Study On Coupling Simulation And Suppression Method Of Deepwater Riser VIV

The vortex-induced vibration (VIV) of a deepwater riser may occur when the long riser with lower natural frequency encounters certain sea current, but the prediction of such phenomenon is always a difficult problem in deepwater riser design. In this thesis, an iteration method between CFD analysis and structural FE analysis is proposed. In the iteration process, the vibration of the riser obtained through structure FE analysis is applied to define the riser wall movement in the flow field by dynamic meshing technique and fluid forces caused by the vortex shedding are calculated in CFD analysis.Both uniform flow and shear flow are studied in this thesis and the process is verified according to some experiment data from relevant literature. The analysis results indicate that the riser's movement enhances the vortex's shedding, and the fluid-structure coupling state in the VIV phenomenon can be simulated under certain accuracy which depends on the iteration times. Through the calculation, it can be validated that the period of lift force is about twice of the drag force. Though the peak value of drag force is a little higher than lift force, the amplitude of lift force is about 10 times of drag force. This thesis concludes that both cross-flow vibration and in-line vibration should be considered in the deepwater riser design process.In order to suppress VIV, the effect of a shedding-suppression device called riser fairing is also studied. Calculations indicate that the intensity of vortex shedding is destroyed greatly. Arrangements of fairing are also studied and the suppression effects are embodied by comparison to the analysis results of the bare riser.CFD software FLUENT is used to analyze the fluid field and FE software ANSYS to analyze the riser dynamic response.