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Experimental investigation on vortex-induced force of a flexible pipe under oscillatory flow
Applied Ocean Research ( IF 4.3 ) Pub Date : 2022-07-17 , DOI: 10.1016/j.apor.2022.103269
Mengmeng Zhang, Shixiao Fu, Haojie Ren, Yuwang Xu, Xu Qin

In this paper, vortex-induced force (VIF) characteristics of a flexible pipe under oscillatory flow are experimentally investigated with different KC numbers ranging from 10 to 178, and reduced velocities from 4 to 7.9. The strain information caused by vortex-induced vibration (VIV) at different cross-sections on the flexible cylinder is measured in the model test. Combined with the modal superposition method and inverse analysis method for hydrodynamic force, the hydrodynamic forces on the flexible cylinder are inverted, including the excitation force in phase with velocity and added mass force in phase with acceleration. Then, through a least square method with forgetting factors, the excitation coefficients and added mass coefficients at each time step are identified. The results show that the VIV excitation coefficient of a flexible pipe under oscillatory flow has a significant “acceleration and deceleration” effect, that is, the excitation coefficients are mostly positive at the acceleration section of the oscillatory flow and negative at the deceleration section. This “acceleration and deceleration” effect also explains the response amplitude modulation feature of VIV under oscillatory flow. And this effect can be represented by the dimensionless acceleration parameter γ of the flow field, and the range of γ corresponding to the positive excitation coefficient is affected by the KC number and the maximum reduced velocity. In addition, the added mass coefficients present different time-varying features under oscillatory flow with different maximum reduced velocity. When the maximum reduced velocity is larger than 6.5, the time-varying trend of the added mass coefficient is opposite to that of the flow velocity. While when the maximum reduced velocity is smaller than 6.5, the added mass coefficient is maintained around 2.0 in VIV excitation region; and it is around 1.0 in the non-excited region which is close to the added mass coefficient of a cylinder in still water.



中文翻译:

振荡流下柔性管涡激力的实验研究

在本文中,我们通过实验研究了在 10 到 178 范围内的不同 KC 数和从 4 到 7.9 的降低速度下,柔性管在振荡流动下的涡激力 (VIF) 特性。在模型试验中测量了柔性圆柱体不同截面的涡激振动(VIV)引起的应变信息。结合模态叠加法和水动力反演分析方法,对柔性圆柱体上的水动力进行反演,包括与速度同相的激振力和与加速度同相的附加质量力。然后,通过带遗忘因子的最小二乘法,识别出每个时间步的激励系数和附加质量系数。结果表明,振荡流下柔性管的VIV激励系数具有显着的“加减速”效应,即激励系数在振荡流的加速段多为正,在减速段为负。这种“加减速”效应也解释了VIV在振荡流下的响应调幅特性。而这种效应可以用无量纲加速度参数来表示 这种“加减速”效应也解释了VIV在振荡流下的响应调幅特性。而这种效应可以用无量纲加速度参数来表示 这种“加减速”效应也解释了VIV在振荡流下的响应调幅特性。而这种效应可以用无量纲加速度参数来表示流场的γ,正激励系数对应的γ范围KC数和最大折减速度的影响。此外,添加的质量系数在具有不同最大降低速度的振荡流下呈现出不同的时变特征。当最大降低速度大于6.5时,附加质量系数的时变趋势与流速相反。而当最大降低速度小于6.5时,VIV激发区的附加质量系数保持在2.0左右;在非激发区约为1.0,接近于静水中圆柱体的附加质量系数。

更新日期:2022-07-17
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