Analysis On Vortex-induced Vibration Of Riser With Wave And Current Coupling Effect

In recent years, marine petroleum development project is planning in deepwater, so the safety problem of marine riser is becoming increasingly conspicuous. Under the action of characteristic wave, the Vortex-Induced Vibration (VIV) of a deepwater riser may induce fatigue failure when the riser with lower natural frequency.This paper mainly focuses on Vortex-Induced Vibration of marine riser and research on the influence of natural frequency. In order to reduce disasters and fatigue destroy, this paper analyses deeply on riser's tension, length, diameter and thickness. Otherwise, it is helpful to research on dynamics of marine riser and simulate the drift motion with the second boundary condition on top of riser with more proper structural displacement and moment. After dynamic analyzing under the second boundary condition, it is indicated that riser VIV and vortex shedding frequency deviates Strouhal rule when the vibration and Vr of riser reach and exceed a certain degree. But the variation of frequency remains constant all the time. The amplitude of axial vibration is much smaller than the cross-flow vibration, so it can be ignored. Although the amplitude of cross-flow vibration is very larger than the in-line vibration, the cross-flow frequency is larger than the in-line vibration. When the current velocity rises, the vibration of riser undergoes a process of increasing and reducing.At last, riser is numerical simulation calculating by using FEM software ABAQUS. In the analysis process, the wave and current coupling force is solved and transferred to the riser after using the Morison equation. Each step result is used for the initial condition of next step in the vibration analysis.