This paper investigates the hydrodynamic damping of a circular cylinder with helical strakes at Keulegan-Carpenter (KC) number from 0.07 to 3 in the presence of steady currents. Experiments were performed with a straked cylinder oscillating in either in-line or cross currents over Reynolds number (based on the oscillating velocity amplitude) varying from 1260 to 54,000. With in-line current being present, the measured drag coefficients of the straked cylinder are found to depend on the ratio between the oscillating velocity amplitude and the steady current velocity. This phenomenon is further confirmed by computational fluid dynamics using large-eddy simulations. The drag coefficients obtained from the numerical simulations agree well with the experimentally determined values. Similar phenomenon is observed for the cases with cross background current. Based on the experimental data, empirical formulae are proposed to evaluate drag coefficients. These results are of importance in estimating the resonant motion and the fatigue life of risers, e.g. water intake risers, in the flow regime of low KC. Finally, recommendations are provided for fatigue analysis of risers with helical strakes from the perspective of engineering practice.

本文研究了在Keulegan-Carpenter（KC）在有稳定电流的情况下从0.07到3的数字。实验是用行程在1260至54,000范围内的雷诺数（基于振荡速度幅度）的串联或交叉电流振荡的行程气缸进行的。在存在在线电流的情况下，发现测得的行程缸的阻力系数取决于振荡速度振幅与稳定电流速度之间的比率。使用大涡模拟的计算流体动力学进一步证实了这一现象。从数值模拟获得的阻力系数与实验确定的值非常吻合。对于具有跨背景电流的情况，观察到类似的现象。基于实验数据，提出了经验公式来评估阻力系数。KC。最后，从工程实践的角度为螺旋形冒口冒口的疲劳分析提供了建议。