Evolution of barchan dune interactions investigated by a downscaled water tunnel experiment: the temporal characteristics and a soliton-like behavior

The downscaled water tunnel experiment can achieve local similarity in sand dune morphology with the field results while avoiding the large spatiotemporal scales in field observations. A classic example is the solitary-wave-like behavior of dunes. A small dune merges in the upstream face of a large dune and pushes out a dune of similar size from the leeside of the large dune, which appears as if this small dune goes straight through the large one under monochromatic conditions. For this phenomenon, the existence in water tunnel experiments has been confirmed before the satellite image evidence was established. Aside from the solitary-wave-like behavior, researchers have discovered several different dune interaction patterns through water tunnel experiments, which are affected by various factors, such as flow rate and initial mass ratio of the two dunes. Assumptions show that when two dunes are close in size, they keep moving at the same celerity because the size of a dune is inversely proportional to its speed. In this paper, a new pattern emerges unexpectedly because of the flow structure between the two dunes. Specifically, the tip of the downstream dune is captured by the reversing flow produced by the upstream dune and disengages from the body of downstream one under the conditions of suitable mass ratio and spacing. Together with the upstream dune, this tip dune displays an amazing soliton-like behavior. Different from the abovementioned solitary-wave-like behavior, this soliton realizes the mutual crossing of dunes and the maintenance of self-mass at the same time within a certain space-time range. The reasons for its occurrence and the conditions affecting its survival are analyzed.The data includes an XLS documenting the collision pattern versus the initial mass ratio for a total of 95 cases, 21 representative collision cases (GIFs and TIFF images), and 19 other selected GIFs.缩尺水洞实验（downscaled water tunnel experiment）可实现沙丘形态（sand dune morphology）与野外实测结果的局部相似性，同时规避野外观测中存在的超大时空尺度问题。其中典型案例为沙丘的类孤波（solitary-wave-like）行为：小型沙丘于大型沙丘的迎流面融合，并从大型沙丘的背流侧推挤出尺寸相近的新沙丘，在单频来流条件下，该现象看似小型沙丘径直穿过了大型沙丘。针对该现象，水洞实验的验证早于卫星影像证据的确立。除上述类孤波行为外，研究者通过水洞实验还发现了多种沙丘相互作用模式，这些模式受流速、双沙丘初始质量比等多种因素影响。已有研究假设表明，当两座沙丘尺寸相近时，二者将以相同的移动速率行进——这是因为沙丘尺寸与其移动速度呈反比关系。本研究中，因两座沙丘间的流动结构作用，意外观测到了一种全新的沙丘相互作用模式。具体而言，在合适的质量比与间距条件下，下游沙丘的尖端会被上游沙丘产生的逆向流场捕获，并与下游沙丘主体脱离。该脱离出的尖端沙丘将与上游沙丘一同展现出令人惊叹的类孤子（soliton-like）行为。与前述类孤波行为不同，该类孤子现象可在特定时空范围内实现沙丘的相互穿越，同时保持自身质量守恒。本研究对该现象的发生诱因与维持条件进行了分析。本数据集包含一份XLS格式文件，记录了共95组案例的碰撞模式与初始质量比的对应关系；另有21组典型碰撞案例的GIF格式动态图像与TIFF格式影像，以及19组精选GIF动态图像。