Waves, levees and impact pressures in snow avalanches

雪崩中的波浪、堤坝和冲击压力

• 批准号: NE/X013936/1
• 负责人: Nico Gray
• 金额: $ 73.07万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX013936%2F1
• 关键词: Waves; levees; impact; pressures; snow

Snow avalanches are a major natural hazard in mountainous regions and pose a significant risk affecting people and infrastructure in many countries throughout the world. Avalanches typically have a dilute powder cloud that obscures the underlying dense flow beneath. This dense flow often causes much of the damage. Snow scientists have therefore spent many years developing GEODAR, Doppler and FMCW radar, as well as instrumented pylons, to visualize the internal dense flow dynamics (Köhler et al. 2016; 2018). These technologies shows that dense avalanches develop surges and internal waves (figs. 3) (Sovilla et al. 2010). In addition, field observations (fig. 4) show that a significant proportion of avalanches develop levees. These waves and levees are important because (i) they strongly enhance the mobility and run-out of the flow (Edwards et al. 2021, Rocha et al. 2019) and (ii) they vastly concentrate the energy within avalanches, dramatically magnifying the impact forces they exert on buildings and obstacles in their path (see figure 4). Despite their importance, the underlying mechanisms that cause waves and levees in snow avalanches are poorly understood, and consequently they are not well predicted by current models.This proposal combines the breakthroughs in visualisation of dense snow avalanches with a new general theory for wave and levee formation in shallow flows, originally developed in Manchester for small-scale dry granular flows (Gray & Edwards 2014, Edwards & Gray 2015, Viroulet et al. 2018, Rocha et al. 2019, Edwards et al. 2021). This theoretical framework will allow us to use the radar observations of wave amplitude, wavelength and coarsening dynamics, to provide important constraints on the rheological properties of snow avalanches, which are strongly temperature dependent. Köhler et al. (2018) identified seven main types of snow avalanche and this proposal focuses on the three main dense-flow types: (i) cold shear, (ii) warm shear and (iii) warm plug. Cold flows are cohesionless granular flows, while warm flows have some liquid water in them, which allows large snowballs to agglomerate by cohesive forces (Steinkogler et al. 2015). The snowballs dramatically increase the mean particle size, and warm-shear flows then have a tendency to form huge levees in the run-out zone (fig. 4a). This suggests that these flows may be closely analogous to the small-scale self-channelizing flows in Manchester (fig. 4b), for which we have developed a quantitative model (Rocha et al. 2019). This proposal therefore aims to develop a new friction law for snow-avalanche models, that will capture the spontaneous formation and growth of waves, as well as self-channelization in the run-out zone. We will also examine how self-channelization and wave formation are able to concentrate the impact forces on structures and enhance run out.

雪崩是山区的主要自然灾害，对世界各地许多国家的人民和基础设施造成重大风险。雪崩通常会形成稀薄的粉云，遮盖了下面的密集水流。这种密集的水流通常会造成很大的损失。因此，雪地科学家花了多年时间开发 GEODAR、多普勒和 FMCW 雷达以及仪表塔，以可视化内部稠密流动力学（Köhler 等人，2016 年；这些技术表明，密集的雪崩会产生浪涌和内波（图 3）（Sovilla 等人，2010）。此外，现场观察（图 4）表明，很大一部分雪崩会产生堤坝。堤坝很重要，因为 (i) 它们极大地增强了水流的流动性和径流（Edwards 等人，2021 年；Rocha 等人，2019 年）； (ii) 它们极大地集中了雪崩中的能量，极大地放大了它们对路径上的建筑物和障碍物施加的冲击力（见图 4），尽管它们很重要，但人们对雪崩中引起波浪和堤坝的潜在机制知之甚少。因此，当前的模型无法很好地预测它们。该提案将密集雪崩可视化的突破与浅流中波浪和堤坝形成的新一般理论结合起来，该理论最初是在曼彻斯特为小规模干颗粒流开发的（Gray & Edwards 2014、Edwards & Gray 2015、Viroulet et al. 2018、Rocha et al. 2019、Edwards et al. 2021）该理论框架将使我们能够使用雷达观测波幅、波长和粗化动力学，为雪崩的流变特性提供重要的约束，雪崩的流变特性与温度密切相关，Köhler 等人（2018）确定了七种主要类型。雪崩的研究重点是三种主要的密集流类型：（i）冷切变，（ii）温切变和（iii）温塞冷流是无粘性的颗粒流，而暖流中含有一些液态水。 ，这允许大雪球通过内聚力聚集（Steinkogler et al. 2015）。雪球显着增加了平均颗粒尺寸，然后倾向于形成热剪切流。流出区的巨大堤坝（图 4a）这表明这些流量可能与曼彻斯特的小规模自渠道化流量非常相似（图 4b），我们为此开发了一个定量模型（Rocha）。 et al. 2019）因此，该提案旨在为雪崩模型开发一种新的摩擦定律，该定律将捕获波浪的自发形成和增长，以及流出区的自通道化。如何自通道化和波浪形成能够将冲击力集中在结构上并增强跳动。