Multi-mode interactions of curved pipe under external current and internal flow excitation

Highlights: • Multi-mode interactions of curved pipe subject to the coupled excitation of external current and internal flow was studied. • Both the external current and internal flow play important roles in determining the vibration modes. • The multi-modal dominance, mode switch/shift and fluid-structure interaction are clearly observed along the pipe span. The coupling response of flexible pipe subject to external shear current and internal uniform flow is numerically investigated in this paper. Firstly, without the internal flow being considered, the quantified comparisons of root mean square vibration amplitudes in relation with VIV responses between the numerical results and experimental data were made to verify the efficiency of numerical method. Subsequently, the instantaneous root mean square vibration amplitudes, spanwise waveforms, and 3D time-frequency-energy spectra related to the numerical results were analyzed in detail. It is found that both the external current and internal flow play important roles in determining the vibration modes, and that the vibration intensity is tightly associated with the internal flow velocity. It is worth noting that the increase of internal flow velocity can excite new vibration mode response. The position-depended mono- and multi-modal coexistence, multi-modal dominance, mode switch/shift and fluid-structure interaction are clearly observed along the pipe span, followed by the alternative occurrence of standing and traveling waveforms, due to the combination of vortex-induced vibration and flow-induced vibration.