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.

雪雪崩是山区的主要自然危害，在全世界许多国家中影响人们和基础设施的巨大风险。雪崩通常具有稀释粉末云，遮盖着下面的浓密流动。这种密集的流量通常会造成很大的伤害。因此，雪科学家已经花了很多年的时间开发了Geodar，Doppler和FMCW雷达以及仪器塔，以可视化内部密集的流动动力学（Köhler等人，2016; 2018）。这些技术表明，密集的雪崩会产生激增和内部波动（图3）（Sovilla等，2010）。此外，现场观察结果（图4）表明，雪崩的很大一部分会发展水平。这些波和水平很重要，因为（i）它们强烈增强了流动的迁移率和跑步（Edwards等，2021年，Rocha等人，2019年）和（ii）它们在雪崩中极大地集中了能量，极大地放大了它们对建筑物和路径上的障碍的影响力（请参见图4）。 Despite their importance, the underlying mechanisms that cause waves and levels 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 level formation in shallow flows, originally developed in Manchester for small-scale dry granular flows (Gray & Edwards 2014, Edwards & Gray 2015, Viroulet等等。2018年，Rocha等。这个理论框架将使我们能够使用波浪放大器，波长和粗糙动力学的雷达观测，以对雪地雪崩的流变特性提供重要的约束，而雪地雪崩的温度依赖性很强。 Köhler等。 （2018年）确定了七种主要的雪雪崩类型，该提案重点介绍了三种主要的致密流类型：（i）冷剪切，（ii）温暖的剪切和（iii）温暖的塞子。冷流是无内聚的颗粒流，而温暖的流中有一些液态水，这使大雪球通过凝聚力凝结（Steinkogler等，2015）。雪球会大大增加平均粒径，而温剪毛流则具有在跳出区域形成巨大水平的趋势（图4A）。这表明这些流量可能与曼彻斯特的小规模自通道流相似（图4B），为此我们开发了定量模型（Rocha等，2019）。因此，该提案旨在为雪地瓦兰奇模型开发新的摩擦法，该法将捕获发起人的潮流和波浪的增长以及在跳出区域中的自通道。我们还将研究自通道和波浪形成如何将影响力集中在结构上并增强效果。