指数剪切流作用下海洋立管振动特性研究

细长海洋立管在复杂来流作用下的涡激振动（VIV）是海洋工程领域备受关注的热点问题。采用双向流—固耦合方法，对立管在指数剪切来流作用下的涡激振动实施了数值仿真研究。基于均方根振幅包络图的显性模态分析发现，与线性剪切流工况相比，当流速较小时，立管模型在指数剪切流作用下振幅最大值相对较小；流速较大时，指数剪切流的非线性分布致使立管的振动响应增强。通过对立管模型均方根振幅包络峰、谷处的振动响应频率分析发现，在波峰位置处振动频率单一且较为稳定，而在相邻波谷位置处多频共存现象显著，两者有显著差异。沿管的轴向波形主要表现为驻波主导和驻波—行波混合模式，行波一般间歇发生，流速越大发生频次愈高，其在横流向的传播方向通常由高流速区段传递至低流速区段。指数剪切流作用下，沿管体轴向各截面位置处的旋涡脱落模式差异显著，高流速段尾流区的旋涡发放具有较强的周期性，涡管完整且与管轴存在一定偏离角度，低流速段蜂窝状离散涡旋较多。

Study on VIV response of marine riser under exponential shear flow

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 crosssectional 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.