Vortex induced vibrations (VIV) and slug flow are two important aspects for marine risers conveying a multiphase flow, and should be carefully examined due to the influence on the fatigue life of the structure. This article examines a truncated riser exposed to VIV with an internal two-phase slug flow. The main focus of the article was to examine the effect of internal slug flow on the VIV of a riser. The VIV were simulated in time domain with a linear structural model with constant pretension. Approximately 150 vortex shedding periods were simulated after the response reached steady state. An internal two-fluid flow was introduced, with constant internal velocity, pressure and uniform slug lengths. From the numerical study it was apparent that the slug velocity and slug length had an influence on the response pattern, amplitude and frequency. An analytical model that predicts additional response frequencies due to slug flow was also compared to the numerical studies. The analytical study produced similar additional response frequencies as the numerical study. The slug length and internal velocity can influence the response of the riser, and should be considered for marine risers conveying multiphase flow.
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