Vortex-induced vibration (VIV) has been intensively studied both theoretically and experimentally due to its importance in the design of marine risers. In recently years, the effects of single phase, steady internal flow on the VIV of marine risers have received increasing attention. However, the effects of transient two-phase flow on the vibration behavior of marine risers have been seldom studied. In this work, a fluid-structural model for analyzing the dynamic behavior of riser vibration subjected to simultaneous internal gas-liquid two-phase flow and external marine current is proposed. Slug flow regime is considered as it causes most violent vibrations. An analytical model is adopted for the prediction of important flow characteristics of the gas-liquid slug flow. A wake oscillator is employed to model the vortex shedding behind the riser. The dynamic behavior of risers is analytically and numerically investigated by using the generalized integral transform technique (GITT), by which the transverse vibration equation is transformed into a coupled system of second order differential equations in the temporal variable. Parametric studies are performed to analyze the effects of the superficial velocities of liquid and gas on the dynamic behavior of risers.

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