The Influence of Atmospheric Conditions on Thermomechanical Processes and Proprieties of Snow

大气条件对雪热机械过程和特性的影响

• 批准号: 1014497
• 负责人: Edward Adams
• 金额: $ 34.92万
• 依托单位: Montana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1014497&HistoricalAwards=false
• 关键词: Influence; Atmospheric; Conditions; Thermomechanical; Processes

Ice exists near its phase change temperature in the terrestrial environment. Consequently, snow on the ground is a thermodynamically active material with a granular structure that is continuously changing. The snowpack microstructure influences virtually all of its thermo-mechanical and optical properties. We will better determine the coupled environmental parameters governing near surface metamorphism and tie the consequent morphology to snow strength (important to avalanche potential) and energy balance at the terrestrial/atmosphere interface. We will integrate field, laboratory and numerical modeling. The three research hypotheses are: microstructural changes that occur due to natural atmospheric boundary conditions can be replicated in a laboratory environment and the resulting thermo-mechanical properties measured; anisotropic morphology of snow can be quantified and related to thermal conductivity and mechanical properties; process driven microstructure can be deduced based on thermal input. Field studies will be carried out at two existing alpine research sites. Field meteorological data will dictate imposed laboratory conditions to accurately replicate the natural environment and consequent metamorphic processes. Important microstructure will be developed in the state-of-the-art Cold Climate Simulation Chamber through simulation of observed natural conditions. We will develop near surface metamorphism laboratory protocols for radiation recrystallization, surface hoar growth and diurnal recrystallization. Theoretical aspects include developing a microstructure fabric tensor, non-equilibrium thermodynamics analyzing metamorphism and terrain modeling. A fabric tensor to describe thermo-mechanically relevant anisotropic directional morphology, which develops due to metamorphism, will be derived. Entropy production extremum concepts will be used to evaluate heat transport based on microstructure resulting from imposed temperature gradients. The contributions of the individual heat transfer processes (conduction, diffusion, convection) tend toward the most efficient cumulative heat transport (effective thermal conductivity). Taken together, these techniques will be used to analytically and empirically quantify this thermally-induced evolution in fabric and its subsequent effect on snow's effective material properties. We will measure thermo-mechanical properties, including; thermal conductivity, penetration resistance, shear/normal strength and bulk properties. An existing thermal model accounting for topography and terrain thermal properties will be implemented in field studies to assess spatial variability. We will work with the USFS National Avalanche Center to assist its mission to provide information, new developments and technology to snow safety practitioners. Additionally we will interface with the local USFS avalanche center to investigate how best to exploit thermal modeling of the snowcover for practical application. Interaction with a local ski area snow safety team provides an opportunity for this group to be involved in a scientific study in a field in which they have an intense interest. They will then go on to share their findings with colleagues in the field, expanding the impact.

冰存在于陆地环境中接近其相变温度的地方。 因此，地面上的雪是一种热力学活性材料，其颗粒结构不断变化。 积雪的微观结构几乎影响其所有的热机械和光学特性。 我们将更好地确定控制近地表变质作用的耦合环境参数，并将最终的形态与雪强度（对雪崩潜力很重要）和陆地/大气界面的能量平衡联系起来。 我们将整合现场、实验室和数值建模。 这三个研究假设是：由于自然大气边界条件而发生的微观结构变化可以在实验室环境中复制，并测量由此产生的热机械性能；雪的各向异性形态可以量化并与热导率和机械性能相关；可以根据热输入推导出工艺驱动的微观结构。 实地研究将在两个现有的高山研究地点进行。 现场气象数据将决定所施加的实验室条件，以准确地复制自然环境和随后的变质过程。 通过模拟观察到的自然条件，将在最先进的寒冷气候模拟室中开发重要的微观结构。 我们将开发辐射再结晶、表面灰白生长和昼夜再结晶的近地表变质实验室方案。 理论方面包括开发微观结构织物张量、非平衡热力学分析变质作用和地形建模。 将导出用于描述由于变质作用而形成的热机械相关各向异性方向形态的织物张量。 熵产生极值概念将用于评估基于由施加的温度梯度产生的微观结构的热传输。 各个传热过程（传导、扩散、对流）的贡献倾向于最有效的累积传热（有效导热率）。 总而言之，这些技术将用于分析和实证量化织物中的这种热诱导演变及其对雪的有效材料特性的后续影响。 我们将测量热机械性能，包括：导热率、抗穿透性、剪切/正常强度和体积特性。 将在实地研究中实施考虑地形和地形热特性的现有热模型，以评估空间变化。 我们将与 USFS 国家雪崩中心合作，协助其完成向雪地安全从业者提供信息、新发展和技术的使命。 此外，我们将与当地的 USFS 雪崩中心合作，研究如何最好地利用积雪的热模型进行实际应用。 与当地滑雪场雪上安全团队的互动为该小组提供了参与他们感兴趣的领域的科学研究的机会。 然后他们将继续与该领域的同事分享他们的发现，扩大影响。