颗粒床的线性和非线性不稳定性：河流中波纹和沙丘尺度的确定
Linear and nonlinear instabilities of a granular bed: determination of the scales of ripples and dunes in rivers
摘要：
颗粒状介质在自然界和工业中经常被发现，它们通过流体流动的输送对于人类活动非常重要。一个特别令人感兴趣的例子是在明渠和河流中的泥沙输运。在许多情况下，由流体流动施加的剪切应力被限制在一定的限度内，并且一些颗粒被夹带为床载：与颗粒床的固定部分保持接触的移动层。在这些条件下，最初平坦的颗粒床可能不稳定，产生涟漪和沙丘，如在河床上观察到的。在自由表面水流中，沙丘是随水深变化的底形，而波纹不随水深变化，本文提出了波纹和沙丘的形成模型，该模型基于波纹是主要的线性不稳定性，沙丘是波纹聚合与自由表面效应竞争形成的次级不稳定性的命题。虽然很简单，但该模型能够解释涟漪的生长，饱和度（在以前的模型中没有解释）以及从涟漪到沙丘的演变，为沙丘的形成提供了一个完整的画面。
英文摘要：
Granular media are frequently found in nature and in industry and their transport by a fluid flow is of great importance to human activities. One case of particular interest is the transport of sand in open-channel and river flows. In many instances, the shear stresses exerted by the fluid flow are bounded to certain limits and some grains are entrained as bed-load: a mobile layer which stays in contact with the fixed part of the granular bed. Under these conditions, an initially flat granular bed may be unstable, generating ripples and dunes such as those observed on the bed of rivers. In free-surface water flows, dunes are bedforms that scale with the flow depth, while ripples do not scale with it. This article presents a model for the formation of ripples and dunes based on the proposition that ripples are primary linear instabilities and that dunes are secondary instabilities formed from the competition between the coalescence of ripples and free surface effects. Although simple, the model is able to explain the growth of ripples, their saturation (not explained in previous models) and the evolution from ripples to dunes, presenting a complete picture for the formation of dunes.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
