Vortex-induced vibration time domain responses of flexible risers under oscillatory flows

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Journal of Vibration and Shock ›› 2018, Vol. 37 ›› Issue (13) : 56-64.

YUAN Yu-chao1,2， XUE Hong-xiang1,2， TANG Wen-yong1,2

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Abstract

Introducing the hydrodynamic force coefficient database obtained with forced vibration tests and adopting the full-new judgement for lock-in region and the lock-in criterion, aiming at vortex-induced vibration (VIV) problems of flexible risers under oscillatory flows, a set of time domain predicting numerical methods for users to choose was proposed. VIV hydrodynamic forces were depended on instantaneous incoming flow velocity and motion of riser’s cross-section. The corresponding hydrodynamic force coefficients were functions of non-dimensional amplitude and frequency. Based on the proposed methods, the dynamic response of a certain 4m high riser model under oscillatory flows with different KC numbers and maximum reduced velocities was calculated. The prediction results agreed well with those of tests. Amplitude modulation, hysteresis, frequency transition and higher frequency resonances, etc. phenomena were observed in the predicted results. These features of the dynamic response of the riser under combined oscillatory flow cases with different KC numbers and maximum reduced velocities were distinguished from those under steady flow cases. They were analyzed from the view point of VIV occurrence mechanism and explained reasonably. Finally, comparing VIV responses of the riser under oscillatory flows with those under uniform flows, it was shown that under the similar flow velocity, the RMS of riser’s VIV displacement under oscillatory flows is larger than that under uniform flows; under the same maximum reduced velocity, the smaller KC number corresponds to a larger RMS of riser’s VIV displacement.

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YUAN Yu-chao1,2， XUE Hong-xiang1,2， TANG Wen-yong1,2. Vortex-induced vibration time domain responses of flexible risers under oscillatory flows[J]. Journal of Vibration and Shock, 2018, 37(13): 56-64

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