Corridors of size-selected crescent-shaped dunes, known as barchans, are commonly found in water, air, and other planetary environments. The growth of barchans results from the interplay between a fluid flow and a granular bed, but their size regulation involves intricate exchanges between different barchans within a field. One size-regulating mechanism is the binary interaction between nearby dunes, when two dunes exchange mass via the near flow field or by direct contact (collision). In a recent Letter (Assis & Franklin, 2020, https://doi.org/10.1029/2020GL089464), we identified five different patterns arising from binary interactions of subaqueous barchans and proposed classification maps. In this paper, we further inquire into binary exchanges by investigating the motion of individual grains while barchans interact with each other. The experiments were conducted in a water channel where the evolution of pairs of barchans in both aligned and off-centered configurations was recorded by conventional and high-speed cameras. Based on image processing, we obtained the morphology of dunes and motion of grains for all interaction patterns. We present the trajectories of individual grains, from which we show the origin and destination of moving grains, and their typical lengths and velocities. We also show that grains from the impacting dune spread with a diffusion-like component over the target barchan, and we propose a diffusion length. Our results provide new insights into the size-regulating mechanisms of barchans and barchanoid forms found on Earth and other planets.

中文翻译：

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在晶粒尺度上研究的 Barchan-Barchan 相互作用的形态动力学

大小选定的新月形沙丘走廊，称为新月形沙丘，常见于水、空气和其他行星环境中。新月形的生长是流体流动和颗粒床之间相互作用的结果，但它们的大小调节涉及田间不同新月形之间复杂的交换。一种尺寸调节机制是附近沙丘之间的二元相互作用，当两个沙丘通过近流场或直接接触（碰撞）交换质量时。在最近的一封信中（Assis & Franklin，2020，https://doi.org/10.1029/2020GL089464），我们确定了水下新月形和拟议分类图的二元相互作用产生的五种不同模式。在本文中，我们通过研究新月形彼此相互作用时单个颗粒的运动来进一步研究二元交换。实验是在水道中进行的，在那里，传统和高速相机记录了对齐和偏心配置中成对新月形的演变。基于图像处理，我们获得了所有相互作用模式的沙丘形态和颗粒运动。我们展示了单个颗粒的轨迹，从中我们展示了移动颗粒的起源和目的地，以及它们的典型长度和速度。我们还展示了来自撞击沙丘的颗粒在目标新月形上以类似扩散的成分扩散，我们提出了扩散长度。我们的研究结果为地球和其他行星上发现的新月形和新月形的大小调节机制提供了新的见解。