The vortex-induced vibration(VIV)of slender marine risers under the influence of complex incoming flows is a hot topic in the field of ocean engineering.Using a two-way fluid-structure coupling method,numerical simulation studies were conducted on the VIV of risers under exponential shear flow.Based on the explicit modal analysis of the root mean square amplitude envelope diagram,it was found that compared to the linear shear flow conditions,when the flow velocity is low,the maximum amplitude of the riser model under exponential shear flow is relatively small;when the flow velocity is high,the nonlinear distribution of exponential shear flow enhances the vibration response of the riser.Analysis of the vibration response frequencies at the peaks and valleys of the root mean square amplitude envelope of the riser model revealed that the vibration frequency is single and relatively stable at the crest position,while the phenomenon of multi-frequency coexistence is significant at adjacent trough positions,with significant differences between them.The axial waveform along the pipe mainly exhibits dominant standing wave and standing wave-traveling wave mixed modes.The traveling wave generally occurs intermittently,with higher flow velocities resulting in higher frequencies of occurrence,and its propagation direction in the transverse direction is typically from the high-flow velocity section to the low-flow velocity section.Under the influence of exponential shear flow,there are significant differences in the vortex shedding patterns at different cross-sectional positions along the axial direction of the pipe.The vortex shedding in the wake region of the high-flow velocity section exhibits strong periodicity,with complete vortex tubes and a certain deviation angle from the pipe axis,while there are more honeycomb-like discrete vortices in the low-flow velocity section.
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