Bed Force Distributions in Granular Flows
Datum
2021-04-29
Autor:innen
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Verlag
University of Oregon
Zusammenfassung
Granular flows are particle-laden gravity currents that are ubiquitous in nature in a variety of different geologic settings. Their high mobility and potential for harm to human populations and infrastructure motivate workers to better understand their dynamics in hopes of predicting their behavior and runout. Forecasting the movement of these hazardous flows, however, requires understanding the mass and momentum transfer between the flow and its substrate. In this dissertation, I analyze the normalized frequency-magnitude distribution of bed force excursions generated by idealized granular flows through a combination of laboratory experiments and discrete element simulations. I explore a wide range of flow behaviors by varying mean grain size, shear rate, and standard deviation of grain size. In the discrete element simulations, I also explore the role of interstitial fluids in determining the shape of the bed force distributions by varying fluid density and viscosity. The flows explored in this dissertation span three flow regimes, encapsulating elastic-quasi-static, elastic-inertial, and inertial-collisional behaviors. Resulting distributions show a dependence of the best-fit functional form on flow regime with diffuse boundaries between regimes. Bed force distributions are sensitive to changes in shear rate and the standard deviation of grain size, weakly sensitive to changes in fluid properties, and robust to changes in mean grain size. Distribution tails generally become more elongated with increasing values of inertial and Stokes numbers. The results of this work highlight the relative erosive potential for granular flows in different flow regimes, showing a higher erosive potential for flows exhibiting more inertial behaviors. In addition to my analysis of bed force distributions in granular flows, I explore the effects of sediment redistribution on sea level in the Bengal Basin and Ganges-Brahmaputra-Meghna river system which is responsible for transporting roughly 1 billion tons of sediment annually. Using a gravitationally self-consistent sea level model, I show that sediment redistribution in this region is likely responsible for ~ 30 m of sea-level change over the last glacial cycle, but the results of these simulations are sensitive to model input parameters such as the effective elastic lithospheric thickness and mantle viscosity profile.
Beschreibung
Schlagwörter
Bed Force Distributions, Granular Flows, Granular Physics, Sea level, Sediment Redistribution