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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

TACT: A Set of MSC/PATRAN- and MSC/NASTRAN- based Modal Correlation Tools

This paper describes the functionality and demonstrates the utility of the Test Analysis Correlation Tools (TACT), a suite of MSC/PATRAN Command Language (PCL) tools which automate the process of correlating finite element models to modal survey test data. The initial release of TACT provides a basic yet complete set of tools for performing correlation totally inside the PATRAN/NASTRAN environment. Features include a step-by-step menu structure, pre-test accelerometer set evaluation and selection, analysis and test result export/import in Universal File Format, calculation of frequency percent difference and cross-orthogonality correlation results using NASTRAN, creation and manipulation of mode pairs, and five different ways of viewing synchronized animations of analysis and test modal results. For the PATRAN-based analyst, TACT eliminates the repetitive, time-consuming and error-prone steps associated with transferring finite element data to a third-party modal correlation package, which allows the analyst to spend more time on the more challenging task of model updating. The usefulness of this software is presented using a case history, the correlation for a NASA Langley Research Center (LaRC) low aspect ratio research wind tunnel model. To demonstrate the improvements that TACT offers the MSC/PATRAN- and MSC/DIASTRAN- based structural analysis community, a comparison of the modal correlation process using TACT within PATRAN versus external third-party modal correlation packages is presented.

Marlowe, Jill M.↗
NASA NTRS1971

Space radiation hazards to Project Skylab photographic film, phase 2

The results of a study of space radiation hazards to Project Skylab photographic film are presented. Radiation components include trapped protons, trapped electrons, bremsstrahlung, and galactic cosmic radiation. The shielding afforded by the Skylab cluster is taken into account with a 5000 volume element mathematical model. A preliminary survey of expected proton spectrometer data is reported.

Hill, C. W.↗
NASA NTRS1972

Definition of multipath/RFI experiments for orbital testing with a small applications technology satellite

An investigation was made to define experiments for collection of RFI and multipath data for application to a synchronous relay satellite/low orbiting satellite configuration. A survey of analytical models of the multipath signal was conducted. Data has been gathered concerning the existing RFI and other noise sources in various bands at VHF and UHF. Additionally, designs are presented for equipment to combat the effects of RFI and multipath: an adaptive delta mod voice system, a forward error control coder/decoder, a PN transmission system, and a wideband FM system. The performance of these systems was then evaluated. Techniques are discussed for measuring multipath and RFI. Finally, recommended data collection experiments are presented. An extensive tabulation is included of theoretical predictions of the amount of signal reflected from a rough, spherical earth.

Birch, J. N.↗
NASA NTRS1973

Remote sensing in the mixing zone

Characteristics of dispersion and diffusion as the mechanisms by which pollutants are transported in natural river courses were studied with the view of providing additional data for the establishment of water quality guidelines and effluent outfall design protocols. Work has been divided into four basic categories which are directed at the basic goal of developing relationships which will permit the estimation of the nature and extent of the mixing zone as a function of those variables which characterize the outfall structure, the effluent, and the river, as well as climatological conditions. The four basic categories of effort are: (1) the development of mathematical models; (2) laboratory studies of physical models; (3) field surveys involving ground and aerial sensing; and (4) correlation between aerial photographic imagery and mixing zone characteristics.

Villemonte, J. R.↗
NASA NTRS1981

Survey of the supporting research and technology for the thermal protection of the Galileo Probe

The Galileo Probe, which is scheduled to be launched in 1985 and to enter the hydrogen-helium atmosphere of Jupiter up to 1,475 days later, presents thermal protection problems that are far more difficult than those experienced in previous planetary entry missions. The high entry speed of the Probe will cause forebody heating rates orders of magnitude greater than those encountered in the Apollo and Pioneer Venus missions, severe afterbody heating from base-flow radiation, and thermochemical ablation rates for carbon phenolic that rival the free-stream mass flux. This paper presents a comprehensive survey of the experimental work and computational research that provide technological support for the Probe's heat-shield design effort. The survey includes atmospheric modeling; both approximate and first-principle computations of flow fields and heat-shield material response; base heating; turbulence modelling; new computational techniques; experimental heating and materials studies; code validation efforts; and a set of 'consensus' first-principle flow-field solutions through the entry maneuver, with predictions of the corresponding thermal protection requirements.

Howe, J. T.↗
NASA NTRS1982

Line profiles of T Tauri stars - Clues to the nature of the mass flow

A set of high resolution observations of the H-alpha Na D, He I 5876 A, and H-gamma lines in several T Tauri stars is presented. Repeated observations of some of these objects yield some indication of the importance of time-dependent effects. The line profiles should be useful for detailed radiative transfer modeling. A cursory survey of the profiles suggests that 'turbulent' velocities in some cases may not be negligible in comparison with the bulk flow speeds and that many emission lines, such as Na D, may be formed in a narrow layer near the stellar photosphere. It is suggested that the effects of geometrical occulation of narrow line-emitting regions in general outflow can account for some of the peculiarities of the line profiles. However, some aspects of the line profiles, such as the large-scale, highly variable redshifted Na D absorption in RW Aur, clearly require more complicated motions.

Hartmann, L.↗
NASA NTRS1987

Singular finite element methods

Singularities which arise in the solution to elliptic systems are often of great technological importance. This is certainly the case in models of fracture of structures. A survey of the ways singularities are modeled is presented with special emphasis on the effects due to nonlinearities.

Fix, George J.↗
NASA NTRS1987

The status of military specifications with regard to atmospheric turbulence

The features of atmospheric disturbances that are significant to aircraft flying qualities are discussed. Next follows a survey of proposed models. Lastly, there is a discussion of the content and application of the model contained in the current flying qualities specification and the forthcoming MIL-Standard.

Moorhouse, David J.↗
NASA NTRS1987

Turbulence modeling

Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.

Rubesin, Morris W.↗
NASA NTRS1989

Treatment of geodetic leveling in the integrated geodesy approach

Integrated geodesy is a method in which a wide variety of surveying measurements are modeled in terms of geometric positions and the earth's geopotential. Using heterogeneous data, both geometric and gravimetric quantities are simultaneously estimated by a least-squares procedure. Heretofore, geodetic leveling differences were reduced into pseudo-observables using assumed values of gravity prior to their inclusion into integrated geodesy least-squares adjustments. The errors in estimates of geometric and gravimetric quantities obtained from integrated geodesy adjustments of geodetic leveling difference, potential differences and Helmert height differences are compared.

Milbert, Dennis G.↗
NASA NTRS1989

Thematic Mapper laser profile resolution of Holocene Lake limit, Great Salt Lake Desert, Utah

The limit of Great Salt Lake's maximum expansion onto the floor of the Great Salt Lake Desert during Holocene time is marked by a break in slope which is clearly depicted in terrain models which merge Thematic Mapper (TM) multispectral scanner data and Aerial Profiling of Terrain System (APTS) laser profile data. Mean elevations of APTS-coincident TM pixels are strongly correlated with reflectance in TM Bands 5 and 7 when and where sufficient moisture contrasts among terrain components are high. TM-APTS models and field surveys place the highest Holocene standing water at an elavation of 4221 ft (1286.7 m).

Merola, John A.↗
NASA NTRS1990

A model for the infrared emission from an OB star cluster environment

Researchers developed an interactive radiative transfer code that predicts the infrared emission from an HII region containing diffuse ionized and atomic gas and dense molecular clouds. This model complements the investigation of the redistribution of OB star luminosity in the interstellar medium (Leisawitz and Hauser 1988, Ap. J., 332, 954). The model can be used as a diagnostic tool to probe the radiation field and matter density in an HII region, place constraints on the proximity and orientation of an illuminated molecular cloud with respect to the ionizing stars, test for the presence of small, transiently heated dust grains, and determine whether the dust-to-gas ratio is normal. Predictions of the model agree qualitatively and quantitatively with observations of blister-type HII regions ionized by well-studied OB clusters in which the distribution of dense neutral material is known. This is illustrated by a model for Infrared Astronomy Satellite (IRAS) observations of the region around NGC 7380 (S142). Researchers plan to use the model in a survey of regions of massive star formation in the outer Galaxy to study OB stars embedded to various degrees in their parental molecular clouds.

Leisawitz, D.↗
NASA NTRS1990

An experimental study of the turbulent boundary layer on a transport wing in subsonic and transonic flow

The upper surface boundary layer on a transport wing model was extensively surveyed with miniature yaw probes at a subsonic and a transonic cruise condition. Additional data were obtained at a second transonic test condition, for which a separated region was present at mid-semispan, aft of mid-chord. Significant variation in flow direction with distance from the surface was observed near the trailing edge except at the wing root and tip. The data collected at the transonic cruise condition show boundary layer growth associated with shock wave/boundary layer interaction, followed by recovery of the boundary layer downstream of the shock. Measurements of fluctuating surface pressure and wingtip acceleration were also obtained. The influence of flow field unsteadiness on the boundary layer data is discussed. Comparisons among the data and predictions from a variety of computational methods are presented. The computed predictions are in reasonable agreement with the experimental data in the outboard regions where 3-D effects are moderate and adverse pressure gradients are mild. In the more highly loaded mid-span region near the trailing edge, displacement thickness growth was significantly underpredicted, except when unrealistically severe adverse pressure gradients associated with inviscid calculations were used to perform boundary layer calculations.

Spaid, Frank W.↗
NASA NTRS1993

Hidden supernova remnants in the Large Magellanic Cloud H II complex N44

We have obtained ROSAT PSPC observations of N44, one of the largest H II complexes in the Large Magellanic Cloud. The X-ray emission mostly fails within the ionized shell structures in N44. We find that one faint shell is a classical supernova remnant overlooked by previous surveys. If we model the two largest shells as pressure-driven superbubbles, the predicted X-ray luminosity falls far below the observed value. Instead, we show that off-center supernova remnants hitting superbubble shells can explain the excess X-ray emission.

Chu, You-Hua↗
NASA NTRS1994

Galaxy mergers and gravitational lens statistics

We investigate the impact of hierarchical galaxy merging on the statistics of gravitational lensing of distant sources. Since no definite theoretical predictions for the merging history of luminous galaxies exist, we adopt a parameterized prescription, which allows us to adjust the expected number of pieces comprising a typical present galaxy at z approximately 0.65. The existence of global parameter relations for elliptical galaxies and constraints on the evolution of the phase space density in dissipationless mergers, allow us to limit the possible evolution of galaxy lens properties under merging. We draw two lessons from implementing this lens evolution into statistical lens calculations: (1) The total optical depth to multiple imaging (e.g., of quasars) is quite insensitive to merging. (2) Merging leads to a smaller mean separation of observed multiple images. Because merging does not reduce drastically the expected lensing frequency, it cannot make lambda-dominated cosmologies compatible with the existing lensing observations. A comparison with the data from the Hubble Space Telescope (HST) Snapshot Survey shows that models with little or no evolution of the lens population are statistically favored over strong merging scenarios. A specific merging scenario proposed to Toomre can be rejected (95% level) by such a comparison. Some versions of the scenario proposed by Broadhurst, Ellis, & Glazebrook are statistically acceptable.

Rix, Hans-Walter↗
NASA NTRS1998

Remote Sensing Methods

Remotely sensed data allows archeologists and historic preservationists the ability to non-destructively detect phenomena previously unobservable to them. Archeologists have successfully used aerial photography since the turn of the century and it continues to be an important research tool today. Multispectral scanners and computer-implemented analysis techniques extend the range of human vision and provides the investigator with innovative research designs at scales previously unimaginable. Pioneering efforts in the use of remote sensing technology have demonstrated its potential, but it is the recent technological developments in remote sensing instrumentation and computer capability that provide for unlimited, cost-effective applications in the future. The combination of remote sensing, Global Positioning System (GPS) technology, and Geographic Information Systems (GIS) are radically altering survey, inventory, and modelling approaches.

Sever, Thomas L.↗
NASA NTRS1999

Mars Crustal Remanent Magnetism: An Extinct Dynamo Leaves a Record of Field Reversals in the Heavily Cratered Highlands

The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit about Mars, obtained vector magnetic field measurements just above the surface of Mars (altitudes > 100 kilometers). Crustal magnetization, largely confined to the most ancient, heavily cratered Mars highlands, is frequently organized in east-west trending linear features, the largest of which extends over 2000 km. A representative set of survey passes are modeled using uniformly magnetized thin plates and a generalized inverse methodology. Crustal remanent magnetization exceeds that deduced for the largest terrestrial magnetic anomalies by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity are found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale.

Connerney, John E.↗