Hydraulic characteristics in vegetated open channel flows.

为了研究弹性竖直粗糙度单元的摆动对平均流速、湍动强度和雷诺应力分布的影响，并建立一个可以解释实验结果的理论模型，研究了芦苇挠度与水流速度的关系，以了解芦苇的弯曲刚度等物理特性。粗糙度单元放置在一个0.9m长的正方形格子中，床与床之间的距离相等。对于每个粗糙度，实验分为三种情况，该模型推导了恒定均匀流的动量方程，并将粗糙度单元的位移分析为悬臂梁的静态挠度问题，其中水动力转换为作用在粗糙度单元上的外力。流场可以方便地分成两个区域；(1)外部区域对应于粗糙单元上方区域，(2)内部区域对应于粗糙单元内部区域。分析速度分布表明，该理论可以有效地用于预测水流特性。假定作用在一个粗糙单元上的水动力与水流方向上的投影面积和平均速度的平方成正比，粗糙单元的位移由任意位置处的弯矩得到。计算得到的粗糙单元的挠度除低速情况外与所有实验剖面一致。

The objectives of this study are to investigate the effects of the sway of flexible standing roughness elements on the profiles of mean velocity, turbulence intensities and Reynolds stress, and to develop a theoretical model which can explain the experimental results.A relationship between the deflection of reeds and water velocity was investigated in order to understand the physical characteristice of reeds, e.g.flexural rigidity.The reeds as the roughness elements were used Hydrilla verticillata(L.f).Casp.KUROMO and Potamogeton oxyphyllus Miquel, YANAGIMO.The experiments were conducted in a recirculating open channel 7.0m long, 0.4m wide, and 0.4m deep. The roughness elements were placed in a bed 0.9m long with the same distance in a between in a square lattice. For each roughness, the experiment was divided to three cases.In this model, the momentum equations are derived for the steady uniform flow and the displacement of roughness elements is analyzed as the static deflection problem of cantilever, in which the hydrodynamic force is converted into the external force acting on the roughness elements. The flow field may be conveniently separated into two region ; (1)the outer region, which corresponds to the region above roughness elements, (2)the inner region, which corresponds to the region within roughness elements.The analytical velocity profile show that the theory could bu used efficiently to predict the characteristics of flow.The hydrodynamic force acting on one roughness element is assumed to be proportional to the projected area in the flow-direction and to the square of mean velocity, and the displacement of roughness elements is derived from the bending moment at an arbitrary position.The calculated deflection of the roughness element agree to all of the experimental profiles with exception of the case of slow velocities.