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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Boundary conditions for the paleoenvironment: Chemical and Physical Processes in dense interstellar clouds

The present research includes searches for important new interstellar constituents; observations relevant to differentiating between different models for the chemical processes that are important in the interstellar environment; and coordinated studies of the chemistry, physics, and dynamics of molecular clouds which are the sites or possible future sites of star formation. Recent research has included the detection and study of four new interstellar molecules; searches which have placed upper limits on the abundance of several other potential constituents of interstellar clouds; quantitative studies of comparative molecular abundances in different types of interstellar clouds; investigation of reaction pathways for astrochemistry from a comparison of theory and the observed abundance of related species such as isomers and isotopic variants; studies of possible tracers of energenic events related to star formation, including silicon and sulfur containing molecules; and mapping of physical, chemical, and dynamical properties over extended regions of nearby cold molecular clouds.

Irvine, W. M.↗
NASA NTRS1986

Boundary conditions on the early Sun from ancient cosmogenic neon in meteorites

Isotopic analysis of neon from individual grains of the meteorites Murchison (CM) and Kapoeta (howardite) shows large enrichments of cosmogenic neon in grains with solar flare tracks. The quantity of this component is incompatible with galactic cosmic ray or solar cosmic ray irradiation under present conditions and is attributed to irradiation by energetic flares from an early active Sun. Handpicked grains from each meteorite were grouped according to the presence or absence of solar flare heavy ion tracks, and these four samples were analyzed with an ion counting noble gas mass spectrometer.

Hohenberg, C. M.↗
NASA NTRS1986

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

The first interstellar hydrocarbon ring, cyclopropenylidene (C3H2) is being studied. Both a survey of galactic sources in several C3H2 transitions and a more detailed study of a subset of these sources are under way. In the latter category is a study of the nearby cold dark cloud TMC-1, which is a potential formation site for solar type stars. A spectra is shown of seven rotational transitions which have been observed at the Five College Radio Astronomy Observatory. Three of these were detected for the first time in any astronomical source: the 3 sub 30 to 2 sub 21 transition at 216 GHz, the 2 sub 21 to 1 sub 10 transition at 122 GHz, and the 1 sub 11 to 0 sub 00 transition at 52 GHz. From the data it is apparent that C3H2 is quite spacially extended in typical interstellar molecular clouds, and that at least in TMC-1 it is one of the most abundant organic molecules.

Irvine, W. M.↗
NASA NTRS1986

Conservative boundary conditions for 3D gas dynamics problems

A method is described for 3D-gas dynamics computer simulation in regions of complicated shape by means of nonadjusted rectangular grids providing unified treatment of various problems. Some test problem computation results are given.

Gerasimov, B. P.↗
NASA NTRS1987

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

Detailed study of the first interstellar hydrocarbon ring, cyclopropenylidene (C3H2), is continuing. The singly deuterated isotope of this molecule, C3HD, was observed in several cold interstellar clouds. The results of a large survey for C3H2 in galactic sources of various types will soon be completed. It appears that cyclopropenylidene is present in virtually all interstellar clouds of at least moderate density. In order to make the first determinations of the CO2/CO abundance ratio in interstellar sources, observations of protonated CO2 were pursued. The spectrum from 18.5 to 22 GHz for several interstellar clouds is being systematically measured. Particular attention is being given to the cold, dark clouds TMC-1 and L124N, which may be formation sites for solar mass stars. The phenomena of maser emission from molecules of methanol is being studied in certain interstellar clouds. A comparison of 1 millimeter continuum emission from dust with the column density of carbon monoxide as determined from the rare C(18)O isotope for 4 molecular clouds in the Galaxy is nearing completion. Papers published during the period of this report are listed.

Irvine, William M.↗
NASA NTRS1987

A new formulation of electromagnetic wave scattering using an on-surface radiation boundary condition approach

A new formulation of electromagnetic wave scattering by convex, two-dimensional conducting bodies is reported. This formulation, called the on-surface radiation condition (OSRC) approach, is based upon an expansion of the radiation condition applied directly on the surface of a scatterer. It is now shown that application of a suitable radiation condition directly on the surface of a convex conducting scatterer can lead to substantial simplification of the frequency-domain integral equation for the scattered field, which is reduced to just a line integral. For the transverse magnetic case, the integrand is known explicitly. For the transverse electric case, the integrand can be easily constructed by solving an ordinary differential equation around the scatterer surface contour. Examples are provided which show that OSRC yields computed near and far fields which approach the exact results for canonical shapes such as the circular cylinder, square cylinder, and strip. Electrical sizes for the examples are ka = 5 and ka = 10. The new OSRC formulation of scattering may present a useful alternative to present integral equation and uniform high-frequency approaches for convex cylinders larger than ka = 1. Structures with edges or corners can also be analyzed, although more work is needed to incorporate the physics of singular currents at these discontinuities. Convex dielectric structures can also be treated using OSRC.

Kriegsmann, Gregory A.↗
NASA NTRS1988

Vibration frequencies of tapered bars with nonclassical boundary conditions

The goals for this research were revised and clarified. The goals are restated along with an evaluation of the accomplishment of the goal. All of the cases of the truncated-cone beams that were originally proposed to be solved were solved. A summary of these solutions is presented. Some cases of beams with unequal tapers were solved and are discussed.

Craver, W. Lionel, Jr.↗
NASA NTRS1990

Analytical solutions with Generalized Impedance Boundary Conditions (GIBC)

The diffraction by a material discontinuity in a thick dielectric/ferrite layer is considered by modeling the layer as a distributed current sheet obeying generalized sheet transition conditions (GSTC's). The sheet currents are then formulated and solved via the standard dual integral equation approach. This yields the diffracted field in terms of unknown constants which underscore the non-uniqueness of the GSTC current sheet representation. The constants are dependent on the geometry and properties of the discontinuity and are determined by enforcing field continuity across the material junction. This requires the field internal to the slab which are determined from the external ones via analytic continuity. Results are given which validate the solution and demonstrate the importance of the constants.

Ricoy, Mark A.↗
NASA NTRS1991

Charge collected by diffusion from an ion track under mixed boundary conditions

Charge-carrier diffusion from an ion track in a silicon substrate at least a few hundred microns thick is analyzed. The substrate upper surface is treated as reflective except for a small section, intended to represent a reverse-biased junction, which is treated as a sink. Total charge collected by the sink is calculated by assuming transport to be governed by an ambipolar diffusion equation with temporally constant and spatially uniform carrier lifetime and diffusion coefficient. Present results apply to a normally incident track but could easily be generalized to arbitrary track direction. The collected charge is found to depend on track length and on the electrostatic capacitance, rather than the area, of the sink. Theoretical predictions are compared to the results of a numerical simulation called the Poisson and Continuity Equation Solver (PISCES) for three cases and are found to agree within a factor of two in the worst case.

Edmonds, Larry D.↗
NASA NTRS1990

The intergalactic medium - Initial and boundary conditions for galaxy and primeval star formation

New detailed numerical calculations are presented of the evolution of the intergalactic medium (IGM) in a post recombination Friedmann universe, including a solution of the nonequilibrium rate equations for the ionization and recombination of H and He, the energy equation, and the equation of radiative transfer. The implications of this study for the characteristic mass scale and the epoch of gravitational collapse for the average 'first' star-forming clouds are discussed. The star-formation rate and associated metallicity generation implied if the IGM is fully ionized by starlight by redshift greater than 4 as suggested by recent interpretations of the Gunn-Peterson effect are examined. It is shown that the relative strengths of metal lines from a quasar absorption-line Lyman limit system cloud at z = 3 photoionized by the present intergalactic UV radiation background are compatible with the observations, at least for background sources of either AGN-type or star-forming galaxy spectra.

Giroux, Mark L.↗
NASA NTRS1992

Effects of buoyancy-driven flow and thermal boundary conditions on physical vapor transport

A 2D numerical model was developed in order to ascertain if reduced gravity conditions are beneficial to physical vapor transport (PVT) and to determine its tolerance limits to residual accelerations. This was solved using the PHOENICS finite-volume code. Reduction of gravitational accelerations to less than 0.1 g0 was found to be sufficient to suppress buoyancy-driven convection to an extent that diffusion was the dominant transport mode, whence a greater uniformity in the growth rate could be obtained. It is shown that a uniform temperature gradient on the ampoule walls causes the vapor to be supersaturated throughout the ampoule, potentially resulting in undesirable nucleation at the walls. A 'hump' in the wall temperature profile can be used to avoid this. The prevailing transport conditions determine the size of the hump needed.

Nadarajah, Arunan↗
NASA NTRS1992

Adaptation of multidimensional group particle tracking and particle wall-boundary condition model to the FDNS code

A particulate two-phase flow CFD model was developed based on the FDNS code which is a pressure based predictor plus multi-corrector Navier-Stokes flow solver. Turbulence models with compressibility correction and the wall function models were employed as submodels. A finite-rate chemistry model was used for reacting flow simulation. For particulate two-phase flow simulations, a Eulerian-Lagrangian solution method using an efficient implicit particle trajectory integration scheme was developed in this study. Effects of particle-gas reaction and particle size change to agglomeration or fragmentation were not considered in this investigation. At the onset of the present study, a two-dimensional version of FDNS which had been modified to treat Lagrangian tracking of particles (FDNS-2DEL) had already been written and was operational. The FDNS-2DEL code was too slow for practical use, mainly because it had not been written in a form amenable to vectorization on the Cray, nor was the full three-dimensional form of FDNS utilized. The specific objective of this study was to reorder to calculations into long single arrays for automatic vectorization on the Cray and to implement the full three-dimensional version of FDNS to produce the FDNS-3DEL code. Since the FDNS-2DEL code was slow, a very limited number of test cases had been run with it. This study was also intended to increase the number of cases simulated to verify and improve, as necessary, the particle tracking methodology coded in FDNS.

Chen, Y. S.↗
NASA NTRS1991

Tension/torsion loading of composite laminates with free-edge boundary conditions

A finite element analysis of a family of quasi-isotropic graphite/epoxy laminates was conducted for tension, torsion, and combined tension/torsion loading. The model was employed to investigate the effects of delaminations on torsional stiffness and also to evaluate the total strain energy release rates associated with these delaminations.

Hooper, Steven J.↗