Abstract New experiments involving the three-dimensional current-induced live-bed scour beneath submerged horizontal pipelines are presented, spanning larger Shields parameter and cylinder-to-sediment diameter ratio than previous studies. Specific emphasis is on gaining a better understanding of, and ability to predict, the span migration velocity during the initial and subsequent development of such a scour hole. Consistent with previous experimental observations, both a primary (faster) and secondary (slower) span migration are observed. Process visualization of suspended sediment patterns are in line with prior speculation that this transition coincides with reduced local bed shear stress amplifications as the scour hole both deepens and widens. Dimensional analysis and physical insight are combined, leading to a new rational model for predicting the span migration velocity in both live-bed and clear-water regimes, with predictions naturally coinciding at the limit of far field incipient motion conditions. In both regimes the data cluster as predicted, and fitted closed-form expressions are provided for predicting the span migration velocity. The rational approach likewise includes a new and simple criterion for the transition from primary to secondary migration in the live-bed regime. In the clear-water regime the model incorporates primary dependence on the ratio of the Shields parameter to its critical value, resolving apparent contradictions with a previous study which suggests that the depth-based Froude number is the most important governing parameter. The developed rational model can be used to quantitatively predict all known major features of the span migration velocity in the early stages of the three-dimensional (live-bed and clear-water) scour beneath submerged horizontal cylinders induced by perpendicular flow, and can hence be regarded as the first complete model for this evolution.

中文翻译：

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水下管道下三维电流感应冲刷中的跨肩迁移

摘要 介绍了涉及水下水平管道下方三维电流感应活床冲刷的新实验，其跨越了比以往研究更大的盾构参数和圆柱与沉积物的直径比。具体重点是更好地了解和预测此类冲刷孔初始和后续开发过程中的跨度迁移速度。与先前的实验观察一致，观察到主要（更快）和次要（更慢）跨度迁移。悬浮沉积物模式的过程可视化与先前的推测一致，即这种转变与随着冲刷孔加深和扩大而减少的局部床剪切应力放大相一致。维度分析与物理洞察相结合，导致了一个新的合理模型，用于预测活床和清水状态下的跨度迁移速度，预测自然符合远场初始运动条件的极限。在这两种情况下，都提供了预测的数据集群和拟合的封闭形式表达式，用于预测跨度迁移速度。合理的方法同样包括一个新的和简单的标准，用于在活床制度中从初级迁移到次级迁移。在清水状态下，该模型主要依赖于 Shields 参数与其临界值的比率，解决了与先前研究的明显矛盾，该研究表明基于深度的弗劳德数是最重要的控制参数。