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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Monitoring the sea surface with a short pulse radar

A solution is presented for the scattering of short pulses from a stochastic, corrugated surface relative to the sea for the case of a narrow-beam transmitting antenna pointing near nadir. The spectrum of the received power and its time history are calculated and this solution is used to show that a measure of the variance of the surface ordinant can be obtained from the backscattered power. Included explicitly in the analysis is the finite nature of the source and the role of the small-scale wave structure (capillary wave range). It is shown that when sufficiently short pulses are transmitted, one can obtain a measure of the variance of the large scale surface ordinant from either the temporal spacing of the peaks in the returned power or from the envelope of the spectrum of the received power. Assuming an appropriate model for the statistics and spectrum of the surface ordinate, the variance can be used to compute the wind speed and the significant wave height of the surface.

Le Vine, D. M.↗
NASA NTRS1975

Solar stills for agricultural purposes

Basic concepts of using desalinated water for agricultural purposes are outlined. A mathematical model describing heat and mass transfer in a system combining a solar still with a greenhouse, its solution, and test results of a small-scale unit built at the Middle East Technical University, Ankara, Turkey, are discussed. The unit was employed to demonstrate the technical feasibility of the system. Further development and modifications are necessary for larger-scale operations. The basis of an optimization study which is underway at the Brace Research Institute of McGill University in Montreal, Canada, aimed at finding the best combination of design and operation parameters is also presented.

Selcuk, M. K.↗
NASA NTRS1975

Investigation of low-latitude hydrogen emission in terms of a two-component interstellar gas model

High-resolution 21-cm hydrogen line observations at low galactic latitude are analyzed to determine the large-scale distribution of galactic hydrogen. Distribution parameters are found by model fitting, optical depth effects are computed using a two-component gas model suggested by the observations, and calculations are made for a one-component uniform spin-temperature gas model to show the systematic departures between this model and data obtained by incorrect treatment of the optical depth effects. Synthetic 21-cm line profiles are computed from the two-component model, and the large-scale trends of the observed emission profiles are reproduced together with the magnitude of the small-scale emission irregularities. Values are determined for the thickness of the galactic hydrogen disk between half density points, the total observed neutral hydrogen mass of the galaxy, and the central number density of the intercloud hydrogen atoms. It is shown that typical hydrogen clouds must be between 1 and 13 pc in diameter and that optical thinness exists on large-scale despite the presence of optically thin gas.

Baker, P. L.↗
NASA NTRS1975

A three-dimensional dynamical-chemical model of atmospheric ozone

A three-year integration of a global three-dimensional model including dynamics and simple photochemistry is used to predict ozone. Good agreement with observation is obtained for stratospheric motion patterns, meridional circulations, ozone density as a function of height and latitude, eddy transports of ozone, surface destruction of ozone, and correlations of ozone with other variables. The annual cycle of columnar ozone in high latitudes is present, but at a smaller amplitude than observed. Vertical transport of ozone downward from the main generation level at 30 km is accomplished primarily by small-scale eddy diffusion between 20 and 30 km and again near the ground; large-scale vertical transport dominates in between. The model predicts a secondary maximum in ozone mixing ratio at 45 km somewhat equatorward of the winter polar-night zone. This feature, recently observed from satellite measurements, is thought to be caused by the temperature dependence of reaction rates in the Chapman scheme. The principal deficiency of the model is an underprediction of the spring ozone concentration in high latitudes in the lower stratosphere.

Cunnold, D.↗
NASA NTRS1975

Coal refuse site inventories

Small-scale color-infrared aerial photography at 1:120,000 scale is used to carry out an operational survey of coal refuse sites. Site analyses and reclamation cost estimates are completed in less than 90 days by using remote sensing techniques. Analysis of photographs provided dependable and accurate data for the location and environmental assessment of nearly 200 coal refuse banks and slurry ponds. The inventory constitutes a comprehensive reference for establishing priorities for coal refuse site reclamation and for complementing future field surveys.

Wobber, F. J.↗
NASA NTRS1975

The application of pulse excitation to ground and flight vibration tests

A discussion of the relative merits of sinusoidal versus nonharmonic excitation for flight flutter testing is presented. It is concluded that the use of transient excitation is rapidly becoming a necessity. The application of small-scale rocket motors to the excitation of the aircraft is suggested. The design and development of rocket motors specifically for flight flutter testing is described. Methods of measuring and analyzing the transient response of the aircraft are discussed, and the techniques of theoretically predicting the structural response are described.

Laidlaw, W. R.↗
NASA NTRS1975

Flow visualization of vortex interactions in multiple vortex wakes behind aircraft

A flow visualization technique was developed which allows the nature of lift-generated wakes behind aircraft models to be investigated. The technique was applied to models being towed underwater in a ship model basin. Seven different configurations of a small-scale model of a 747 transport aircraft were used to allow observation of typical vortex interactions and merging in multiple vortex wakes. It was established that the motion of the wake vortices is often sensitive to small changes in either wing span loading or model attitude. Landing gear deployement was found to cause a far-field reformation of vorticity behind a model configuration which dissipated concentrated vorticity in the near-field wake. Alleviation of wake vorticity is achievable by configuring the wing span loading to cause the wake vortices to move in paths that result in their interactions and merging. The vortices shed from the horizontal stabilizer always moved down rapidly into the wake and merged with the other vortices, primarily the inboard flap vortices.

Ciffone, D. L.↗
NASA NTRS1975

Optimization of an oxide dispersion strengthened Ni-Cr-Al alloy for gas turbine engine vanes

The investigation was carried out to determine the optimum alloy within the Ni-16Cr-Al-Y2O3 system for use as a vane material in advanced aircraft gas turbine engines. Six alloys containing nominally 4%, 5% and 6% Al with Y2O3 levels of 0.8% and 1.2% were prepared by mechanical attrition. Six small-scale, rectangular extrusions were produced from each powder lot for property evaluation. The approximate temperatures for incipient melting were found to be 1658 K (2525 F), 1644 K (2500 F) and 1630 K (2475 F) for the 4%, 5% and 6% aluminum levels, respectively. With the exception of longitudinal crystallographic texture, the eight extrusions selected for extensive evaluation either exceeded or were close to mechanical property goals. Major differences between the alloys became apparent during dynamic oxidation testing, and in particular during the 1366 K (2000 F)/500 hour Mach 1 tests carried out by NASA-Lewis. An aluminum level of 4.75% was subsequently judged to be optimum based on considerations of dynamic oxidation resistance, susceptibility to thermal fatigue cracking and melting point.

Klarstrom, D. L.↗
NASA NTRS1975

Water color and circulation southern Chesapeake Bay, part 1

Satellite imagery from two EREP passes over the Rappahannock Estuary of the Chesapeake region is analyzed to chart colored water types, to delineate color boundaries and define circulatory patterns. Surface observations from boats and helicopters concurrent with Skylab overpass define the distributions of suspended sediment, transparency, temperature, salinity, phytoplankton, color of suspended material and optical ratio. Important features recorded by the imagery are a large-scale turbidity maximum and massive red tide blooms. Water movement is revealed by small-scale mixing patterns and tidal plumes of apparent sediment-laden water. The color patterns broadly reflect the bottom topography and the seaward gradient of suspended material between the river and the bay. Analyses of red, green and natural color photos by microdensitometry demonstrate the utility of charting water color types of potential use for managing estuarine water quality. The Skylab imagery is superior to aerial photography and surface observations for charting water color.

Nichols, M. M.↗
NASA NTRS1975

Stochastic simulation of vertically nonhomogeneous gusts

The small-scale horizontal gust structure of detailed wind profiles along the vertical in the first 20 km of the atmosphere is a vertically nonhomogeneous process. A linear stochastic model was developed based on the process covariance function. This model was formulated through the use of a scaling hypothesis which transforms the nonhomogeneous gust process into a nondimensional gust process which is homogeneous in a nondimensional gust height coordinate. The velocity scaling parameter for the gust process is the gust standard deviation, and the length scale used to nondimensionalize the altitude is the vertical space lag associated with the first zero of the gust covariance function. State space theory was used to derive a digital filter from the model, which can be readily used to simulate gusts for space vehicle design applications.

Fichtl, G. H.↗
NASA NTRS1975

Duct wall impedance control as an advanced concept for acoustic impression

Models and tests on an acoustic duct liner system which has the property of controlled-variable acoustic impedance are described. This is achieved by a novel concept which uses the effect of steady air flow through a multi-layer, locally reacting, resonant-cavity absorber. The scope of this work was limited to a 'proof of concept.' The test of the concept was implemented by means of a small-scale, square-section flow duct facility designed specifically for acoustic measurements, with one side of the duct acoustically lined. The test liners were designed with the aid of previously established duct acoustic theory and a semi-empirical impedance model of the liner system. Over the limited range tested, the liner behaved primarily as predicted, exhibiting significant changes in resistance and reactance, thus providing the necessary concept validation.

Dean, P. D.↗
NASA NTRS1975

Coherence properties of wideband satellite signals caused by ionospheric scintillation

Radio scintillation on satellite signals caused by small-scale irregularities in F-region ionospheric electron density can be an important limitation on earth-satellite communication and navigation systems. Scintillation imposes distortion in both amplitude and phase on wideband signals. In the present work, the shallow-modulated phase screen theory is developed in terms of coherence bandwidth including a model based on a turbulent-like power-law description of the irregularities. The model results usually show a greater coherence bandwidth in the signal phase than in the signal amplitude. Therefore, systems that require phase coherence over a large bandwidth should be less affected than those requiring amplitude coherence.

Rufenach, C. L.↗
NASA NTRS1976

On the causes of spectral enhancements in solar wind power spectra

Enhancements in power spectra of the solar-wind ion flux in the frequency neighborhood of 0.5 Hz had been noted by Unti et al. (1973). It was speculated that these were due to convected small-scale density irregularities. In this paper, 54 flux spectra calculated from OGO 5 data are examined. It is seen that the few prominent spectral peaks which occur were not generated by density irregularities, but were due to several different causes, including convected discontinuities and propagating transverse waves. A superposition of many spectra, however, reveals a moderate enhancement at a frequency corresponding to convected features with a correlation length of a proton gyroradius, consistent with the results of Neugebauer (1975).

Unti, T.↗
NASA NTRS1975

On the effects of flight on jet engine exhaust noise

Recent flight data on jet engine exhaust noise do not agree with projections based on classical jet noise theories. This paper demonstrates that these differences may be reconciled by considering the combined effects of jet mixing noise and internally-generated engine exhaust noise. The source strength of the internally-generated noise is assumed to be unaffected by flight, as has been shown in small-scale free-jet experiments. The directivity of the internally-generated noise is assumed to be the same statically as that given in the NASA interim prediction method for core engine noise. However, it is assumed that in flight the internally generated noise is subject to the convective amplification effect of a simple source. The absolute levels of the internally-generated noise are obtained from an empirical fit of some typical engine data. The static and flight jet noise are predicted using the NASA interim prediction method for jet noise. It is shown that in many cases, although jet mixing may be the dominant noise source statically, much of the flyover noise signature is dominated by internally-generated noise.

Stone, J. R.↗
NASA NTRS1976

Apparatus and methodology for fire gas characterization by means of animal exposure

While there is a great deal of information available from small-scale laboratory experiments and for relatively simple mixtures of gases, considerable uncertainty exists regarding appropriate bioassay techniques for the complex mixture of gases generated in full-scale fires. Apparatus and methodology have been developed based on current state of the art for determining the effects of fire gases in the critical first 10 minutes of a full-scale fire on laboratory animals. This information is presented for its potential value and use while further improvements are being made.

Marcussen, W. H.↗
NASA NTRS1976

Radar imaging of ocean surface patterns

The paper presents some examples of imaging radar oceanographic observations and discusses physical phenomena on the surface that may cause the radar image. The different ocean scattering theories are briefly discussed, including the tangent plane model, the Bragg-Rice model, and the Rayleigh scattering model. All but one of the images presented were obtained with an L-band HH-polarized radar; they include deep-ocean swells, coastal swells, wave refractions, internal waves, ship wakes, abrupt transitions in open-ocean surface roughness, surface slicks, island wind shadowing, and currents. Analyses are shown to suggest that the primary source of the L-band imagery of ocean surface patterns is the variation of small-scale surface roughness and local tilt angle. It is also noted that surface irregularities behave as isotropic scatterers for a radar wavelength of 25 cm.

Brown, W. E., Jr.↗
NASA NTRS1976

Solar modulation and a galactic origin for the anomalous component observed in low-energy cosmic rays

The current theory of solar modulation can be used to argue that the cosmic-ray component at low energies, which is observed to have an anomalous composition, is not of galactic origin, i.e., it is not a component of the galactic cosmic-ray flux. The current theory predicts, from quite general considerations, that an unreasonably large intensity of cosmic rays, by many orders of magnitude, would be required in the interstellar medium to account for the observed fluxes. Conceivably, the current modulation theory could be modified so that only reasonable interstellar fluxes are predicted. One such modification involves an unusual scheme for particle diffusion in the interplanetary medium. Particles are assumed to diffuse not as a result of their own motion among small-scale irregularities in the magnetic field, but rather in a process in which they are trapped between time-varying constrictions in the large-scale field.

Fisk, L. A.↗
NASA NTRS1975

Measurement of auroral Birkeland currents

Results are presented for measurements of the auroral current made with a rocket-borne experiment over Fort Churchill, Canada, during the February-May period in 1968. On the upward leg of the rocket flight there were detected a westward auroral current of 10,000 A near 96 km altitude and two oppositely directed Birkeland currents of about 0.00005 A per sq m at about 160 km altitude. On the downward leg there were revealed a westward filament of current of about 0.0008 A per sq m at about 220 km altitude, two oppositely directed Birkeland sheet currents of about 0.00014 A per sq m at about 230 km altitude, and two oppositely directed Birkeland currents of about 0.00007 A per sq m which fed a westward auroral electrojet of about 0.0010 A per sq m at about 100 km altitude and were associated with a bright rayed arc. A reversal in the Birkeland current system near midnight was also observed. These observations are probably manifestations of the complex nature of small-scale currents associated with complicated auroral forms.

Ifedili, S. O.↗