Categorizing the types of roughness in environmental flows is important to establish the scaling laws for the roughness and bottom friction parameterization. The dependence of roughness height on roughness element geometry is discussed to clarify the difference between the two distinct d-type and k-type roughness under oscillatory flows. Direct numerical simulations (DNS) of oscillatory flow over transverse square and triangle bars were conducted, by varying the height-to-space ratio w/k and the shape of bars. DNS results show that the major difference between d-type and k-type roughness is the contribution from the frictional drag and pressure drag to the total stress. For d-type of roughness, relatively large frictional drag may play important roles in larvae recruitment and sediment transport. In addition to the ratio w/k, the shape of the roughness element also affect the transition from d-type to k-type roughness. At intermediate range of Keulegan-Carpenter number (KC), the inertial force and drag force are of equal importance. Simulation results of wave friction factor were compared with theoretical results, and the results are very sensitive of the choice of the characteristic roughness length scale.

对环境流中的粗糙度类型进行分类对于建立粗糙度和底部摩擦参数化的比例法则很重要。讨论了粗糙度高度对粗糙度元素几何形状的依赖性，以阐明振荡流下两种不同的 d 型和 k 型粗糙度之间的差异。通过改变高空比w / k对横向方形和三角形条上的振荡流进行直接数值模拟 (DNS)和酒吧的形状。DNS 结果表明，d 型和 k 型粗糙度之间的主要区别在于摩擦阻力和压力阻力对总应力的贡献。对于 d 型粗糙度，相对较大的摩擦阻力可能在幼虫补充和沉积物运输中起重要作用。除了比率w / k 之外，粗糙度元素的形状也会影响从 d 型到 k 型粗糙度的过渡。在 Keulegan-Carpenter 数 ( KC ) 的中间范围内，惯性力和阻力同等重要。波浪摩擦系数的模拟结果与理论结果进行了比较，结果对特征粗糙度长度尺度的选择非常敏感。