ACERC
Abstracts - 1996 |
ACERC
Abstracts - 1996 |
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Thrust Area 5: Comprehensive Model Development |
Ueng, S.-K. and Sikorski,
K.
Visual Computer, 12:1-6, 1996. Funded by ACERC.
In this paper, we present an algorithm for constructing adjacency graphs of 3D finite element analysis (FEA) data. Adjacency graphs are created to represent the connectivities of FEA data cells. They are used in most visualization methods for FEA data. We stress that in many engineering applications FEA data sets do not contain the adjacency information. This is opposite to computer-aided geometric design where, e.g., the winged edge geometrical representation is usually generated and utilized. By establishing intermediate data structures and using bin sorting, we develop an efficient algorithm for constructing such graphs. The total time complexity of the algorithm is linear in the number of data cells.
Ueng, S.-K.; Sikorski, K.
and Ma, K.-L.
IEEE Transactions on Visualization and Computer Graphics, 2(2):100-108,
1996. Partially funded by ACERC.
Streamline construction is one of the most fundamental techniques for visualizing steady flow fields. Streamribbons and streamtubes are extensions for visualizing the rotation and the expansion of the flow. This paper presents efficient algorithms for constructing streamlines, streamribbons, and streamtubes on unstructured grids. A specialized Runge-Kutta method is developed to speed up the tracing of streamlines. Explicit solutions are derived for calculating the angular rotation rates of streamribbons and the radii of streamtubes. In order to simplify mathematical formulations and reduce computational costs, all calculations are carried out in the canonical coordinate system instead of the physical coordinate system. The resulting speed-up in overall performance helps explore large flow fields.
Chen, W.; Smoot, L.D.; Hill,
S.C. and Fletcher, T.H.
Energy & Fuels, 10(5):1046-1052, 1996. Funded by ACERC.
An investigation of a global reburning-NO reaction, SigmaijCiHj + NO --> HCN + . . ., which is a reduction pathway of nitric oxide (NO) by reaction with gaseous hydrocarbons, was conducted. The global reburning-NO rate expression was deduced from a combination of elemental reactions. The global rate expression and its rate constants were then determined by correlating predicted species profiles from simple hydrocarbon flames. This global reburning-NO rate constant can be expressed as 2.7 x 106 exp(-18,800/RT) (gmol/cm³s). This expression and constants are applicable to atmospheric pressure with an equivalence ratio rang of 1.2-2.08 for light hydrocarbon reburning ghases (CH4 and C2H4).
Sikorski, K.
Geophysics, 1996/1997. Funded by Gas Research Institute.
A mathematical breakthrough was recently achieved in understanding the tractability of multidimensional integration using nearly optimal quasi-Monte Carlo methods. Inspired by the new mathematical insights, we have studied the feasibility of applying quasi-Monte Carlo methods to seismic imaging by 3-D pre-stack Kirchhoff migration. This earth imaging technique involves computing a large (10^9) number of 3- or 4-dimensional integrals. Our numerical studies show that nearly optimal quasi-Monte Carlo migration can produce the same or better quality erth images using only a small fraction (one fifth or less) of the data required by a conventional Kirchhoff migration.
The explanation is that an image migrated form a coarse quasi-random array of seismic data is less likely, on average, to be aliased than an image migrated form a regular array of data. In migrating these data, the geophones act as an incoherent arrangement of loudspeakers that broadcast the reflected wavefield back into the earth; the broadcast will produce reinforcement or cancellation of seismic energy at the , respectively, diffractor or grating lobe locations. Thus quasi-Monet Carlo migration contains an inherent anti-aliasing feature that tends to suppress migration artifacts without losing bandwidth. The penalty, however, is a decrease in the dynamic range of the migrated image compared to an image from a regular array of geophones. Our limited numerical results suggest that this loss in dynamic range is acceptable and so justifies the anti-aliasing benefits of migrating a random array of data.
Muzio, L.J. and Quartucy,
G.C.
Progress in Energy and Combustion Science: (in press). (Also presented
at the Advanced Combustion Engineering Research Center 1996 Tenth Annual
Technical Conference, Salt Lake City, Utah, March, 1996.)
Research in NOx formation and control has advanced significantly since Zeldovich first postulated the thermal NO formation mechanism in 1943. This paper reviews the history of NOx formation and control has advanced significantly since Zeldovich first postulated the therm control implementation over this time period, with and emphasis on the role that research has played on NOx formation and control has advanced significantly since Zeldovich first postulated the therm control technology, development and implementation. The discussions are divided by decades, to facilitate comprehension of the progress made. Key representative research during each decade is reviewed, covering topics from fundamental combustion studies to the effect of additives on Selective Non-Catalytic NOx formation and control has advanced significantly since Zeldovich first postulated the therm Reduction performance. NOx formation and control has advanced significantly since Zeldovich first postulated the therm control regulations that drove (and continue to drive) the technology are also discussed. The primary focus is on Southern California and Federal regulations. Southern California was chosen because it has always had the strictest NOx formation and control has advanced significantly since Zeldovich first postulated the therm emissions limits in the nation, while other states and federal government have followed at a somewhat slower pace. Federal regulations are reviewed since they represent the minimum control requirements nationwide. The application of NOx formation and control has advanced significantly since Zeldovich first postulated the therm controls discussed ranges from the simple combustion modifications implemented in the late 1950's and early 1960's through the development of ultra low NOx burners and the retrofit of advanced Selective Catalytic Reductions systems of today.
Chen, W.; Smoot, L.D.; Fletcher,
T.H. and Boardman, R.D.
Energy & Fuels, 10(5):1036-1045, 1996. Funded by ACERC.
Global chemical reaction rates used in the modeling of NOx formation in comprehensive combustion codes have traditionally been obtained trough correlation of experimental data. In this paper, a computational approach for obtaining global rates is presented. Several premixed flames were simulated, and sensitivity analysis of species concentration profiles was used to suggest global pathways in fuel-nitrogen conversion to NO. Based on these analyses, the global reaction rates were formulated. The predicted species concentration profiles and their derivatives were then used in the determination of the global rate constants. The correlation of rate constants for the two fuel-NO global rates (HCN + NO N2 + . . . and HCN + O2 NO + . . .) are discussed. Comparisons of the computed global rate constants with those rate constants with those deduced from experimental data show good agreement. The global rates provide practical kinetics for simulating nitrogen pollutant chemistry in complex flames.
Sikorski, K.
Presented at Colloquium, Computer Science Department, Brigham Young University,
February, 1996. Funded by Brigham Young University.
We review our recent research results in 3-D Visualization and the computation of fixed points of nonlinear equations.
The 3-D parallel volume-rendering algorithm is based on projection methods and master-slave model of distributed computation. We achieve almost linear speed-up in network implementation with a number of workstations.
The 3-D vector field algorithms for rendering streamlines, streamtubes and streamribbons are based on a new, specialized version of the RK-4 method, as well as on explicit solutions to differential equations describing angular rotation and expansion of the flow. The algorithms can render up to 100 streamlines (for 5000 time steps) with CPU of less than 2 sec. (IBM RS6000/560). This performance is achieved by applying specialized data structures and precomputation of essential interpolation functions on the unstructured tetrahedral data.
We describe Fixed Point Envelope (FPEN) and Fixed Point Ellipsoid (FPEL) algorithms for approximating fixed points of contractive functions. We proved the FPEN algorithm to be the most efficient method for univariate functions using the absolute and relative error criteria. In the multivariate case we developed the FPEL algorithm, which is much more efficient than the simple iteration for moderate dimension and mildly contractive functions. This algorithm is based on the ellipsoid construction of Kchachiyan for solving linear programming problems. For large dimension it is impossible to essentially improve the efficiency of the simple iteration.
Hill, S.C. and Smoot, L.D.
Proceedings at the Thirteenth Annual International Pittsburgh Coal Conference,
Pittsburgh, Pennsylvania, September 3-7, 1996. Funded by ACERC.
Comprehensive combustion modeling is becoming an indispensable tool for the design and optimization of practical combustion systems. Comprehensive combustion modeling involves the numerical solution of partial differential equations that describe the physical processes occurring in combustion systems. This paper discusses the information required to create such a model of practical combustion systems and the computational and personnel resources required to apply the model. The procedures to create the model, solve the problem and analyze the results are also described. The information that can be obtained from comprehensive combustion simulations is discussed, and typical applications and some limitations of these simulations are also described. The paper also presents the results of several applications of practical combustion systems compared with experimental data to illustrate potential applications of combustion modeling.
Meng, F.L.; Farmer, J.R.;
Brewster, B.S. and Smoot, L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section / The
Combustion Institute, The University of Southern California, Los Angeles,
California, October 28-29, 1996. Funded by ACERC.
A new model has been developed for simulating modern gas turbine combustors. The new model includes the capability of simulating lean, premixed combustion of methane (or natural gas) and air, and uses and unstructured-grid flow solver to accommodate geometrical complexity. The set of incompressible, steady state, Navier-Stokes equations is solved using a co-located, equal-order, control volume finite element method. The convection term is treated using the mass-weighted, skew upwind scheme, and the diffusion, pressure gradient, and source terms are interpolated linearly in each element. Turbulence is modeled using the kappa-epsilon model. Convective and radiative heat losses are modeled using a wall function method and a discrete ordinates method, respectively. The interaction between turbulence and chemistry is modeled using the velocity-composition Monte-Carlo PDF approach, coupled with a multiple-step reaction mechanism for methane and air. Validation of the code has been initiated by modeling lean, premixed combustion (Phi = 0.8) of natural gas and air in a laboratory-scale, gas turbine combustor with a simple, two-step kinetic mechanism for CH4-O2. Comparison with detailed measurements is forthcoming. Application to industrial gas turbine combustor components is also underway.
Cannon, S.M.; Brewster,
B.S. and Smoot L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section/The Combustion
Institute, The University of Southern California, Los Angeles, California,
October 28-29, 1996. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NOx emissions in lean premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with mathematically reduced 4-, 5- and 9-step mechanism and a detailed 276-step mechanism. NOx emission form thermal, N2O-intermediate, and prompt pathways were described with the 5-, and 9-step reduced mechanisms provided accurate instantaneous reaction rate calculations for a broad region of the accessed composition space in the PaSR. The 4-step mechanism and the partial equilibrium assumption for OH. Practicality of using the 5- and 9-step mechanisms in industrial, 3-dimensional calculations may require the use of a novel, in situ look-up table.
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