The drag and side force coefficients of a half-submerged cylinder in a free-surface flow were calculated through numerical simulations, with the aim of supporting the numerical modelling of log transport in rivers. The variability of these coefficients with the yaw angle with respect to the flow direction and with the ratio between the flow depth and the diameter of the cylinder were investigated. Simulations were performed with the three-dimensional code ANSYS/CFX, employing the volume of fluid multiphase technique to reproduce the critical interaction between the free surface and the cylinder. The numerical tests, showing the rise of the drag force coefficient for increasing yaw angles passing from flow-parallel to flow-perpendicular cylinder and the peak of the side force coefficient for flow-oblique cylinder, were validated by comparison with the results of laboratory experiments. The simulations were then extended to conditions with significant blockage in the vertical direction which had not been previously experimented, revealing a strong increase in the force coefficients for decreasing ratios between the flow depth and the cylinder diameter. A detailed description of the reproduced flow features in the proximity of the cylinder for the different cases was furthermore obtained. Such report, in addition to the analysis of the force coefficients, could serve a much wider range than that of log transport, i.e., any case in which a floating cylinder interacts with free-surface flow.

通过数值模拟计算了半淹没圆柱在自由表面流中的阻力系数和侧向力系数，以支持河流中原木运输的数值模拟。研究了这些系数随偏航角相对于流动方向的变化以及随流动深度与圆柱直径之间的比率的变化。使用三维代码ANSYS / CFX进行了仿真，采用了体积多相流体技术来重现自由表面和圆柱体之间的关键相互作用。数值测试，显示了从平行于流向垂直于垂直圆柱的偏航角增加时，阻力系数的上升以及斜向圆柱的侧向力系数的峰值，通过与实验室实验结果进行比较来验证。然后将模拟扩展到在垂直方向上有明显阻塞的条件，而以前没有进行过实验，从而揭示了力系数的强劲增加，从而减小了流量深度和圆柱直径之间的比率。此外，获得了针对不同情况的缸附近再现的流动特征的详细描述。除了对力系数的分析外，这种报告的范围比原木运输的范围大得多，也就是说，在任何情况下浮动圆柱体与自由表面流相互作用的情况。然后将模拟扩展到在垂直方向上有明显阻塞的条件，而以前没有进行过实验，从而揭示了力系数的强劲增加，从而减小了流量深度和圆柱直径之间的比率。此外，获得了针对不同情况的缸附近再现的流动特征的详细描述。除了对力系数的分析外，这种报告的范围比原木运输的范围大得多，也就是说，在任何情况下浮动圆柱体与自由表面流相互作用的情况。然后将模拟扩展到在垂直方向上有明显阻塞的条件，而以前没有进行过实验，从而揭示了力系数的强劲增加，从而减小了流量深度和圆柱直径之间的比率。此外，获得了针对不同情况的缸附近再现的流动特征的详细描述。除了对力系数的分析外，这种报告的范围比原木运输的范围大得多，也就是说，在任何情况下浮动圆柱体与自由表面流相互作用的情况。此外，获得了针对不同情况的缸附近再现的流动特征的详细描述。除了对力系数的分析外，这种报告的范围比原木运输的范围大得多，也就是说，在任何情况下浮动圆柱体与自由表面流相互作用的情况。此外，获得了针对不同情况的缸附近再现的流动特征的详细描述。除了对力系数的分析外，这种报告的范围比原木运输的范围大得多，也就是说，在任何情况下浮动圆柱体与自由表面流相互作用的情况。