Matching Items (6)
Description
In this dissertation, the results of our comprehensive computational studies of disordered jammed (i.e., mechanically stable) packings of hard particles are presented, including the family of superdisks in 2D and ellipsoids in 3D Euclidean space. Following a very brief introduction to the hard-particle systems, the event driven molecular dynamics (EDMD) employed to generate the packing ensembles will be discussed. A large number of 2D packing configurations of superdisks are subsequently analyzed, through which a relatively accurate theoretical scheme for packing-fraction prediction based on local particle contact configurations is proposed and validated via additional numerical simulations. Moreover, the studies on binary ellipsoid packing in 3D are briefly discussed and the effects of different geometrical parameters on the final packing fraction are analyzed.
ContributorsXu, Yaopengxiao (Author) / Jiao, Yang (Thesis advisor) / Oswald, Jay (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
The study of deflagration to detonation transition (DDT) in explosives is of prime importance with regards to insensitive munitions (IM). Critical damage owing to thermal or shock stimuli could translate to significant loss of life and material. The present study models detonation and deflagration of a commonly used granular explosive: cyclotetramethylene-tetranitramine, HMX. A robust literature review is followed by computational modeling of gas gun and DDT tube test data using the Sandia National Lab three-dimensional multi-material Eulerian hydrocode CTH. This dissertation proposes new computational practices and models that aid in predicting shock stimulus IM response. CTH was first used to model experimental data sets of DDT tubes from both Naval Surface Weapons Center and Los Alamos National Laboratory which were initiated by pyrogenic material and a piston, respectively. Analytical verification was performed, where possible, for detonation via empirical based equations at the Chapman Jouguet state with errors below 2.1%, and deflagration via pressure dependent burn rate equations. CTH simulations include inert, history variable reactive burn and Arrhenius models. The results are in excellent agreement with published HMX detonation velocities. Novel additions include accurate simulation of the pyrogenic material BKNO3 and the inclusion of porosity in energetic materials. The treatment of compaction is especially important in modeling precursory hotspots, caused by hydrodynamic collapse of void regions or grain interactions, prior to DDT of granular explosives. The CTH compaction model of HMX was verified within 11% error via a five pronged validation approach using gas gun data and employed use of a newly generated set of P-α parameters for granular HMX in a Mie-Gruneisen Equation of State. Next, the additions of compaction were extended to a volumetric surface burning model of HMX and compare well to a set of empirical burn rates. Lastly, the compendium of detonation and deflagration models was applied to the aforementioned DDT tubes and demonstrate working functionalities of all models, albeit at the expense of significant computational resources. A robust hydrocode methodology is proposed to make use of the deflagration, compaction and detonation models as a means to predict IM response to shock stimulus of granular explosive materials.
ContributorsMahon, Kelly Susan (Author) / Lee, Taewoo (Thesis advisor) / Herrmann, Marcus (Committee member) / Chen, Kangping (Committee member) / Jiao, Yang (Committee member) / Huang, Huei-Ping (Committee member) / Arizona State University (Publisher)
Created2015
Description
Granular activated carbon (GAC) is effectively used to remove natural organic matter (NOM) and to assist in the removal of disinfection byproducts (DBPs) and their precursors. However, operation of GAC is cost- and labor-intensive due to frequent media replacement. Optimizing the use of GAC is necessary to ensure treatment efficiency while reducing costs. This dissertation presents four strategies to reduce improve GAC usage while reducing formation of DBPs. The first part of this work adopts Rapid Small Scale Tests (RSSCTs) to evaluate removal of molecular weight fractions of NOM, characterized using size exclusion chromatography (SECDOC). Total trihalomethanes (TTHM), haloacetic acids (HAA5) and haloacetonitriles (HAN) formation were quantified after treatment with GAC. Low MW NOM was removed preferentially in the early bed volumes, up until exhaustion of available adsorption sites. DBP formation potential lowered with DOC removal. Chlorination prior to GAC is investigated in the second part of this work as a strategy to increase removal of NOM and DBP precursors. Results showed lower TTHM formation in the effluent of the GAC treatment when pre-chlorination was adopted, meaning this strategy could help optimize and extend the bed life if GAC filters. The third part of this work investigates in-situ GAC regeneration as an alternative to recover adsorption capacity of field-spent GAC that could potentially offer new modes of operation for water treatment facilities while savng costs with reactivation of spent GAC in an external facility. Field-spent GACs were treated with different oxidant solutions and recovery in adsorption capacity was evaluated for NOM and for two micro pollutants. Recovery of GAC adsorption capacity was not satisfactory for most of conditions evaluated. This indicates that in-situ GAC regeneration could be more effective when the adsorbates are present at high concentrations. Lastly, this work investigates the impact of low molecular weight polyDADMAC on N-nitrosodimethylamine (NDMA) formation. Water treatment facilities rely on polyDADMAC as a coagulant aid to comply with NOM removal and turbidity requirements. Since polymer-derived NDMA precursors are not removed by GAC, it is essential to optimize the use and synthesis of polyDADMAC to reduce NDMA precursors during water treatment.
ContributorsFischer, Natalia (Author) / Westerhoff, Paul (Thesis advisor) / Hristovski, Kiril (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2017
Description
This thesis investigates the effects of differing diameters, removal of antistatic forces, and varying moisture content on the shear stress properties of granular glass beads through use of a Freeman FT4 Powder Rheometer. A yield locus results from plotting the experimental shear stress values (kPa) vs. the applied normal stress value (kPa). From these yield loci, Mohr’s Circles are constructed to quantitatively describe flowability of tested materials in terms of a flow function parameter.
By testing 120-180 µm, 120-350 µm, 250-350 µm, and 430-600 µm dry glass bead ranges, an increase in diameter size is seen to result in both higher shear stress values and an increasing slope of plotted shear stress vs. applied normal stress. From constructed Mohr’s Circles, it is observed that flow function is quite high amongst tested dry materials, all yielding values above 20. A high flow function value (>10) is indicative of a good flow.1 Flow function was observed to increase with increasing diameter size until a slight drop was observed at the 430-600 µm range, possibly due to material quality or being near the size limitation of testing within the FT4, where materials must be less than 1000 µm in diameter.However, no trend could be observed in flowability as diameter size was increased.
Through the use of an antistatic solution, the effect of electrostatic forces generated by colliding particles was tested. No significant effect on the shear stress properties was observed.
Wet material testing occurred with the 120-180 µm glass bead range using a deionized water content of 0%, 1%, 5%, 15%, and 20% by mass. The results of such testing yielded an increase in shear stress values at applied normal stress values as moisture content is increased, as well as a decrease in the resulting flow function parameter. However, this trend changed as 20% moisture content was achieved; the wet material became a consistent paste, and a large drop in shear stress values occurred along with an increase in flowability.
By testing 120-180 µm, 120-350 µm, 250-350 µm, and 430-600 µm dry glass bead ranges, an increase in diameter size is seen to result in both higher shear stress values and an increasing slope of plotted shear stress vs. applied normal stress. From constructed Mohr’s Circles, it is observed that flow function is quite high amongst tested dry materials, all yielding values above 20. A high flow function value (>10) is indicative of a good flow.1 Flow function was observed to increase with increasing diameter size until a slight drop was observed at the 430-600 µm range, possibly due to material quality or being near the size limitation of testing within the FT4, where materials must be less than 1000 µm in diameter.However, no trend could be observed in flowability as diameter size was increased.
Through the use of an antistatic solution, the effect of electrostatic forces generated by colliding particles was tested. No significant effect on the shear stress properties was observed.
Wet material testing occurred with the 120-180 µm glass bead range using a deionized water content of 0%, 1%, 5%, 15%, and 20% by mass. The results of such testing yielded an increase in shear stress values at applied normal stress values as moisture content is increased, as well as a decrease in the resulting flow function parameter. However, this trend changed as 20% moisture content was achieved; the wet material became a consistent paste, and a large drop in shear stress values occurred along with an increase in flowability.
ContributorsKleppe, Cameron Nicholas (Author) / Emady, Heather (Thesis director) / Vajrala, Spandana (Committee member) / Chemical Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2018-12
Description
This thesis investigated the effects of differing diameters and varying moisture content on the flowability properties of granular glass beads through use of a Freeman FT4 Powder Rheometer. These parameters were tested in order to construct an empirical model to predict flowability properties of glass beads at differing size ranges and moisture contents. The final empirical model outputted an average error of 8.73% across all tested diameters and moisture ranges.
Mohr's circles were constructed from experimentally-obtained shear stress values to quantitatively describe flowability of tested materials in terms of a flow function parameter. A high flow function value (>10) was indicative of a good flow.
By testing 120-180 µm, 120-350 µm, 180-250 µm, 250-350 µm, 430-600 µm, and 600-850 µm glass bead diameter ranges, an increase in size was seen to result in higher flow function values. The limitations of testing using the FT4 became apparent as inconsistent flow function values were obtained at 0% moisture with size ranges above 120-180 µm, or at flow function values of >21. Bead sizes larger than 430 µm showed significant standard deviation over all tested trials--when excluding size ranges above that value, the empirical model showed an average error of only 6.45%.
Wet material testing occurred at all tested glass bead size ranges using a deionized water content of 0%, 1%, 5%, 15%, and 20% by weight. The results of such testing showed a decrease in the resulting flow function parameter as more water content was added. However, this trend changed as 20% moisture content was achieved; the wet material became supersaturated, and an increase in flow function values was observed. The empirical model constructed, therefore, neglected the 20% moisture content regime.
Mohr's circles were constructed from experimentally-obtained shear stress values to quantitatively describe flowability of tested materials in terms of a flow function parameter. A high flow function value (>10) was indicative of a good flow.
By testing 120-180 µm, 120-350 µm, 180-250 µm, 250-350 µm, 430-600 µm, and 600-850 µm glass bead diameter ranges, an increase in size was seen to result in higher flow function values. The limitations of testing using the FT4 became apparent as inconsistent flow function values were obtained at 0% moisture with size ranges above 120-180 µm, or at flow function values of >21. Bead sizes larger than 430 µm showed significant standard deviation over all tested trials--when excluding size ranges above that value, the empirical model showed an average error of only 6.45%.
Wet material testing occurred at all tested glass bead size ranges using a deionized water content of 0%, 1%, 5%, 15%, and 20% by weight. The results of such testing showed a decrease in the resulting flow function parameter as more water content was added. However, this trend changed as 20% moisture content was achieved; the wet material became supersaturated, and an increase in flow function values was observed. The empirical model constructed, therefore, neglected the 20% moisture content regime.
ContributorsKleppe, Cameron (Author) / Emady, Heather (Thesis advisor) / Marvi, Hamidreza (Committee member) / Deng, Shuguang (Committee member) / Arizona State University (Publisher)
Created2019
Description
Granular materials demonstrate complexity in many physical attributes with various shapes and sizes, varying from several centimeters down to less than a few microns. Some materials are highly cohesive, while others are free-flowing. Despite such complexity in their physical properties, they are extremely important in industries dealing with bulk materials. Through this research, the factors affecting flowability of particulate solids and their interaction with projectiles were explored. In Part I, a novel set of characterization tools to relate various granular material properties to their flow behavior in confined and unconfined environments was investigated. Through this work, a thorough characterization study to examine the effects of particle size, particle size distribution, and moisture on bulk powder flowability were proposed. Additionally, a mathematical model to predict the flow function coefficient (FFC) was developed, based on the surface mean diameter and moisture level, which can serve as a flowability descriptor.
Part II of this research focuses on the impact dynamics of low velocity projectiles on granular media. Interaction of granular media with external foreign bodies occurs in everyday events like a human footprint on the beach. Several studies involving numerical and experimental methods have focused on the study of impact dynamics in both dry and wet granular media. However, most of the studies involving impact dynamics considered spherical projectiles under different conditions, while practical models should involve more complex, realistic shapes. Different impacting geometries with conserved density, volume, and velocity on a granular bed may experience contrasting drag forces upon penetration. This is due to the difference in the surface areas coming into contact with the granular media. In this study, a set of non-spherical geometries comprising cuboids, cylinders, hexagonal prisms and triangular prisms with constant density, volume, and impact velocities, were released onto a loosely packed, non-cohesive, dry granular bed. From these experimental results, a model to determine the penetration depth of projectiles upon impact was developed and how it is influenced by the release height and surface area of the projectiles in contact with the granular media was studied.
ContributorsVajrala, Spandana (Author) / Emady, Heather N (Thesis advisor) / Marvi, Hamidreza (Committee member) / Jiao, Yang (Committee member) / Arizona State University (Publisher)
Created2021