Experimental Study on Four-Degree-of-Freedom Vortex-Induced Motion of S-Spar Platform at High Reynolds Numbers

Abstract

Vortex-induced motion (VIM) substantially accelerates fatigue damage in platform risers and mooring systems, thereby reducing their service life. To obtain a deeper understanding of the VIM characteristics of the S-Spar platform, a series of experiments was conducted over a high Reynolds number (Re) range (3 × 10⁴ < Re < 1.8 × 10⁵). The study focused on analyzing the response amplitudes in sway, surge, heave, and roll motions and investigating the coupling characteristics at different degrees of freedom and the evolution of motion trajectories. Furthermore, the influence of the platform’s center of gravity (CG) height on sway and surge responses was examined. Results show that sway, surge, and heave amplitudes initially increased with decreasing reduced velocity (U_r) before gradually decreasing, whereas the roll amplitude displays a continuous increasing trend across the entire U_r range. Strong coupling effects were observed among the different degrees of freedom, accompanied by pronounced variations in motion trajectories as the U_r value increased. Additionally, at different CG heights, the overall trend of the sway response amplitude was consistent with that of the surge response. However, the maximum sway amplitude increased as CG height decreased, whereas the surge amplitude exhibited minimal sensitivity to changes in CG height.

Keywords

Vortex-induced motion / S-Spar platform / High reynolds number / Four-degree-of-freedom / Coupling characteristic

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Harbin Engineering University and Springer-Verlag GmbH Germany, part of Springer Nature