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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Pressure- and buoyancy-driven thermal convection in a rectangular enclosure

Results are presented for unsteady laminar thermal convection in compressible fluids at various reduced levels of gravity in a rectangular enclosure which is heated on one side and cooled on the opposite side. The results were obtained by solving numerically the equations of conservation for a viscous, compressible, heat-conducting, ideal gas in the presence of a gravitational body force. The formulation differs from the Boussinesq simplification in that the effects of variable density are completely retained. A conservative, explicit, time-dependent, finite-difference technique was used and good agreement was found for the limited cases where direct comparison with previous investigations was possible. The solutions show that the thermally induced motion is acoustic in nature at low levels of gravity and that the unsteady-state rate of heat transfer is thereby greatly enhanced relative to pure conduction. The nonlinear variable density profile skews the streamlines towards the cooler walls but is shown to have little effect on the steady-state isotherms.

Spradley, L. W.↗
NASA NTRS1975

Automated wing structural design

Research on the optimization of wing structures under multiple constraint such as strength, displacement, buckling, flutter, and divergence limits is reported. Advances were made in improving mathematical programming techniques as well as in improving the efficiency of constraint calculation. The WIDOWAC (Wing Design Optimization With Aeroelastic Constraints) computer program served as the main vehicle for this research. The methods developed were implemented in a general user oriented finite element program.

Haftka, R. T.↗
NASA NTRS1977

Diodes stabilize LED output

Small-signal diodes are placed in series with light-emitting diodes (LED's) to stabilize LED output against temperature fluctuations. Simple inexpensive method compensates for thermal fluctuations over a broad temperature range. Requiring few components, technique is particularly useful where circuit-board space is limited.

Deters, R. A.↗
NASA NTRS1976

Diffusion analysis for two-phase metal-matrix composite

Diffusion controlled filament matrix interaction in a metal matrix composite, where the filaments and matrix comprise a two phase binary alloy system, was mathematically modeled. The problem of a diffusion controlled, two phase moving interface by means of a one dimensional, variable grid, finite difference technique was analyzed. Concentration dependent diffusion coefficients and equilibrium solubility limits were used, and the change in filament diameter and compositional changes in the matrix were calculated as a function of exposure time at elevated temperatures. With the tungsten nickel (W-Ni) system as a model composite system, unidirectional composites containing from 0.06 to 0.44 initial filament volume fraction were modeled. Compositional changes in the matrix were calculated by superposition of the contributions from neighboring filaments. Alternate methods for determining compositional changes between first and second nearest neighbor filaments were also considered. The results show the relative importance of filament volume fraction, filament diameter, exposure temperature, and exposure time as they affect the rate and extent of filament matrix interaction.

Tenney, D. R.↗
NASA NTRS1980

Differential radio astronomy of galactic objects

A differential astrometry technique is discussed. An improved proper motion and a parallax limit for pulsar 1929 + 10 is presented as well as a limit on the space velocity of the enigmatic object in SgrA.

Backer, D. C.↗
NASA NTRS1980

Simultaneous observations of field-aligned currents and plasma drift velocities by Atmosphere Explorer C

The three-axis flux gate magnetometer on board the Atmosphere Explorer C (AE-C) has provided an additional magnetic field data set to the already broad spectrum of AE-C measurement. The results of an investigation into the feasibility of using the magnetometer for scientific purposes are described. It is shown that within the limitations inherent in the device and in the data reduction technique used, meaningful results can be obtained when the spacecraft is in the spinning mode. From a comparison between the field-aligned current signatures and the simultaneously observed ion convection velocity, it proved possible to locate regions of ionospheric conductivity gradients.

Bythrow, P. F.↗
NASA NTRS1981

Infrared fiber optic focal plane dispersers

Far infrared transmissive fiber optics as a component in the design of integrated far infrared focal plane array utilization is discussed. A tightly packed bundle of fibers is placed at the focal plane, where an array of infrared detectors would normally reside, and then fanned out in two or three dimensions to individual detectors. Subsequently, the detectors are multiplexed by cryogenic electronics for relay of the data. A second possible application is frequency up-conversion (v sub 1 + v sub 2 = v sub 3), which takes advantage of the nonlinear optical index of refraction of certain infrared transmissive materials in fiber form. Again, a fiber bundle is utilized as above, but now a laser of frequency v sub 1 is mixed with the incoming radiation of frequency v sub 1 within the nonlinear fiber material. The sum, v sub 2 is then detected by near infrared or visible detectors which are more sensitive than those available at v sub 2. Due to the geometrical size limitations of detectors such as photomultipliers, the focal plane dispersal technique is advantageous for imaging up-conversion.

Goebel, J. H.↗
NASA NTRS1980

Software reliability: A comparison of results obtained from established software reliability models

Two models of the software error detection process are compared, the Jelinski-Moranda model and a Bayes inference model. Simulation techniques are used to generate software related system failure data which is analyzed by both models. Point estimates and confidence limits are compared. It is demonstrated that uncertainty may be considerable for reasonable samples sizes and should be considered in any application of these techniques. The Jelinski-Moranda model is sensitive to the failure of data to follow internal assumptions of the model, often not providing any point estimates, a factor which may limit its usefulness in many real world situations. The Bayes model is shown to respond to the introduction of additional errors in the software correction process, a condition where error counting models such as the Jelinski-Moranda generally fail to converge.

Horn, M. H.↗
NASA NTRS1982

Criteria for the use of regression analysis for remote sensing of sediment and pollutants

An examination of limitations, requirements, and precision of the linear multiple-regression technique for quantification of marine environmental parameters is conducted. Both environmental and optical physics conditions have been defined for which an exact solution to the signal response equations is of the same form as the multiple regression equation. Various statistical parameters are examined to define a criteria for selection of an unbiased fit when upwelled radiance values contain error and are correlated with each other. Field experimental data are examined to define data smoothing requirements in order to satisfy the criteria of Daniel and Wood (1971). Recommendations are made concerning improved selection of ground-truth locations to maximize variance and to minimize physical errors associated with the remote sensing experiment.

Whitlock, C. H.↗
NASA NTRS1982

On the energy dependence of the radial diffusion coefficient and spectra of inner radiation belt particles - Analytic solutions and comparison with numerical results

A theoretical method by which the energy dependence of the radial diffusion coefficient may be deduced from spectral observations of the particle population at the inner edge of the earth's radiation belts is presented. This region has previously been analyzed with numerical techniques; in this report an analytical treatment that illustrates characteristic limiting cases in the L shell range where the time scale of Coulomb losses is substantially shorter than that of radial diffusion (L approximately 1-2) is given. It is demonstrated both analytically and numerically that the particle spectra there are shaped by the energy dependence of the radial diffusion coefficient regardless of the spectral shapes of the particle populations diffusing inward from the outer radiation zone, so that from observed spectra the energy dependence of the diffusion coefficient can be determined. To insure realistic simulations, inner zone data obtained from experiments on the DIAL, AZUR, and ESRO 2 spacecraft have been used as boundary conditions. Excellent agreement between analytic and numerical results is reported.

Westphalen, H.↗
NASA NTRS1982

Manual for extending the laser specklegram technique to strain analysis of rotating components

The theory, techniques, and equipment necessary for extending laser speckle techniques to analyze stresses in rotating blades are described. Details for setting up the equipment, for timing the events, for data recording, and for data analysis are discussed. Finite element techniques are investigated for analysis of speckle data. Advantages and limitations of the finite element analysis for the speckle data are discussed. The finite element program is listed.

Chien, L. C.↗
NASA NTRS1982

Study of and proposals for the correction of errors in a radar ranging device designed to facilitate docking of a teleoperator maneuvering system

A frequency modulated continuous wave radar system was developed. The system operates in the 35 gigahertz frequency range and provides millimeter accuracy range and range rate measurements. This level of range resolution allows soft docking for the proposed teleoperator maneuvering system (TMS) or other autonomous or robotic space vehicles. Sources of error in the operation of the system which tend to limit its range resolution capabilities are identified. Alternative signal processing techniques are explored with emphasis on determination of the effects of inserting various signal filtering circuits in the system. The identification and elimination of an extraneous low frequency signal component created as a result of zero range immediate reflection of radar energy from the surface of the antenna dish back into the mixer of the system is described.

Mcdonald, M. W.↗
NASA NTRS1983

Controlled stimulation of magnetospheric electrons by radio waves Experimental model for lightning effects

Magnetospheric electrons precipitated by ground-based coded very low frequency radio transmissions have been detected by rocket measurement of bremsstrahlung X-rays, caused by impact of the electrons with the upper atmosphere. The direct correlations obtained between the very low frequency signals and the X-rays demonstrate the limits of sensitivity required and indicate that this remote sensing technique would be useful for future study of very low frequency effects induced by single lightning strokes.

Goldberg, R. A.↗
NASA NTRS1983

Boundary conditions at grain boundaries

Grain boundaries in polycrystalline semiconductor material are frequently idealized as surfaces possessing a characteristic surface recombination velocity. Minority carrier densities generated by external sources (electron beams, light, etc.) in polycrystalline p-n junctions must satisfy certain boundary conditions at these grain boundaries which will be derived. It will also be shown that a 'folding technique' introduced recently to deal with this problem is of limited value.

Von Roos, O.↗
NASA NTRS1983

Pulse compression using binary phase codes

In most MST applications pulsed radars are peak power limited and have excess average power capacity. Short pulses are required for good range resolution, but the problem of range ambiguity (signals received simultaneously from more than one altitude) sets a minimum limit on the interpulse period (IPP). Pulse compression is a technique which allows more of the transmitter average power capacity to be used without sacrificing range resolution. As the name implies, a pulse of power P and duration T is in a certain sense converted into one of power nP and duration T/n. In the frequency domain, compression involves manipulating the phases of the different frequency components of the pulse. One way to compress a pulse is via phase coding, especially binary phase coding, a technique which is particularly amenable to digital processing techniques. This method, which is used extensively in radar probing of the atmosphere and ionosphere is discussed. Barker codes, complementary and quasi-complementary code sets, and cyclic codes are addressed.

Farley, D. T.↗
NASA NTRS1985

Advanced Very High Resolution Radiometer (AVHRR) sensor comparison characteristics

Advantages and limitations of the AVHRR multichannel sea surface temperature (MCSST) detecting technique using NOAA satellites are discussed. The error characteristics of MCSST's from statistical tables and regional AVHRR error characteristics from global anomaly charts are also discussed. Some soruces of errors and positive findings are reviewed.

Mcclain, E. P.↗
NASA NTRS1987

Growth of Triglycine Sulfate (TGS) crystals aboard Spacelab-3

An experiment to study the growth of single crystals of triglycine sulfate (NH2CH2COOH)3 H2SO4 (TGS) was successfully carried out on the Spacelab-3 mission during April 29 to May 6, 1985. Two crystals of TGS were grown during the flight, using a specially developed cooled sting technique of solution crystal growth. For the first time in any flight experiment the growth was monitored on-board as well as on ground by video-schlieren technique. Hundreds of holograms were taken for the solution/crystal interaction during the growth process. Preliminary results indicate that the optical system worked very well and the quality of reconstructed holograms is satisfactory. The cooled sting technique was successfully demonstrated. Holographic interferograms indicate convection free, diffusion limited growth. Some of the preliminary results of crystal quality are also presented.

Lal, R. B.↗
NASA NTRS1987

Cloud cover over the equatorial eastern Pacific derived from July 1983 International Satellite Cloud Climatology Project data using a hybrid bispectral threshold method

A set of visible and IR data obtained with GOES from July 17-31, 1983 is analyzed using a modified version of the hybrid bispectral threshold method developed by Minnis and Harrison (1984). This methodology can be divided into a set of procedures or optional techniques to determine the proper contaminate clear-sky temperature or IR threshold. The various optional techniques are described; the options are: standard, low-temperature limit, high-reflectance limit, low-reflectance limit, coldest pixel and thermal adjustment limit, IR-only low-cloud temperature limit, IR clear-sky limit, and IR overcast limit. Variations in the cloud parameters and the characteristics and diurnal cycles of trade cumulus and stratocumulus clouds over the eastern equatorial Pacific are examined. It is noted that the new method produces substantial changes in about one third of the cloud amount retrieval; and low cloud retrievals are affected most by the new constraints.

Minnis, Patrick↗