Theses and Dissertations at Montana State University (MSU)
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Item 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 Preliminary analysis and hanger adjustment of tied arch bridges(Montana State University - Bozeman, College of Engineering, 1984) Beyer, William EdwardPreliminary design of a tied arch bridge is complex due to the many possible parameters of the problem. After obtaining a design the minimization of dead load moment is an important consideration. Similarly, obtaining proper tensions in the hangers of a tied arch bridge is very important, to prevent overstressing of the arch. By using matrix structural analysis, the effects of certain parameters upon tied arch behavior are investigated. The parameters include rise to span ratio, hanger spacing, ratio of areas of rib and tie, and ratio of moments of inertia of rib and tie. The geometry of an existing span was used for analysis. The results of the parametric study are portrayed graphically for a range of the parameters. Methods for analysis of dead load moment and hanger tension adjustment are developed. Finally a preliminary design example is considered.Item A continuum approach to sintering kinetics(Montana State University - Bozeman, College of Engineering, 1984) Reid, Carl RicklefSintering is the process by which an initially unconnected collection of particles form bonds at their points of contact resulting in a single, solid framework. As this process proceeds, the relative density increases from that of the initial loose particle stack to a density which may approach that of the solid material. The material rearrangement which is necessary for densification is driven by a surplus of energy associated with the excess of free surface area in the material and also by the particular arrangement of this free surface. A continuum theory for granular (or porous) materials is proposed to describe the kinetics of sintering. The stresses which promote densification of the material are quantified in terms of two microstructural parameters associated with a granular material: the specific surface area and the mean curvature of the void-solid interface. The theory was applied to two materials which can be sintered: copper and snow. In the case of copper, the microstructural data were available and the stresses induced in the material as it sintered could be evaluated. In the case of snow, the microstructural data were not available so only an estimate of the stresses induced in snow as it sinters was found. The application of the theory to copper gave very good results. This indicates that the proposed theory is an accurate representation of the processes that occur in a material as it sinters. The result of applying the theory to snow indicates that the stresses produced by sintering are of comparable magnitude to other stresses found in a natural snowpack.Item Metamorphism of dry snow as a result of temperature gradient and excess vapor density(Montana State University - Bozeman, College of Engineering, 1982) Adams, Edward EaganA heat conduction equation to determine the temperature profile in a snowpack is developed. The magnitude of temperature gradient tends to increase as the snow surface is approached, with local minimums through high snow density layers and local maximums above and below these layers. Calculations are made which determine the excess vapor density over the ice grain surfaces which border the pore space. In the presence of a temperature gradient faceted crystals will develop near the top of the pore, as ice is sublimated off of the surfaces in the lower region. Necks will deteriorate most readily, causing an overall weakening of the snowpack. There will be a reduction in the percentage of rounded grains as the faceted form develops. The process is enhanced at warmer temperature and larger temperature gradients. Temperature and excess vapor density are known to determine the habit of ice crystals grown in air. The model predicts excess vapor densities in the snowpack which are similar to those which exist in the atmosphere. Comparison of crystal habits predicted by the model are in good agreement with experimental evidence, when the pore geometry and temperature conditions are specified.Item Studies on surface hoar : formation and physical properties(Montana State University - Bozeman, College of Engineering, 1985) Lang, Renee M.Field studies on surface hoar were conducted during the winter months of 1982-83 and 1983-84, at the Big Sky Ski Area, Big Sky, Montana. Mechanical shear strength tests, conducted on established surface hoar layers, indicated that although a layer would become visually undetectable, shear strength remained too low to measure for extended periods of time. The initiation of surface hoar growth was dependent on a variety of near-surface and atmospheric conditions. Nocturnal clear-sky radiative heat loss from the snow surface did not necessarily predispose condensation onto the surface, although near-surface air temperature gradients would be in excess of +200°C/m. A steady-state approximation for conservation of mass and momentum, in conjunction with the temperature data, predicts that surface crystal growth cannot be a diffusion limited process.