Abstract
The vibration excited by gas-liquid multiphase flow endangers the structural instability and fatigue life of subsea jumpers due to the cyclic behavior. In this paper, the multiphase flow-induced vibration (MFIV) of an M-shaped jumper is numerically investigated using a two-way fluid-structure interaction (FSI) approach. The effect of gas-liquid ratios (β) ranging from 1:1 to 1:5 is examined with a fixed flow velocity of 3 m/s, and the influence of mixture velocity (vm) in the range 2–6 m/s is evaluated with a gas-liquid ratio of 1:1. The numerical results reveal the detailed flow evolution of the gas-liquid mixture along the jumper. With inflow of slugs, the pattern successively experiences the slug flow, wavy flow, imperfect annular flow, stratified flow, churn flow, wavy flow and imperfect annular flow in the pipe segments when β = 1:1 and vm = 3 m/s. This development of mixture flow is significantly altered by changing either the gas-liquid ratio or the mixture velocity. In comparison with the flow evolution in a stationary jumper, the pattern in each pipe segment is not been substantially changed due to the limited response amplitude of order of 10−3D (D is the outer diameter of the jumper). Due to the complex flow evolution, the pressure acting on the six bends of the jumper fluctuate in multiple frequencies. Nevertheless, the dominant fluctuation frequency is approximately equal to the inflow slug frequency. Moreover, the inflow slug frequency also dominates the in-plane response of the jumper. Both the in-plane and out-of-plane responses of the jumper exhibit spatial-temporal variation characteristics. The most vigorous oscillation occurs at the midspan of the jumper. As β is reduced, the out-of-plane response of the jumper midspan is suppressed while the in-plane response is enhanced. In contrast, both the in-plane and out-of-plane oscillations of the jumper midspan are amplified with the increase of vm.
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