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Stochastic sediment transport: anomalous diffusions and random movement
Stochastic Environmental Research and Risk Assessment ( IF 4.2 ) Pub Date : 2020-02-06 , DOI: 10.1007/s00477-020-01775-3
Christina W. Tsai , Serena Y. Hung , Tsung-Han Wu

Abstract

A sediment particle in a flow not only follows the flow direction but also randomly diffuses through the surrounding fluid, because of the turbulence in the flow. In this study, particle movement is regarded as a stochastic process. The stochastic-diffusion particle tracking model is able to simulate the random characteristics of particle trajectories based on stochastic methodologies and physical mechanisms. This study proposes a state-of-the-art two-particle stochastic-diffusion particle tracking model, which considers particle correlation. The spatial correlation depends on the distance between paired particles. Particles are highly correlated and have similar random movement because of large-scale eddies when paired particles are located in the immediate vicinity of each other. The model is applied to open-channel flows, and simulation results of ensemble means and variances of particle positions are examined. Concentration results can be expressed as time-varying probability density functions. The proposed models are validated against the experimental data through ensemble mean velocities and sediment concentrations. This study also examines whether movements of sediment particles in open-channel flow follow the Fickian law. Simulation results of ensemble variances of particle displacements in longitudinal and vertical directions reveal a deviation from the Fickian hypothesis. The influence of the resuspension mechanism on the observed anomalous diffusions is discussed.



中文翻译:

随机泥沙输送:异常扩散和随机运动

摘要

流动中的沉积物颗粒不仅会遵循流动方向,而且还会由于流动中的湍流而随机扩散通过周围的流体。在这项研究中,粒子运动被视为随机过程。随机扩散粒子跟踪模型能够基于随机方法和物理机制模拟粒子轨迹的随机特性。这项研究提出了一种最新的两粒子随机扩散粒子追踪模型,该模型考虑了粒子相关性。空间相关性取决于成对粒子之间的距离。当成对的粒子彼此紧邻时,由于具有大型涡流,粒子之间具有高度相关性并具有相似的随机运动。该模型适用于明渠流量,检验了整体均值和粒子位置方差的模拟结果。集中结果可以表示为时变概率密度函数。通过集合平均速度和沉积物浓度,针对实验数据验证了所提出的模型。这项研究还研究了明渠中沉积物颗粒的运动是否遵循菲克定律。纵向和垂直方向上粒子位移的整体方差的模拟结果表明与Fickian假设存在偏差。讨论了重悬机制对观察到的异常扩散的影响。通过集合平均速度和沉积物浓度,针对实验数据验证了所提出的模型。这项研究还研究了明渠中沉积物颗粒的运动是否遵循菲克定律。纵向和垂直方向上粒子位移的整体方差的模拟结果表明,与Fickian假设存在偏差。讨论了重悬机制对观察到的异常扩散的影响。通过集合平均速度和沉积物浓度,针对实验数据验证了所提出的模型。这项研究还研究了明渠中沉积物颗粒的运动是否遵循菲克定律。纵向和垂直方向上粒子位移的整体方差的模拟结果表明,与Fickian假设存在偏差。讨论了重悬机制对观察到的异常扩散的影响。

更新日期:2020-03-20
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