Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “effective changes”

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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Behavioral and biological interactions with confined microsocieties in a programmed environment

This paper presents a summary of the background, objectives, and methodological approach of an ongoing research project devoted to the analysis of individual and small group performance effectiveness under conditions of isolation and confinement during extended residences in a continuously programmed environment. A more detailed description is provided of the results of a recent series of experiments designed and conducted to assess hormonal and behavioral effects of a change in group membership and size.

Emurian, H. H.↗
NASA NTRS1983

Oxygen atom reaction with shuttle materials at orbital altitudes

Significant effects of the environment on payload bay materials observed on all flights are discussed. The STS 5 experiment is described. Increased outgassing rates resulting in possible localized effects on experiments, changes in optical control surfaces, and photoemission from reaction products are considered.

Leger, L. J.↗
NASA NTRS1983

Steady-state and dynamic evaluation of the electric propulsion system test bed vehicle on a road load simulator

The propulsion system of the Lewis Research Center's electric propulsion system test bed vehicle was tested on the road load simulator under the DOE Electric and Hybrid Vehicle Program. This propulsion system, consisting of a series-wound dc motor controlled by an infinitely variable SCR chopper and an 84-V battery pack, is typical of those used in electric vehicles made in 1976. Steady-state tests were conducted over a wide range of differential output torques and vehicle speeds. Efficiencies of all of the components were determined. Effects of temperature and voltage variations on the motor and the effect of voltage changes on the controller were examined. Energy consumption and energy efficiency for the system were determined over the B and C driving schedules of the SAE J227a test procedure.

Dustin, M. O.↗
NASA NTRS1983

MHD stability of incompressible coronal loops with radiative energy loss

Previous studies of the magnetohydrodynamic (MHD) stability of solar coronal loops have not taken into account the effects of radiative energy loss in the energy equation. However, since coronal loops continuously lose energy by radiation and heat conduction, it is important to understand how these energy loss mechanisms affect MHD stability. We investigate the problem assuming that a magnetic loop has cylindrical geometry. As a first step, stability is studied for a localized mode, and the result is applied to a specific equilibrium. We find that the radiative energy loss effect not only changes the growth rate of ideally unstable modes, but also alters the stability boundary predicted by ideal MHD theory.

An, C.-H.↗
NASA NTRS1983

A mixing-length model for the prediction of convex curvature effects on turbulent boundary layers

A mixing-length model is developed for the prediction of turbulent boundary layers with convex streamwise curvature. For large layer thickness ratio, delta/R greater than 0.05, the model scales mixing length on the wall radius of curvature, R. For small delta/R, ordinary flat wall modeling is used for the mixing-length profile with curvature corrections, following the recommendations of Eide and Johnston (1976). Effects of streamwise change of curvature are considered; a strong lag from equilibrium is required when R increases downstream. Fifteen separate data sets were compared, including both hydrodynamic and heat transfer results. Six of these computations are presented and compared to experiment.

Adams, E. W.↗
NASA NTRS1984

Thermal response of Space Shuttle wing during reentry heating

A structural performance and resizing (SPAR) finite element thermal analysis computer program was used in the heat transfer analysis of the space shuttle orbiter that was subjected to reentry aerodynamic heatings. One wing segment of the right wing (WS 240) and the whole left wing were selected for the thermal analysis. Results showed that the predicted thermal protection system (TPS) temperatures were in good agreement with the space transportation system, trajectory 5 (STS-5) flight-measured temperatures. In addition, calculated aluminum structural temperatures were in fairly good agreement with the flight data up to the point of touchdown. Results also showed that the internal free convection had a considerable effect on the change of structural temperatures after touchdown.

Gong, L.↗
NASA NTRS1984

Predictive thermal-vacuum modeling by variable coefficients

In computer-assisted thermal-vacuum testing, an accurate mathematical thermal model is necessary. This model can indicate what effect a given change in control temperature will produce on the test article. A three-node thermal model is used to illustrate some numerical methods for increasing the accuracy by generating more accurate coefficients for the model.

Chuvala, J. T.↗
NASA NTRS1983

Hardness of dense beta-Si3N4

The effects of small changes in the concentration of an oxygen content densification aid on the room temperature microhardness of hot isostatically pressed and sintered beta-Si3N4 ceramics are studied. The compositions studied were Si3N4 containing 7 wt. pct BeSiN2, a fixed nonoxide densification aid, and 1.9-3.7 wt. pct oxygen as a second, variable densification aid. A proportional relationship between high density and high oxygen content, regardless of heat treatment type, is noted.

Greskovich, C.↗
NASA NTRS1984

Dynamics of two-phase face seals

An analytic study is presented of the effects of phase change on load support for parallel and tapered face seals. Consideration is given to an adiabatic model for low Reynolds number flow. Numerical integration is carried out of the descriptive fluid equations, giving the opening force due to fluid film pressure. The loci of steady-state solutions are then plotted for water to provide curves of load support as a function of film thickness. For axial excursions of the seal rings, a quasi-steady transient analysis is made. It is found that the load support generated by fluid pressure can be multivalued for a given film thickness. Another finding is that axial disturbances of the seal rings may lead to sudden drops in load support generated by fluid pressure with three possible results. The first is that sufficient damping may permit the seal to return to the previous equilibrium operating position. The second is that the seal may collapse to an equilibrium position of smaller film thickness where face contact is more likely and a significantly higher operating temperature is assured. The third is that a limit cycle of self-sustained oscillation in the axial direction may occur if damping is sufficiently low.

Beeler, R. M.↗
NASA NTRS1984

Thermal response of Space Shuttle wing during reentry heating

A structural performance and resizing (SPAR) finite element thermal analysis computer program was used in the heat transfer analysis of the Space Shuttle Orbiter that was subjected to reentry aerodynamic heatings. One wing segment of the right wing (WS 240) and the whole left wing were selected for the thermal analysis. Results showed that the predicted thermal protection system (TPS) temperatures were in good agreement with the space transportation system, trajectory 5 (STS-5) flight-measured temperatures. In addition, calculated aluminum structural temperatures were in fairly good agreement with flight data up to the point of touchdown. Results also showed that the internal free convection has a considerable effect on the change of structural temperatures after touchdown.

Gong, L.↗
NASA NTRS1985

The Martian climate: Energy balance models with CO2/H2O atmospheres

Coupled equations are developed for mass and heat transport in a seasonal Mars model with condensation and sublimation of CO2 at the polar caps. Topics covered include physical considerations of planetary as mass and energy balance; effects of phase changes at the surface on mass and heat flux; atmospheric transport and governing equations; and numerical analysis.

Hoffert, M. I.↗
NASA NTRS1985

Bearings working group

The service life of the Space Shuttle Main Engine (SSME) turbomachinery bearings was a predominant factor in engine durability and maintenance problems. Recent data has indicated that bearing life is about one order of magnitude lower than the goal of seven and one-half hours particularly those in the High Pressure Oxidizer Turbopump (HPOTP). Bearing technology, primarily cryogenic turbomachinery bearing technology, is expanded by exploring the life and performance effects of design changes; design concept changes; materials changes; manufacturing technique changes; and lubrication system changes. Each variation is assessed against the current bearing design in full scale cryogenic tests.

Source record↗
NASA NTRS1985

Technical overview structural dynamics

Structural dynamics technology development in support of SSME was initiated in November 1980. The objective identified was to develop improved understanding of the operating dynamic characteristics of high-performance liquid rocket systems in order to: increase lifetime and performance; decrease weight; identify incipient failures; meet deflection requirements; decrease costs; predict effect of imposed changes; and determine changes to meet specified requirements. A series of tasks was identified and work was started on the most urgent tasks. In 1983, the program was made into a joint program with NASA-Lewis Research Center.

Kiefling, L.↗
NASA NTRS1985

A New CO2 Transmittance Parameterization and Its Impact on the GLA GCM

The Wu-Kaplan radiation parameterization (Krishnamurthy, 1982) used in the GLA Global Circulation Model (GCM) was improved by replacing its fixed tables of CO2 transmittance in the 15 micron band with models developed by regression on line-by-line transmittances. The transmittances between layers are modeled as products of effective sublayer transmittances. The GLA GCM was integrated for 20 days starting at OZ, January 21, 1979, using the transmittance model. In the control run the fixed table of 15 micron CO2 transmittances is used. The effect of the change of initial cooling rate is illustrated by a map of the difference of 50 mb temperature after 6 hours. The cooling is reduced over high topography, where the fixed table underestimates the transmittance, and is reduced slightly throughout the tropics and the north polar area where the stratosphere is relatively cold. Over elevated topography the surface cooling increases, also as expected. The stratospheric temperature increases over a degree in the arctic and smaller amounts over Antarctica and elsewhere. Tropospheric equilibrium temperature response is obscured by time dependent differences in synoptic disturbances.

Wobus, R.↗
NASA NTRS1985

Sulfide and sulfate saturation in hydrous silicate melts

A series of hydrothermal experiments was performed over a wide range of pressures, temperatures, oxygen fugacities, and melt FeO content, in order to examine the effects of physical changes on sulfur solubility in fractionated hydrous silicate melts. On the basis of the experimental results, it is concluded that upper crustal oxidation-reduction reactions and crystal fractionation processes may exert considerable influence on the amount of sulfur contained in magmas erupted at the surface. The application of the experimental results to investigations of volatile transport and volcanic degassing processes on the earth, Venus, and Mars is discussed

Carroll, M. R.↗
NASA NTRS1984

On the stereoselective aminoacylation of RNA

Gabbay and Kleinman (1970) have found that stereospecific complex formation (noncovalent) occurs between nucleic acids and a number of derivatives of amino acids. However, until recently, chiral selection in any nonenzymatic RNA-aminoacylation reaction was unknown. Profy and Usher (1984) reported that aminoacylation of the 'internal' 2-prime-ester occurred with a significant amount of stereoselection. Profy and Usher (1984) have also observed that aminoacylation of the 'internal' 2-prime-hydroxyl groups of polyribonucleotides by the imidazolide of N-3,5-dinitrobenzoylalanine occurs with chiral selection. In order to obtain further information regarding the considered phenomena, a systematic investigation was initiated of the factors which contribute to the observed stereoselectivity of the aminoacylation reaction. In the present paper, the effect of a change in the amino acid from alanine to leucine is considered along with an investigation of the D- and L-alanyl internal' 2-prime esters of the dinucleoside monophosphate of 3-prime,5-prime-ApA.

Usher, D. A.↗
NASA NTRS1985

A new method for determining temperature and emission measure during solar flares from light curves of soft X-ray line fluxes

A method for using the shapes of the light curves of soft X-ray line fluxes observed during the decay phase of solar flares to infer the temperature and emission measure with time is described. Light curves of the November 5, 1980 flare and several additional flares that exhibit breaks are presented, and possible causes for these breaks are discussed. Numerical models that incorporate the effects of temperature changes on the emissivity function are examined, and the model calculations are compared with the line fluxes observed during the November 5, 1980 flare. The model results are used to derive other properties of the flare.

Bornmann, P. L.↗
NASA NTRS1985

Determination of corrections to flow direction sensor measurements over an angle-of-attack range from 0 degree to 85 degrees

An investigation was conducted into the nature of corrections for angle-of-attack and angle-of-sideslip measurements obtained with sensors mounted in front of each wingtip of a general aviation airplane. These flow corrections have been obtained from both wind-tunnel and flight tests over an angle-of-attack range from 0 to 85 deg. Both the angle-of-attack and angle-of-sideslip flow corrections were found to be substantial. The corrections were a function of the angle of attack and angle of sideslip and were fairly insensitive to configuration changes and rotational effects. The angle-of-attack flow correction determined from the static wind-tunnel tests agreed reasonably well with the correction determined from flight tests.

Moul, T. M.↗