Fluid structure interaction analysis of gas-liquid two-phase flow in marine riser system on an elastic foundation

Key words:  gas-liquid two-phase flow  marine risers  elastic foundation  FEM  modal analysis  fluid structure interaction

Abstract:

To predict and evaluate the vibration characteristics of the marine risers caused by two phase flow in different flow regimes, the modal analysis and the gas-liquid tow-phase flow experiments were carried out. The influences of fluid density distribution and elastic foundation coefficients on vibration mode were considered in the modal analysis. The flow pattern maps including seven types of flow patterns were plotted in the study. The time domain and frequency domain analysis of the pressure fluctuation characteristics for different flow patterns were conducted, the possibility of resonance caused by seven types of flow patterns in different elastic foundations was analyzed, and the coupling vibration characteristics of the riser system were predicted. In addition, the dynamic response of the riser system was tested to verify the accuracy of the coupling vibration analysis method. The analysis results show that gas-liquid tow-phase flow and elastic foundation have significant impacts on natural frequency and vibration mode of the riser system. Severe slugging I, severe slugging III, slug flow and disturbed bubble flow can cause resonance when the riser system has no elastic foundation. If the elasticity coefficient of the foundation is large enough, two-phase flow can 't cause resonance of the riser system. The vibration response of the riser system is consistent with the fluctuation of the gas-liquid two-phase flow characteristics in the riser.