Effects of horizontal pressure gradients on bed destabilization under waves
Effects of horizontal pressure gradients on bed destabilization under waves
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波浪作用下水平压力梯度对河床失稳的影响
DOI：
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发表时间：
2017
影响因子：
3.7
通讯作者：
E. Barthélemy
中科院分区：
文献类型：
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作者：
C. Berni;H. Michallet;E. Barthélemy
我们报告了旨在研究海滩二维波槽物理模型中河床失稳过程的新实验。移动床由低密度的非粘性颗粒材料组成。波条件是通过重复由不同周期的两个双色组构成的波的循环来提供的。水平和垂直速度是从自由流高度到冲浪区静止河床水平的垂直声学剖面图。在沉积物床内和稍高于沉积物床的水平和垂直紧密排列的位置处进行流体压力的额外测量。通过声学和光学方法检测移动床界面、静止床和顶部界面。两种方法进行交叉比较并给出相似的结果。分析了床上方的流动湍流，发现雷诺湍流剪切应力与轨道流引起的动量扩散相比可以忽略不计。剪切应力和水平压力梯度是在近床高程处计算的，并用于 Sleath 的床层初期塞流模型（Cont. Shelf Res.，第 19 卷（13），1999 年，第 1643-1664 页）。模型和测量结果均证实，当无量纲压力梯度（或 Sleath 数）超过阈值 0.3（与强流动加速同时发生）时，就会发生失稳。通过实验发现，在陡峭波前的这些流动加速过程中检测到的近底部流体剪切应力为负值，这是通过非稳态活塞流模型恢复的。这表明床上方的流体在这些特定阶段抵抗沉积物层运动。
We report on new experiments designed to investigate bed destabilization processes in a two-dimensional wave flume physical model of a beach. The mobile bed consists of non-cohesive granular material of low density. The wave conditions are provided by repeating a cycle of waves made of two bichromatic groups of different period. The horizontal and vertical velocities are acoustically profiled vertically from free-stream elevation down to the still bed level in the surf zone. Additional measurements of the fluid pressure at positions closely aligned horizontally and vertically in and slightly above the sediment bed are undertaken. Mobile bed interfaces, still bed and top interface, are detected via acoustic and optical methods. Both methods are cross-compared and give similar results. Flow turbulence over the bed is analysed, the Reynolds turbulent shear stress is found negligible compared to the orbital flow induced momentum diffusion. The shear stress and the horizontal pressure gradient are computed at near-bed elevation and used in the bed incipient plug flow model of Sleath (Cont. Shelf Res., vol. 19 (13), 1999, pp. 1643–1664). Both the model and the measurements confirm that destabilization occurs when the non-dimensional pressure gradient (or Sleath number) exceeds the threshold value of 0.3 which is simultaneous with strong flow acceleration. The near-bottom fluid shear stress detected during these flow accelerations at steep wave fronts is found experimentally to be negative, which is retrieved with an unsteady plug flow model. This is suggesting that the fluid above the bed resists the sediment layer motion at these particular phases.
DOI：
10.1061/(asce)ww.1943-5460.0000209
发表时间：
2014-01-01
影响因子：
2.2
作者：
Lanckriet, Thijs;Puleo, Jack A.;Russell, Paul
通讯作者：
Russell, Paul