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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 145 records · Page 8
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NASA NTRS1972

A shielding application of perturbation theory to determine changes in neutron and gamma doses due to changes in shield layers

The perturbation theory for fixed sources was applied to radiation shielding problems to determine changes in neutron and gamma ray doses due to changes in various shield layers. For a given source and detector position the perturbation method enables dose derivatives due to all layer changes to be determined from one forward and one inhomogeneous adjoint calculation. The direct approach requires two forward calculations for the derivative due to a single layer change. Hence, the perturbation method for obtaining dose derivatives permits an appreciable savings in computation for a multilayered shield. For an illustrative problem, a comparison was made of the fractional change in the dose per unit change in the thickness of each shield layer as calculated by perturbation theory and by successive direct calculations; excellent agreement was obtained between the two methods.

Fieno, D.↗
NASA NTRS1972

Electromagnetic diffraction by plane reflection diffraction gratings

A plane wave theory was developed to study electromagnetic diffraction by plane reflection diffraction gratings of infinite extent. A computer program was written to calculate the energy distribution in the various orders of diffraction for the cases when the electric or magnetic field vectors are parallel to the grating grooves. Within the region of validity of this theory, results were in excellent agreement with those in the literature. Energy conservation checks were also made to determine the region of validity of the plane wave theory. The computer program was flexible enough to analyze any grating profile that could be described by a single value function f(x). Within the region of validity the program could be used with confidence. The computer program was used to investigate the polarization and blaze properties of the diffraction grating.

Bocker, R. P.↗
NASA NTRS1971

Development of MHD flow in the entrance region of a channel.

A general method has been developed for determining the developing magnetohydrodynamic flow in the entrance region of a parallel-plate channel. Closed form solutions are obtained. Numerical results are presented for the development of velocity distribution, pressure drop, and magnetohydrodynamic entrance length at different Hartmann numbers. At large Hartmann numbers, the magnetic field effect becomes dominant and the magnetohydrodynamic entrance length becomes negligible. Also, the pressure drop is enhanced by the magnetic field. Comparison of results with direct numerical analysis shows excellent agreement.-

Wu, S. T.↗
NASA NTRS1972

Enrichment of very heavy nuclei in the composition of solar accelerated particles.

Measurement of the abundances of the nuclei C, N, O, Ne, Mg, Si, Ar, and Ca and the group Cr-Co relative to oxygen from seven solar energetic-particle events in the energy range from about 14 to 61 MeV per nucleon with a solid-state detector telescope on the OGO-5 satellite, 1968-1971. The differential energy spectra of O (14 to 29 MeV per nucleon) and Cr-Co (3 to 61 MeV per nucleon) have a spectral index of about (-3) for a power law in kinetic energy. The relative abundances of C, N, O, and Ne are in excellent agreement with emulsion studies. However, when compared with the solar photospheric and coronal abundances, the OGO-5 measurements show a large enhancement of relative abundances beginning with Si, and extending to the Cr-Co group. The enhancement over the solar and universal abundances is in rough agreement with the composition of the galactic cosmic radiation.

Mogro-Campero, A.↗
NASA NTRS1971

Elevation-relief ratio, hypsometric integral, and geomorphic area-altitude analysis.

Mathematical proof establishes identity of hypsometric integral and elevation-relief ratio, two quantitative topographic descriptors developed independently of one another for entirely different purposes. Operationally, values of both measures are in excellent agreement for arbitrarily bounded topographic samples, as well as for low-order fluvial watersheds. By using a point-sampling technique rather than planimetry, elevation-relief ratio (defined as mean elevation minus minimum elevation divided by relief) is calculated manually in about a third of the time required for the hypsometric integral.

Pike, R. J.↗
NASA NTRS1972

Comparison of characteristics and shock capturing methods with application to the space shuttle vehicle.

A critical appraisal is presented of a method-of-characteristics (MOC) and a shock-capturing technique (SCT) for calculating three-dimensional supersonic flow. Detailed comparisons are made for pointed and blunt-nosed bodies with a thick delta wing at angles of attack from 5 to 15 deg. The results show excellent agreement between the methods and with experiment. It is established that the SCT code yields accurate shock locations and jump conditions. The SCT code typically requires about three times as many mesh points as the MOC code in order to resolve the bow shock, but the total computation time is about the same. On a point for point basis, the SCT code is about four times faster than the MOC code.

Rakich, J. V.↗
NASA NTRS1972

The farfield structure of aircraft wake turbulence.

Detailed mean flow measurements were obtained at stations up to thirty chordlengths downstream in an airfoil trailing vortex using a yawhead pressure probe in the Virginia Tech Six-Foot Subsonic Tunnel. Mass injection at the wingtip was shown to hasten the vortex decay. A theoretical method has been developed to show the effect of wing circulation distribution on the structure of the outer portion of the vortex and excellent agreement with the experimental data is demonstrated. Experimental results indicate a much slower decay and higher tangential velocities than previously expected.

Mason, W. H.↗
NASA NTRS1972

Small-scale wind shear definition for aerospace vehicle design.

Rawinsonde wind profile data provide adequate wind shear information for vertical height intervals greater than 1 km. To specify wind shears for intervals below 1 km for space vehicle design, detailed wind-profile information like that provided by the FPS-16 Radar/Jimsphere system or an extrapolation procedure is required. This paper is concerned with the latter alternative. It is assumed that any realization from an ensemble of wind profiles can be represented in terms of a Fourier integral. This permits the calculation of the ensemble standard deviation and mean of the corresponding shear ensemble for any altitude and shear interval in terms of the power spectrum of the ensemble of wind profiles. The results of these calculations show that the mean and standard deviation of the wind shear ensemble, as well as the wind shear for any percentile, asymptotically behave like the vertical interval to the 0.7 power. This result is in excellent agreement with shear data from Cape Kennedy, Fla.

Fichtl, G. H.↗
NASA NTRS1972

Sonic-boom propagation through a stratified atmosphere.

Theoretical approach to the problem of predicting the sonic-boom signature due to a maneuvering aircraft, with outline of the resulting calculation method. This method includes the effects of a variable, stratified atmosphere, and is based on geometric-acoustic principles. A nonlinear distortion is used to account for the weak shock field. The analytical results are compared with experimental data and excellent agreement was found, particularly with regard to signature length.

Hayes, W. D.↗
NASA NTRS1972

Low energy electron precipitation and the ionospheric F-region in and north of the auroral zone.

Use of low-elevation sounding rocket (Polar 1) in the exploration of the F region morphology in and north of the auroral zone over northern Norway. The rocket which moved over a horizontal distance of some 400 km inside the F region, monitored low-energy electron precipitation and various upper-atmosphere excitation and ionization processes. The latitudinal variations of the less than 1 keV energy electron fluxes showed excellent agreement with corresponding variations in the F-region electron density and the O I (6300 A) emission below the rocket, indicating that the low-energy electrons are the main sources for these phenomena at these high latitudes. An N2(+) (4278 A) arc was located near the decrease in the 40-keV electron fluxes. This arc was produced by a nearly monoenergetic influx of some 3-keV electrons. The expected luminosity profile derived from this energy spectrum differs significantly from the observed one, and possible explanations for the discrepancy are discussed.

Evans, D. S.↗
NASA NTRS1971

Transport properties of atomic hydrogen.

Determination of a new set of values for the coefficients of viscosity and thermal conductivity of atomic hydrogen in the range from 1 to 100,000 K. The estimated error is about 5%. Quantal theory was used for low temperatures and classical theory for high temperatures. There is excellent agreement between the two theories as low as 20 K.-

Allison, A. C.↗
NASA NTRS1972

The lithium-like spectra of K XVII through Mn XXIII in the extreme-ultraviolet region.

Identifications and classifications of spectral lines in the lithium-like spectra of the elements K through Mn is presented for the first time. The extrapolation procedures used to calculate these spectra are presented in detail. The excellent agreement between the predicted and measured lines establish the long-range extrapolation.

Goldsmith, S.↗
NASA NTRS1972

Four years of dust particle measurements in cislunar and selenocentric space from Lunar Explorer 35 and OGO 3.

Since July 1967, knowledge concerning the distributions of picogram size particulate matter in selenocentric space has been obtained from the Lunar Explorer 35 dust particle experiment. For almost 40% of the time, the mean sporadic cumulative flux is quite similar to the flux in interplanetary space. However, there are fluctuations of an order of magnitude during major meteor showers. The coincident increase of the flux in selenocentric space during the shower periods has been observed for the fourth year. The 100-picogram sensor does not show an increase during shower times, indicating a mass threshold of less than 100 picograms for particles with velocities equal to or greater than lunar escape velocity. The flux values from Lunar Explorer 35 are compared to other long-lifetime measurements in selenocentric, cislunar and interplanetary space with excellent agreement for masses less than one nanogram.

Alexander, W. M.↗
NASA NTRS1972

Shock wave-turbulent boundary layer interactions in rectangular channels.

Interaction regions created by the impingement of full span, externally generated, shock waves on a nozzle wall boundary layer were investigated. Incident shock strength was varied to produce unseparated, incipient, and fully separated flow fields. Significant departures from two-dimensionality were observed over the entire range of shock strengths tested and were identified with sidewall and corner boundary layer effects. However, comparisons of present centerline results with published two-dimensional data, obtained under similar test conditions and geometrical constraints, showed excellent agreement (e.g., incipient separation pressure levels, wall pressure distributions, free-interaction, and scale of the interaction region). This raises some question concerning the degree of two-dimensionality achieved in these previous investigations.

Reda, D. C.↗
NASA NTRS1972

Elastic scattering of 600-MeV protons from H, D, He-3, and He-4.

Study of the elastic scattering of 600-MeV protons from light nuclei. Differential cross sections have been obtained for the scattering of protons from hydrogen, deuterium, helium-3, and helium-4. Polarization was measured for deuterium and He-4 nuclei. The p-p cross-section data are in excellent agreement with the predictions from the Livermore phase shifts. Small-angle p-D, p-He-3 elastic scattering data are compared with calculations based on the multiple-scattering theories of Watson and Glauber.

Boschitz, E. T.↗
NASA NTRS1972

Plane elastostatic analysis of V-notched plates.

Solutions are given for several plane elastostatic problems of plates having a V-notch on one edge, and subjected to a variety of boundary conditions. The effect of the magnitude of the V-notch angle and specimen geometry on stress intensity factors KI and KII are obtained for unloaded notch surfaces. There is less than one per cent difference in opening model stress intensity factor in going from a zero degree notch angle to a 30 degree notch angle. Notch opening displacements at the plate edge were measured experimentally, and the results obtained were in excellent agreement with the computed results.

Gross, B.↗
NASA NTRS1972

Shock wave oscillation driven by turbulent boundary layer fluctuations

Pressure fluctuations due to the interaction of a shock wave with a turbulent boundary layer were investigated. A simple model is proposed in which the shock wave is convected from its mean position by velocity fluctuations in the turbulent boundary layer. Displacement of the shock is assumed limited by a linear restoring mechanism. Predictions of peak root mean square pressure fluctuation and spectral density are in excellent agreement with available experimental data.

Plotkin, K. J.↗
NASA NTRS1972

An experimental investigation of turbulent boundary layers at high Mach number and Reynolds numbers

Skin friction, heat transfer and pressure measurements were obtained in laminar, transitional and turbulent boundary layers on flat plates at Mach numbers from 7 to 13 at wall-to-free stream stagnation temperature ratios from 0.1 to 0.3. Measurements in laminar flows were in excellent agreement with the theory of Cheng. Correlations of the transition measurements with measurements on flight vehicles and in ballistic ranges show good agreement. Our transition measurements do not correlate well with those of Pate and Schueler. Comparisons have been made between the skin friction and heat transfer measurements and the theories of Van Driest, Eckert and Spalding and Chi. These comparisons reveal in general that at the high end of our Mach number range (10-13) the theory of Van Driest is in best agreement with the data, whereas at lower Mach numbers (6.5-10) the Spalding Chi theory is in better agreement with the measurements.

Holden, M. S.↗