Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Topic Models”

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.

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

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Techniques for shuttle trajectory optimization

The application of recently developed function-space Davidon-type techniques to the shuttle ascent trajectory optimization problem is discussed along with an investigation of the recently developed PRAXIS algorithm for parameter optimization. At the outset of this analysis, the major deficiency of the function-space algorithms was their potential storage problems. Since most previous analyses of the methods were with relatively low-dimension problems, no storage problems were encountered. However, in shuttle trajectory optimization, storage is a problem, and this problem was handled efficiently. Topics discussed include: the shuttle ascent model and the development of the particular optimization equations; the function-space algorithms; the operation of the algorithm and typical simulations; variable final-time problem considerations; and a modification of Powell's algorithm.

Edge, E. R.↗
NASA NTRS1975

Program to Optimize Simulated Trajectories (POST). Volume 1: Formulation manual

A general purpose FORTRAN program for simulating and optimizing point mass trajectories (POST) of aerospace vehicles is described. The equations and the numerical techniques used in the program are documented. Topics discussed include: coordinate systems, planet model, trajectory simulation, auxiliary calculations, and targeting and optimization.

Brauer, G. L.↗
NASA NTRS1978

OSO-8 X-ray spectra of clusters of galaxies. 2: Discussion

X-ray spectral parameters obtained from 2 to 20 keV OSO-8 data on X-ray clusters and optical cluster properties were examined to obtain information for restricting models for hot intracluster gas structures. Topics discussed include the radius of the X-ray core in relation to the galaxy core radius, the viral mass of hotter clusters, and galaxy density and optical central cluster properties. A population of cool, dim X-ray clusters which have not been observed is predicted. The iron abundance determinations recently quoted for intracluster gas are uncertain by 50 to greater than 100 percent from this nonstatistical cause alone.

Smith, B. W.↗
NASA NTRS1977

Dynamical implications of the petrology and distribution of impact melt rocks

Petrographic and structural relations of rocks resulting from melting of target materials during impact indicate constraints that can be applied to theoretical models and experimental production of craters. Topics discussed in this context include the motion of shock melted material, the mixing of melts, the energies required for heating and melting the necessary volumes of target rocks, diameter to depth ratios, and the formation of structural modifications. The motion of shock melted material involves ejection of some of the lowermost parts of the target, incorporation of distant fragmental material, outward flow, settling into cracks after breccia formation, and completion in a short time span. Melts must be completed within tens of seconds to a couple of minutes after impact.

Phinney, W. C.↗
NASA NTRS1979

Earth-Moon system: Dynamics and parameter estimation

The following topics are discussed: (1) the Unified Model of Lunar Translation/Rotation (UMLTR); (2) the effect of figure-figure interactions on lunar physical librations; (3) the effect of translational-rotational coupling on the lunar orbit; and(4) an error analysis for estimating lunar inertias from LURE (Lunar Laser Ranging Experiment) data.

Breedlove, W. J., Jr.↗
NASA NTRS1985

Silicon material and JPL Web Team

Silicon material activities are described. Topics discussed include: fluidized bed technology, model predictions (reaction kinetics and grid design parameters), seed-particle cleaning procedure, runaway nucleation, thermal analysis of dendritic ribbons, and residual stress in dendritic ribbons.

Lutwack, R.↗
NASA NTRS1986

Cellular solidification of transparent monotectics

Understanding how liquid phase particles are engulfed or pushed during freezing of a monotectic is addressed. The additional complication is that the solid-liquid interface is nonplanar due to constitutional undercooling. Some evidence of particle pushing where the particles are the liquid phase of the montectic was already observed. Cellular freezing of the succinonitrile-glycerol system also occurred. Only a few compositions were tested at that time. The starting materials were not especially pure so that cellular interface observed was likely due to the presence of unkown impurities, the major portion of which was water. Topics addressed include: the effort of modeling the particle pushing process using the computer, establishing an apparatus for the determination of phase diagrams, and the measurement of the temperature gradients with a specimen which will solidify on the temperature gradient microscope stage.

Kaulker, W. F.↗
NASA NTRS1990

Reports on block rotations, fault domains and crustal deformation

Studies of block rotations, fault domains and crustal deformation in the western United States, Israel, and China are discussed. Topics include a three-dimensional model of crustal fracture by distributed fault sets, distributed deformation and block rotation in 3D, stress field rotation, and multiple strike slip fault sets.

Nur, Amos↗
NASA NTRS1990

South Pacific convergence zone and global-scale circulations

Current research is focused on four topics. First, the GLA Global Circulation Model (GCM) is used for a series of experiments to examine the relationship between tropical heating and subtropical westerly wind maxima. Second, barotropic and baroclinic energy mechanisms associated with summertime subtropical wind maxima in the Southern Hemisphere is studied. Third, tropical/extratropical interactions in the Southern Hemisphere summer circulation is studied; the focus is on the importance of the 30 to 60 day tropical oscillation as a cause of enhancing the subtropical westerly winds. Finally, a study of precipitation efficiency in the tropics, comparing mean monthly distributions of precipitation over a three-year period to precipitable water and moisture convergency is being conducted.

Vincent, Dayton G.↗
NASA NTRS1991

LIDAR studies on microbursts

Preliminary analysis of requirements for future airborne windshear detection systems is presented. The following topics are covered: flight mechanics; microbursts modeling; microburst detection with airborne systems (LIDAR, radar, passive IR sensors); microbursts prediction with ground systems (VHF interferometry). A short overview of these studies is presented and some results are discussed.

Aurenche, Y.↗
NASA NTRS1991

Model comparison of July 7, 1990 microburst

Model comparison of July 7, 1990 microburst is presented in the form of view-graphs. The following topics are covered: 7 July 1990 Orlando, FL simulations; model input sounding for 7 July 1990 Orlando case; 7 July 1990 Orlando microburst; and comparison of simulated and observed characteristics of microburst event.

Proctor, Fred↗
NASA NTRS1993

Magnetospheric space plasma investigations

The topics addressed are: (1) generalized semikinetic models; (2) collision-collisionless transition model; (3) observation of O+ outflows; (4) equatorial transitions; (5) inner plasmasphere-ionosphere coupling; (6) plasma wave physical processes; (7) ULF wave ray-tracing; and (8) nighttime anomalous electron heating events.

Comfort, Richard H.↗
NASA NTRS1990

Marshall Space Flight Center ECLSS technology activities

Viewgraphs on Environmental Control and Life Support System (ECLSS) technology activities are presented. Topics covered include: analytical development; ECLSS modeling approach; example of water reclamation modeling needs; and hardware development and testing.

Wieland, Paul↗
NASA NTRS1992

Strain actuated aeroelastic control

Viewgraphs on strain actuated aeroelastic control are presented. Topics covered include: structural and aerodynamic modeling; control law design methodology; system block diagram; adaptive wing test article; bench-top experiments; bench-top disturbance rejection: open and closed loop response; bench-top disturbance rejection: state cost versus control cost; wind tunnel experiments; wind tunnel gust alleviation: open and closed loop response at 60 mph; wind tunnel gust alleviation: state cost versus control cost at 60 mph; wind tunnel command following: open and closed loop error at 60 mph; wind tunnel flutter suppression: open loop flutter speed; and wind tunnel flutter suppression: closed loop state cost curves.

Lazarus, Kenneth B.↗
NASA NTRS1992

Dynamics of interacting galaxies

The dynamics of interacting galaxies as observed in the present epoch is reviewed. Topics discussed include numerical methods for modeling galactic interactions, the signatures of interacting galaxies due to tidal forces, and events that add mass to a galaxy. The review also covers major mergers between systems of comparable mass, forms of activity triggered or induced by galactic interactions, and galaxies' return to normality and related cosmological issues. Finally, some questions that yet have to be answered are examined.

Barnes, Joshua E.↗
NASA NTRS1993

Ultraviolet photometry of OB associations in M31

The study obtains near-UV and FUV magnitudes for 76 massive stars in 24 OB associations in the central and southern portions of M31 from images obtained by the Ultraviolet Imaging Telescope (UIT) during the Astro 1 spacelab mission. A comparison is made with the previous UIT photometry of 30 stars in the giant association NGC 206. Extinctions are estimated from the relation between E(B - V) and the distance from the center of M31 derived by Hodge and Lee (1988) from topical CCD stellar photometry. From evolutionary models, lower limits to the maximum stellar mass are estimated at about 60-100 solar masses in NGC 206, A29, A61, A63, A130, and A132. For other associations, the limits are in the range of about 20-55 solar masses.

Hill, Jesse K.↗