新月形沙丘内部的力分布
Force distribution within a barchan dune
摘要：
新月形沙丘（Barchan dunes），或简称为barchans，是在不同环境中发现的新月形沙丘，如河流底部，地球的沙漠和火星表面。在最近的一篇论文[Phys. Rev. E 101，012905（2020）]中，我们通过使用计算流体动力学-离散元方法（CFD-DEM）研究了水下新月形沙丘的演化，我们的模拟很好地捕捉了初始桩向新月形沙丘在床形和颗粒尺度上的演化。数值方法已被证明是足够的，我们现在得到的力作用在每个颗粒上，隔离的接触相互作用，并调查如何在新月形沙丘力的分布和传输。我们提出的力的地图和概率密度函数（PDF）的值在流向和展向方向，并表明，更强的力量经历的晶粒既不是波峰，也不是前缘的新月形，但在上游的位置上的沙丘中心的沙丘的外围。我们还表明，很大一部分的晶粒进行纵向力的顺序为10 $^{-7}$ N，与周围的波峰负值，导致在该地区的减速和晶粒沉积。这些数据表明，力的分布倾向于路线的很大一部分颗粒的波峰和角的水下barchans，理解其形态动力学的基础。然而，据作者所知，他们是无法从目前的实验，使我们的研究结果朝着了解新月形沙丘的行为的重要一步。
英文摘要：
Barchan dunes, or simply barchans, are crescent-shaped dunes found in diverse environments such as the bottom of rivers, Earth's deserts and the surface of Mars. In a recent paper [Phys. Rev. E 101, 012905 (2020)], we investigated the evolution of subaqueous barchans by using computational fluid dynamics - discrete element method (CFD-DEM), and our simulations captured well the evolution of an initial pile toward a barchan dune in both the bedform and grain scales. The numerical method having shown to be adequate, we obtain now the forces acting on each grain, isolate the contact interactions, and investigate how forces are distributed and transmitted in a barchan dune. We present force maps and probability density functions (PDFs) for values in the streamwise and spanwise directions, and show that stronger forces are experienced by grains at neither the crest nor leading edge of the barchan, but in positions just upstream the dune centroid on the periphery of the dune. We show also that a great part of grains undergo longitudinal forces of the order of 10$^{-7}$ N, with negative values around the crest, resulting in decelerations and grain deposition in that region. These data show that the force distribution tends to route a great part of grains toward the crest and horns of subaqueous barchans, being fundamental to comprehend their morphodynamics. However, to the best of the authors' knowledge, they are not accessible from current experiments, making of our results an important step toward understanding the behavior of barchan dunes.
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