Simple power law for transport ratio with bimodal distributions of coarse sediments under waves
Simple power law for transport ratio with bimodal distributions of coarse sediments under waves
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DOI：
10.1029/2007jc004237
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发表时间：
2008-03
影响因子：
--
通讯作者：
J. Calantoni;C. Thaxton
中科院分区：
文献类型：
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作者：
J. Calantoni;C. Thaxton
[1]海岸演变的地貌动力学模型需要相对简单的泥沙输送参数，以便在更大的尺度上应用。在这里，我们提出了一个传输参数的双峰分布的粗石英颗粒使用模拟从离散颗粒模型的薄层流动和近薄层流动条件。离散颗粒模型使用由颗粒运动耦合的混合长度确定的湍流涡粘性来模拟最简单的一维流体。用球面单元模拟了单个沙粒的运动。对于由颗粒-颗粒和颗粒-流体相互作用决定的区域中的每个粒子，平移和旋转形式的牛顿第二定律都得到了求解。理想单色波的强迫是通过指定作用在模拟域上的空间恒定、时变的水平压力梯度来完成的。因此，自由流流体的加速度和速度的时间序列也是固定的。模拟范围包括波浪强迫范围、双峰尺寸分布中大颗粒和小颗粒的直径比以及模拟域中大颗粒和小颗粒的质量比，总共有243个独特的模拟条件。模拟结果被一个简单的幂定律成功地参数化，该定律允许预测双峰分布中每个尺寸分数的输运率。当应用于具有双峰尺寸分布的板状流的现有实验室数据时，由模拟确定的简单的幂定律提供了对每个尺寸分数的输运率的有利预测。重要的是要注意，颗粒按大小的垂直运动的快速分选是用该模型显式模拟的，因此隐式地被幂定律捕获。讨论的重点是幂定律的实际应用。
[1] Morphodynamic models of coastal evolution require relatively simple parameterizations of sediment transport for application over larger scales. Here we present a transport parameterization for bimodal distributions of coarse quartz grains using simulations from a discrete particle model for sheet flow and near sheet flow conditions. The discrete particle model simulates the simplest one-dimensional fluid using a turbulent eddy viscosity determined from a mixing length coupled to particle motions. The motions of individual sand grains are simulated using spherical elements. Newton’s second law in translational and rotational forms is solved for every particle in the domain as determined by both grain-grain and grain-fluid interactions. The forcing from idealized monochromatic waves is accomplished by specifying a spatially constant, time varying horizontal pressure gradient acting on the simulation domain. Consequently, the time series of the free-stream fluid acceleration and velocity are also fixed. Simulations cover a range of wave forcing, diameter ratios for the large and small grains in the bimodal size distribution, and mass ratios of large to small grains in the simulation domain, for a total of 243 unique simulation conditions. The simulation results are successfully parameterized with a simple power law that allows for the prediction of the transport rates of each size fraction in the bimodal distribution. The simple power law determined from simulations provides favorable predictions of transport rates for each size fraction when applied to available laboratory data for sheet flow with bimodal size distributions. It is important to note that rapid vertical kinematic sorting of grains by size is explicitly simulated with the model and thus implicitly captured by the power law. Discussion focuses on practical application of the power law.