrodynamic nonlinearities. A VIV prediction model with a combination of both CF and axial (AX) motions for a flexible pipe transporting two-phase flow, including top tension and nonlinear hydrodynamic forces, is established in section ‘‘Mathematical models.’’ The validation of model and method are discussed in section ‘‘Model validation.’’ The frequency analyses and nonlinear dynamic responses are investigated in section ‘‘Parametric investigations and discussions.’’ In section ‘‘Conclusion,’’ some conclusions and suggestions are summarized. The void fraction a, the slip factor K, and the volumetric gas friction eg can be expressed as follows
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