跳跃粒子模型的灵敏度分析和统计收敛性
Sensitivity Analysis and Statistical Convergence of a Saltating Particle Model
摘要：
跃移模型为近床泥沙输运提供了相当深入的研究。本文概述了一个简单，有效的随机跃移的数值模型，这是验证对以前发表的实验数据在近水平床的渠道跃移。收敛性测试系统地应用，以确保该模型是免费的统计误差所产生的粒子跳数考虑。统计收敛的两个标准，根据第一个标准，至少$10^3$跳似乎是必要的收敛结果，而$10^4$跳跃似乎是最低要求，以实现统计收敛，根据第二个标准。升力的两个经验公式被认为是：一个依赖于滑移（相对）速度乘以水平流速分量的垂直梯度的颗粒;另一个依赖于在顶部和底部的颗粒的滑移速度分量的平方之间的差异。发现前者给出更稳定的结果。参数的研究表明，跃移长度有一个最小值与颗粒直径的增加（在无量纲$D_* \sim 12$）为一个给定的运输阶段。在所考虑的范围内，摩擦系数和碰撞线水平的变化对跃移统计的影响可以忽略不计。回归方程得到的每一个跃移特性。最后，该模型被用来评估推移质输沙率，这是在令人满意的协议与常见的公式的基础上水槽数据，特别是当与其他跃移派生的表达式相比。
英文摘要：
Saltation models provide considerable insight into near-bed sediment transport. This paper outlines a simple, efficient numerical model of stochastic saltation, which is validated against previously published experimental data on saltation in a channel of nearly horizontal bed. Convergence tests are systematically applied to ensure the model is free from statistical errors emanating from the number of particle hops considered. Two criteria for statistical convergence are derived; according to the first criterion, at least $10^3$ hops appear to be necessary for convergent results, whereas $10^4$ saltations seem to be the minimum required in order to achieve statistical convergence in accordance with the second criterion. Two empirical formulae for lift force are considered: one dependent on the slip (relative) velocity of the particle multiplied by the vertical gradient of the horizontal flow velocity component; the other dependent on the difference between the squares of the slip velocity components at the top and bottom of the particle. The former is found to give more stable results. A parameter study indicates that the saltation length has a minimum value with increasing particle diameter (at non-dimensional $D_* \sim 12$) for a given transport stage. Variations in the friction coefficient and collision line level have negligible effect on the saltation statistics within the ranges considered. Regression equations are obtained for each of the saltation characteristics. Finally, the model is used to evaluate the bed load transport rate, which is in satisfactory agreement with common formulae based on flume data, especially when compared against other saltation-derived expressions.
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