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.

在陆地环境中，冰附近存在其相变温度。 因此，地面上的雪是一种热力学活性材料，其颗粒结构正在不断变化。 Snowpack微观结构几乎影响其所有热机械和光学特性。 我们将更好地确定在地面变质上控制的耦合环境参数，并将其随之而来的形态与降雪强度（对雪崩潜力很重要）和陆地/大气接口处的能量平衡联系起来。 我们将整合场，实验室和数值建模。 这三个研究假设是：可以在实验室环境和所得的热机械特性中复制由于自然大气边界条件而发生的微观结构变化；可以量化雪的各向异性形态，并与导热率和机械性能有关。可以根据热输入来推导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实验室条件，以准确复制自然环境并随之而来的变质过程。 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。 我们将开发近表面变质实验室方案，用于辐射重结晶，表面HOAR生长和昼夜再结晶。 理论方面包括开发微结构织物张量，非平衡热力学分析变质和地形建模。 将得出一种描述热机械相关的各向异性方向形态的织物张量，该方向形态将因变质而发展。 熵产生的极值概念将用于根据施加的温度梯度产生的微观结构来评估热传输。 单个传热过程（传导，扩散，对流）的贡献趋向于最有效的累积热传输（有效的热导率）。 综上所述，这些技术将用于分析和经验地量化织物中这种热诱导的进化及其对雪的有效材料特性的影响。 我们将测量机械特性，包括：导热率，渗透性，剪切/正常强度和散装特性。 现有的对地形和地形热特性的热模型将在现场研究中实施，以评估空间可变性。 我们将与USFS国家雪崩中心合作，协助其为雪地安全从业人员提供信息，新的发展和技术的使命。 此外，我们将与当地USFS雪崩中心进行交互，以调查如何最好地利用雪地的热建模进行实际应用。 与当地滑雪区雪地安全团队的互动为该小组提供了一个机会，可以参与他们引起极大兴趣的领域的科学研究。 然后，他们将继续与该领域的同事分享他们的发现，从而扩大影响。