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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Development of a vector-based 3D grain entrainment model with application to X-ray computed tomography scanned riverbed sediment
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Development of a vector-based 3D grain entrainment model with application to X-ray computed tomography scanned riverbed sediment

机译：基于向量的3D粒夹带模型的开发应用于X射线计算机断层扫描扫描河床沉积物

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Sediment transport equations typically produce transport rates that are biased by orders of magnitude. A causal component of this inaccuracy is the inability to represent complex grain-scale interactions controlling entrainment. Grain-scale incipient motion has long been modelled using geometric relationships based on simplified particle geometry and two-dimensional (2D) force or moment balances. However, this approach neglects many complexities of real grains, including grain shape, cohesion and the angle of entrainment relative to flow direction. To better represent this complexity, we develop the first vector-based, fully three-dimensional (3D) grain rotation entrainment model that can be used to resolve any entrainment formulation in 3D, and which also includes the effect of matrix cohesion. To apply this model we use X-ray computed tomography to quantify the 3D structure of water-worked river grains. We compare our 3D model results with those derived from application of a 2D entrainment model. We find that the 2D approach produces estimates of dimensionless critical shear stress (tau cr*) that are an order of magnitude lower than our 3D model. We demonstrate that it is more appropriate to use the c-axis when calculating 2D projections, which increases values of tau cr* to more closely match our 3D estimates. The 3D model reveals that the main controls on critical shear stress in our samples are projection of grains, cohesive effects from a fine-grained matrix, and bearing angle for the plane of rotation (the lateral angle of departure from downstream flow that, in part, defines the grain's direction of pivot about an axis formed by two contact points in 3D). The structural precision of our 3D model demonstrates sources of geometric error inherent in 2D models. By improving flow properties to better replicate local hydraulics in our 3D model, entrainment modelling of scanned riverbed grains has the potential for benchmarking 2D model enhancements. (c) 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.
机译：沉积物传输方程通常产生偏置数量级的运输速率。这种不准确的因果分量是无法代表复杂的晶粒度相互作用控制夹带。基于简化的粒子几何形状和二维（2D）力或力矩平衡，使用几何关系模拟晶粒量表初期运动。然而，这种方法忽略了真实晶粒的许多复杂性，包括纹状，内聚力和夹带角度相对于流动方向。为了更好地代表这种复杂性，我们开发了一种基于矢量的全自三维（3D）旋转夹带夹带模型，其可用于解决3D中的任何夹带制剂，并且还包括矩阵内聚的效果。要应用此模型，我们使用X射线计算机断层扫描来量化水上河流谷物的3D结构。我们将3D模型结果与从应用2D夹带模型的应用程序进行比较。我们发现，2D方法产生无量纲临界剪切应力（TAU CR *）的估计，该避孕压力（TAU CR *）低于我们的3D模型的数量级。我们证明在计算2D投影时使用C轴更适合，这增加了TAU CR *的值更紧密地匹配我们的3D估计。 3D模型显示，我们样品中临界剪切应力的主要控制是谷物的投影，从细粒矩阵，旋转平面的轴承角度（从下游流动的横向偏离的横向角度）部分，限定围绕由3D中的两个接触点形成的轴线的枢轴方向。我们的3D模型的结构精度展示了2D模型中固有的几何误差的来源。通过改善流动性能，以更好地复制我们的3D模型中的本地液压，扫描河床谷物的夹带建模具有基准测试2D模型增强的可能性。 （c）2019年作者。 John Wiley＆Sons Ltd.出版的地球表面流程和地貌

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