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Excitation of a TEM Cell by a Vertical Electric Hertzian Dipole

Description: From abstract: The excitation of a transverse electromagnetic (TEM) cell by a vertical electric Hertzian dipole is analyzed where the gap between the septum and side wall is assumed to be small. Approximate expressions for the field distribution and characteristic impedance are derived. These expressions are numerically evaluated for some typical geometries, and good agreement with previously published results is shown. The formation also allows a vertical offset for the septum position, thus offering more flexibility of increasing the size of the test area to accommodate larger pieces of test equipment.
Date: March 1981
Creator: Wilson, Perry F.; Chang, David C. & Ma, Mark T.
Partner: UNT Libraries Government Documents Department

Input Impedance of a Probe Antenna Exciting a TEM Cell

Description: Abstract: The input impedance of a probe antenna exciting a transverse electromagnetic (TEM) transmission line cell is formulated by a variational approach. The formulation also utilizes the results from a previous work on the field distribution inside a TEM cell excited by a vertical electrical Hertzian dipole. The final result of imoedance is shown to consist of two distinct terms, which are respectively contributed by the ordinary rectangular waveguide and the gap perturbation. Numerical results for both the real and imaginary parts of the impedance are given. The resistive part is found to be proportional to the square of the probe length, and the reactive part largely capacitive.
Date: April 1982
Creator: Wilson, Perry F.; Chang, David C. & Ma, Mark T.
Partner: UNT Libraries Government Documents Department

Oil and Gas Supply Modeling

Description: Abstract: The symposium on Oil and Gas Supply Modeling, held at the Department of Commerce, Washington, DC (June 18-20, 1980), was funded by the Energy Information Administration of the Department of Energy and co-sponsored by the National Bureau of Standards' Operations Research Division. The symposium was organized to be a forum in which the theoretical and applied state-of-the-art of oil and gas supply models could be presented and discussed. Speakers addressed the following areas: the realities of oil and gas supply, prediction of oil and gas production, problems in oil and gas modeling, resource appraisal procedures, forecasting field size and production, investment and production strategies, estimating cost and production schedules for undiscovered fields production regulations, resource data, sensitivity analysis of forecasts, econometric analysis of resource depletion, oil and gas finding rates, and various models of oil and gas supply. This volume documents the proceedings (papers and discussion) of the symposium.
Date: May 1982
Creator: Gass, Saul I.
Partner: UNT Libraries Government Documents Department

Binary Solution Model for Computation of Equilibrium Compositions

Description: A NASA computer program (CEC) for calculation of complex equilibrium compositions has been modified to take into account the formation of an ideal binary solution from pure condensed species. The thermodynamics of the modification are discussed. Applications are presented.
Date: June 1978
Creator: Hsu, Chen C.; Land, Robert H. & Blander, Milton
Partner: UNT Libraries Government Documents Department

Dynamics of Wheeled Vehicles, Report 1: A Mathematical Model for the Traversal of Rigid Obstacles by a Pneumatic Tire, Appendix B: Digital Implementation of Segmented Tire Model

Description: Summary: "This appendix presents the procedures for digital implementation of the segmented tire model, developed in the basic report for an analog computer. Two procedures are required: (a) determination of the segment spring coefficient from measured load-deflection test results, and (b) computation of the resultant force vector transmitted to the axle. Digital programs for both procedures were written in Fortran IV for a GE-420 system, and are included" (p. xi).
Date: August 1969
Creator: Murphy, N. R., Jr.
Partner: UNT Libraries Government Documents Department

Numerical Modeling Analysis of Stress Transfer Modification Concepts for Deep Longwall Mines

Description: Abstract: This U. S. Bureau of Mines (USBM) report evaluates three stress-transfermodification concepts for their potential in reducing longwall gate road stresses and closures. In each of the three concepts - packwalling, gob infilling, and entry filling - support structures are constructed on the headgate side of the panel parallel with or inby the face line. When the headgate becomes the tailgate of the adjacent panel, these structures are in place to accept stresses transferred from the mined-out panel. Using the USBM nonlinear boundary-element program MULSIM/NL, baseline models of typical longwall stress transfer behavior were developed for both intermediate depth and deep mining conditions. These models were verified by comparing model results with field measurements and observations. The stresstransfer-modification concepts were then incorporated into the deep baseline model to quantify the effects of each concept on tailgate closure. Modeling results indicated that entry filling is the most effective concept in reducing tailgate escapeway closure. Using only 18 m3 of a weak fill per meter of face advance (7.3 yd3 per ft of face advance), tailgate escapeway closure was reduced by 33%. By improving the quality of the fill, similar results were achieved using 50% less volume.
Date: 1995
Creator: Vandergrift, Thomas L. & Jude, Charles V.
Partner: UNT Libraries Government Documents Department

LLNL's program on multiscale modeling of polycrystal plasticity

Description: At LLNL a multiscale modeling program based on information-passing has been established for modeling the strength properties of a body-centered-cubic metal (tantalum) ,. under conditions of extreme plastic deformation. The plastic deformation experienced by an explosively-formed shaped-charge jet is an example of �extreme deformation�. The shaped charge liner material undergoes high strain rate deformation at high hydrostatic pressure. The constitutive model for flow stress, which describes the deformation, is highly dependent on pressure, temperature, and strain-rate. Current material models can not be extrapolated to these extreme conditions because the underlying mechanisms of plastic deformation are poorly reflected in the models and laboratory experiments are limited to pressures orders of magnitude less than actual pressures. This disparity between actual deformation conditions and those that can be attained in laboratory experiments is the principle motivation behind the multiscale modeling program. The fundamental elements of LLNL� s multiscale modeling program are distinct models at the atomistic, microscale and mesoscale/continuum length scales. The information that needs to be passed from the lower to higher length scales has been carefully defined to bound the levels of effort required to ''bridge'' length scales. Information that needs to be generated by the different simulations has been specified by a multidisciplinary steering group comprised of physicists, materials scientists and engineers. The ultimate goal of the program is to provide critical information on strength properties to be used in continuum computer code simulations. The technical work-plan involves three principle areas which are highly coupled: 1) simulation development, 2) deformation experiments and 3) characterizations of deformed crystals. The three work areas are presented which provide examples of the progress of LLNL's program.
Date: April 27, 1998
Creator: Diaz De La Rubia, T.; Holmes, N. H.; King, W. E.; Lassila, D. H.; Moriarty, J. A. & Nikkel, D. J.
Partner: UNT Libraries Government Documents Department

Using artifical neutral networks and the genetic algorithm to optimize well-field design: Phase I

Description: Reservoir simulation is a well-established component of reservoir management throughout much of the petroleum industry. Black oil simulators and more complex compositional, thermal, and chemical models are used as forecasting tools in both the day-to-day operational management of production facilities and longer-term field development planning. As yet, however, little use has been made of reservoir simulation coupled with systematic optimization techniques. The main advantage of applying these mathematical tools to decision- making problems is that they are less restricted by human imagination than conventional case-by- case comparisons. As the number of competing engineering, economic, and environmental planning objectives and constraints increases, it becomes difficult for human planners to track complex interactions and select a manageable set of promising scenarios for examination. Using optimization techniques, the search can range over all possible combinations of variables, locating strategies whose effectiveness is not always obvious to planners. Optimization also generates large sets of promising scenarios from which planners can choose:
Date: March 1, 1998
Creator: Johnson, V. M. & Rogers, L. L.
Partner: UNT Libraries Government Documents Department

Numerical Methods for a Porous Medium Equation

Description: The degenerate parabolic equation has been used to model the flow of gas through a porous medium. Error estimates for continuous and discrete time finite element procedures to approximate the solution of this equation are proved and a new regularity result is described.
Date: August 1978
Creator: Rose, Michael Edward
Partner: UNT Libraries Government Documents Department

Opacity of stellar matter

Description: New efforts to calculate opacity have produced significant improvements in the quality of stellar models. The most dramatic effect has been large opacity enhancements for stars subject to large amplitude pulsations. Significant improvement in helioseismic modeling has also been obtained. A description and comparisons of the new opacity efforts are give
Date: September 17, 1998
Creator: Rogers, F J
Partner: UNT Libraries Government Documents Department

Comparison with European observations of meteor impact

Description: A model for the inference of object size and speed from observations is used to discuss European observations of impact. It compares the observed and predicted breakup altitudes for the objects larger than one meter and observes useful correlations. Trends in magnitude correlate well with measured velocities, altitudes, and trajectories and inferred size and strength parameters, but each parameter is subject to dispute, which can only be addressed when the sensitivity of predictions to uncertainties in these parameters is assessed.
Date: June 1, 1997
Creator: Canavan, G.H.
Partner: UNT Libraries Government Documents Department

Subgrid-scale model for the scalar dissipation rate in nonpremixed combustion

Description: A subgrid-scale model is presented for the scalar dissipation rate in nonpremixed turbulent reacting flows. Inputs to the model are the filtered density, the Favre- filtered temperature and the Favre-filtered misture-fraction. The model contains a coefficient which is determined by assuming a form for the scalar energy spectrum. Inputs to the presumed spectrum are the integral and dissipation length scales of the scalar field. These quantities are estimated locally from the Favre-filtered velocity field, resulting in a model coefficient which is spatially and temporally dependent. The model is tested a priori using data from a Direct Numerical Simulation (DXS) of a temporal reacting mixing layer. Estimated values of the dissipation rate are found in good agreement with dissipation rates computed directly from the DXS data. Furthermore, the presumed spectrum methodology is found to accurately predict the mean value of the model coefficient as well as its spatial and temporal variations.
Date: August 31, 1998
Creator: Bushe, W. K. & Cook, A. W.
Partner: UNT Libraries Government Documents Department

Value of Laboratory Experiments for Code Validations

Description: Numerical codes have become indispensable for designing underground structures and interpretating the behavior of geologic systems. Because of the complexities of geologic systems, however, code calculations often are associated with large quantitative uncertainties. This papers presents three examples to demonstrate the value of laboratory(or bench scale) experiments to evaluate the predictive capabilities of such codes with five major conclusions: Laboratory or bench-scale experiments are a very cost-effective, controlled means of evaluating and validating numerical codes, not instead of but before or at least concurrent with the implementation of in situ studies. The design of good laboratory validation tests must identifj what aspects of a code are to be scrutinized in order to optimize the size, geometry, boundary conditions, and duration of the experiments. The design of good and sometimes difficult numerical analyses and sensitivity studies. Laboratory validation tests must involve: Good validation experiments will generate independent data sets to identify the combined effect of constitutive models, model generalizations, material parameters, and numerical algorithms. Successfid validations of numerical codes mandate a close collaboration between experimentalists and analysts drawing from the full gamut of observations, measurements, and mathematical results.
Date: December 14, 1998
Creator: Wawersik, W.R.
Partner: UNT Libraries Government Documents Department

Climate Change Modeling and Downscaling

Description: The National Climate Assessment (NCA) Report Series summarizes regional, sectoral, and process-related workshops and discussions being held as part of the third National Climate Assessment process. This workshop focused on questions, issues, and methodological perspectives regarding the use of mathematical models for the NCA, as well as the complexities that arise when applying data and models to multiple spatial and temporal scales.
Date: 2010-12-08/2010-12-10
Creator: U.S. Global Change Research Program
Partner: UNT Libraries Government Documents Department

Reference Flat Pulse Generator

Description: Introduction: A reference step-like pulse generator is described which has been developed at NBS. This generator can be used for accurately characterizing the step response of various kinds of trap ient recording equipment (oscilloscopes, waveform recorders, transient digitizers, etc.). Basic design principles are given as well as complete circuit diagrams and descriptions. An analysis of the output stage of the generator is presented together with the circuit models for developing a time-domain computer simulation program using extended- SCEPTRE. Preliminary specifications indicate that the NBS Reference Flat Pulse Generator provides a negative-going reference transition duration (90 to 10 percent) of 600 ps, *20 percent with baseline perturbations of less than *2 percent for less than 5 ns.
Date: October 1983
Creator: Andrews, J. R.; Bell, B. A. & Baldwin, E. E.
Partner: UNT Libraries Government Documents Department

Integrated astrophysical modeling

Description: In this project, we have developed prototype techniques for defining and extending a variety of astrophysical modeling capabilities, including those involving multidimensional hydrodynamics, complex transport, and flexibly-coupled equation-of state and nuclear reaction networks. As expected, this project is having both near-term payoffs in understanding complex astrophysical phenomena, as well as significant spin-offs in terms of people and ideas to related ASCI code efforts. Most of our work in the first part of this project was focused on the modularization, extension, and initial integration of 4 previously separate and incommensurate codes: the stellar evolution/explosion code KEPLER; the non-LTE spectral line transport code, EDDINGTON, used for modeling supernovae spectra; the 3-D smooth particle hydro code, PIP; and the discontinuous-finite-element, 3D hydro module from the lCF3D code.
Date: June 3, 1997
Creator: Weaver, T. A.; Weaver, T. A.; Eastman, R. G.; Dubois, P.; Eltgroth, P. G.; Gentile, N. et al.
Partner: UNT Libraries Government Documents Department