Effect of internal flow on vortex-induced vibration dynamics of a flexible mining riser in external shear current

The dynamics of a full-scale pipe conveying fluid inside is investigated based on the finite element method (FEM). During the numerical simulation, the Euler–Bernoulli beam equations are used to model the motion of the full-scale pipe while the effect of internal flow is considered. And the semi-empirical time-domain model is applied to simulate the external hydrodynamic forces exerted on the pipe. Then the typical vortex-induced vibration (VIV) characteristics of the full-scale pipe considering both internal and external flows are analyzed. The results show that with the increase of the internal flow velocity, the natural frequencies of the full-scale pipe decrease and the in-line (IL) and cross-flow (CF) dominating modes are increased. Furthermore, the dominating frequencies in both IL and CF directions are not notably changed. And the IL and CF root-mean-square (RMS) values of amplitudes fluctuate at around the stable values due to the stable external hydrodynamic forces. It should be noticed that the IL and CF RMS strain values of the full-scale pipe are increased, especially for high external and internal flow velocities. The maximal RMS strain values in both IL and CF directions appear next to the pipe top, which could have an influence on the motion of the ship on the sea surface.

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Vortex-induced vibration dynamics of a flexible fluid-conveying marine riser subjected to axial harmonic tension

Journal of the Brazilian Society of Mechanical Sciences and Engineering ◽

10.1007/s40430-018-1289-z ◽

2018 ◽

Vol 40 (8) ◽

Cited By ~ 9

Author(s):

Xiaodong Zhang ◽

Ruyi Gou ◽

Wenwu Yang ◽

Xueping Chang

Keyword(s):

Marine Riser ◽

Vortex Induced Vibration ◽

Vibration Dynamics

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Effect of Top Tension on Vortex-Induced Vibration of Deep-Sea Risers

Journal of Marine Science and Engineering ◽

10.3390/jmse8020121 ◽

2020 ◽

Vol 8 (2) ◽

pp. 121

Author(s):

Jie Zhang ◽

He Guo ◽

Yougang Tang ◽

Yulong Li

Keyword(s):

Deep Sea ◽

Natural Vibration ◽

Dominant Frequency ◽

Bending Stress ◽

Van Der Pol ◽

Vibration Displacement ◽

Vortex Induced Vibration ◽

Towing Tank ◽

Wake Oscillator ◽

Shear Current

With the increase of water depth, the design and use of the top-tensioned risers (TTR) are facing more and more challenges. This research presents the effect of top tension on dynamic behavior of deep-sea risers by means of numerical simulations and experiments. First, the governing equation of vortex-induced vibration (VIV) of TTR based on Euler-Bernoulli theory and Van der Pol wake-oscillator model was established, and the effect of top tension on natural vibration of TTR was discussed. Then, the dynamic response of TTR in shear current was calculated numerically by finite difference method. The displacement, bending stress and vibration frequency of TTR with the variation of top tension were investigated. Finally, a VIV experiment of a 5 m long flexible top-tensioned model was carried out at the towing tank of Tianjin University. The results show that the vibration displacement of TTR increases and the bending stress decreases as the top tension increases. The dominant frequency of VIV of TTR is controlled by the current velocity and is barely influenced by the top tension. With the increase of top tension, the natural frequency of TTR increases, the lower order modes are excited in the same current.

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