2007

H.R. Zhang, E.G. Eddings, A.F. Sarofim.
**“Criteria for Selection of Components for Surrogate of Natural Gas and Transportation Fuels,”** In *Proceedings of the Combustion Institute*, Vol. 31, No. 1, pp. 401--409. January, 2007.

DOI: 10.1016/j.proci.2006.08.001

The present paper addressed the production of soot precursors, acetylene, benzene and higher aromatics, by the paraffinic (*n-*, *iso-*, and *cyclo-*) and aromatic components in fuels. To this end, a normal heptane mechanism compiled from sub-models in the literature was extended to large *normal-*, *iso-*, and *cyclo-*paraffins by assigning generic rates to reactions involving paraffins, olefins, and alkyl radicals in the same reaction class. Lumping was used to develop other semi-detailed sub-models. The resulting mechanism for components of complex fuels (named the Utah Surrogate Mechanism) includes detailed sub-models of *n-*butane, *n-*hexane, *n-*heptane, *n-*decane, *n-*dodecane, *n-*tetradecane and *n-*hexadecane, and semi-detailed sub-models of *i-*butane, *i-*pentane, *n-*pentane, 2,4-dimethyl pentane, *i-*octane, 2,2,3,3-tetramethyl butane, cyclohexane, methyl cyclohexane, tetralin, 2-methyl 1-butene, 3-methyl 2-pentene and aromatics. Generic rates of reaction classes were found adequate to generate reaction mechanisms of large paraffinic components. The predicted maximum concentrations of the fuel, oxidizer, and inert species, major products and important combustion intermediates, which include critical radicals and soot precursors, were in good agreement with the experimental data of three premixed flames of composite fuels under various conditions. The relative importance in benzene formation of each component in the kerosene surrogate was found to follow the trend aromatics > *cyclo-*paraffins > *iso-*paraffins > *normal-*paraffins. In contrast, acetylene formation is not that sensitive to the fuel chemical structure. Therefore, in formulation of surrogate fuels, attention should be focused on selecting components that will yield benzene concentrations comparable to those produced by the fuel, with the assurance that the acetylene concentration will also be well approximated.

2006

J. Bigler, J. Guilkey, C. Gribble, C.D. Hansen, S.G. Parker.
**“A Case Study: Visualizing Material Point Method Data,”** In *Proceedings of Euro Vis 2006*, pp. 299--306, 377. May, 2006.

W. Ciro, E.G. Eddings, A.F. Sarofim.
**“Experimental and Numerical Investigation of Transient Soot Buildup on a Cylindrical Container Immersed in a Jet Fuel Pool Fire,”** In *Combustion Science and Technology*, Vol. 178, No. 12, pp. 2199--2218. 2006.

DOI: 10.1080/00102200600626108

Soot buildup and its effects on heat transfer have been investigated as part of an effort to understand the thermal response of containers of high-energy materials immersed in fires. Soot deposition rates were measured for cooled and uncooled cylindrical containers immersed in a jet fuel pool fire. The soot buildup was measured at different time intervals with a wet film gage with an uncertainty of 20%. These rates were compared with those calculated by solving the boundary layer equations along the cylinder surface including the thermophoretic transport of soot particles. Thermophoresis was the dominant soot transport mechanism controlling the deposition of soot on the container wall and gave deposition rates in good agreement with the measured values. The soot buildup was found to have an important insulating effect on the heat transfer to the container. A soot deposit thickness of 1.2 mm resulted in as much as a 35% reduction in heat flux.

J.E. Guilkey, J.B. Hoying, J.A. Weiss.
**“Computational Modeling of Multicellular Constructs with the Material Point Method,”** In *Journal of Biomechanics*, Vol. 39, No. 11, pp. 2074--2086. 2006.

Y. Guo, J.A. Nairn.
**“Three-Dimensional Dynamic Fracture Analysis using the Material Point Method,”** In *Computer Modeling in Engineering and Sciences*, Vol. 1, No. 1, pp. 11--25. 2006.

This paper describes algorithms for three-dimensional dynamic stress and fracture analysis using the material point method (MPM). By allowing dual velocity fields at background grid nodes, the method provides exact numerical implementation of explicit cracks in a predominantly meshless method. Crack contact schemes were included for automatically preventing crack surfaces from interpenetration. Crack-tip parameters, dynamic *J*-integral vector and mode I, II, and III stress intensity factors, were calculated from the dynamic stress solution. Comparisons to finite difference method (FDM), finite element method (FEM), and boundary element method (BEM), as well as to static theories showed that MPM can efficiently and accurately solve three-dimensional dynamic fracture problems. Since the crack description is independent of the object description, MPM could be useful for simulation of three-dimensional dynamic crack propagation in arbitrary directions.

I. Ionescu, J.E. Guilkey, M. Berzins, R.M. Kirby, J.A. Weiss.
**“Simulation of Soft Tissue Failure Using the Material Point Method,”** In *Journal of Biomechanical Engineering*, Vol. 128, No. 6, pp. 917--924. 2006.

G. Krishnamoorthy, R. Rawat, P.J. Smith.
**“Parallelization of the P-1 Radiation Model,”** In *Numerical Heat Transfer, Part B: Fundamentals*, Vol. 49, No. 1, pp. 1--17. 2006.

DOI: 10.1080/10407790500344068

The P-1 radiation model is spatially decomposed to solve the radiative transport equation on parallel computers. Mathematical libraries developed by third parties are employed to solve the linear systems that result during the solution procedure. Multigrid preconditioning accelerated the convergence of iterative methods. The parallel performance did not depend strongly on the radiative properties of the medium or the boundary conditions. Predictions from coupling the weighted-sum-of-gray-gases model with the P-1 approximation are compared against benchmarks for model problems. The P-1 approximation resulted in only a moderate loss in accuracy while being significantly faster than the discrete ordinates method.

S. Parker, K. Zhang, C. Damevski, C.R. Johnson.
**“Integrating Component-Based Scientific Computing Software,”** In *Parallel Processing for Scientific Computing*, Edited by M.A. Heroux and P. Raghavan and H.D. Simon, SIAM, pp. 271--288. January, 2006.

R.P. Pawlowski, J.N. Shadid, J.P. Simonis, H.F. Walker.
**“Globalization Techniques for Newton--Krylov Methods and Applications to the Fully-coupled Solution of the Navier-Stokes Equations,”** In *SIAM Review*, Vol. 48, No. 4, pp. 700--721. 2006.

DOI: 10.1137/S0036144504443511

A Newton-Krylov method is an implementation of Newton's method in which a Krylov subspace method is used to solve approximately the linear subproblems that determine Newton steps. To enhance robustness when good initial approximate solutions are not available, these methods are usually globalized, i.e., augmented with auxiliary procedures (globalizations) that improve the likelihood of convergence from a starting point that is not near a solution. In recent years, globalized Newton-Krylov methods have been used increasingly for the fully coupled solution of large-scale problems. In this paper, we review several representative globalizations, discuss their properties, and report on a numerical study aimed at evaluating their relative merits on large-scale two- and three-dimensional problems involving the steady-state Navier–Stokes equations.

A. Santamaria, F. Mondragon, A Molina, N.D. Marsh, E.G. Eddings, A.F. Sarofim.
**“FT-IR and 1H-NMR Characterization of the Products of an Ethylene Inverse Diffusion Flame,”** In *Combustion and Flame*, Vol. 146, No. 1-2, pp. 52--62. July, 2006.

DOI: 10.1016/j.combustflame.2006.04.008

Knowledge of the chemical structure of young soot and its precursors is very useful in the understanding of the paths leading to soot particle inception. This paper presents analyses of the chemical functional groups, based on FT-IR and ^{1}H NMR spectroscopy of the products obtained in an ethylene inverse diffusion flame. The trends in the data indicate that the soluble fraction of the soot becomes progressively more aromatic and less aliphatic as the height above the burner increases. Results from ^{1}H NMR spectra of the chloroform-soluble soot samples taken at different heights above the burner corroborate the infrared results based on proton chemical shifts (Ha, H*α*, H*β*, and H*γ*). The results indicate that the aliphatic *β* and *γ* hydrogens suffered the most drastic reduction, while the aromatic character increased considerably with height, particularly in the first half of the flame.

**Keywords:** Soot, FT-IR, 1H NMR, Inverse diffusion flame

L. Zheng, D.L. Thompson.
**“On the Accuracy of Force Fields for Predicting the Physical Properties of Dimethylnitramine,”** In *Journal of Physical Chemistry, B*, Vol. 110, No. 10, pp. 16082--16088. July, 2006.

The accuracy of three force fields for predicting the physical properties of dimethylnitramine (DMNA) has been investigated by using molecular dynamics simulations. The Sorescu, Rice, and Thompson (SRT) *(J. Phys. Chem. B 1997, 101*, 798) rigid-molecule, flexible generalized AMBER (

2005

C. Ayyagari, D. Bedrov, G.D. Smith.
**“Equilibrium Sampling of Self-Associating Polymer Solutions: A Parallel Selective Tempering Approach,”** In *Journal of Chemical Physics*, Vol. 123, No. 12, 2005.

DOI: 10.1063/1.1979494

We present a novel simulation algorithm based on tempering a fraction of relaxation-limiting interactions to accelerate the process of obtaining uncorrelated equilibrium configurations of self-associating polymer solutions. This approach consists of tempering (turning off) the attractive interactions for a fraction of self-associating groups determined by a biasing field *h*. A number of independent configurations (replicas) with overlapping Hamiltonian distributions in the expanded (*NVTh*) ensemble with constant *NVT* but different biasing fields, forming a chain of Hamiltonians, were simulated in parallel with occasional attempts to exchange the replicas associated with adjacent fields. Each field had an associated distribution of tempered interactions, average fraction of tempered interactions, and structuraldecorrelation time. Tempering parameters (number of replicas, fields, and exchange frequencies) were chosen to obtain the highest efficiency in sampling equilibrium configurations of a self-association polymer solution based on short serial simulation runs and a statistical model. Depending on the strength of the relaxation-limiting interactions, system size, and thermodynamic conditions, the algorithm can be orders of magnitude more efficient than conventional canonical simulation and is superior to conventional temperature parallel tempering.

B. Banerjee.
**“MPM Validation: A Myriad of Taylor Impact Tests,”** C-SAFE Internal Report, No. C-SAFE-CD-IR-05-001, *Department of Mechanical Engineering, University of Utah*, 2005.

Taylor impacts tests were originally devised to determine the dynamic yield strength of materials at moderate strain rates. More recently, such tests have been used extensively to validate numerical codes for the simulation of plastic deformation. In this work, we use the material point method to simulate a number of Taylor impact tests. The goal is to par- tially validate some plasticity models used by the UINTAH multi-physics code. In addition, we would like to determine the plasticity model that is most appropriate for fire-structure interaction problems that are being simulated using UINTAH. We compare the Johnson- Cook, Steinberg-Cochran-Guinan-Lund, Zerilli-Armstrong, Mechanical Threshold Stress, and the Preston-Tonks-Wallace plasticity models. We evaluate these models for OFHC cop- per, 6061-T6 aluminum alloy, and 4340 steel alloy at various temperatures and strain rates. A number of validation metrics are presented for quantitative comparisons of numerical simulations and experimental data. It is observed that the accuracy of all the models drops when the initial conditions involve high temperatures and high impact velocities.

S.G. Bardenhagen, A.D. Brydon, J.E. Guilkey.
**“Insight into the Physics of Foam Densification via Numerical Solution,”** In *Journal of Mechanics and Physics of Solids*, Vol. 53, No. 3, pp. 597--617. March, 2005.

DOI: 10.1016/j.jmps.2004.09.003

Foamed materials are increasingly finding application in engineering systems on account of their unique properties. The basic mechanics which gives rise to these properties is well established, they are the result of collapsing the foam microstructure. Despite a basic understanding, the relationship between the details of foam microstructure and foam bulk response is generally unknown. With continued advances in computational power, many researchers have turned to numerical simulation to gain insight into the relationship between foam microstructure and bulk properties. However, numerical simulation of foam microscale deformation is a very challenging computational task and, to date, simulations over the full range of bulk deformations in which these materials operate have not been reported. Here a particle technique is demonstrated to be well-suited for this computational challenge, permitting simulation of the compression of foam microstructures to full densification. Computations on idealized foam microstructures are in agreement with engineering guidelines and various experimental results. Dependencies on degree of microstructure regularity and material properties are demonstrated. A surprising amount of porosity is found in fully-densified foams. The presence of residual porosity can strongly influence dynamic material response and hence needs to be accounted for in bulk (average) constitutive models of these materials.

O. Borodin, D. Bedrov, G.D. Smith, J.A. Nairn, S. Bardenhagen.
**“Multiscale Modeling of Viscoelastic Properties of Polymer Nanocomposites,”** In *Journal of Polymer Science*, Vol. 43, No. 8, pp. 1005--1013. April, 2005.

DOI: 10.1002/polb.20390

A methodology for simple multiscale modeling of mechanical properties of polymer nanocomposites has been developed. This methodology consists of three steps: (1) obtaining from molecular dynamics simulations the viscoelastic properties of the bulklike polymer and approximating the position-dependent shear modulus of the interfacial polymer on the basis of the polymer-bead mean-square displacements as a function of the distance from the nanoparticle surface, (2) using bulk- and interfacial-polymer properties obtained from molecular dynamics simulations and performing stress–relaxation simulations of the nanocomposites with material-point-method simulations to extract the nanocomposite viscoelastic properties, and (3) performing direct validation of the average composite viscoelastic properties obtained from material-point-method simulations with those obtained from the molecular dynamics simulations of the nanocomposites.

J.A. Cooke, M. Bellucci, M.D. Smooke, A. Gomez, A. Violi, T. Faravelli, E. Ranzi.
**“Computational and Experimental Study of JP-8, a Surrogate, and its Components in Counterflow Diffusion Flames,”** In *Proceedings of the Combustion Institute*, Vol. 30, No. 1, pp. 439--446. January, 2005.

DOI: 10.1016/j.proci.2004.08.046

Non-sooting counterflow diffusion flames have been studied both computationally and experimentally, using either JP-8, or a six-component JP-8 surrogate mixture, or its individual components. The computational study employs a counterflow diffusion flame model, the solution of which is coupled with arc length continuation to examine a wide variety of inlet conditions and to calculate extinction limits. The surrogate model includes a semi-detailed kinetic mechanism composed of 221 gaseous species participating in 5032 reactions. Experimentally, counterflow diffusion flames are established, in which multicomponent fuel vaporization is achieved through the use of an ultrasonic nebulizer that introduces small fuel droplets into a heated nitrogen stream, fostering complete vaporization without fractional distillation. Temperature profiles and extinction limits are measured in all flames and compared with predictions using the semi-detailed mechanism. These measurements show good agreement with predictions in single-component *n-*dodecane, methylcyclohexane, and iso-octane flames. Good agreement also exists between predicted and measured variables in flames of the surrogate, and the agreement is even better between the experimental JP-8 flames and the surrogate predictions.

H. Davande, O. Borodin, G.D. Smith, T.D. Sewell.
**“Quantum Chemistry-Based Force Field for Simulations of Energetic Dinitro Compounds,”** In *Journal of Energetic Materials*, Vol. 23, No. 4, pp. 205--237. 2005.

DOI: 10.1080/07370650591006885

A quantum chemistry–based force field for molecular dynamics simulations of energetic dinitro compounds has been developed, based on intermolecular binding energies, molecular geometries, molecular electrostatic potentials, and conformational energies obtained from quantum chemistry calculations on model compounds. Nonbonded parameters were determined by fitting experimental densities and heats of vaporizations of model compounds. Torsional parameters were parameterized to reproduce accurately the relative conformational energy minima and barriers in 2,2-dinitropropane, di-methoxy di-methyl ether, 2,2-dinitro-3-methoxypropane, and bis(2,2-dinitropropyl)formal. Molecular dynamics simulations using the developed force field accurately reproduce thermodynamic and transport properties of 1,1-dinitroethane, 2,2-dinitropropane, and a eutectic mixture of bis(2,2-dinitropropyl)formal and bis(2,2-dinitropropyl)acetal.

D.E. DeMarle, C.P. Gribble, S. Boulos, S.G. Parker.
**“Memory Sharing for Interactive Ray Tracing on Clusters,”** In *Parallel Computing*, Vol. 31, No. 2, pp. 221--242. 2005.

E.G. Eddings, S. Yan, W. Ciro, A.F. Sarofim.
**“Formulation of a Surrogate for the Simulation of Jet Fuel Pool Fires,”** In *Combustion Science and Technology*, Vol. 177, No. 4, pp. 715--739. 2005.

DOI: 10.1080/00102200590917248

The simulation of pool fires involving complex hydrocarbon fuels requires the development of a simplified surrogate with a limited number of compounds having known oxidation mechanisms. A series of six-component surrogates was developed for the simulation of JP-8 pool fires, and experiments were carried out with a 30-cm-diameter pool fire to allow comparison of the surrogate fuel behavior to that of the jet fuel. The surrogate was shown to simulate the burning rate, radiant heat flux, and sooting tendency of jet fuel under steady-state pool fire conditions. This study also illustrated the transient nature of batch pool fire experiments and highlighted the difficulties associated with formulating an appropriate surrogate to mimic jet fuel behavior over the lifetime of a batch pool fire. These difficulties were shown to arise from fuel compositional changes, with preferential destruction of lighter components and accumulation of heavier components during the course of the fire.

P. Fife, J. Klewicki, P.A. McMurtry, T. Wei.
**“Multiscaling in the Presence of Indeterminacy: Wall-Induced Turbulence,”** In *Multiscale Modeling and Simulation*, Vol. 4, No. 3, pp. 936--959. 2005.

DOI: 10.1137/040611173

This paper provides a multiscale analytical study of steady incompressible turbulent flow through a channel of either Couette or pressure-driven Poiseuille type. Mathematically, the paper’s two most novel features are that (1) the analysis begins with an underdetermined singular perturbation problem, namely the Reynolds averaged mean momentum balance equation, and (2) it leads to the existence of an infinite number of length scales. (These two features are probably linked, but the linkage will not be pursued.) The paper develops a credible assumption of a mathematical nature which, when added to the initial underdetermined problem, results in a knowledge of almost the complete layer (scaling) structure of the mean velocity and Reynolds stress profiles. This structure in turn provides a lot of other important information about those profiles. The possibility of almost-logarithmic sections of the mean velocity profile is given special attention. The sense in which the length scales are asymptotically proportional to the distance from the wall is determined. Most traditional theoretical analyses of these wall-bounded flows are based ultimately on either the classical overlap hypothesis, mixing length concepts, or similarity arguments. The present paper avoids those approaches and their attendant assumptions. Empirical data are also not used, except that the Reynolds stress takes on positive values. Instead, reasonable criteria are proposed for recognizing scaling layers in the flow, and they are then used to determine the scaling structure and much more information.