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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Multiscale Modeling of Damage Processes in fcc Aluminum: From Atoms to Grains

Molecular dynamics (MD) methods are opening new opportunities for simulating the fundamental processes of material behavior at the atomistic level. However, current analysis is limited to small domains and increasing the size of the MD domain quickly presents intractable computational demands. A preferred approach to surmount this computational limitation has been to combine continuum mechanics-based modeling procedures, such as the finite element method (FEM), with MD analyses thereby reducing the region of atomic scale refinement. Such multiscale modeling strategies can be divided into two broad classifications: concurrent multiscale methods that directly incorporate an atomistic domain within a continuum domain and sequential multiscale methods that extract an averaged response from the atomistic simulation for later use as a constitutive model in a continuum analysis.

Glaessgen, E. H.↗
NASA NTRS1985

Refined potentials for rare gas atom adsorption on rare gas and alkali-halide surfaces

The utilization of models of interatomic potential for physical interaction to estimate the long range attractive potential for rare gases and ions is discussed. The long range attractive force is calculated in terms of the atomic dispersion properties. A data base of atomic dispersion parameters for rare gas atoms, alkali ion, and halogen ions is applied to the study of the repulsive core; the procedure for evaluating the repulsive core of ion interactions is described. The interaction of rare gas atoms on ideal rare gas solid and alkali-halide surfaces is analyzed; zero coverage absorption potentials are derived.

Wilson, J. W.↗
NASA NTRS1994

A full-coordinate model of the polymerase domain of HIV-1 reverse transcriptase and its interaction with a nucleic acid substrate

We present a full-coordinate model of residues 1-319 of the polymerase domain of HIV-I reverse transcriptase. This model was constructed from the x-ray crystallographic structure of Jacobo-Molina et al. (Jacobo-Molina et al., P.N.A.S. USA 90, 6320-6324 (1993)) which is currently available to the degree of C-coordinates. The backbone and side-chain atoms were constructed using the MAXSPROUT suite of programs (L. Holm and C. Sander, J. Mol. Biol. 218, 183-194 (1991)) and refined through molecular modeling. A seven base pair A-form dsDNA was positioned in the nucleic acid binding cleft to represent the template-primer complex. The orientation of the template-primer complex in the nucleic acid binding cleft was guided by the positions of phosphorus atoms in the crystal structure.

Non-NASA Center↗
NASA NTRS2008

A New Concurrent Multiscale Methodology for Coupling Molecular Dynamics and Finite Element Analyses

The coupling of molecular dynamics (MD) simulations with finite element methods (FEM) yields computationally efficient models that link fundamental material processes at the atomistic level with continuum field responses at higher length scales. The theoretical challenge involves developing a seamless connection along an interface between two inherently different simulation frameworks. Various specialized methods have been developed to solve particular classes of problems. Many of these methods link the kinematics of individual MD atoms with FEM nodes at their common interface, necessarily requiring that the finite element mesh be refined to atomic resolution. Some of these coupling approaches also require simulations to be carried out at 0 K and restrict modeling to two-dimensional material domains due to difficulties in simulating full three-dimensional material processes. In the present work, a new approach to MD-FEM coupling is developed based on a restatement of the standard boundary value problem used to define a coupled domain. The method replaces a direct linkage of individual MD atoms and finite element (FE) nodes with a statistical averaging of atomistic displacements in local atomic volumes associated with each FE node in an interface region. The FEM and MD computational systems are effectively independent and communicate only through an iterative update of their boundary conditions. With the use of statistical averages of the atomistic quantities to couple the two computational schemes, the developed approach is referred to as an embedded statistical coupling method (ESCM). ESCM provides an enhanced coupling methodology that is inherently applicable to three-dimensional domains, avoids discretization of the continuum model to atomic scale resolution, and permits finite temperature states to be applied.

Yamakov, Vesselin↗
NASA NTRS2008

An Embedded Statistical Method for Coupling Molecular Dynamics and Finite Element Analyses

The coupling of molecular dynamics (MD) simulations with finite element methods (FEM) yields computationally efficient models that link fundamental material processes at the atomistic level with continuum field responses at higher length scales. The theoretical challenge involves developing a seamless connection along an interface between two inherently different simulation frameworks. Various specialized methods have been developed to solve particular classes of problems. Many of these methods link the kinematics of individual MD atoms with FEM nodes at their common interface, necessarily requiring that the finite element mesh be refined to atomic resolution. Some of these coupling approaches also require simulations to be carried out at 0 K and restrict modeling to two-dimensional material domains due to difficulties in simulating full three-dimensional material processes. In the present work, a new approach to MD-FEM coupling is developed based on a restatement of the standard boundary value problem used to define a coupled domain. The method replaces a direct linkage of individual MD atoms and finite element (FE) nodes with a statistical averaging of atomistic displacements in local atomic volumes associated with each FE node in an interface region. The FEM and MD computational systems are effectively independent and communicate only through an iterative update of their boundary conditions. With the use of statistical averages of the atomistic quantities to couple the two computational schemes, the developed approach is referred to as an embedded statistical coupling method (ESCM). ESCM provides an enhanced coupling methodology that is inherently applicable to three-dimensional domains, avoids discretization of the continuum model to atomic scale resolution, and permits finite temperature states to be applied.

Saether, E.↗
NASA NTRS2007

A Statistical Approach for the Concurrent Coupling of Molecular Dynamics and Finite Element Methods

Molecular dynamics (MD) methods are opening new opportunities for simulating the fundamental processes of material behavior at the atomistic level. However, increasing the size of the MD domain quickly presents intractable computational demands. A robust approach to surmount this computational limitation has been to unite continuum modeling procedures such as the finite element method (FEM) with MD analyses thereby reducing the region of atomic scale refinement. The challenging problem is to seamlessly connect the two inherently different simulation techniques at their interface. In the present work, a new approach to MD-FEM coupling is developed based on a restatement of the typical boundary value problem used to define a coupled domain. The method uses statistical averaging of the atomistic MD domain to provide displacement interface boundary conditions to the surrounding continuum FEM region, which, in return, generates interface reaction forces applied as piecewise constant traction boundary conditions to the MD domain. The two systems are computationally disconnected and communicate only through a continuous update of their boundary conditions. With the use of statistical averages of the atomistic quantities to couple the two computational schemes, the developed approach is referred to as an embedded statistical coupling method (ESCM) as opposed to a direct coupling method where interface atoms and FEM nodes are individually related. The methodology is inherently applicable to three-dimensional domains, avoids discretization of the continuum model down to atomic scales, and permits arbitrary temperatures to be applied.

Saether, E.↗
NASA NTRS1989

Densification and coarsening during solid state sintering of ceramics: A review of the models. II - Grain growth

Two processes occur simultaneously during the sintering of a ceramic powder compact: densification and coarsening (or grain growth). Both processes have as their driving force the reduction of the excess free surface energy of the powder particles. Several different mechanisms of atom transport, operating concurrently or consecutively, may be responsible for the two processes. Algebraic, geometric and topological models have been proposed and refined in attempts to determine the mechanism, or mechanisms, responsible for densification under defined processing conditions. These efforts have met with varying degrees of success. Recently, it has become apparent that more attention must be paid to the coarsening processes during sintering. The models for both densification and coarsening during solid state sintering are reviewed with particular emphasis on their applicability to engineering ceramics.

Shaw, Nancy J.↗
NASA NTRS1995

Characterization of Arcjet Flows Using Laser-Induced Fluorescence

A sensor based on laser-induced fluorescence has been installed at the 20-MW NASA Ames Aerodynamic Heating Facility. The sensor has provided new, quantitative, real-time information about properties of the arcjet flow in the highly dissociated, partially ionized, nonequilibrium regime. Number densities of atomic oxygen, flow velocities, heavy particle translational temperatures, and collisional quenching rates have been measured. These results have been used to test and refine computational models of the arcjet flow. The calculated number densities, translational temperatures, and flow velocities are in moderately good agreement with experiment

Bamford, Douglas J.↗
NASA NTRS1985

Extended atmospheres of outer planet satellites and comets

Model analysis of the extended atmospheres of outer planet satellites and comets are discussed. Understanding the neutral hydrogen distribution in the Saturn system concentrated on assessing the spatial dependence of the lifetime of hydrogen atoms and on obtaining appropriately sorted Lyman ALPHA data from the Voyager 1 UVS instrument. Progress in the area of the extended cometary atmospheres included analysis of Pioneer Venus Layman alpha observations of Comet P/Encke with the fully refined hydrogen cloud model, development of the basic carbon and oxygen models, and planning for the Pioneer Venus UVS observations of Comets P/Giacobini-Zinner and P/Halley.

Smyth, W. H.↗
NASA NTRS1993

Calculation of molecular excitation rates

State-to-state collisional excitation rates for interstellar molecules observed by radio astronomers continue to be required to interpret observed line intensities in terms of local temperatures and densities. A problem of particular interest is collisional excitation of water which is important for modeling the observed interstellar masers. In earlier work supported by a different NASA Grant, excitation of water in collisions with He atoms was studied; after many years of successively more refined calculations that problem now seems to be well understood, and discrepancies with earlier experimental data for related (pressure broadening) phenomena are believed to reflect experimental errors. Because of interstellar abundances, excitation by H2, the dominant interstellar species, is much more important than excitation by He, although it has been argued that rates for excitation by these are similar. Under the current grant theoretical study of this problem has begun which is greatly complicated by the additional degrees of freedom which must be included both in determining the interaction potential and also in the molecular scattering calculation. We have now computed the interaction forces for nearly a thousand molecular geometries and are close to having an acceptable global fit to these points which is necessary for the molecular dynamics calculations. Also, extensive modifications have been made to the molecular scattering code, MOLSCAT. These included coding the rotational basis sets and coupling matrix elements required for collisions of an asymmetric top with a linear rotor. A new method for numerical solution of the coupled equations has been incorporated. Because of the long-ranged nature of the water-hydrogen interaction it is necessary to integrate the equations to rather large intermolecular separations, and the integration methods previously available in MOLSCAT are not ideal for such cases. However, the method used by Alexander in his HIBRIDON code is particularly suited for such cases. We have obtained this code and incorporated that part which solves the coupled differential equations as an option in the MOLSCAT program.

Flynn, George↗
NASA NTRS1999

Studies for the Loss of Atomic and Molecular Species from IO

The general objective of this project has been to advance our theoretical understanding of lo's atmosphere and how various atomic and molecular species are lost from this atmosphere and are distributed in the circumplanetary environment of Jupiter. This grant has provided support for the activities of Dr. Michael Combi at the University of Michigan to serve as a small part in collaboration with a larger project awarded to Atmospheric & Environmental Research, Inc., with primary principal investigator Dr. William H. Smyth. Dr. Combi is the Principal Investigator and Project Manager for the Michigan grant NAG5-6187. This Michigan grant has provided for a continuation of a collaboration between Drs. Smyth and Combi in related efforts beginning in 1981, and with the object to develop and apply sophisticated theoretical models to interpret and to relate a number of new and exciting observations for the atmospheric gases of the satellite. The ability to interpret and then to relate through the theoretical fabric a number of these otherwise independent observations are a central strength of this program. This comprehensive approach provides a collective power, extracting more from the sum of the parts and seeing beyond various limitations that are inherent in any one observation. Although the approach is designed to unify, the program is divided into well-defined studies for the likely dominant atmospheric gases involving species of the SO2 family (SO2, SO, O2, S and O) and for the trace atmospheric gas atomic sodium and a likely escaping molecular ion NaX(+) (where Na(X) is the atmospheric molecule and X represents one or more atoms).Attachments: IO's sodium corona and spatially cloud: a consistent flux speed distribution. and Io's plasma environment during the Galileo flyby: global three-dimensional MHD modeling with adaptive mesh refinement.

Combi, Michael R.↗
NASA NTRS2005

Large Engine Technology Program. Task 22: Variable Geometry Concepts for Rich-Quench-Lean Combustors

The objective of the task reported herein was to define, evaluate, and optimize variable geometry concepts suitable for use with a Rich-Quench-Lean (RQL) combustor. The specific intent was to identify approaches that would satisfy High Speed Civil Transport (HSCT) cycle operational requirements with regard to fuel-air ratio turndown capability, ignition, and stability margin without compromising the stringent emissions, performance, and reliability goals that this combustor would have to achieve. Four potential configurations were identified and three of these were refined and tested in a high-pressure modular RQL combustor rig. The tools used in the evolution of these concepts included models built with rapid fabrication techniques that were tested for airflow characteristics to confirm sizing and airflow management capability, spray patternation, and atomization characterization tests of these models and studies that were supported by Computational Fluid Dynamics analyses. Combustion tests were performed with each of the concepts at supersonic cruise conditions and at other critical conditions in the flight envelope, including the transition points of the variable geometry system, to identify performance, emissions, and operability impacts. Based upon the cold flow characterization, emissions results, acoustic behavior observed during the tests and consideration of mechanical, reliability, and implementation issues, the tri-swirler configuration was selected as the best variable geometry concept for incorporation in the RQL combustor evolution efforts for the HSCT.

Tacina, Robert R.↗
NASA NTRS1993

Measurements of Excitation Functions and Line Polarizations for Electron Impact Excitation of the n = 2, 3 States of Atomic Hydrogen in the Energy Range 11 - 2000 eV

The electron-atomic hydrogen scattering system is an important testing ground for theoretical models and has received a great deal of attention from experimentalists and theoreticians alike over the years. A complete description of the excitation process requires a knowledge of many different parameters, and experimental measurements of these parameters have been performed in various laboratories around the world. As far as total cross section data are concerned it has been noted that the discrepancy between the data of Long et al. and Williams for n = 2 excitations needs to be resolved in the interests of any further refinement of theory. We report new measurements of total cross sections and atomic line polarizations for both n=2 and n=3 excitations at energies from threshold to 2000 eV...

James, G. K.↗
NASA NTRS2002

ISO Key Project: Exploring The Full Range of Quasar/AGN Properties

While most of the work on this program has been completed, as previously reported, the portion of the program dealing with the sub topic of ISO LWS data analysis and reduction for the LWS Extragalactic Science Team and its leader, Dr. Howard Smith, is still active. This program in fact continues to generate results, and newly available computer modeling has extended the value of the datasets, As a result the team has requested and been granted an obtained a no-cost extension to this program, through December 31, 2003. The essence of the proposal is to perform ISO spectroscopic studies, including data analysis and modeling, of star formation regions using an ensemble of archival space-based data from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, but including as well some other spectroscopic data bases. Four kinds of regions are considered in the studies: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star formation regions; (3) star formation in external, bright IR galaxies; and (4) the galactic center. One prime focus of the program is the OH lines in the far infrared. The program has the following goals: (1) refine the data analysis of ISO observations, to obtain deeper and better SNR results on selected sources. The ISO data itself underwent "pipeline 10" reductions in early 2001, and additional "hands-on data reduction packages" were supplied by the ISO teams in 2001. The Fabry-Perot database in particularly sensitive to noise can slight calibration errors. (2) model the atomic and molecular line shapes, in particular the OH lines, using revised Monte-Carlo techniques developed by the SWAS team at the Center for Astrophysics; (3) attend scientific meetings and workshops; (4) do E&PO activities related to infrared astrophysics and/or spectroscopy.

Wilkes, Belinda↗
NASA NTRS2003

ISO Key Project: Exploring the Full Range of Quasar/Agn Properties

While most of the work on this program has been completed, as previously reported, the portion of the program dealing with the subtopic of ISO LWS data analysis and reduction for the LWS Extragalactic Science Team and its leader, Dr. Howard Smith, is still active. This program in fact continues to generate results, and newly available computer modeling has extended the value of the datasets. As a result the team requests a one-year no-cost extension to this program, through 31 December 2004. The essence of the proposal is to perform ISO spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, but including as well some other spectroscopic databases. Four kinds of regions are considered in the studies: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR galaxies; and (4) the galactic center. One prime focus of the program is the OH lines in the far infrared. The program has the following goals: 1) Refine the data analysis of ISO observations to obtain deeper and better SNR results on selected sources. The ISO data itself underwent 'pipeline 10' reductions in early 2001, and additional 'hands-on data reduction packages' were supplied by the ISO teams in 2001. The Fabry-Perot database is particularly sensitive to noise and slight calibration errors; 2) Model the atomic and molecular line shapes, in particular the OH lines, using revised Monte-Carlo techniques developed by the SWAS team at the Center for Astrophysics; 3) Attend scientific meetings and workshops; 4) Perform E&PO activities related to infrared astrophysics and/or spectroscopy.

Wilkes, Belinda↗
NASA NTRS2005

Explore Full Range of QSO/AGN Properties

The goal of the proposal is to perform ISO spectroscopic studies, including data analysis and modeling, of star formation regions using an ensemble of archival space-based data from the Infrared Space Observatory s Long Wavelength Spectrometer and Short Wavelength Spectrometer, but including as well some other spectroscopic databases. Four kinds of regions are considered in the studies: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star formation regions; (3) star formation in external, bright IR galaxies; and (4) the galactic center. One prime focus of the program is the OH lines in the far infrared. The program had the following goals: 1) Refine the data analysis of IS0 observations to obtain deeper and better SNR results on selected sources. The IS0 data itself underwent "pipeline 10" reductions in early 2001, and additional "hands-on data reduction packages" were supplied by the IS0 teams in 2001. The Fabry-Perot database is particularly sensitive to noise and slight calibration errors. 2) Model the atomic and molecular line shapes, in particular the OH lines, using revised monte- carlo techniques developed by the SWAS team at the Center for Astrophysics; 3) Attend scientific meetings and workshops; 4) Do E&PO activities related to infrared astrophysics and/or spectroscopy.

Oliversen, Ronald↗
NASA NTRS2018

Solar Wind Implantation into Lunar Regolith II: Monte Carlo Simulations of Hydrogen Retention in a Surface with Defects and the Hydrogen (H, H2) Exosphere

Recently, the near-infrared observations of the OH veneer on the lunar surface by the Moon Mineralogy Mapper (M3) have been refined to constrain the OH content to 500-750 parts per million (ppm). The observations indicate diurnal variations in OH up to 200 ppm possibly linked to warmer surface temperatures at low latitude. We examine the M3 observations using a statistical mechanics approach to model the diffusion of implanted H in the lunar regolith. We present results from Monte Carlo simulations of the diffusion of implanted solar wind H atoms and the subsequently derived H and H2 exospheres.

Exosphere↗
NASA NTRS2003

Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

In this program we proposed to perform a series of spectroscopic studies, including data analysis and modeling, of star formation regions using an ensemble of archival space-based data from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and to take advantage of other spectroscopic databases including the first results from SIRTF. Our emphasis has been on star formation in external, bright IR galaxies, but other areas of research have included young, low or high mass pre-main sequence stars in star formation regions, and the galactic center. The OH lines in the far infrared were proposed as one key focus of this inquiry, because the Principal Investigator (H. Smith) had a full set of OH IR lines from IS0 observations. It was planned that during the proposed 2-1/2 year timeframe of the proposal other data (including perhaps from SIRTF) would become available, and we intended to be responsive to these and other such spectroscopic data sets. The program has the following goals: 1) Refine the data analysis of IS0 observations to obtain deeper and better SNR results on selected sources. The IS0 data itself underwent pipeline 10 reductions in early 2001, and the more 'hands-on data reduction packages' have been released. The IS0 Fabry-Perot database is particularly sensitive to noise and can have slight calibration errors, and improvements are anticipated. We plan to build on these deep analysis tools and contribute to their development. Model the atomic and molecular line shapes, in particular the OH lines, using revised montecarlo techniques developed by the Submillimeter Wave Astronomy Satellite (SWAS) team at the Center for Astrophysics. 2) 3) Use newly acquired space-based SIRTF or SOFIA spectroscopic data as they become available, and contribute to these observing programs as appropriate. 4) Attend scientific meetings and workshops. 5) E&PO activities, especially as related to infrared astrophysics and/or spectroscopy.

Smith, Howard A.↗