Uintah and Related C-SAFE Publications

2009


H.R. Zhang, E.G. Eddings, A.F. Sarofim, C.K. Westbrook. “Fuel dependence of benzene pathways,” In Proceedings of the Combustion Institute, Vol. 32, No. 1, pp. 377--385. 2009.
DOI: 10.1016/j.proci.2008.06.011

ABSTRACT

The relative importance of formation pathways for benzene, an important precursor to soot formation, was determined from the simulation of 22 premixed flames for a wide range of equivalence ratios (1.0–3.06), fuels (C1–C12), and pressures (20–760 torr). The maximum benzene concentrations in 15 out of these flames were well reproduced within 30% of the experimental data. Fuel structural properties were found to be critical for benzene production. Cyclohexanes and C3 and C4 fuels were found to be among the most productive in benzene formation; and long-chain normal paraffins produce the least amount of benzene. Other properties, such as equivalence ratio and combustion temperatures, were also found to be important in determining the amount of benzene produced in flames. Reaction pathways for benzene formation were examined critically in four premixed flames of structurally different fuels of acetylene, n-decane, butadiene, and cyclohexane. Reactions involving precursors, such as C3 and C4 species, were examined. Combination reactions of C3 species were identified to be the major benzene formation routes with the exception of the cyclohexane flame, in which benzene is formed exclusively from cascading fuel dehydrogenation via cyclohexene and cyclohexadiene intermediates. Acetylene addition makes a minor contribution to benzene formation, except in the butadiene flame where C4H5 radicals are produced directly from the fuel, and in the n-decane flame where C4H5 radicals are produced from large alkyl radical decomposition and H atom abstraction from the resulting large olefins.


2008


O. Borodin, G.D. Smith, T.D. Sewell, D. Bedrov. “Polarizable and Nonpolarizable Force Fields for Alkyl Nitrates,” In Journal of Physical Chemistry, B, Vol. 112, No. 3, pp. 734--742. 2008.
DOI: 10.1021/jp076149f

ABSTRACT

Quantum-chemistry-based many-body polarizable and two-body nonpolarizable atomic force fields were developed for alkyl nitrate liquids and pentaerythritol tetranitrate (PETN) crystal. Bonding, bending, and torsional parameters, partial charges, and atomic polarizabilities for the polarizable force field were determined from gas-phase quantum chemistry calculations for alkyl nitrate oligomers and PETN performed at the MP2/aug-cc-pvDz level of theory. Partial charges for the nonpolarizable force field were determined by fitting the dipole moments and electrostatic potential to values for PETN molecules in the crystal phase obtained from molecular dynamics simulations using the polarizable force field. Molecular dynamics simulations of alkyl nitrate liquids and two polymorphs of PETN crystal demonstrate the ability of the quantum-chemistry-based force fields to accurately predict thermophysical and mechanical properties of these materials.



H. Davande, D. Bedrov, G.D. Smith. “Thermodynamic, Transport and Viscoelastic Properties of PBX-9501 Binder: A Molecular Dynamics Simulation Study,” In Journal of Energetic Materials, Vol. 26, No. 2, pp. 115--138. 2008.
DOI: 10.1080/07370650701801937

ABSTRACT

Atomistic molecular dynamics simulations were performed on a low-molecular-weight nitroplasticized Estane® mixture representative of the binder used in PBX-9501. Pressure-volume-temperature (PVT) behavior over a wide range of pressures and temperatures above the order-disorder temperature (ODT) of Estane was determined and represented with the empirical Tait and Sun equations of state. The effect of temperature, pressure, and plasticization on transport properties of the mixture was also examined. A combination of molecular dynamics simulations and theoretical reptation models was used to predict the shear stress relaxation modulus G(t) of PBX-9501 binder at 473 K and 1 atm pressure. Data obtained from simulations of the model PBX-9501 binder presented here can be utilized to predict the temperature and pressure dependence of the shear stress relaxation modulus for temperatures above the ODT.



C. Gribble, C. Brownlee, S.G. Parker. “Practical Global Illumination for Interactive Particle Visualization,” In Computers and Graphics, Vol. 32, No. 1, pp. 14--24. February, 2008.
DOI: 10.1016/j.cag.2007.11.001

ABSTRACT

Particle-based simulation methods are used to model a wide range of complex phenomena and to solve time-dependent problems of various scales. Effective visualizations of the resulting state will communicate subtle changes in the three-dimensional structure, spatial organization, and qualitative trends within a simulation as it evolves. We present two algorithms targeting upcoming, highly parallel multicore desktop systems to enable interactive navigation and exploration of large particle data sets with global illumination effects. Monte Carlo path tracing and texture mapping are used to capture computationally expensive illumination effects such as soft shadows and diffuse interreflection. The first approach is based on precomputation of luminance textures and removes expensive illumination calculations from the interactive rendering pipeline. The second approach is based on dynamic luminance texture generation and decouples interactive rendering from the computation of global illumination effects. These algorithms provide visual cues that enhance the ability to perform analysis and feature detection tasks while interrogating the data at interactive rates. We explore the performance of these algorithms and demonstrate their effectiveness using several large data sets.

Keywords: Interactive particle visualization, Global illumination, Ray tracing



T.L. Henriksen, T.A. Ring, E.G. Eddings, G.J. Nathan. “Puffing Frequency and Soot Extinction Correlation in JP-8 and Heptane Pool Fires,” In Combustion Science and Technology, Vol. 180, No. 4, 2008.
DOI: 10.1080/00102200701845524

ABSTRACT

A new approach for characterizing puffing frequency was established by performing total extinction measurements on pool fires of JP-8 (Jet Propulsion Fuel 8) and heptane using a multiple beam extinction experiment. A maximum entropy method (MEM) was applied to extract a characteristic extinction frequency that was found to correlate well with puffing frequency. The measured extinction frequency for both flames was found to have some variation with height, though this is small. The amplitude of the frequency of the measured oscillations was found to be higher for JP-8 than for heptane, and became constant one diameter above the fuel pan for both flames. The variance of total extinction in the JP-8 and heptane pool fires was approximately 20% and 17%, respectively. Correlation statistics between the various extinguished beams reveal an increase in axi-symmetry of the instantaneous oscillations with height above the pool.



J. Luitjens, Q. Meng, M. Berzins, T. Henderson. “Improving the Load Balance of Parallel Adaptive Mesh Refined Simulations,” SCI Technical Report, No. UUSCI-2008-007, University of Utah School of Computing, 2008.



J. Luitjens, B. Worthen, M. Berzins, T. Henderson. “Scalable Parallel AMR for the Uintah Multiphysics Code,” In Petascale Computing Algorithms and Applications, Ch. 4, CRC Press LLC., pp. 67--82. 2008.



Q. Meng, J. Luitjens, M. Berzins. “A Comparison of Load Balancing Algorithms for AMR in Uintah,” SCI Technical Report, No. UUSCI-2008-006, University of Utah, 2008.



R.P. Pawlowski, J.P. Simonis, H.F. Walker, J.N. Shadid. “Inexact Newton Dogleg Methods,” In SIAM Journal on Numerical Analysis, Vol. 46, No. 4, pp. 2112--2132. 2008.
DOI: 10.1137/050632166

ABSTRACT

The dogleg method is a classical trust-region technique for globalizing Newton's method. While it is widely used in optimization, including large-scale optimization via truncated-Newton approaches, its implementation in general inexact Newton methods for systems of nonlinear equations can be problematic. In this paper, we first outline a very general dogleg method suitable for the general inexact Newton context and provide a global convergence analysis for it. We then discuss certain issues that may arise with the standard dogleg implementational strategy and propose modified strategies that address them. Newton–Krylov methods have provided important motivation for this work, and we conclude with a report on numerical experiments involving a Newton–GMRES dogleg method applied to benchmark CFD problems.



J.A. Schmidt. “Uintah Application Development,” SCI Technical Report, No. UUSCI-2008-005, University of Utah, 2008.



M. Steffen, S. Curtis, R.M. Kirby, J.K. Ryan. “Investigation of Smoothness-Increasing Accuracy-Conserving Filters for Improving Streamline Integration Through Discontinuous Fields,” In IEEE Transactions on Visualization and Computer Graphics, Vol. 14, No. 3, pp. 680--692. 2008.



M. Steffen, R.M. Kirby, M. Berzins. “Analysis and Reduction of Quadrature Errors in the Material Point Method (MPM),” In International Journal for Numerical Methods in Engineering, Vol. 76, No. 6, pp. 922--948. 2008.
DOI: 10.1002/nme.2360



M. Steffen, P.C. Wallstedt, J.E. Guilkey, R.M. Kirby, M. Berzins. “Examination and Analysis of Implementation Choices within the Material Point Method (MPM),” In Computer Modeling in Engineering & Sciences, Vol. 31, No. 2, pp. 107--127. 2008.



L.T. Tran, J. Kim, M. Berzins. “An Introduction to the Material Point Method using a Case Study from Gas Dynamics,” In Numerical Analysis and Applied Mathematics: International Conference on Numerical Analysis and Applied Mathematics 2008. AIP Conference Proceedings, Vol. 1048, Edited by T.E. Simos and G. Psihoyios and Ch. Tsitouras, pp. 26--29. 2008.
ISBN: 978-0-7354-0576-9



P.C. Wallstedt, J.E. Guilkey. “An Evaluation of Explicit Time Integration Schemes for use with the Generalized Interpolation Material Point Method,” In Journal of Computational Physics, Vol. 227, No. 22, pp. 9628--9642. November, 2008.
DOI: 10.1016/j.jcp.2008.07.019

ABSTRACT

The stability and accuracy of the generalized interpolation material point (GIMP) Method is measured directly through carefully-formulated manufactured solutions over wide ranges of CFL numbers and mesh sizes. The manufactured solutions are described in detail. The accuracy and stability of several time integration schemes are compared via numerical experiments. The effect of various treatments of particle “size” are also considered. The hypothesis that GIMP is most accurate when particles remain contiguous and non-overlapping is confirmed by comparing manufactured solutions with and without this property.

Keywords: Material point method, Manufactured solutions, Time integration, MPM, GIMP, MMS, PIC



H.R. Zhang, E.G. Eddings, A.F. Sarofim. “A Journey From n-Heptane to Liquid Transportation Fuels. 1. The Role of the Allylic Radicals and Its Related Species in Aromatic Precursor Chemistry,” In Energy and Fuels, No. 22, pp. 945--953. 2008.

ABSTRACT

The Utah normal heptane mechanism compiled from submechanisms in the literature was extended into a detailed normal decane combustion mechanism, which is a subset of the Utah surrogate mechanisms. Few species have greater impact on the concentrations of other species than the allyl radical CH2CH=CH2 . Reactions involving the allyl radical and its isomers determine the concentration levels of all olefins, most higher unsaturated species, and benzene. To correctly predict the concentration of benzene, the reaction rates involving allyl-radical-related species need to be accurate and the concentration profiles of these species need to be satisfactory. Kinetic rates found in the literature are compared in the current work for various reference reactions that involve the allylic radicals. The improvements in numerical predictions of unsaturated species are achieved after a rigorous study in finding reliable reaction rates and kinetic correlations between various species. Some of these rates are adopted as the generic rates that have been used in the Utah surrogate mechanisms in previous studies. The modified mechanism is able to predict the concentration profiles of unsaturated species in n-decane and n-heptane flames with good numerical accuracy. The concentrations of these species are closely related to those of various allylic radicals, and reliable kinetics of allylic reactions are critical in predicting the concentrations of benzene and higher aromatics.



H.R. Zhang, E.G. Eddings, A.F. Sarofim. “Pollutant Emissions from Gasoline Combustion: 1. Dependence on Fuel Structural Functionalities,” In Environmental Science and Technology, Vol. 42, No. 15, pp. 5615--5621. June, 2008.
DOI: 10.1021/es702536e

ABSTRACT

To study the formation of air pollutants and soot precursors (e.g., acetylene, 1,3-butadiene, benzene, and higher aromatics) from aliphatic and aromatic fractions of gasoline fuels, the Utah Surrogate Mechanisms is extended to include submechanisms of gasoline surrogate compounds using a set of mechanism generation techniques. The mechanism yields very good predictions of species concentrations in premixed flames of n-heptane, isooctane, benzene, cyclohexane, olefins, oxygenates, and gasoline using a 23-component surrogate formulation. The 1,3-butadiene emission comes mainly from minor fuel fractions of olefins and cyclohexane. The benzene formation potential of gasoline components shows the following trends as functions of (i) chemical class: n-paraffins isoparaffns olefins nphthalnes alkylbenzees cycloparaffis toluene; (ii)carbon number: n-butane < n-pentane < n-hexane; and (iii) branching: n-hexane ne 2,4-trimethylpentane utane. In contrast, fuel structure is not the main factor in determining acetylene formation. Therefore, matching the benzene formation potential of the surrogate fuel to that produced by the real fuel should have priority when selecting candidate surrogate components for combustion simulations.


2007


B. Banerjee. “The Mechanical Threshold Stress Model for Various Tempers of AISI 4340 Steel,” In International Journal of Solids and Structures, Vol. 44, No. 3-4, pp. 834--859. February, 2007.
DOI: 10.1016/j.ijsolstr.2006.05.022

ABSTRACT

Numerical simulations of high strain rate and high temperature deformation of pure metals and alloys require realistic plastic constitutive models. Empirical models include the widely used Johnson-Cook model and the semi-empirical Steinberg-Cochran-Guinan-Lund model. Physically based models such as the Zerilli-Armstrong model, the Mechanical Threshold Stress model, and the Preston-Tonks–Wallace model are also coming into wide use. In this paper, we determine the Mechanical Threshold Stress model parameters for various tempers of AISI 4340 steel using experimental data from the open literature. We also compare stress–strain curves and Taylor impact test profiles predicted by the Mechanical Threshold Stress model with those from the Johnson-Cook model for 4340 steel. Relevant temperature- and pressure-dependent shear modulus models, melting temperature models, a specific heat model, and an equation of state for 4340 steel are discussed and their parameters are presented.



C. Duncan, R. Scherer, J. Guilkey, T. Harman. “Simulations of Vocal Fold Movement and Aerodynamics Using the Uintah Computational Framework,” In Journal of the Acoustical Society of America, Vol. 121, No. 5, pp. 3201-3202. 2007.
DOI: 10.1121/1.4782473

ABSTRACT

This study applies a tightly coupled fluid‐structure interaction algorithm to the modeling of phonation. The Uintah Computational Framework models vocal fold material using the Material Point Method (MPM), which permits arbitrarily large material displacements and multiple materials characterizing the vocal fold properties. The air is modeled using a compressible Navier‐Stokes solver, the Implicit Continuous‐fluid Eulerian (ICE) method developed at Los Alamos National Laboratory by B. A. Kashiwa. The MPM and ICE methods are coupled together to generate a unique simulation tool. Preliminary simulations are shown of 2‐D model vocal folds interacting with prescribed transglottal pressures between 100 Pa and 800 Pa illustrating the intrinsic coupling between the vocal folds and the air. Results are presented showing how the new simulation scheme characterizes the materials and how the aerodynamics that results displays the essential characteristics of glottal flow. The next steps of incorporating three‐dimensionality and acoustics will be discussed. The present simulations set the stage for a realistic computational glottis and for eventual modeling of the effects of vocal fold pathologies on the acoustical output. [Work supported at Bowling Green State University in part by the National Institutes of Health and at the University of Utah by the Department of Energy.]



J.E. Guilkey, T.B. Harman, B. Banerjee. “An Eulerian-Lagrangian Approach for Simulating Explosions of Energetic Devices,” In Computers and Structures, Vol. 85, No. 11-14, pp. 660--674. June-July, 2007.
DOI: 10.1016/j.compstruc.2007.01.031

ABSTRACT

An approach for the simulation of explosions of "energetic devices" is described. In this context, an energetic device is a metal container filled with a high explosive (HE). Examples include bombs, mines, rocket motors or containers used in storage and transport of HE material. Explosions may occur due to detonation or deflagration of the HE material, with initiation resulting from either mechanical or thermal input. This approach is applicable to a wide range of fluid–structure interaction scenarios, the application to energetic devices is chosen because it demonstrates the full capability of this methodology.

Simulations of this type are characterized by a number of interesting and challenging behaviors. These include the transformation of the solid HE into highly pressurized gaseous products that initially occupy regions which formerly contained only solid material. This rapid pressurization of the container leads to large deformations at high strain rates and eventual case rupture. Once the container breaks apart, the highly pressurized product gas that escapes the failing container generates shock waves that propagate through the initially quiescent surrounding fluid.

The approach, which uses a finite-volume, multi-material compressible CFD formulation, within which solid materials are represented using a particle method known as the Material Point Method, is described, including certain of the sub-grid models required to close the governing equations. Results are first presented for "rate stick" and "cylinder test" scenarios, each of which involves detonating unconfined and confined HE material, respectively. Experimental data are available for these configurations and as such they serve as validation tests. Finally, results from an unvalidated "fast cookoff" simulation in which the HE is initiated by thermal input, which causes deflagration, are shown.