41 Matching Results

Search Results

Advanced search parameters have been applied.

Evolution of nuclear shapes at high spins as determined by lifetime measurements

Description: Lifetime measurements of high spin states are obtained by the Doppler-shift recoil-distance method. Transition quadrupole moments are extracted from these data. Expanding on earlier experimental work, lifetime and moment of inertia measurements were made for /sup 172/W. The data for transition quadrupole moments for the yrast states reveals an unexpected drop at high spin which can be explained by the simultaneous alignment of h/sub 9/2/ protons and i/sub 13/2/ neutrons. This conclusion is supported by moment of inertia measurements which show evidence of a 3-band crossing. 9 refs., 10 figs., 2 tabs. (DWL)
Date: January 1, 1986
Creator: Johnson, N.
Partner: UNT Libraries Government Documents Department

Evolution of nuclear shapes at high spins

Description: The dynamic electric quadrupole (E2) moments are a direct reflection of the collective aspects of the nuclear wave functions. For this, Doppler-shift lifetime measurements have been done utilizing primarily the recoil-distance technique. The nuclei with neutron number N approx. 90 possess many interesting properties. These nuclei have very shallow minima in their potential energy surfaces, and thus, are very susceptible to deformation driving influences. It is the evolution of nuclear shapes as a function of spin or rotational frequency for these nuclei that has commanded much interest in the lifetime measurements discussed here. There is growing evidence that many deformed nuclei which have prolate shapes in their ground states conform to triaxial or oblate shapes at higher spins. Since the E2 matrix elements along the yrast line are sensitive indicators of deformation changes, measurements of lifetimes of these states to provide the matrix elements has become the major avenue for tracing the evolving shape of a nucleus at high spin. Of the several nuclei we have studied with N approx. 90, those to be discussed here are /sup 160,161/Yb and /sup 158/Er. In addition, the preliminary, but interesting and surprising results from our recent investigation of the N = 98 nucleus, /sup 172/W are briefly discussed. 14 refs., 5 figs.
Date: January 1, 1985
Creator: Johnson, N.R.
Partner: UNT Libraries Government Documents Department

Information on nuclear shapes at high spins from lifetime measurements

Description: Using Doppler shift techniques, lifetimes of high spin states have been measured in a number of nuclei near N-90 in order to get their dynamic electric quadrupole moments, which are a direct reflection of the collective aspects of the nuclear wave functions. The potential energy surfaces of /sup 160/Yb (N = 90) reveal that it is very shallow in the ..gamma.. degree of freedom as well as in epsilon/sub 2/ and thus should be susceptible to deformation driving influences. Quadrupole transition moments extracted from lifetime data show that especially in /sup 160,161/Yb this is true. Lifetime measurements were carried out on /sup 158/Er in the ..gamma..-..gamma.. coincidence mode. The /sup 158/Er data were analyzed in four ways. Shifted and unshifted peak intensities were first extracted from the total-projected coincidence spectra. Similarly, they were extracted from spectra generated by the sum of all gates below the state of interest, by the gate on the first transition above and by the gate on the second transition above the one of interest. There is evidence for centrifugal stretching in the ground band and a dropoff of collectivity in the s band. 4 figs.
Date: January 1, 1985
Creator: Johnson, N.R.
Partner: UNT Libraries Government Documents Department

Hydrogen as a zero-emission, high-efficiency fuel: Uniqueness, experiments and simulations

Description: The planned use of hydrogen as the energy carrier of the future introduces new challenges and opportunities, especially to the engine design community. Hydrogen is a bio-friendly fuel that can be produced from renewable resources and has no carbon dioxide combustion products; and in a properly designed ICE, almost zero NO{sub x} and hydrocarbon emissions can be achieved. Because of the unique properties of hydrogen combustion - in particular the highly wrinkled nature of the laminar flame front due to the preferential diffusion instability - modeling approaches for hydrocarbon gaseous fuels are not generally applicable to hydrogen combustion. This paper reports on the current progress to develop an engine design capability based on the KIVA family of codes for hydrogen-fueled, spark-ignited engines in support of the National Hydrogen Program. A turbulent combustion model, based on a modified eddy-turnover model in conjunction with an intake flow valve model, is found to describe well the efficiency and NO{sub x} emissions for an experimental engine over a wide range of ignition timings. The NO{sub x} emissions of this engine satisfy the Equivalent Zero Vehicle (EZEV) standard established by the California Resource Board.
Date: November 1, 1997
Creator: Johnson, N.L.
Partner: UNT Libraries Government Documents Department

The legacy and future of CFD at Los Alamos

Description: The early history is presented of the prolific development of CFD methods in the Fluid Dynamics Group (T-3) at Los Alamos National Laboratory in the years from 1958 to the late 1960`s. Many of the currently used numerical methods--PIC, MAC, vorticity-stream-function, ICE, ALE methods and the {kappa}-{var_epsilon} method for turbulence--originated during this time. The rest of the paper summarizes the current research in T-3 for CFD, turbulence and solids modeling. The research areas include reactive flows, multimaterial flows, multiphase flows and flows with spatial discontinuities. Also summarized are modern particle methods and techniques developed for large scale computing on massively parallel computing platforms and distributed processors.
Date: June 1, 1996
Creator: Johnson, N.L.
Partner: UNT Libraries Government Documents Department

OUT Success Stories: Solar Roofing Shingles

Description: Thin-film photovoltaic (PV) cells are now doubling as rooftop shingles. PV shingles offer many advantages. The energy generated from a building's PV rooftop shingles can provide power both to the building and the utility's power grid.
Date: August 31, 2000
Creator: Johnson, N.
Partner: UNT Libraries Government Documents Department

Bismuth germanate's role in the new revolution in gamma-ray spectroscopy

Description: Some of the considerations on how to effectively incorporate bismuth germanate into complex detection systems are covered, and some of these new systems now in operation or under construction are discussed. Significant achievements in gamma ray spectroscopy are reviewed as well as some recent results based on data taken with coincidence arrays of germanium detectors and Compton-suppression spectrometers. Then the first impact of bismuth germanate detectors on our understanding of the properties of nuclei that have high energy and very high angular momentum states are addressed. (LEW)
Date: January 1, 1983
Creator: Johnson, N.R.; Baktash, C. & Lee, I.Y.
Partner: UNT Libraries Government Documents Department

Nuclear collectivity and complex alignment mechanisms in light tungsten and osmium nuclei

Description: During the past few years there have been significant advances in our understanding of nuclei excited into states of high angular momentum. The development of large multi-detector arrays for {gamma}-{gamma} coincidence spectroscopy studies has propelled the amount of new experimental information available and this has been complemented by notable advances in the theoretical treatments of high-spin phenomena. To provide yet a more detailed understanding of the structure of these high-spin states and to provide a stringent test of these models, we have resorted to measurements of their dynamic electromagnetic multipole moments which are a direct reflection of the collective aspects of the nuclear wave functions. For the most part, these multipole moments are obtained by lifetime measurements utilizing Doppler-shift techniques. Let me stress that the great value of lifetime measurements is that they provide the transition matrix elements without the necessity to rely on nuclear models. 24 refs., 10 figs.
Date: January 1, 1989
Creator: Johnson, N.R.
Partner: UNT Libraries Government Documents Department

Comparison of methods for solving nonlinear finite-element equations in heat transfer

Description: We have derived two new techniques for solving the finite-element heat-transfer equations with highly nonlinear boundary conditions and material properties. When compared with the more commonly employed successive substitution and Newton-Raphson procedures, the new methods speed convergence rates and simultaneously increase the radius of convergence. We have observed reductions in computation time in excess of 80% when the new techniques are employed. The first method accelerates the standard Newton-Raphson approach when the degree of the nonlinearity is known (for example, radiation boundary conditions or a prescribed temperature dependence in the thermal conductivity). The second technique employs feedback to regulate the solution algorithm during execution. Comparisons of these techniques are given for several practical examples.
Date: January 1, 1981
Creator: Cort, G.E.; Graham, A.L. & Johnson, N.L.
Partner: UNT Libraries Government Documents Department

DNA analysis of epithelial cell suspensions

Description: Cell suspensions of skin were obtained by animals exposed by skin painting of several crude oils. DNA analysis of these cell suspensions labeled with mithramycin provide determination of percentages of cells in the G/sub 1/, S and G/sub 2/M phases of the cell cycle. Data acquired showed differences from control animals occurring as early as 7 days after treatment and persisting through 21 days afterwards. There was histological evidence of erythema and hyperplasia in shale oil-exposed skins. Flow cytometric analysis of DNA content in shale-oil-exposed skin cells showed an increased percentage of cycling cells plus evidence of aneuploidy. Similar data from simply abraded skin showed increased percentages of cycling cells, but no aneuploidy. The shale-oil-exposed group, when compared to a standard petroleum-exposed group, had significantly increased percentages of cycling cells. This early indication of differing response to different complex mixtures was also seen in long-term skin exposures to these compounds. Similar analytical techniques were applied to tracheal cell suspensions from ozone-exposed rats. 12 refs., 4 figs., 4 tabs. (DT)
Date: January 1, 1985
Creator: Wilson, J.S.; Johnson, N.F. & Holland, L.M.
Partner: UNT Libraries Government Documents Department

Nonlinear Legendre Spectral Finite Elements for Wind Turbine Blade Dynamics: Preprint

Description: This paper presents a numerical implementation and examination of new wind turbine blade finite element model based on Geometrically Exact Beam Theory (GEBT) and a high-order spectral finite element method. The displacement-based GEBT is presented, which includes the coupling effects that exist in composite structures and geometric nonlinearity. Legendre spectral finite elements (LSFEs) are high-order finite elements with nodes located at the Gauss-Legendre-Lobatto points. LSFEs can be an order of magnitude more efficient that low-order finite elements for a given accuracy level. Interpolation of the three-dimensional rotation, a major technical barrier in large-deformation simulation, is discussed in the context of LSFEs. It is shown, by numerical example, that the high-order LSFEs, where weak forms are evaluated with nodal quadrature, do not suffer from a drawback that exists in low-order finite elements where the tangent-stiffness matrix is calculated at the Gauss points. Finally, the new LSFE code is implemented in the new FAST Modularization Framework for dynamic simulation of highly flexible composite-material wind turbine blades. The framework allows for fully interactive simulations of turbine blades in operating conditions. Numerical examples showing validation and LSFE performance will be provided in the final paper.
Date: January 1, 2014
Creator: Wang, Q.; Sprague, M. A.; Jonkman, J. & Johnson, N.
Partner: UNT Libraries Government Documents Department

[sup 3]He neutron detector performance in mixed neutron gamma environments

Description: A test program of the performance of 3He neutron proportional detectors with varying gas pressures, and their response to lligh level gamma-ray exposure in a mixed neutrodgamma environment, ha$ been performed Our intent was to identie the optimal gas pressure to reduce the gamma-ray sensitivity of these detectors. These detectors were manufxtured using materials to minimize their gamma response. Earlier work focused on 3He fill pressures of four atmospheres and above, whereas the present work focuses on a wider range of pressures. Tests have shown that reducing the .filling pressure will M e r increase the gamma-ray dose range in which the detectors can be operated.
Date: January 1, 2002
Creator: Johnson, N. H. (Nathan H.) & Beddingfield, D. H. (David H.)
Partner: UNT Libraries Government Documents Department

ISX toroidal field coil design and analysis

Description: Structural design and analysis aspects of the toroidal field coils for the Impurity Study Experiment (ISX) tokamak are discussed. The overall mechanical design of ISX is predicated on the ability to remove the upper segment of the toroidal field coils to allow access to the toroidal vacuum vessel. The high current, 120 kA, capability of the new 74 MW power supply, coupled with the modest field requirement of ISX, allows the use of room temperature copper coils. Seventy-two turns, grouped into 18 coils, generate a magnet field of 18 kG at the major radius of 90 cm. Finite element structural analysis codes were utilized to determine the distribution of stresses and deflections around a typical turn. Initial material distribution on a coil was sized using the two-dimensional program FEATS. The resulting coil design was then coupled to the center bucking and out-of-plane restraint systems utilizing the NASTRAN code. The boundary conditions for the analytical models used in the two programs were then iterated, reaching satisfactory agreement as to stress contours and location for the joints. (auth)
Date: January 1, 1975
Creator: Hussung, R.O.; Lousteau, D.C.; Johnson, N.E. & Weed, R.A.
Partner: UNT Libraries Government Documents Department

Computer modeling in the design and evaluation of electric and hybrid vehicles

Description: This demonstration project uses modern simulation techniques to illustrate the important technologies and design variables that an auto-designer would consider in production a high efficiency, low emissions vehicle. Simulation and modeling techniques use the idea of capturing the relationships between real components of the systems with mathematical equations. These equations are then solved on a computer to simulate the behavior or performance of the system under various conditions. In the current demonstration project, we focus on many variations of a hydrogen-powered vehicle.
Date: August 16, 1996
Creator: Aceves, S.M.; Smith, J.R. & Johnson, N.L.
Partner: UNT Libraries Government Documents Department

Numerical modeling of hydrogen-fueled internal combustion engines

Description: The planned use of hydrogen as the energy carrier of the future introduces new challenges and opportunities, especially to the engine design community. Hydrogen is a bio-friendly fuel that can be produced from renewable resources and has no carbon dioxide combustion products; and in a properly designed ICE, almost zero NO{sub x} and hydrocarbon emissions can be achieved. Because of the unique properties of hydrogen combustion - in particular the highly wrinkled nature of the laminar flame front due to the preferential diffusion instability - modeling approaches for hydrocarbon gaseous fuels are not generally applicable to hydrogen combustion. This paper reports on the current progress to develop a engine design capability based on KIVA family of codes for hydrogen-fueled, spark-ignited engines in support of the National Hydrogen Program. A turbulent combustion model, based on a modified eddy-turnover model in conjunction with an intake flow valve model, is found to describe well the efficiency and NO{sub x} emissions of this engine satisfy the Equivalent Zero Emission Vehicle (EZEV) standard established by the California Resource Board. 26 refs., 10 figs., 1 tab.
Date: December 31, 1996
Creator: Johnson, N.L. & Amsden, A.A.
Partner: UNT Libraries Government Documents Department

Numerical modeling of hydrogen-fueled internal combustion engines

Description: Major progress was achieved in the last year in advancing the modeling capabilities of hydrogen-fueled engines, both in support of the multi-laboratory project with SNL and LLNL to develop a high-efficiency, low emission powerplant and to provide the engine design tools to industry and research laboratories for hydrogen-fueled engines and stationary power generators. The culmination of efforts on many fronts was the excellent comparison of the experimental data from the Onan engine, operated by SNL.These efforts include the following. An extensive study of the intake flow culminated in a major understanding of the interdependence of the details of the intake port design and the engine operating condition on the emissions and efficiency. This study also resulted in design suggestions for future engines and general scaling laws for turbulence that enables the KIVA results to be applied to a wide variety of operating conditions. The research on the turbulent combustion of hydrogen brought into perspective the effect of the unique aspects of hydrogen combustion and their influence on possible models of turbulent combustion. The effort culminated in a proposed model for turbulent hydrogen combustion that is in agreement with available literature. Future work will continue the development in order to provide a generally predictive model for hydrogen combustion. The application of the combustion model to the Onan experiments elucidated the observed improvement of the efficiency of the engine with the addition of a shroud on the intake valve. This understanding will give guidance to future engine design for optimal efficiency. Finally, a brief summary is given of the extensions and refinements of the KIVA-3 code, in support of future designers of hydrogen-fueled engines.
Date: July 1, 1996
Creator: Johnson, N.L.; Amsden, A.A. & Butler, T.D.
Partner: UNT Libraries Government Documents Department

Progress toward an optimized hydrogen series hybrid engine

Description: The design considerations and computational fluid dynamics (CFD) modeling of a high efficiency, low emissions, hydrogen-fueled engine for use as the prime mover of a series hybrid automobile is described. The series hybrid automobile uses the engine to generate electrical energy via a lightweight generator, the electrical energy is stored in a power peaking device (like a flywheel or ultracapacitor) and used as required to meet the tractive drive requirements (plus accessory loads) through an electrical motor. The engine/generator is stopped whenever the energy storage device is fully charged. Engine power output required was determined with a vehicle simulation code to be 15 to 20 kW steady state with peak output of 40 to 45 kW for hill climb. Combustion chamber and engine geometry were determined from a critical review of the hydrogen engine experiments in the literature combined with a simplified global engine model. Two different engine models are employed to guide engine design. The models are a simplified global engine performance model that relies strongly on correlations with literature data for heat transfer and friction losses, and a state-of-the-art CFD combustion model, KIVA-3, to elucidate fluid mechanics and combustion details through full three-dimensional modeling. Both intake and exhaust processes as well as hydrogen combustion chemistry and thermal NO{sub x} production are simulated. Ultimately, a comparison between the simulation and experimental results will lead to improved modeling and will give guidance to changes required in the next generation engine to achieve the goal of 45% brake thermal efficiency.
Date: June 1, 1995
Creator: Smith, J.R.; Aceves, S.M.; Johnson, N.L. & Amsden, A.A.
Partner: UNT Libraries Government Documents Department

Hydrogen program combustion research: Three dimensional computational modeling

Description: We have significantly increased our computational modeling capability by the addition of a vertical valve model in KIVA-3, code used internationally for engine design. In this report the implementation and application of the valve model is described. The model is shown to reproduce the experimentally verified intake flow problem examined by Hessel. Furthermore, the sensitivity and performance of the model is examined for the geometry and conditions of the hydrogen-fueled Onan engine in development at Sandia National Laboratory. Overall the valve model is shown to have comparable accuracy as the general flow simulation capability in KIVA-3, which has been well validated by past comparisons to experiments. In the exploratory simulations of the Onan engine, the standard use of the single kinetic reaction for hydrogen oxidation was found to be inadequate for modeling the hydrogen combustion because of its inability to describe both the observed laminar flame speed and the absence of autoignition in the Onan engine. We propose a temporary solution that inhibits the autoignition without sacrificing the ability to model spark ignition. In the absence of experimental data on the Onan engine, a computational investigation was undertaken to evaluate the importance of modeling the intake flow on the combustion and NO{sub x} emissions. A simulation that began with the compression of a quiescent hydrogen-air mixture was compared to a simulation of the full induction process with resolved opening and closing of the intake valve. Although minor differences were observed in the cylinder-averaged pressure, temperature, bulk-flow kinetic energy and turbulent kinetic energy, large differences where observed in the hydrogen combustion rate and NO{sub x} emissions. The flow state at combustion is highly heterogeneous and sensitive to the details of the bulk and turbulent flow and that an accurate simulation of the Onan engine must include the modeling of the air-fuel ...
Date: May 1, 1995
Creator: Johnson, N.L.; Amsden, A.A. & Butler, T.D.
Partner: UNT Libraries Government Documents Department

Spall measurements in shock-loaded hemispherical shells from free-surface velocity histories. [Dynamic fracture of hemishells of copper and tantalum]

Description: Copper and tantalum hemishells are externally loaded by a hemishell of PBX 9501 detonated at its pole. Free-surface velocity histories of the metal hemishells are measured at the pole and at 50 from the pole with a Fabry-Perot interferometer. These histories are used to determine spall strengths and depths by simple wave-interaction analyses and are compared with hydro-code (CAVEAT) predictions using simple and void-growth spall models. 8 refs., 4 figs., 1 tab.
Date: January 1, 1987
Creator: Cagliostro, D.J.; Warnes, R.H.; Johnson, N.L. & Fujita, R.K.
Partner: UNT Libraries Government Documents Department

Structural analysis of magnetic fusion energy systems in a combined interactive/batch computer environment

Description: A system of computer programs has been developed to aid in the preparation of input data for and the evaluation of output data from finite element structural analyses of magnetic fusion energy devices. The system utilizes the NASTRAN structural analysis computer program and a special set of interactive pre- and post-processor computer programs, and has been designed for use in an environment wherein a time-share computer system is linked to a batch computer system. In such an environment, the analyst must only enter, review and/or manipulate data through interactive terminals linked to the time-share computer system. The primary pre-processor programs include NASDAT, NASERR and TORMAC. NASDAT and TORMAC are used to generate NASTRAN input data. NASERR performs routine error checks on this data. The NASTRAN program is run on a batch computer system using data generated by NASDAT and TORMAC. The primary post-processing programs include NASCMP and NASPOP. NASCMP is used to compress the data initially stored on magnetic tape by NASTRAN so as to facilitate interactive use of the data. NASPOP reads the data stored by NASCMP and reproduces NASTRAN output for selected grid points, elements and/or data types.
Date: January 1, 1979
Creator: Johnson, N.E.; Singhal, M.K.; Walls, J.C. & Gray, W.H.
Partner: UNT Libraries Government Documents Department