SEARCH · Engineering Papers

Results for “1D”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS1991

The directional dependence of cometary magnetic energy density in the quasi-parallel and quasi-perpendicular regimes

The direction of propagation of low frequency magnetic fluctuations generated by cometary ion pick-up is examined by means of 1D electromagnetic hybrid simulations. The newborn ions are injected at a constant rate, and the helicity and direction of propagation of magnetic fluctuations are explored for cometary ion injection angles of 0 and 90 deg relative to the solar wind magnetic field. The parameter eta represents the relative contribution of wave energy propagating in the direction away from the comet, parallel to the beam. For small (quasi-parallel) injection angles eta was found to be of order unity, while for larger (quasi-perpendicular) angles eta was found to be of order 0.5.

Miller, R. H.↗

NASA NTRS1991

Hybrid simulations of rotational discontinuities

1D hybrid simulations of rotational discontinuities (RDs) are presented. When the angle between the discontinuity normal and the magnetic field (theta-BN) is 30 deg, the RD broadens into a quasi-steady state of width 60-80 c/omega-i. The hodogram has a characteristic S-shape. When theta-BN = 60 deg, the RD is much narrower (10 c/omega-i). For right handed rotations, the results are similar to theta-BN = 30 deg. For left handed rotations, the RD does not evolve much from its initial conditions and the S-shape in the hodogram is much less visible. The results can be understood in terms of matching a fast mode wavelike structure upstream of the RD with an intermediate mode one downstream.

Goodrich, C. C.↗

NASA NTRS1991

Vectorization of a Monte Carlo simulation scheme for nonequilibrium gas dynamics

Significant improvement has been obtained in the numerical performance of a Monte Carlo scheme for the analysis of nonequilibrium gas dynamics through an implementation of the algorithm which takes advantage of vector hardware, as presently demonstrated through application to three different problems. These are (1) a 1D standing-shock wave; (2) the flow of an expanding gas through an axisymmetric nozzle; and (3) the hypersonic flow of Ar gas over a 3D wedge. Problem (3) is illustrative of the greatly increased number of molecules which the simulation may involve, thanks to improved algorithm performance.

Boyd, Iain D.↗

NASA NTRS1991

Structure of medium Mach number quasi-parallel shocks - Upstream and downstream waves

The transition from steady low-Mach-number to unsteady high-Mach-number quasi-parallel shocks was investigated by performing large-scale 1D hybrid code simulations at increasing Mach numbers. It was found that only at very low Mach number shocks the steepening is limited by upstream phase-standing whistlers, as predicted by the classical theory (Tidman and Northrop, 1968). In the intermediate region of Mach numbers between 1.5 and 3.5, a very diverse behavior is observed. Backstreaming ions generate fast magnetosonic waves which dominate the upstream, with wavelengths longer than phase-standing whistlers. At increasing Mach numbers, the phase and group velocities of the dominant waves are reduced until they point back toward the shock; when there is sufficient energy flux in these waves, they lead to unsteady shock behavior and eventually to shock reformation.

Krauss-Varban, D.↗

NASA NTRS1991

Linear stability of free planetary waves in the presence of radiative-photochemical feedbacks

The diabatic effects of Newtonian cooling and ozone-dynamics interaction on the linear stability of free planetary waves in the atmosphere have been studied using a simple beta-plane model. The model couples radiative transfer, ozone advection, and ozone photochemistry with the quasi-geostrophic dynamical circulation. An analytical expression is derived which demonstrates the following: (1) the influence of meridional ozone advection on wave growth or decay depends on the wave and basic state vertical structures; and (2) photochemically accelerated cooling, which predominates in the upper stratosphere, augments the Newtonian cooling rate and is stabilizing. Attention is also given to the 1D linear stability problem which is numerically solved for a Charney basic state and for zonal mean basic states. It is shown that ozone heating generated by ozone-dynamics interaction in the stratosphere can reduce (enhance) the damping rates due to Newtonian cooling by as much as 50 percent for planetary waves of large vertical scale and maximum amplitude in the stratosphere.

Nathan, Terrence R.↗

NASA NTRS1991

Two-dimensional simulations of the ion/ion acoustic instability and electrostatic shocks

A newly developed 2D electrostatic code with particle ions and Boltzmann electrons is used to investigate the details of the ion/ion acoustic instability and the structure of electrostatic shocks. The simulation results show that, for the parameters relevant to the plasma sheet boundary layer, the saturation mechanism of the ion/ion acoustic instability is ion trapping. It is also shown that the 2D structure of electrostatic shocks is considerably different from that suggested by previous 1D simulations. The main reason for this difference is the presence of shock reflected ions, which through the ion/ion acoustic instability lead to the generation of large amplitude waves in the upstream region propagating obliquely to the shock normal. These waves play an important role in the shock dissipation process.

Karimabadi, H.↗

NASA NTRS1992

Effect of InAlAs window layer on efficiency of indium phosphide solar cells

Indium phosphide (InP) solar cell efficiencies are limited by surface recombination. The effect of a wide bandgap, lattice-matched indium aluminum arsenide (In(0.52)Al(0.48)As) window layer on the performance of InP solar cells was investigated by using the numerical code PC-1D. The p(+)n InP solar cell performance improved significantly with the use of the window layer. No improvement was seen for the n(+)p InP cells. The cell results were explained by the band diagram of the heterostructure and the conduction band energy discontinuity. The calculated current voltage and internal quantum efficiency results clearly demonstrated that In(0.52)Al(0.48)As is a very promising candidate for a window layer material for p(+)n InP solar cells.

Jain, Raj K.↗

NASA NTRS1991

A Carolina coastal low-level jet during GALE IOP 2

A persistent, diurnally varying low-level jet (LLJ) was observed along the Carolina coastal plain during the early part of GALE IOP 2 between 0000 UTC January 24 and 0600 UTC January 25. A 1D PBL model (Zhang and Anthes, 1982) is utilized to examine the various dynamic forcing mechanisms controlling the formation and evolution of the LLJ. The experiments suggest that a specific geostrophic wind velocity profile in the lower troposphere was necessary to produce a number of the observed Carolina LLJ characteristics.

Doyle, James D.↗

NASA NTRS1991

Charged dust dynamics - Orbital resonance due to planetary shadows

The dynamics of a weakly charged dust grain orbiting in the equatorial plane of a planet surrounded by a rigidly corotating magnetospehre is examined. It is shown that an introduction of an effectilve 1D potential causes a perturbation due to electrostatic forces, which induces a motion of the pericenter, similar to the effect of the planetary oblateness. A case is examined where the charge varies periodically due to the modulation of the photoelectron current occurring as the grain enters and leaves the planetary shadow, causing the electromagnetic perturbation to resonate with the orbital period and to modify the size and eccentricity of the orbit. This effect is demonstrated both numerically and analytically for small grains comprising the Jovian ring, showing that their resulting changes are periodic, and their amplitude is much larger than that of the periodic changes due to light-pressure perturbation or the secular changes due to resonant charge variations that develop over a comparable time span.

Horanyi, M.↗

NASA NTRS1991

Simulation of the nonlinear evolution of electron plasma waves

Electrostatic waves driven by an electron beam in an ambient magnetized plasma were studied using a quasi-1D PIC simulation of electron plasma waves (i.e., Langmuir waves). The results disclose the presence of a process for moving wave energy from frequencies and wavenumbers predicted by linear theory to the Langmuir-like frequencies during saturation of the instability. A decay process for producing backward propagating Langmuir-like waves, along with low-frequency waves, is observed. The simulation results, however, indicate that the backscattering process is not the conventional Langmuir wave decay. Electrostatic waves near multiples of the electron plasma frequency are generated by wave-wave coupling during the nonlinear stage of the simulations, confirming the suggestion of Klimas (1983).

Nishikawa, K.-I.↗

NASA NTRS1991

Calculated performance of p(+)n InP solar cells with In(0.52)Al(0.48)As window layers

The performance of indium phosphide solar cells with lattice matched wide band-gap In(0.52)Al(0.48)As window layers was calculated using the PC-1D computer code. The conversion efficiency of p(+)n InP solar cells is improved significantly by the window layer. No improvement is seen for n(+)p structures. The improvement in InP cell efficiency was studied as a function of In(0.52)Al(0.48)As layer thickness. The use of the window layer improves both the open circuit voltage and short circuit current.For a typical In(0.52)Al(0.48)As window layer thickness of 20 nm, the cell efficiency improves in excess of 27 percent to a value of 18.74 percent.

Jain, R. K.↗

NASA NTRS1990

Modelling the effect of vegetation on the formation of boundary layer cumulus during FIFE

A 1D model is discussed which permits prediction of the effect of vegetation cover on the area-averaged boundary layer. Special attention is given to the manner in which the relative contributions of sensible and latent heat fluxes to the surface-energy budget are determined by the vegetation. The model can be effectively applied to the heterogeneous prairie environment to predict cloud cover at different times of the year demonstrating good agreement with observed conditions.

Wetzel, Peter J.↗

NASA NTRS1990

Radiometric calibration and monitoring of NOAA AVHRR visible data

Results and corrections to calibration for the NOAA-7, -8, -9, -10, and -11 AVHRR Channel 1 data, covering the period from July 1983 through December 1989, are presented. Results from the NOAA-7 and NOAA-9 analysis are used as examples to illustrate key points and present detailed results. In the AVHRR monitor procedure, the spatial variability index is calculated first to classify the data as CLEAR or CLOUD. This classification is then used to sort the data to produce three 1D radiance histograms for different surface types. The surface reflectances are retrieved from the radiances, and a set of reflectance filters are applied to sort the data into global surface reflectance maps. An examination of the NOAA-7 results shows that the NOAA-7 radiometer sensitivity actually decreased at a rate of about 0.5-1.0 percent per year. Trends inferred from the point measurements representing independent calibrations at different times, using models, known sites, and coincident aircraft measurements, agree well with the satellite methods.

Brest, Christopher L.↗

NASA NTRS1990

The diurnal variability of marine stratocumulus clouds

Observations of the diurnal variation of marine stratocumulus clouds obtained during July 1987 as part of the First ISCCP Regional Experiment are described. The observations show a clear diurnal signature in the structure of the cloud-topped marine boundary layer, with a large variation in the height of the cloud base, with lower heights observed at night. The observational results are numerically simulated using a 1D second-moment turbulence-closure model of Koracin and Rogers (1990) for a hydrostatically incompressible fluid. The model results indicate that the differential heating of the cloud layer promotes mixing in the upper part of the cloud and stabilizes the lower part of the layer.

Rogers, David P.↗

NASA NTRS1991

CO2 condensation and the climate of early Mars

The possibility of the early Mars' greenhouse warming by a dense CO2 atmosphere is presently examined by means of a 1D radiative-convective climate model which differs from earlier ones in considering the effects of CO2 clouds on both the convective lapse rate and the planetary radiation budget. The phenomenon of CO2 condensation, which decreases the lapse rate and thereby reduces the greenhouse effect, increases in importance at low solar luminosities; it may accordingly preclude globally averaged surface temperatures as high as 0 C before about 2 billion years ago in the absence of such other greenhouse gases as CO2 and H2O. Alternative explanations for early Mars warming and channel-formation processes are noted.

Kasting, James F.↗

NASA NTRS1991

Sources of error in planetary photoclinometry

A quantitative analysis of error sources in 1D planetary photoclinometry is presented. The technique is affected by error sources arising from the spacecraft image, the planetary body, and the scan line orientation. Slope errors are calculated for each of these sources, using examples of Voyager imaging of Ganymede and Viking orbiting imaging of Mars. Slope errors are investigated for a variety of viewing and lighting geometries, slope angles, and slope orientations. The results are broken down into nonsystematic and systematic errors. Derivations that allow the calculation of photoclinometric slope errors for any photometric function are presented, and the implications of these results for 2D photoclinometric techniques are discussed.

Jankowski, David G.↗

NASA NTRS1991

Comet P/Halley - Spatial distributions and scale lengths for C2, CN, NH2, and H2O

Long-slit spectroscopic observations of Comet P/Halley on 12 dates between October 1985 and May 1986 were used to extract spatial profiles for C2, CN, NH2, and O I (1D) (which effectively map out the comet's H2O distribution), and Haser model scale lengths were fitted to these data. The preperihelion analysis yielded Haser model scale lengths of sufficient consistency that they could be used for the production rate determinations. It was found that the average parent scale lengths found for NH2 were consistent with photodissociation lifetimes for NH3 and confirm the dissociation chain NH3-NH2-NH.

Fink, Uwe↗

NASA NTRS1991

A model for the frequency fine structure of auroral kilometric radiation

A model for AKR frequency fine structure in which the fine structure is a natural consequence of the emission of electron cyclotron maser radiation in a nonuniform magnetic field is presented. The model is examined by using 1D electromagnetic particle-in-cell simulations. It is found that maser radiation is emitted as individual wave packets combine to form the drifting emission features that make up the fine structure. Rising frequency drifts are associated with wave packets emitted independently of one another. Wave packets that interact with one another produce features with falling frequency drift. The emission features produced have a large spread in both positive and negative frequency drift rates. The average positive drift rate of rapidly drifting features is found to be approximately proportional to the maser growth rate.

Mckean, M. E.↗