'NERC-FAPESP' Migrating dunes over hilly terrains

颗粒材料无处不在，无处不在，从雪崩的毁灭性力量到药品的制造，从磨碎的咖啡豆到海滩上的沙堡。尽管颗粒材料在我们的日常生活中很普遍，但从物理的角度来看，它们很难被描述和理解。沙丘是自然环境中粒状物质的表现形式。移动的极度干旱沙丘威胁着全球多达10亿人的定居点和基础设施。由于气候变化，世界上一些地区每年都变得更加干燥，为了保护社区和基础设施免受荒漠化的影响，我们需要了解沙丘的演变动力学，从河床的生长到成熟沙丘的稳定状态过程。沙丘的运动和移动要求控制沙丘的移动，影响、改变甚至停止沙丘的移动。这一建议侧重于一个多方面的方法来连接在颗粒水平上的雪崩过程与大尺度沙丘移动特征。正在研究的特殊类型的沙丘是新月形沙丘，这是一种快速移动的新月形沙丘，存在于单向风区，沙子供应有限。我们选择研究barchan沙丘，因为它们形成了一个独特的系统：它们很小，线性扩展，移动速度足够快，可以在实验中进行研究。移动速度与高度成反比，因此单个沙丘在各种相互作用中相互追逐或逃跑。近年来，沙丘迁移的物理缩放和数学模型已经取得了巨大的进展，但这些都是建立在理想化的平坦地球上的迁移模型上的，这不是一个现实的场景。在这个合作项目中，我们将研究外部景观变化和地形对这些快速移动的沙丘的速度和形状的影响。具体来说，我们正在研究三种不同的变化：沙丘在(1)倾斜/下降的斜坡上，(2)丘陵地形和(3)从光滑到凹凸不平的景观。我们正在使用两种不同的实验设备：在剑桥，我们在一个周期系统中模拟2D沙丘很长一段时间，而在坎皮纳斯，我们能够创造真正的3D沙丘，在一个有限的通道中以固定的时间进化。这种实验设备的结合，以及研究人员在小组之间的有效流动，将确保我们既定目标的成功。

Granular materials are universal and all around us, from the devastating powers of a snow avalanche to the fabrication of medicines, and from ground coffee beans to sand castles on the beach. Despite their prevalence in our daily life, granular materials are hard to characterize and understand from a physical point of view. Dunes are manifestations of granular materials in our natural environment. Mobile hyper-arid desert dunes threaten settlements and infrastructure of as many as one billion people worldwide. In order to protect communities and infrastructure from desertification in parts of the world that become dryer each year due to climate change, we need to understand the dynamics of the evolution of a dune, from growth of a bedform to the steady-state processes of a mature dune. Sand dune movement and mobility demands controls on influencing, altering or even stopping the marching of desert dunes. This proposal focuses on a multifaceted approach to connect the avalanching processes at the grain-level with the large-scale dune marching characteristics.The particular type of dune under investigation is a barchan dune - a fast-moving and crescentic-shaped dune present in unidirectional wind regimes with a limited sand supply. We choose to study barchan dunes as they form a unique system: they are small, scale linearly and move fast enough to study in experiments. The progression velocity scales inversely with height and therefore individual dunes chase or run away from each other in a variety of interactions. Physical scalings and mathematical models of dune migration have made huge steps forward in recent years, but are grounded on modelling migration on an idealized flat earth, which is not a realistic scenario.In this collaborative project, we will investigate the effect of external landscape variations and topography on the speed and the shape of these fast-moving dunes. Specifically, we are investigating three different variations: dunes on (1) an inclining/declining slope, (2) a hilly topography and (3) from a polished to a bumpy landscape. We are using two different experimental facilities: in Cambridge, we mimic 2D dunes in a periodic system over very long times, while in Campinas we are able to create true 3D dunes, evolving in fixed-time in a finite channel. This combination of experimental facilities, and effective mobility of researchers between groups, will ensure success of our set goals.