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应用基于浸入边界法(IBM)的三维水动力并行计算程序Cg LES_IBM,并结合隐式结构动力计算程序X-code,研究了低雷诺数条件下细长柔性立管的涡激振动问题。研究发现:立管的振动体现出明显的驻波振动特征。立管在顺流向主要激发奇数阶模态,而横流向处于激发状态模态的奇偶性取决于涡激振动卓越频率和立管固有频率之间的关系。涡激振动的频谱呈现为单谱模式,所有的振动能量都集中在一个窄频段上,波节处能量较弱,波腹处能量较强。波节处,时均能量传递系数为负值,涡激振动处于抑制状态,相邻波节之间,时均能量传递系数为正值,并沿展向呈现出“马鞍形”分布,涡激振动处于激发状态。柔性立管涡激振动的泻涡模式呈现出三维特性,近尾流区为2S模式,但由于倾斜泻涡造成尾涡沿展向移动,尾涡模式随后变为2P0模式,随着较弱漩涡的耗散,在远尾流区,尾涡模式又回到2S模式。
The vortex-induced vibration of slender flexible risers under low Reynolds number conditions is studied by using Cg LES_IBM, a three-dimensional hydrodynamic parallel computing program based on Immersion Boundary Method (IBM), and X-code of implicit structural dynamics. It is found that the vibration of riser shows obvious vibration characteristics of standing wave. The standpipe mainly excites the Odd Order mode in the downflow, and the parity of the Inverse Flow mode in the Excited mode depends on the relationship between the predominant frequency of the Vortex Vibration and the natural frequency of the standpipe. Vortex excited vibration spectrum presented as a single spectral model, all of the vibration energy are concentrated in a narrow band, the node energy is weak, strong energy at the antinode. At the node, the mean energy transfer coefficient is negative and the vortex-induced vibration is in a restrained state. The energy transfer coefficient between adjacent nodes is positive and exhibits a “saddle-shaped” distribution along the span. Vortex-induced vibration in the excited state. The vortices of the flexible riser have three-dimensional vortices and the near-wake region has a 2S mode. However, due to the sloping vortex causing the vortex to move in the span direction, the wake vortex mode then changes to the 2P0 mode. With the weak vortex Dissipation, in the wake region, wake vortex mode is back to 2S mode.