Uintah and Related C-SAFE Publications

2003


J.E. Guilkey, T. Harman, A. Xia, B. Kashiwa, P.A. McMurtry. “An Eulerian-Lagrangian Approach for Large Deformation Fluid Structure Interaction Problems, Part 1: Algorithm Development,” In Fluid Structure Interaction II, In Fluid Structure Interaction II: Proceedings of Fluid Structure Interaction , WIT Press, pp. 14. 143--156, 2003.
DOI: 10.2495/FSI030141



T. Harman, J.E. Guilkey, B. Kashiwa, J. Schmidt, P. McMurtry. “An Eulerian-Lagrangian Approach for Large Deformation Fluid Structure Interaction Problems, Part 2: Multi-Physics Simulations within a Modern Computational Framework,” In Fluid Structure Interaction II, WIT Press, pp. 157--166. 2003.

ABSTRACT

A tightly coupled fluid-structure interaction (FSI) solution technique incorporating fluid and solid mechanics, phase change and chemical reactions is presented. The continuum equations are solved with a cell-centered, multi-material ICE solution method. This formulation is integrated with a Lagrangian, particle based, solid mechanics technique, known as the Material Point Method, as described by Kashiwa et al. [1] and Guilkey et al. [2]. The combined method can handle large deformations and phase change within a single grid, without the need of separate domains for fluids and solids, or the passing of boundary conditions. This paper discusses algorithmic issues involved in accounting for chemical reactions and phase transition among material phases (e.g., solid → gas). Validation is presented as are simulations showing large deformation with phase change. These simulations were performed within a computational framework that contains tools for parallelization, performance analysis, data management, algorithm integration, and data visualization. Features of this framework are described.



G. Krishnamoorthy, J.M. Veranth. “Computational Modeling of CO-CO2 Ratio Inside Single Char Particles during Pulverized Coal Combustion,” In Energy and Fuels, Vol. 17, No. 5, pp. 1367--1371. August, 2003.
DOI: 10.1021/ef030006k

ABSTRACT

A recently developed model was used to study the CO/CO2 ratio inside a burning pulverized coal particle, to better understand the effect of bulk gas composition on the equilibrium partial pressure of reduced metal species at the surface of ash inclusions. The motivation was to improve the ability to model submicrometer particle formation by ash vaporization, as a function of furnace conditions. Assumptions for the CO/CO2 ratio that have been made in previous studies are compared to predictions from a psuedo-steady-state model for a single porous particle that considers homogeneous and heterogeneous reaction kinetics and mass transfer both in particle pores and in the boundary layer. This is the first publication of model predictions for the CO/CO2 ratio as a function of radius for a coal char particle in a furnace with a bulk gas CO2 concentration in the range of 0%−79%. A method is proposed for summarizing the effects on the CO/CO2 ratio that are due to changes in the bulk furnace gas O2 and CO2 concentration, furnace temperature, and particle size, using an empirical equation that is suitable for incorporation as a submodel into comprehensive computational fluid dynamics-based codes for combustion simulation. Trends from the model simulations show general agreement with experimental data; however, the accuracy of the predictions is limited by the lack of fuel-specific input data.



J.P. Lewis. “Energetics of intermolecular HONO formation in condensed-phase octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX),” In Chemical Physics Letters, Vol. 371, No. 5-6, pp. 588--593. April, 2003.
DOI: 10.1016/S0009-2614(03)00309-9

ABSTRACT

We present preliminary work on the formation of HONO in condensed-phase HMX for the three pure polymorphic phases. Our results show that the energetics of the intermolecular hydrogen transfer (to form HONO on an adjacent molecule) is more favorable in δ-HMX than in α-HMX and β-HMX. The energetics of this intermolecular hydrogen transfer process follow the same trends of HMX sensitivity, where δ-HMX is found to be more sensitive to explosion compared to β-HMX.



S.G. Parker. “C-SAFE Uses Linux HPCC in Fire Research,” In Syllabus, Technology for Higher Education, Vol. 16, No. 7, Feburary, 2003.



T.D. Sewell, R. Menikoff, D. Bedrov, G.D. Smith. “A Molecular Dynamics Simulation Study of Elastic Properties of HMX,” In Journal of Chemical Physics, Vol. 119, No. 14, pp. 7471--7426. 2003.
DOI: 10.1063/1.1599273



S. Shellman, K. Sikorski. “A Recursive Algorithm for the Infinity-Norm Fixed Point Problem,” In Journal of Complexity, Vol. 19, No. 6, pp. 799--834. 2003.
DOI: 10.1016/j.jco.2003.06.001



S.D. Shellman, K. Sikorski. “Algorithm 825: A deep-cut bisection envelope algorithm for fixed points,” In ACM Transactions on Mathematical Software (TOMS), Vol. 29, No. 3, pp. 309--325. September, 2003.
DOI: 10.1145/838250.838255

ABSTRACT

We present the BEDFix (Bisection Envelope Deep-cut Fixed point) algorithm for the problem of approximating a fixed point of a function of two variables. The function must be Lipschitz continuous with constant 1 with respect to the infinity norm; such functions are commonly found in economics and game theory. The computed approximation satisfies a residual criterion given a specified error tolerance. The BEDFix algorithm improves the BEFix algorithm presented in Shellman and Sikorski [2002] by utilizing "deep cuts," that is, eliminating additional segments of the feasible domain which cannot contain a fixed point. The upper bound on the number of required function evaluations is the same for BEDFix and BEFix, but our numerical tests indicate that BEDFix significantly improves the average-case performance. In addition, we show how BEDFix may be used to solve the absolute criterion fixed point problem with significantly better performance than the simple iteration method, when the Lipschitz constant is less than but close to 1. BEDFix is highly efficient when used to compute residual solutions for bivariate functions, having a bound on function evaluations that is twice the logarithm of the reciprocal of the tolerance. In the tests described in this article, the number of evaluations performed by the method averaged 31 percent of this worst-case bound. BEDFix works for nonsmooth continuous functions, unlike methods that require gradient information; also, it handles functions with minimum Lipschitz constants equal to 1, whereas the complexity of simple iteration approaches infinity as the minimum Lipschitz constant approaches 1. When BEDFix is used to compute absolute criterion solutions, the worst-case complexity depends on the logarithm of the reciprocal of 1-q, where q is the Lipschitz constant, as well as on the logarithm of the reciprocal of the tolerance.



G.D. Smith, D. Bedrov, O. Borodin. “Structural Relaxation and Dynamic Heterogeneity in a Polymer Melt at Attractive Surfaces,” In Physical Review Lett., Vol. 90, No. 22, pp. 226103.1--226103.4. 2003.
DOI: 10.1103/PhysRevLett.90.226103

ABSTRACT

Molecular dynamics simulations of polymer melts at flat and structured surfaces reveal that, for the former, slow dynamics and increased dynamic heterogeneity for an adsorbed polymer is due to densification of the polymer in a surface layer, while, for the latter, the energy topography of the surface plays the dominant role in determining dynamics of interfacial polymer. The dramatic increase in structural relaxation time for polymer melts at the attractive structured surface is largely the result of dynamic heterogeneity induced by the surface and does not resemble dynamics of a bulk melt approaching Tg.



G.D. Smith, D. Bedrov, O. Byutner, O. Borodin, C. Ayyagari, T.D. Sewell. “A Quantum-Chemistry-Based Potential for a Poly(ester urethane),” In Journal of Physical Chemistry, A, Vol. 107, No. 38, pp. 7552--7560. August, 2003.
DOI: 10.1021/jp0225018

ABSTRACT

We have carried out extensive high-level quantum chemistry studies of the geometry, charge distribution, conformational energies, and hydrogen-bonding energies of model compounds for a family of Estane thermoplastic urethanes (TPUs). Upon the basis of these studies, we have parametrized a classical potential for use in atomistic simulations of Estane TPUs that can also be applied directly or with minor extensions to a wide variety of polyesters and polyurethanes.



J.S. Smith, D. Bedrov, G.D. Smith. “A molecular dynamics simulation study of nanoparticle interactions in a model polymer-nanoparticle composite,” In Composites Science and Technology, Vol. 63, No. 11, pp. 1599--1605. August, 2003.
DOI: 10.1016/S0266-3538(03)00061-7

ABSTRACT

Molecular dynamics (MD) simulations were performed on a model polymer–nanoparticle composite (PNPC) consisting of spherical nanoparticles in a bead-spring polymer melt. The polymer-mediated effective interaction (potential of mean force) between nanoparticles was determined as a function of polymer molecular weight and strength of the polymer–nanoparticle interaction. For all polymer–nanoparticle interactions and polymer molecular weights investigated the range of the matrix-induced interaction was greater than the direct nanoparticle–nanoparticle interaction employed in the simulations. When the polymer–nanoparticle interactions were relatively weak the polymer matrix promoted nanoparticle aggregation, an effect that increased with polymer molecular weight. Increasingly attractive nanoparticle–polymer interactions led to strong adsorption of the polymer chains on the surface of the nanoparticles and promoted dispersion of the nanoparticles. For PNPCs with strongly adsorbed chains the matrix-induced interaction between nanoparticles reflected the structure (layering) imposed on the melt by the nanoparticle surface and was independent of polymer molecular weight. The nanoparticle second virial coefficient obtained from the potential of mean force was utilized as an indicator of dispersion or aggregation of the particles in the PNPC, and was found to be in qualitative agreement with the aggregation properties obtained from simulations of selected PNPCs with multiple nanoparticles.



J.P. Spinti, D.W. Pershing. “The Fate of Char-N at Pulverized Coal Conditions,” In Combustion and Flame, Vol. 135, No. 3, pp. 299--313. November, 2003.
DOI: 10.1016/S0010-2180(03)00168-8

ABSTRACT

The fate of char-N (nitrogen removed from the coal matrix during char oxidation) has been widely studied at fluidized bed conditions. This work extends the study of char-N to pulverized coal conditions. Coal chars from five parent coals were prepared and burned in a laboratory-scale pulverized coal combustor in experiments designed to identify the parameters controlling the fate of char-N. The chars were burned with natural gas (to simulate volatiles combustion) in both air and in a nitrogen-free oxidant composed of Ar, CO2, and O2. In some experiments, the char flames were doped with various levels of NO or NH3 to simulate formation of NOx from volatile-N (nitrogen removed during coal devolatilization). The conversion of char-N to NOx in chars burned in the nitrogen-free oxidant was 50–60% for lignites and 40–50% for bituminous coals. In char flames doped with NOx, the apparent conversion of char-N to NOx (computed using the NOx measurements made before and after the addition of char to the system) decreased significantly as the level of NOx doping increased. With 900 ppm NOx present before the addition of char, apparent conversion of char-N to NOx was close to 0% for most chars. While there is no clear correlation between nitrogen content of the char and char-N to NOx conversion at any level of NOx in the flame, the degree of char burnout within a given family of chars does play a role. Increasing the concentration of O2 in the system in both air and nitrogen-free oxidant experiments increased the conversion of char-N to NOx. The effects of temperature on NOx emissions were different at low (0 ppm) and high (900 ppm) levels of NOx present in the flame before char addition.



A. Violi, G.A. Voth, A.F. Sarofim. “A Time-scale Problem for the Formation of Soot Precursors in Premixed Flames,” In American Chemical Society, Division of Fuel Chemistry, Vol. 48, No. 2, pp. 545--547. 2003.


2002


B. Banerjee, D.O. Adams. “Micromechanics-Based Prediction of Thermoelastic Properties of High Energy Materials,” In Constitutive Modeling of Geomaterials, In Constitutive Modeling of Geomaterials, Edited by H.I. Ling et al., CRC Press, New York, pp. 158--164. 2002.

ABSTRACT

High energy materials such as polymer bonded explosives are commonly used as propellants. These particulate composites contain explosive crystals suspended in a rubbery binder. However, the explosive nature of these materials limits the determination of their mechanical properties by experimental means. Therefore micromechanics-based methods for the determination of the effective thermoelastic properties of polymer bonded explosives are investigated in this research. Polymer bonded explosives are twocomponent particulate composites with high volume fractions of particles (volume fraction > 90%) and high modulus contrast (ratio of Young’s modulus of particles to binder of 5,000-10,000). Experimentally determined elastic moduli of one such material, PBX 9501, are used to validate the micromechanics methods examined in this research. The literature on micromechanics is reviewed; rigorous bounds on effective elastic properties and analytical methods for determining effective properties are investigated in the context of PBX 9501. Since detailed numerical simulations of PBXs are computationally expensive, simple numerical homogenization techniques have been sought. Two such techniques explored in this research are the Generalized Method of Cells and the Recursive Cell Method. Effective properties calculated using these methods have been compared with finite element analyses and experimental data.



D. Bedrov, G.D. Smith, K.F. Freed, J. Dudowicz. “A Comparison of Self-Assembly in Lattice and Off-Lattice Model Amphiphile Solutions,” In Journal of Chemical Physics, Vol. 116, No. 12, pp. 4765--4768. 2002.
DOI: 10.1063/1.1461355

ABSTRACT

Lattice Monte Carlo and off-lattice molecular dynamics simulations of h1t4 and h4t1 (head/tail) amphiphile solutions have been performed as a function of surfactant concentration and temperature. The lattice and off-lattice systems exhibit quite different self-assembly behavior at equivalent thermodynamic conditions. We found that in the weakly aggregating regime (no preferred-size micelles), all models yield similar micelle size distributions at the same average aggregation number, albeit at different thermodynamic conditions (temperatures). In the strongly aggregating regime, this mapping between models (through temperature adjustment) fails, and the models exhibit qualitatively different micellization behavior.



D. Bedrov, G.D. Smith, T.D. Sewell. “Molecular Dynamics Simulations of HMX Crystal Polymorphs Using A Flexible Molecule Force Field,” In Journal of Computer-Aided Materials Design, Vol. 8, No. 2-3, pp. 77--85. 2002.
DOI: 10.1023/A:1020046817543

ABSTRACT

Molecular dynamics simulations using a recently developed quantum chemistry-based atomistic force field [J. Phys. Chem. B, 103 (1999) 3570 ] were performed in order to obtain unit cell parameters, coefficients of thermal expansion, and heats of sublimation for the three pure crystal polymorphs of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The predictions for β-, α-, and δ-HMX showed good agreement with the available experimental data. For the case of β-HMX, anisotropic sound speeds were calculated from the molecular dynamics simulation-predicted elastic coefficients and compared with recent Impulsive Stimulated Light Scattering (ISLS) sound speed measurements. The level of agreement is encouraging.



O. Byutner, G.D. Smith. “Viscoelastic Properties of Polybutadiene in the Glassy Regime from Molecular Dynamic Simulations,” In Macromolecules, Vol. 35, No. 9, pp. 3769--3771. 2002.
DOI: 10.1021/ma0105690



J.D. de St. Germain, A. Morris, S.G. Parker, A.D. Malony, S. Shende. “Integrating Performance Analysis in the Uintah Software Development Cycle,” In Proceedings of The 4th International Symposium on High Performance Computing, pp. 190--206. May 15-17, 2002.



C.R. Johnson, S.G. Parker, D. Weinstein, S. Heffernan. “Component-Based Problem Solving Environments for Large-Scale Scientific Computing,” In J. Conc. & Comp.: Prac. & Exper., Vol. 14, pp. 1337--1349. 2002.



G.T. Long, B.A. Brems, C.A. Wight. “Thermal Activation of the High Explosive NTO: Sublimation, Decomposition, and Autocatalysis,” In Journal of Physical Chemistry, B, Vol. 106, No. 15, pp. 4022--4026. March, 2002.
DOI: 10.1021/jp012894v

ABSTRACT

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) show that the heating of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) leads to competitive sublimation and condensed-phase exothermic decomposition. Model-free isoconversional analysis has determined activation energies (Eα) for these processes as a function of the extent of conversion, α. Sublimation occurs most readily in an open pan; although more than simple sublimation was observed, a global activation energy of Eα = 130−140 kJ mol-1 for sublimation was determined. Nonisothermal TGA and DSC traces run on pierced pan samples provide convincing evidence for competitive sublimation and condensed-phase decomposition of NTO. Confining NTO samples in a closed pan results in condensed-phase decomposition that leads to the formation of gaseous reaction products and shows autocatalytic behavior during the latter stages. Isoconversional analysis of DSC traces of closed pan samples yield activation energies for exothermic decomposition that increase from Eα = 273 kJ mol-1 for α = 0.01 to a plateau of 333 kJ mol-1 for 0.17 ≤ α ≤ 0.35 prior to decreasing to 184 kJ mol-1 for α = 0.99. The decrease in Eα with α during the latter stages of decomposition agrees with previous reports of autocatalytic behavior.