Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Meteorological controls on wind slab properties(Montana State University - Bozeman, College of Letters & Science, 2023) de Leeuw, Nathalie Marika; Chairperson, Graduate Committee: Jordy HendrikxSnow avalanches are dangerous phenomena, which can be made increasingly consequential through wind transport of snow. Wind-deposited snow has a broad range of possible physical and mechanical properties which can vary greatly over short distances, creating inconsistent and thus difficult avalanche conditions. This variability causes particular challenges for avalanche workers in data-sparse regions where important snowpack information at desired scales may be unavailable. Instead, snowpack properties are commonly inferred from available meteorological data. Though wind slab properties vary in space and time as meteorological conditions change, previous work has not explicitly studied these relationships at the slope-scale. In this research I aim to better understand how changes in meteorological variables relate to changes in wind slab physical properties. During two winters I recorded temperature, humidity, and wind speed at study sites in Montana's Madison Range (45.237, -111.424) and collected snowpack data during or immediately following blowing snow events. I found that average wind speeds at 0.5m and 1.5m above the snow surface were significantly higher during hard wind slab formation than soft wind slab formation, while unobstructed wind speed, maximum gust, and the length of time of wind transport were not associated with wind slab hardness. Temperature was higher during hard than soft wind slab formation, while humidity was not different between the two hardness categories. Although wind speed at 1.5m had a significant positive linear relationship with both wind slab density and blade hardness gauge force, it was a poor predictor of actual values for both of these parameters. Our findings help improve the understanding of the impact of near surface winds on wind slabs, which will aid avalanche forecasting and mitigation planning particularly in windy climates.Item Micromechanical analysis of energy expenditure in snow fracture(Montana State University - Bozeman, College of Engineering, 2017) LeBaron, Anthony Michael; Chairperson, Graduate Committee: Daniel MillerA microstructure-based evaluation of snow combining experimental and analytical approaches was performed. Shear tests were performed on both homogeneous and layered samples of un-notched snow. Force and displacement during loading were recorded. Immediately after testing, small subsamples of snow were subjected to micro-CT scanning to capture 3D microstructure details. Microstructure was then modeled as a grain-bond network. The grain-bond network was subject to minimum energy fracture path calculations as well as discrete element modeling. The discrete element model showed good agreement with experiments. Taken together, results from models and experiments show a widespread damage accumulation process in snow. A large fracture process zone (FPZ) is observed, even in samples with weak layers. Evidence indicates that even in snow avalanches, there is likely significant energy dissipation within the slab.Item An experimental investigation of metamorphism induced microstructure evolution in a 'model' cohesive snow(Montana State University - Bozeman, College of Letters & Science, 1997) Edens, Michael QuastItem A computational model of two-phase, turbulent atmospheric boundary layers containing blowing snow(Montana State University - Bozeman, College of Engineering, 1991) Liston, Glen EddyItem A new instrument for determining strength and temperature profiles in snowpack(Montana State University - Bozeman, College of Engineering, 1984) Dowd, Timothy FrancisThe purpose of this thesis project was the development of a new field instrument for determining strength and temperature profiles in snowpack. The standard tool now used for strength determination is the ram penetrometer, which is slow, cumbersome, inaccurate, and does not provide immediate results. Temperatures are generally taken with a dial stem thermometer in a snowpit wall, which is difficult to do accurately at specific intervals. The Digital Thermo-Resistograph was designed and built in an attempt to improve field snowpack data collection. The Digital Thermo-Resistograph is a portable microprocessor-based data acquisition system for quick and accurate field collection of snowpack compressive strength and temperature data. This was accomplished by building a probe with a load cell and thermistor, a small snow platform for probe position information, and a Z-80 microprocessor-based data acquisition system. The system provides information in digital form for every sampled point. A 64 x 240 dot matrix LCD graphic display unit is used to show complete strength and temperature profiles in the field. Provision is made to transfer these profiles to paper via an ordinary X-Y recorder for a permanent record of field data. Sufficient memory for the storage of 25 profiles is provided. The results of winter 1984 field tests are presented. The thermistor could not be made- to work accurately, and so was not integrated into the system. The Digital Thermo-Resistograph proved to be fast and reliable in collecting compressive snow strength information, which is measured from 0.0 to 2.55 kg/sq cm at five mm increments through the snowpack. Comparisons with the ram penetrometer are shown. Ideas for future developments are discussed.Item A microstructure based constitutive theory for granular materials with snow as an example(Montana State University - Bozeman, College of Engineering, 1990) Mahajan, PuneetItem A constitutive theory for high rate multiaxial deformation of snow(Montana State University - Bozeman, College of Engineering, 1985) Hansen, Andrew ChristianItem A continuum mixture theory applied to stress waves in snow(Montana State University - Bozeman, College of Engineering, 1991) Austiguy, George EdwardIn avalanche control work the types of explosives and delivery methods used are primarily determined by trial and error. Understanding the propagation of stress waves in snow is a step towards eliminating some of this guesswork. A continuum theory of mixtures is applied to model snow as a mixture of an elastic solid and an elastic fluid. Three wave types, two dilational and one rotational wave are shown to exist. Theoretical expressions are developed for the wave attenuation and propagation velocity of each of the wave types. Numerical evaluation shows velocity and attenuation increasing with frequency for all three waves. Wave velocity increases with increasing density while attenuation decreases with increasing density for all three waves. The first dilational wave has a slow wave speed and is highly attenuated. This wave exhibits diffusive behavior at low frequencies and nondispersive behavior at high frequencies. The second dilation wave is the fastest of the three wave types and does not appreciably attenuate. Nondispersive wave behavior characterizes this wave at low and high frequencies. The rotational wave is the least attenuated of all three waves and propagates at velocities greater than that of the first dilational . wave but less than that of the second dilational wave. The rotational wave exhibits nondispersive behavior at low and high frequencies. Wave velocities and attenuation show behavior that is in agreement with existing experimental data.Item Use of mixture theory to represent a cohesive elastic-viscoplastic material(Montana State University - Bozeman, College of Engineering, 1997) Barber, Michael JamesThe analysis of material properties depends upon detailed information of the physical, geometric, and chemical properties of the materials. Relating these properties to a set of mathematical models is the principle objective of mechanics. Mixtures of materials made up of several constituents require special consideration since the constituent behavior must be reconciled with the overall behavior of the mixture. Mathematical models and their validity must be established to represent these materials. This thesis establishes a methodology whereby a logical sequence of considerations may be followed to represent complex mixtures adequately. Several existing theories of mechanics are assimilated into a cohesive theory to demonstrate the validity of the mathematical model used to represent mixtures. A structured development of the second law of thermodynamics is constructed to allow additional constraint equations which will restrict the form of new parameters. An example of a wood-snow mixture is used to show how the analysis is to be completed. Laboratory tests were run to use as a means of constructing the values of the new constitutive parameters. Proposed ways of including more constituents and spatial dimensions suggested.Item The spatial variability of snow resistance on potential avalanche slopes(Montana State University - Bozeman, College of Letters & Science, 1990) Birkeland, Karl Wessel