Lower‐Stage Plane Bed Topography Is an Outcome of Rarefied, Intermittent Sediment Transport
Lower‐Stage Plane Bed Topography Is an Outcome of Rarefied, Intermittent Sediment Transport
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DOI：
10.1029/2020jf005754
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发表时间：
2021-04
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影响因子：
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通讯作者：
T. Ashley;S. Naqshband;B. McElroy
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文献类型：
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作者：
T. Ashley;S. Naqshband;B. McElroy
在弱流体驱动的输运条件下稳定的沉积床结构可分为两组：（1）通过粗糙度和阻力分配效应影响水流和沉积物输运的中尺度特征（“中尺度”）和（2）在宏观尺度上可有效忽略的颗粒尺度特征（“微观”）。在实践中，这些群体从准平面床配置中描绘出涟漪和沙丘。它们被认为是分开的过渡过程中的管理床的救济;然而，负责这种过渡的物理机制知之甚少。先前的研究表明，当移动颗粒之间的相互作用导致稳定床扰动从而启动形态动力图案粗化时，平面地形是不稳定的。这项研究提出了动力学解释这一假设的参数描述粒子运动。我们发现，微形态/介观形态的过渡对应于一个关键的过渡粒子的行为与粒子碰撞的重要性日益增加。这种转变也对应于基于连续介质的形态动力学模型在线性稳定性理论预测的最不稳定波长处是允许的，提供了描述性和数学理论之间的联系。
Sedimentary bed configurations that are stable under weak fluid‐driven transport conditions can be divided into two groups: (1) mesoscale features that influence flow and sediment transport through roughness and drag partitioning effects (“mesoforms”) and (2) grain‐scale features that can effectively be ignored at the macroscopic scale (“microforms”). In practice, these groups delineate ripples and dunes from quasi‐planar bed configurations. They are thought to be separated by a transition in processes governing the relief of the bed; however, the physical mechanisms responsible for this transition are poorly understood. Previous studies suggest that planar topography is unstable when interactions between moving particles lead to stabilized bed disturbances that initiate morphodynamic pattern coarsening. This study presents a kinetic interpretation of this hypothesis in terms of parameters describing particle motion. We find that the microform/mesoform transition corresponds to a critical transition in particle behavior associated with increasing importance of particle collisions. This transition also corresponds to the point where continuum‐based morphodynamic models are permissible at the most unstable wavelength predicted from linear stability theory, providing a link between descriptive and mathematical theories of bedform initiation.