涡激振动行波动力学特征的数值模拟

采用数值模拟分析了水中大长径比结构物涡激振动行波动力学特征,以及水动力学阻尼和模型初始张力对于行波动力学特征的影响.数值模拟模型采用改进的尾流振子模型,该模型考虑了涡激振动横向运动和顺流向运动之间的耦合,考虑了张力沿模型长度的变化和流体的耗散.给出了用于评估行波在整个振动波中所占比例的方法,该方法采用行波椭圆来定量表征行波所占的比例,即行波比.数值模拟结果显示,行波比总体上呈现随流速增加的趋势,但在模态阶数变化的临界流速上突然降低.水动力学阻尼显著影响着行波比,阻尼比越大,行波比越大,行波对于整个振动波的贡献就越大.不同张力情况下,行波比突然下降的临界速度不同.初始张力影响模型的固有频率,影响模态阶数发生转变的流速,从而影响了行波比突然下降的临界流速.

NUMERICAL SIMULATION OF TRAVELING-WAVE DYNAMIC FEATURES OF VORTEX-INDUCED VIBRATION

The paper examines the dynamic features of traveling wave by numerical simulation, and the effect of hydrodynamic damping and initial tension on traveling wave were presented for the vortex?induced vibration(VIV) of a long slender cylinder. The simulation was carried out by using a modified wake oscillator model which considered the coupling of in?line (IL) and cross?flow (CF) motions for VIV. The variation of the tension along the length of the model and the wake diffusion were considered. A method that was used to assess the contribution of traveling waves in whole vibration waves was also introduced, where the traveling wave ellipse was employed to scale the ratio of travelling wave component to overall vibration wave. The simulation results show that the traveling wave ratio presents a roughly increasing tendency with the increase of velocity, but falls suddenly at a critical velocity where the mode number is changed. Meanwhile, it is found that the hydrodynamic damping influences the contribution of traveling waves greatly. The lager the fluid damping is, the greater the contribution of traveling wave in whole vibration wave is. For the case with a hydrodynamic damping of 1.1, the traveling wave ratio is greater than that for the cases with hydrodynamic damping of 0.9 and 0.7. The velocity where the traveling wave ratio suddenly falls is controlled by the initial tension, while the initial tension influenced the mode order.