The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform

Donald Scott Stewart - One of the best experts on this subject based on the ideXlab platform.

  • two Phase Modeling of deflagration to detonation transition in granular materials reduced equations
    Physics of Fluids, 2001
    Co-Authors: A K Kapila, Ralph Menikoff, John B Bdzil, Steven F Son, Donald Scott Stewart
    Abstract:

    Of the two-Phase mixture models used to study deflagration-to-detonation transition in granular explosives, the Baer–Nunziato model is the most highly developed. It allows for unequal Phase velocities and Phase pressures, and includes source terms for drag and compaction that strive to erase velocity and pressure disequilibria. Since typical time scales associated with the equilibrating processes are small, source terms are stiff. This stiffness motivates the present work where we derive two reduced models in sequence, one with a single velocity and the other with both a single velocity and a single pressure. These reductions constitute outer solutions in the sense of matched asymptotic expansions, with the corresponding inner layers being just the partly dispersed shocks of the full model. The reduced models are hyperbolic and are mechanically as well as thermodynamically consistent with the parent model. However, they cannot be expressed in conservation form and hence require a regularization in order to fully specify the jump conditions across shock waves. Analysis of the inner layers of the full model provides one such regularization [Kapila et al., Phys. Fluids 9, 3885 (1997)], although other choices are also possible. Dissipation associated with degrees of freedom that have been eliminated is restricted to the thin layers and is accounted for by the jump conditions.

  • two Phase Modeling of deflagration to detonation transition in granular materials reduced equations
    Physics of Fluids, 2001
    Co-Authors: A K Kapila, J B Bdzil, Ralph Menikoff, Donald Scott Stewart
    Abstract:

    Of the two-Phase mixture models used to study deflagration-to-detonation transition in granular explosives, the Baer–Nunziato model is the most highly developed. It allows for unequal Phase velocities and Phase pressures, and includes source terms for drag and compaction that strive to erase velocity and pressure disequilibria. Since typical time scales associated with the equilibrating processes are small, source terms are stiff. This stiffness motivates the present work where we derive two reduced models in sequence, one with a single velocity and the other with both a single velocity and a single pressure. These reductions constitute outer solutions in the sense of matched asymptotic expansions, with the corresponding inner layers being just the partly dispersed shocks of the full model. The reduced models are hyperbolic and are mechanically as well as thermodynamically consistent with the parent model. However, they cannot be expressed in conservation form and hence require a regularization in order t...

  • two Phase Modeling of deflagration to detonation transition in granular materials a critical examination of Modeling issues
    Physics of Fluids, 1999
    Co-Authors: J B Bdzil, A K Kapila, Ralph Menikoff, Donald Scott Stewart
    Abstract:

    The two-Phase mixture model developed by Baer and Nunziato (BN) to study the deflagration-to-detonation transition (DDT) in granular explosives is critically reviewed. The continuum-mixture theory foundation of the model is examined, with particular attention paid to the manner in which its constitutive functions are formulated. Connections between the mechanical and energetic phenomena occurring at the scales of the grains, and their manifestations on the continuum averaged scale, are explored. The nature and extent of approximations inherent in formulating the constitutive terms, and their domain of applicability, are clarified. Deficiencies and inconsistencies in the derivation are cited, and improvements suggested. It is emphasized that the entropy inequality constrains but does not uniquely determine the Phase interaction terms. The resulting flexibility is exploited to suggest improved forms for the Phase interactions. These improved forms better treat the energy associated with the dynamic compacti...

William L Jorgensen - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of cm5 charges for nonaqueous condensed Phase Modeling
    Journal of Chemical Theory and Computation, 2015
    Co-Authors: Leela S Dodda, Jonah Z. Vilseck, Kara J Cutrona, William L Jorgensen
    Abstract:

    Partial atomic charges for neutral molecules from quantum mechanical calculations are typically scaled for use in molecular Modeling of liquid-Phase systems. Optimal scale factors of 1.14 for CM1A and 1.27 for CM5 charges were previously determined for minimizing errors in free energies of hydration. The adequacy of the 1.14*CM1A and 1.27*CM5 models are evaluated here in pure liquid simulations in combination with the OPLS-AA force field. For 22 organic liquids, the 1.14*CM1A and 1.27*CM5 models yield mean unsigned errors (MUEs) of ca. 1.40 kcal/mol for heats of vaporization. Not surprisingly, this reflects overpolarization with the scale factors derived for aqueous media. Prediction of pure liquid properties using CM5 charges is optimized using a scale factor of 1.14, which reduces the MUE for heats of vaporization to 0.89 kcal/mol. However, due to the impracticality of using different scale factors in different explicit-solvent condensed-Phase simulations, a universal scale factor of 1.20 emerged for CM...

  • evaluation of cm5 charges for condensed Phase Modeling
    Journal of Chemical Theory and Computation, 2014
    Co-Authors: Jonah Z. Vilseck, Julian Tiradorives, William L Jorgensen
    Abstract:

    The recently developed Charge Model 5 (CM5) is tested for its utility in condensed-Phase simulations. The CM5 approach, which derives partial atomic charges from Hirshfeld population analyses, provides excellent results for gas-Phase dipole moments and is applicable to all elements of the periodic table. Herein, the adequacy of scaled CM5 charges for use in Modeling aqueous solutions has been evaluated by computing free energies of hydration (ΔGhyd) for 42 neutral organic molecules via Monte Carlo statistical mechanics. An optimal scaling factor for the CM5 charges was determined to be 1.27, resulting in a mean unsigned error (MUE) of 1.1 kcal/mol for the free energies of hydration. Testing for an additional 20 molecules gave an MUE of 1.3 kcal/mol. The high precision of the results is confirmed by free energy calculations using both sequential perturbations and complete molecular annihilation. Performance for specific functional groups is discussed; sulfur-containing molecules yield the largest errors. I...

A K Kapila - One of the best experts on this subject based on the ideXlab platform.

  • two Phase Modeling of deflagration to detonation transition in granular materials reduced equations
    Physics of Fluids, 2001
    Co-Authors: A K Kapila, J B Bdzil, Ralph Menikoff, Donald Scott Stewart
    Abstract:

    Of the two-Phase mixture models used to study deflagration-to-detonation transition in granular explosives, the Baer–Nunziato model is the most highly developed. It allows for unequal Phase velocities and Phase pressures, and includes source terms for drag and compaction that strive to erase velocity and pressure disequilibria. Since typical time scales associated with the equilibrating processes are small, source terms are stiff. This stiffness motivates the present work where we derive two reduced models in sequence, one with a single velocity and the other with both a single velocity and a single pressure. These reductions constitute outer solutions in the sense of matched asymptotic expansions, with the corresponding inner layers being just the partly dispersed shocks of the full model. The reduced models are hyperbolic and are mechanically as well as thermodynamically consistent with the parent model. However, they cannot be expressed in conservation form and hence require a regularization in order t...

  • two Phase Modeling of deflagration to detonation transition in granular materials reduced equations
    Physics of Fluids, 2001
    Co-Authors: A K Kapila, Ralph Menikoff, John B Bdzil, Steven F Son, Donald Scott Stewart
    Abstract:

    Of the two-Phase mixture models used to study deflagration-to-detonation transition in granular explosives, the Baer–Nunziato model is the most highly developed. It allows for unequal Phase velocities and Phase pressures, and includes source terms for drag and compaction that strive to erase velocity and pressure disequilibria. Since typical time scales associated with the equilibrating processes are small, source terms are stiff. This stiffness motivates the present work where we derive two reduced models in sequence, one with a single velocity and the other with both a single velocity and a single pressure. These reductions constitute outer solutions in the sense of matched asymptotic expansions, with the corresponding inner layers being just the partly dispersed shocks of the full model. The reduced models are hyperbolic and are mechanically as well as thermodynamically consistent with the parent model. However, they cannot be expressed in conservation form and hence require a regularization in order to fully specify the jump conditions across shock waves. Analysis of the inner layers of the full model provides one such regularization [Kapila et al., Phys. Fluids 9, 3885 (1997)], although other choices are also possible. Dissipation associated with degrees of freedom that have been eliminated is restricted to the thin layers and is accounted for by the jump conditions.

  • two Phase Modeling of deflagration to detonation transition in granular materials a critical examination of Modeling issues
    Physics of Fluids, 1999
    Co-Authors: J B Bdzil, A K Kapila, Ralph Menikoff, Donald Scott Stewart
    Abstract:

    The two-Phase mixture model developed by Baer and Nunziato (BN) to study the deflagration-to-detonation transition (DDT) in granular explosives is critically reviewed. The continuum-mixture theory foundation of the model is examined, with particular attention paid to the manner in which its constitutive functions are formulated. Connections between the mechanical and energetic phenomena occurring at the scales of the grains, and their manifestations on the continuum averaged scale, are explored. The nature and extent of approximations inherent in formulating the constitutive terms, and their domain of applicability, are clarified. Deficiencies and inconsistencies in the derivation are cited, and improvements suggested. It is emphasized that the entropy inequality constrains but does not uniquely determine the Phase interaction terms. The resulting flexibility is exploited to suggest improved forms for the Phase interactions. These improved forms better treat the energy associated with the dynamic compacti...

  • two Phase Modeling of ddt structure of the velocity relaxation zone
    Physics of Fluids, 1997
    Co-Authors: A K Kapila, J B Bdzil, Ralph Menikoff, D S Stewart
    Abstract:

    The structure of the velocity relaxation zone in a hyperbolic, nonconservative, two-Phase model is examined in the limit of large drag, and in the context of the problem of deflagration-to-detonation transition in a granular explosive. The primary motivation for the study is the desire to relate the end states across the relaxation zone, which can then be treated as a discontinuity in a reduced, equivelocity model, that is computationally more efficient than its parent. In contrast to a conservative system, where end states across thin zones of rapid variation are determined principally by algebraic statements of conservation, the nonconservative character of the present system requires an explicit consideration of the structure. Starting with the minimum admissible wave speed, the structure is mapped out as the wave speed increases. Several critical wave speeds corresponding to changes in the structure are identified. The archetypal structure is partly dispersed, monotonic, and involves conventional hydr...

Ralph Menikoff - One of the best experts on this subject based on the ideXlab platform.

  • two Phase Modeling of deflagration to detonation transition in granular materials reduced equations
    Physics of Fluids, 2001
    Co-Authors: A K Kapila, J B Bdzil, Ralph Menikoff, Donald Scott Stewart
    Abstract:

    Of the two-Phase mixture models used to study deflagration-to-detonation transition in granular explosives, the Baer–Nunziato model is the most highly developed. It allows for unequal Phase velocities and Phase pressures, and includes source terms for drag and compaction that strive to erase velocity and pressure disequilibria. Since typical time scales associated with the equilibrating processes are small, source terms are stiff. This stiffness motivates the present work where we derive two reduced models in sequence, one with a single velocity and the other with both a single velocity and a single pressure. These reductions constitute outer solutions in the sense of matched asymptotic expansions, with the corresponding inner layers being just the partly dispersed shocks of the full model. The reduced models are hyperbolic and are mechanically as well as thermodynamically consistent with the parent model. However, they cannot be expressed in conservation form and hence require a regularization in order t...

  • two Phase Modeling of deflagration to detonation transition in granular materials reduced equations
    Physics of Fluids, 2001
    Co-Authors: A K Kapila, Ralph Menikoff, John B Bdzil, Steven F Son, Donald Scott Stewart
    Abstract:

    Of the two-Phase mixture models used to study deflagration-to-detonation transition in granular explosives, the Baer–Nunziato model is the most highly developed. It allows for unequal Phase velocities and Phase pressures, and includes source terms for drag and compaction that strive to erase velocity and pressure disequilibria. Since typical time scales associated with the equilibrating processes are small, source terms are stiff. This stiffness motivates the present work where we derive two reduced models in sequence, one with a single velocity and the other with both a single velocity and a single pressure. These reductions constitute outer solutions in the sense of matched asymptotic expansions, with the corresponding inner layers being just the partly dispersed shocks of the full model. The reduced models are hyperbolic and are mechanically as well as thermodynamically consistent with the parent model. However, they cannot be expressed in conservation form and hence require a regularization in order to fully specify the jump conditions across shock waves. Analysis of the inner layers of the full model provides one such regularization [Kapila et al., Phys. Fluids 9, 3885 (1997)], although other choices are also possible. Dissipation associated with degrees of freedom that have been eliminated is restricted to the thin layers and is accounted for by the jump conditions.

  • two Phase Modeling of deflagration to detonation transition in granular materials a critical examination of Modeling issues
    Physics of Fluids, 1999
    Co-Authors: J B Bdzil, A K Kapila, Ralph Menikoff, Donald Scott Stewart
    Abstract:

    The two-Phase mixture model developed by Baer and Nunziato (BN) to study the deflagration-to-detonation transition (DDT) in granular explosives is critically reviewed. The continuum-mixture theory foundation of the model is examined, with particular attention paid to the manner in which its constitutive functions are formulated. Connections between the mechanical and energetic phenomena occurring at the scales of the grains, and their manifestations on the continuum averaged scale, are explored. The nature and extent of approximations inherent in formulating the constitutive terms, and their domain of applicability, are clarified. Deficiencies and inconsistencies in the derivation are cited, and improvements suggested. It is emphasized that the entropy inequality constrains but does not uniquely determine the Phase interaction terms. The resulting flexibility is exploited to suggest improved forms for the Phase interactions. These improved forms better treat the energy associated with the dynamic compacti...

  • two Phase Modeling of ddt structure of the velocity relaxation zone
    Physics of Fluids, 1997
    Co-Authors: A K Kapila, J B Bdzil, Ralph Menikoff, D S Stewart
    Abstract:

    The structure of the velocity relaxation zone in a hyperbolic, nonconservative, two-Phase model is examined in the limit of large drag, and in the context of the problem of deflagration-to-detonation transition in a granular explosive. The primary motivation for the study is the desire to relate the end states across the relaxation zone, which can then be treated as a discontinuity in a reduced, equivelocity model, that is computationally more efficient than its parent. In contrast to a conservative system, where end states across thin zones of rapid variation are determined principally by algebraic statements of conservation, the nonconservative character of the present system requires an explicit consideration of the structure. Starting with the minimum admissible wave speed, the structure is mapped out as the wave speed increases. Several critical wave speeds corresponding to changes in the structure are identified. The archetypal structure is partly dispersed, monotonic, and involves conventional hydr...

J. Jatkar - One of the best experts on this subject based on the ideXlab platform.

  • transient analysis of heated soil vapor extraction process with air sparging
    ASME 2005 International Mechanical Engineering Congress and Exposition, 2005
    Co-Authors: R S Amano, J. Jatkar
    Abstract:

    This paper presents the Heated Soil Vapor Extraction (HSVE) that has gained significant attention during the past few years. HSVE along with Air sparging has been found to be an effective way of remediating soil of various pollutants including solvents, fuels and Para-nuclear aromatics. The combined system consists of a heater/boiler that pumps and circulates hot oil through heating wells, a blower that helps to suck the contaminants out through the extraction well, and air sparging wells that extend down to the saturated region in the soil. Both the heating wells and extraction wells are installed vertically in the saturated region in contaminated soil and is welded at the bottom and capped at the top. With this technology the soil is heated by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then absorbed by the extraction well. Soil vapor extraction cannot remove contaminants in the saturated zone of the soil that lies below the water table. In that case air sparging may be used. In air sparging system, air is pumped into the saturated zone to help flush the contaminants up into the unsaturated zone where the contaminants are removed by SVE well. In this analysis an attempt has been made to predict the behavior of different chemicals in the unsaturated and saturated regions of the soil. This analysis uses the species transport and discrete Phase Modeling to predict the behavior of different chemicals when it is heated and absorbed by the extraction well. Such an analysis will be helpful in predicting the parameters like the distance between the heating and extraction wells, the temperature to be maintained at the heating well and the time required for removing the contaminants from the soil.Copyright © 2005 by ASME

  • steady state analysis of heated soil vapor extraction process with air sparging
    ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging o, 2005
    Co-Authors: R S Amano, J. Jatkar
    Abstract:

    Heated Soil Vapor Extraction (HSVE), developed by Advanced Remedial Technology is a Soil remediation process that has gained significant attention during the past few years. HSVE along with Air sparging has been found to be an effective way of remediating soil of various pollutants including solvents, fuels and Para-nuclear aromatics. The combined system consists of a heater/boiler that pumps and circulates hot oil through heating wells, a blower that helps to suck the contaminants out through the extraction well, and air sparging wells that extend down to the saturated region in the soil. Both the heating wells and extraction wells are installed vertically in the saturated region in contaminated soil and is welded at the bottom and capped at the top. The heat source heats the soil and the heat is transported inside the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then absorbed by the extraction well. Soil vapor extraction cannot remove contaminants in the saturated zone of the soil that lies below the water table. In that case air sparging may be used. In air sparging system, air is pumped into the saturated zone to help flush the contaminants up into the unsaturated zone where the contaminants are removed by SVE well. In this analysis an attempt has been made to predict the behavior of different chemicals in the unsaturated and saturated regions of the soil. This analysis uses the species transport and discrete Phase Modeling to predict the behavior of different chemicals when it is heated and absorbed by the extraction well. Such an analysis will be helpful in predicting the parameters like the distance between the heating and extraction wells, the temperature to be maintained at the heating well and the time required for removing the contaminants from the soil.Copyright © 2005 by ASME

  • transient analysis of heated soil vapor extraction process with air sparging
    ASME 2005 International Mechanical Engineering Congress and Exposition, 2005
    Co-Authors: R S Amano, J. Jatkar
    Abstract:

    This paper presents the Heated Soil Vapor Extraction (HSVE) that has gained significant attention during the past few years. HSVE along with Air sparging has been found to be an effective way of remediating soil of various pollutants including solvents, fuels and Para-nuclear aromatics. The combined system consists of a heater/boiler that pumps and circulates hot oil through heating wells, a blower that helps to suck the contaminants out through the extraction well, and air sparging wells that extend down to the saturated region in the soil. Both the heating wells and extraction wells are installed vertically in the saturated region in contaminated soil and is welded at the bottom and capped at the top. With this technology the soil is heated by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then absorbed by the extraction well. Soil vapor extraction cannot remove contaminants in the saturated zone of the soil that lies below the water table. In that case air sparging may be used. In air sparging system, air is pumped into the saturated zone to help flush the contaminants up into the unsaturated zone where the contaminants are removed by SVE well. In this analysis an attempt has been made to predict the behavior of different chemicals in the unsaturated and saturated regions of the soil. This analysis uses the species transport and discrete Phase Modeling to predict the behavior of different chemicals when it is heated and absorbed by the extraction well. Such an analysis will be helpful in predicting the parameters like the distance between the heating and extraction wells, the temperature to be maintained at the heating well and the time required for removing the contaminants from the soil.Copyright © 2005 by ASME

  • steady state analysis of heated soil vapor extraction process with air sparging
    ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging o, 2005
    Co-Authors: R S Amano, J. Jatkar
    Abstract:

    Heated Soil Vapor Extraction (HSVE), developed by Advanced Remedial Technology is a Soil remediation process that has gained significant attention during the past few years. HSVE along with Air sparging has been found to be an effective way of remediating soil of various pollutants including solvents, fuels and Para-nuclear aromatics. The combined system consists of a heater/boiler that pumps and circulates hot oil through heating wells, a blower that helps to suck the contaminants out through the extraction well, and air sparging wells that extend down to the saturated region in the soil. Both the heating wells and extraction wells are installed vertically in the saturated region in contaminated soil and is welded at the bottom and capped at the top. The heat source heats the soil and the heat is transported inside the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then absorbed by the extraction well. Soil vapor extraction cannot remove contaminants in the saturated zone of the soil that lies below the water table. In that case air sparging may be used. In air sparging system, air is pumped into the saturated zone to help flush the contaminants up into the unsaturated zone where the contaminants are removed by SVE well. In this analysis an attempt has been made to predict the behavior of different chemicals in the unsaturated and saturated regions of the soil. This analysis uses the species transport and discrete Phase Modeling to predict the behavior of different chemicals when it is heated and absorbed by the extraction well. Such an analysis will be helpful in predicting the parameters like the distance between the heating and extraction wells, the temperature to be maintained at the heating well and the time required for removing the contaminants from the soil.Copyright © 2005 by ASME

  • a transient simulation of heated soil vapor extraction system
    Volume!, 2004
    Co-Authors: R S Amano, J. Jatkar
    Abstract:

    Soil remediation process by heated soil vapor extraction system has drawn considerably attention for the last few years. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. Our present study is concentrated on Modeling one transient Heated Soil Vapor Extraction System and predicting the time required for effective remediation. The process developed by Advanced Remedial Technology, consists of a heating source pipe and the extraction well embedded in the soil. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. A three-dimensional meshed geometry was developed using gambit. Different boundary conditions were used for heating and suction well and for other boundaries. Concentrations of different chemicals were collected from the actual site and this data was used as an initial condition. The analysis uses the species transport and discrete Phase Modeling to predict the time required to clean the soil under specific conditions. This analysis could be used for predicting the changes of chemical concentrations in the soil during the remediation process. This will give us more insight to the physical phenomena and serve as a numerical predictive tool for more efficient process.Copyright © 2004 by ASME