Resonance analyses of a pipeline-riser system conveying gas-liquid two-phase flow with flow-pattern evolution

The pipeline-riser systems are applied extensively in engineering systems. The flow patterns of gas-liquid two-phase flow evolve abundantly in pipeline-riser system, and it might induce the combination and parametric resonance, which threatens the security and stability of the piping system. In order to evaluate the resonance effect caused by internal two-phase flow, a dynamic model capable of describing axial, bending vibrations and fluid-structure interaction was formulated using FEM (Finite Element Method), where the void fractions of the two-phase flow were predicted by empirical correlations. To understand the flow pattern evolution and the pressure fluctuation characteristics, the experiments of observations and pressure testing were carried out, and the flow pattern map has been drawn. The effects of void fraction and elastic foundation on structural natural characteristics were investigated in detail. Then, the resonance analysis of the experimental facility and the verification experiments were performed to study the vibration characteristics. The results presented that the flow patterns in the riser were generalized into five types, and the fluctuating frequencies were mainly concentrated in low frequencies. The supporting foundation could increase the structural natural frequency significantly, and enhancing elastic foundation coefficient was effective to eliminate the resonance caused by internal two-phase flow.