Browsing by Subject "Compressibility"
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Item Estimating File Compressibility Using File Extensions(2021-07) Powers, CarsonAdaptive compression systems dynamically choose a compression strategy — including no compression — by monitoring CPU usage, output rate, expected time to compress, and perhaps most importantly, the estimated compressibility of the data. Many adaptive compression systems were designed with the assumption that files with the same filename extension will compress roughly to the mean compression ratio (the ratio of compressed size to original size) of some set of files with the same extension. This implies that the compression ratio distribution follows a normal distribution. Though a normal distribution of compression ratios may seem intuitive, this assumption lacks strong empirical supporting evidence. To test this assumption, we built a tool to compress real-world files from many participants, storing the compressed size, original size, file extension, and other metadata. The results of three tests for normality indicate that none of the file extensions we analyzed have a normal distribution, though for some extensions, not all three tests agree. Furthermore, quantitative analysis reveals that files with the same extension compress according to multiple different distributions, and we identified some readily accessible metadata that can separate these files into simpler distributions. We conclude with a discussion of the utility of mean compressibility as an estimator and the implications this study has for future research in adaptive compression.Item In-Die Techniques to Characterize Powder Compression(2023-06) Vreeman, GerritPowder compaction plays a large role in many industries, including pharmaceutical tablet, metal part, detergent, cosmetics, and food manufacturing. Assessing the mechanical properties of a powdered material is an important step in developing processes that can effectively transform a powdered material into a product via densification. In-die analyses performed during compaction are fast and materials sparing compared to traditional out-of-die approaches. The goal of this work includes: (1) evaluate the effectiveness of fast, materials- sparing in-die methods for characterizing powder compaction compared to traditional out- of-die methods; (2) explore the benefits of using in-die elastic recovery measures to predict compact lamination via air entrapment; and (3) develop a universal compressibility model framework that can fully describe in-die compaction data, including all low- and high-pressure mechanisms. These goals aim to enable a fast and materials-sparing assessment of powder mechanical properties and lays a foundation for optimal formulation composition, processing strategy, and quality control assessment from such mechanical property assessments.Item On variable-density subgrid effects in turbulent flows(2018-11) GS, SidharthEulerian mass density variations in a flow relate to compressibility and material inhomogeneities in the fluid. These variations can be caused due to high flow speeds, heat transfer, thermo-chemical reactions and/or phase change. From a local perspective, density gradient in space affects the velocity gradient dynamics due to variable inertia, in the presence of pressure-gradient driven acceleration, and therefore indirectly, the dissipation rate of kinetic energy and enstrophy. In turbulent flows, density variations and their effects on the velocity field influences the interscale interactions. Of particular interest is the turbulent dynamics in the presence of large vorticity generation by baroclinic torque. Although these effects are usually transient (in space or time) as turbulent mixing homogenizes the density field, the deviation from constant-density dynamical evolution can be statistically significant, particularly in instability-dominated flows with high sensitivity to initial/boundary conditions. In unsteady reacting flows, sustained chemi-acoustic interactions result in turbulent vorticity dynamics that is markedly different from the well-studied incompressible constant-density turbulence. Large-eddy simulations of high Reynolds number variable-density flows require adequate representation of unresolved small-scale variable-density effects. The present work is an effort to understand subgrid-scale (SGS) variable-density effects to improve the fidelity and accuracy of our simulations in these regimes. The thesis focuses on Reynolds-filtered governing equations to compute the large-scale vorticity dynamics more precisely. A novel equation set for coarse-grained mass, momentum and energy is derived that employs only second order moment based closures, and allows explicit representation of subgrid-scale compressibility and inertial effects. The new form of the filtered equations has terms that represent the SGS mass flux, pressure-gradient acceleration, and velocity-dilatation correlation. We attempt to quantify the dynamical significance of these terms with direct numerical and large eddy simulations.