Abstract
An experiment was conducted in a deep water basin to investigate the vortex-induced vibration mechanism of a drilling riser. Various measurements were obtained by the fiber Bragg grating strain sensors, and data was analyzed by modal analysis method. Results show that the vibration mode of the drilling riser increases with the increasing flow velocity, and the vibration amplitude in the CF direction is larger than that in the IL direction. The vibrations in the CF and IL directions interact and mutually affect each other. The vibration mode in the IL direction is usually larger than that in the CF direction as the dominant vibration frequency is twice of that in the CF direction. Higher stresses may occur rather in the IL direction than in the CF direction. Hence, fatigue induced by the IL direction should also be taken into consideration when analyzing the fatigue life of a drilling riser. The three-time harmonic appears, and the phenomenon becomes more obvious as the flow velocity increased for the effect of the “2T” wake mode under the experiment condition. Displacement trajectories are significantly influenced by dominant vibration frequency and phase angle between the CF and IL directions. Crescent shapes, figure-eight, and inclined figure-eight are appeared in the experiment with the increasing flow velocity.
Highlights
Drilling risers are conduits that provide temporary extension of a subsea blowout preventer on a surface drilling platform
This study aims to investigate the vortex-induced vibration (VIV) mechanism of drilling risers under the effect of uniform flow
2) The vibrations in the CF and IL directions interact and mutually affect each other for the periodic variations in the drilling riser tension induced by the vibrations in both the CF and IL directions
Summary
Drilling risers are conduits that provide temporary extension of a subsea blowout preventer on a surface drilling platform. The drilling riser is a slender, flexible, and cylindrical structure allocated in a marine edifice. When the ocean current flows across the drilling riser, initial deformation in the in-line (IL) direction will take place because of the ocean current induced the initial drag force. A vortex which can induce significant vibrations in the drilling riser in the cross-flow (CF) and IL directions may be generated. This vibration is called as a vortex-induced vibration (VIV). VIV is an important fluid-structure interaction problem that can cause significant fatigue in the drilling riser that could result in accidents
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