Development of a vector-based 3D grain entrainment model with application to X-ray computed tomography scanned riverbed sediment
Development of a vector-based 3D grain entrainment model with application to X-ray computed tomography scanned riverbed sediment
复制标题
开发基于矢量的 3D 颗粒夹带模型，并将其应用于 X 射线计算机断层扫描河床沉积物
DOI：
10.1002/esp.4608
复制
发表时间：
2019
影响因子：
3.3
通讯作者：
Voepel H
中科院分区：
文献类型：
--
作者：
Voepel H
沉积物输运方程通常会产生有几个数量级偏差的输运速率。这种不准确性的一个原因是无法表示控制夹带的复杂的颗粒尺度相互作用。长期以来，人们一直使用基于简化粒子几何和二维（2D）力或力矩平衡的几何关系来模拟颗粒尺度的初始运动。然而，这种方法忽略了真实颗粒的许多复杂性，包括颗粒形状、内聚力以及相对于流动方向的夹带角度。为了更好地表示这种复杂性，我们开发了第一个基于矢量的全三维 (3D) 颗粒旋转夹带模型，该模型可用于解析 3D 中的任何夹带公式，并且还包括矩阵内聚力的影响。为了应用该模型，我们使用 X 射线计算机断层扫描来量化经过水处理的河流颗粒的 3D 结构。我们将 3D 模型结果与应用 2D 夹带模型得出的结果进行比较。我们发现 2D 方法产生的无量纲临界剪切应力 ( ) 估计值比我们的 3D 模型低一个数量级。我们证明，在计算 2D 投影时使用 c 轴更合适，这会增加 的值以更接近地匹配我们的 3D 估计。 3D 模型揭示了样品中临界剪切应力的主要控制因素是颗粒的投影、细颗粒基质的内聚效应以及旋转平面的方位角（与下游流的横向偏离角，部分定义了颗粒绕 3D 中两个接触点形成的轴的枢转方向）。我们的 3D 模型的结构精度证明了 2D 模型中固有的几何误差的来源。通过改进流动特性以更好地在 3D 模型中复制局部水力学，扫描河床颗粒的夹带建模具有对 2D 模型增强进行基准测试的潜力。 © 2019 作者。地球表面过程和地貌由 John Wiley & Sons Ltd 出版。
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 ( ) 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 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. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.