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Author: Publisher: ISBN: Category : Languages : en Pages : 9
Book Description
This grant was funded for the purpose of (1) developing the methodology for measuring the microstructural properties of snow, (2) performing a series of experiments to calibrate the theory developed to measure snow microstructure, and (3) determining in detail how the material microstructure changes with time under uniform temperature conditions. Microstructure includes such parameters as grain size, grain shape, bond size, neck length, pore size, and 3-D coordination number (number of bonds per grain). An essential part of the project included support for a visiting scientist from Japan, Atsushi Sato, who had developed specialized equipment for producing very fine-grained snow with predominantly spherical grain shape. This snow allowed us to perform the experimental part of the project with more precision than using natural snow. The small grain size was responsible for the rapid metamorphism, and the spherical gain shape greatly simplified the task of calibrating the software developed to measure the snow microstructure. The objectives of the grant have been achieved. A number of papers have either been published or are now being written, and the formulation developed by the PI and his doctoral student has been shown to be a very effective method of measuring microstructure.
Author: Publisher: ISBN: Category : Languages : en Pages : 9
Book Description
This grant was funded for the purpose of (1) developing the methodology for measuring the microstructural properties of snow, (2) performing a series of experiments to calibrate the theory developed to measure snow microstructure, and (3) determining in detail how the material microstructure changes with time under uniform temperature conditions. Microstructure includes such parameters as grain size, grain shape, bond size, neck length, pore size, and 3-D coordination number (number of bonds per grain). An essential part of the project included support for a visiting scientist from Japan, Atsushi Sato, who had developed specialized equipment for producing very fine-grained snow with predominantly spherical grain shape. This snow allowed us to perform the experimental part of the project with more precision than using natural snow. The small grain size was responsible for the rapid metamorphism, and the spherical gain shape greatly simplified the task of calibrating the software developed to measure the snow microstructure. The objectives of the grant have been achieved. A number of papers have either been published or are now being written, and the formulation developed by the PI and his doctoral student has been shown to be a very effective method of measuring microstructure.
Author: Daniel August Miller Publisher: ISBN: 9781423510499 Category : Depth hoar Languages : en Pages : 261
Book Description
Snow microstructure significantly influences the mechanical, thermal, and electromagnetic properties of snow. The microstructure is constantly evolving from the time it is deposited on the surface until it sublimates or melts. The resulting time variant material properties make the study of snow metamorphism of fundamental importance to a wide variety of snow science disciplines. Dry snow metamorphism has traditionally been classified by the thermal gradient encountered in the snowpack. Snow experiencing a predominantly equi-temperature environment develops different micro structure than snow that is subjected to a temperature gradient. As such, previous research has evaluated snow metamorphism based upon select thermal gradient dependent processes, when in reality, there is a continuum of physical processes simultaneously contributing to metamorphism. In previous research, a discrete temperature gradient transition between the two thermal environments has been used to activate separate morphological analyses. The current research focuses on a unifying approach to dry snow metamorphism that is applicable to generalized thermal environments. The movement of heat and mass is not prescribed, but is allowed to develop naturally through modeling of physical processes. Heat conduction, mass conservation, and phase change equations are derived in a simplified two-dimensional approach. Each differential equation is non-linearly coupled to the others through phase change. The microstructural network is then discretized into elements and nodes. Finite difference equations are developed for the network, and numerically solved using iterative techniques. The finite difference model provides a unique platform to study the influence of numerous geometric and thermodynamic parameters relating to dry snow metamorphism. Numerical metamorphism studies in an equi-temperature environment agree well with established trends and published experimental results.
Author: Publisher: ISBN: Category : Languages : en Pages : 261
Book Description
Snow microstructure significantly influences the mechanical, thermal, and electromagnetic properties of snow. The microstructure is constantly evolving from the time it is deposited on the surface until it sublimates or melts. The resulting time variant material properties make the study of snow metamorphism of fundamental importance to a wide variety of snow science disciplines. Dry snow metamorphism has traditionally been classified by the thermal gradient encountered in the snowpack. Snow experiencing a predominantly equi-temperature environment develops different micro structure than snow that is subjected to a temperature gradient. As such, previous research has evaluated snow metamorphism based upon select thermal gradient dependent processes, when in reality, there is a continuum of physical processes simultaneously contributing to metamorphism. In previous research, a discrete temperature gradient transition between the two thermal environments has been used to activate separate morphological analyses. The current research focuses on a unifying approach to dry snow metamorphism that is applicable to generalized thermal environments. The movement of heat and mass is not prescribed, but is allowed to develop naturally through modeling of physical processes. Heat conduction, mass conservation, and phase change equations are derived in a simplified two-dimensional approach. Each differential equation is non-linearly coupled to the others through phase change. The microstructural network is then discretized into elements and nodes. Finite difference equations are developed for the network, and numerically solved using iterative techniques. The finite difference model provides a unique platform to study the influence of numerous geometric and thermodynamic parameters relating to dry snow metamorphism. Numerical metamorphism studies in an equi-temperature environment agree well with established trends and published experimental results.
Author: Publisher: ISBN: Category : Languages : en Pages : 3
Book Description
A DC Electric Field Meter was purchased and assembled. This instrument will allow the measurement of the electric field produced near the earth's surface during blowing snow and blowing sand events. These measurements will in turn aid in the quantification of the effects of electrostatic forces on blowing snow and blowing sand particles; leading to better understanding and control of blowing snow and blowing sand and consequent drift formation.
Author: Patrick Joseph Staron Publisher: ISBN: Category : Avalanches Languages : en Pages : 372
Book Description
In the presence of a sufficient temperature gradient, snow evolves from an isotropic network of ice crystals to a transversely isotropic system of depth hoar chains. This morphology is often the weak layer responsible for full depth avalanches. Previous research primarily focused on quantifying the conditions necessary to produce depth hoar. Limited work has been performed to determine the underlying reason for the microstructural changes. Using entropy production rates derived from nonequilibrium thermodynamics, this research shows that depth hoar forms as a result of the snow progressing naturally toward thermal equilibrium. Laboratory experiments were undertaken to examine the evolution of snow microstructure at the macro scale under nonequilibrium thermal conditions. Snow samples with similar initial microstructure were subjected to either a fixed temperature gradient or fixed heat input. The metamorphism for both sets of boundary conditions produced similar depth hoar chains with comparable increases in effective thermal conductivity. Examination of the Gibbs free energy and entropy production rates showed that all metamorphic changes were driven by the system evolving to facilitate equilibrium in the snow or the surroundings. This behavior was dictated by the second law of thermodynamics. An existing numerical model was modified to examine depth hoar formation at the grain scale. Entropy production rate relations were developed for an open system of ice and water vapor. This analysis showed that heat conduction in the bonds had the highest specific entropy production rate, indicating they were the most inefficient part of the snow system. As the metamorphism advanced, the increase in bond size enhanced the conduction pathways through the snow, making the system more efficient at transferring heat. This spontaneous microstructural evolution moved the system and the surroundings toward equilibrium by reducing the local temperature gradients over the bonds and increasing the entropy production rate density. The employment of nonequilibrium thermodynamics determined that the need to reach equilibrium was the underlying force that drives the evolution of snow microstructure. This research also expanded the relevance of nonequilibrium thermodynamics by applying it to a complicated, but well bounded, natural problem.
Author: Xuan Wang Publisher: ISBN: Category : Languages : en Pages : 242
Book Description
Investigation of snow properties can be applied to understand a range of issues including climate change and snow avalanche prediction. Most of the snow properties, i.e. thermal and mechanical, are directly linked to the microstructure of snowpack and those properties evolve simultaneously with deformation of the snow and its metamorphism. Thus, this dissertation primarily explores the characterization of snow microstructural evolution under the effects of temperature gradient and overburden. Snow structural evolution was monitored by the techniques of scanning electron microscopy (SEM), X-ray computed microtomography (micro-CT) and numerical simulation. The temperature gradient setup constructed for this work, commercial compression stage and commercial cooling stage were used to simulate the natural boundary conditions within snow layers. Of the different types of metamorphism that may occur in snow layers, temperature gradient metamorphism (TGM) is perhaps the most significant one. The snow layer undergoing TGM will lose its strength and transform into a weak layer, which is the microstructural cause of avalanches. 1-D arrays of ice spheres were used as a reproducable approach to observe snow microstructural evolution and investigate the mass transfer process. By controlling temperatures on both sides of ice spheres, different vapor transfer directions were studied. Our experiments demonstrated the mass transfer processes and microstructural evolutions under alternating and unidirectional temperature gradient. We also investigated the effects of temperature gradient on natural snow. The specific surface area (SSA) was used to characterize the TGM. The temperature gradient magnitude and the initial snow type both influence the evolution of the SSA. The trend in the SSA is controlled by two mechanisms, grain growth and the formation of complex surfaces. For the relationship between the structure of snow and its mechanical properties, we focused on investigating how the structure of snow evolves under an applied load. Micro-CT images, complemented with SEM images, demonstrate that the mechanical properties of snow depend on the density, the SSA, and bond formation. During our interrupted compression tests, the SSA decreased more rapidly than that determined for snow metamorphism without an overburden. It is clearly evident that pressure sintering of snow contributes to accelerated sintering and coarsening processes.
Author: I. Izumi Publisher: CRC Press ISBN: 9789054108658 Category : Science Languages : en Pages : 658
Book Description
The objective of the conference was to provide a forum for engineers, architects and scientists to discuss a broad range of research and design methods for various problems related to snow engineering. Specialists in building and civil engineering, environmental engineering, energy engineering, urban planning, and regional development as well as snow scientists were brought together for the conference. The technical sessions were in five thematic areas as follows: Snow technology and science; Building and construction engineering; Infrastructure and transportation; Housing and residential planning; Development strategy in snow countries. The 115 papers provide keys to realize more comfortable living conditions in snow countries and to overcome many problems in heavy snow regions.
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Author: Daniel August Miller
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Author: Maurine Montagnat
Author: Bernd R. Pinzer
Author: Patrick Joseph Staron
Author: Xuan Wang
Author: I. Izumi
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