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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Friction induced surface activity of some simple organic chlorides and hydrocarbons with iron.

Sliding friction studies were conducted on an iron surface with exposure of that surface to various hydrocarbons and organic chlorides. The hydrocarbons included ethane, ethylene, ethyl chloride, methyl chloride and vinyl chloride. Auger cylindrical-mirror analysis was used to follow interactions of the hydrocarbon and organic chlorides with the iron surface. Results with vinyl chloride indicate friction-induced surface reactivity, adsorption to surface oxides, friction sensitivity to concentration and polymerization. Variation in the loads employed influence adsorption and, accordingly, friction. Unlike results with ethyl and vinyl chloride, friction-induced surface reactivity was not observed with ethane and ethylene.

Buckley, D. H.↗
NASA NTRS1973

Topology of induced lunar magnetic fields.

Using the asymmetric theory of lunar induction derived by Schubert et al. (1973), a picture of both the total and induced magnetic field line distributions in and around the moon is provided for certain orientations of the interplanetary field fluctuations. These field line pictures are compared with the distributions one would obtain using a spherically symmetric vacuum theory of lunar induction. It is found that the induced lunar field line distribution bears a marked resemblance to the structure of the solar-wind distorted geomagnetic field.

Schwartz, K.↗
NASA NTRS1973

A new technique for Auger analysis of surface species subject to electron-induced desorption.

A method is presented to observe surface species subject to electron-induced desorption by Auger electron spectroscopy. The surface to be examined is moved under the electron beam at constant velocity, establishing a time-independent condition and eliminating the time response of the electron spectrometer as a limiting factor. The dependence of the Auger signal on the sample velocity, incident electron current, beam diameter, and desorption cross section is analyzed. It is shown that it is advantageous to analyze the moving sample with a high beam current, in contrast to the usual practice of using a low beam current to minimize desorption from a stationary sample. The method is illustrated by the analysis of a friction transfer film of PTFE, in which the fluorine is removed by electron-induced desorption. The method is relevant to surface studies in the field of lubrication and catalysis.

Pepper, S. V.↗
NASA NTRS1973

Wave-induced eddy diffusion coefficients in the upper atmosphere of Mars.

A theory and method previously used to calculate terrestrial eddy diffusion coefficients due to instabilities in internal gravity waves have been extended to obtain wave-induced eddy diffusion coefficients in the upper atmosphere of Mars. If the Martian atmosphere is relatively dry (water vapor mixing ratio much less than .001), the effects of radiative damping are minimal for all but the longest-period waves. For greater concentrations of water vapor the effects of radiative damping are increased, but in any event it is reasonable to expect wave-induced turbulence, with eddy diffusion coefficients of the order of 10 to the 7th sq cm/sec in the Martian upper atmosphere.

Beasley, W. H.↗
NASA NTRS1973

Induced magnetosphere of the moon. II - Experimental results from Apollo 12 and Explorer 35.

The asymmetric lunar electromagnetic induction theory of Schubert et al. (1973) is tested by using data from the Apollo 12 Lunar Surface Magnetometer and from the Ames magnetometer on Explorer 35. The comparison of data and theory shows that the moon displays an induction asymmetry due to the flow of the solar wind and the formation of the diamagnetic cavity on the darkside. It is inferred that the induced field forms a magnetospheric-like configuration, with the field confined mostly to the crust of the moon. Although the magnetospheric spectrum is time-dependent for all frequencies examined, the distance traveled by the solar wind is so large that a quasi-static magnetospheric configuration can be assumed. The differential power spectrum of the interplanetary magnetic field that excites the moon is compared with the resulting induction spectrum, which has a linear differential power frequency dependence over the frequency range from .0002 to .02 Hz, falling off on either side of these limits. The integrated power in this band is about 5 gamma squared for the interplanetary field local north-south component and about 12 gamma squared for the induced spectrum of this component on the lunar surface.

Smith, B. F.↗
NASA NTRS1973

Effect of geometry variations on lee-surface vortex-induced heating for flat-bottom three-dimensional bodies at Mach 6

Studies have shown that vortices can produce relatively severe heating on the leeward surfaces of conceptual hypersonic vehicles and that surface geometry can strongly influence this vortex-induced heating. Results which show the effects of systematic geometry variations on the vortex-induced lee-surface heating on simple flat-bottom three-dimensional bodies at angles of attack of 20 deg and 40 deg are presented. The tests were conducted at a free-stream Mach number of 6 and at a Reynolds number of 1.71 x 10 to the 7th power per meter.

Hefner, J. N.↗
NASA NTRS1973

New principles of construction of electromechanical vibration inducers

Electromechanical vibration inducers with high reliability and low noise level were created to study premature operating losses in their support bearings. An investigation was also made of the feasibility of developing stable synchronous operation of two vibrational inducers, rigidily fastened to a solid body with and without flexible suspension.

Ashmonas, K. A. P.↗
NASA NTRS1973

A new criterion for failure of materials by environment-induced cracking

A new criterion has been developed for predicting failure of materials by environment-induced cracking. The criterion has been developed by the use of fracture mechanics concepts and assumes that the relationship between crack-growth rate and stress intensity can be described by three separable regions of behavior as first suggested by Wiederhorn. The analytical form of the criterion relates failure time to the initial crack length and the critical crack length or alternatively, to the initial stress intensity and the fracture toughness for various conditions of stress and the environmental variables. The analytical expression is examined by the use of some experimental data on the hydrogen-induced cracking of Ti-5Al-2.5 Sn, and it is demonstrated that the expression predicts the general expected form of the relationship between the normalized stress intensity parameter and the failure time.

Williams, D. P.↗
NASA NTRS1974

An induced junction photovoltaic cell

Silicon solar cells operating with induced junctions rather than diffused junctions have been fabricated and tested. Induced junctions were created by forming an inversion layer near the surface of the silicon by supplying a sheet of positive charge above the surface. Measurements of the response of the inversion layer cell to light of different wavelengths indicated it to be more sensitive to the shorter wavelengths of the sun's spectrum than conventional cells. The greater sensitivity occurs because of the shallow junction and the strong electric field at the surface.

Call, R. L.↗
NASA NTRS1974

Supercirculation effects induced by vectoring a partial-span rectangular jet

Thrust-induced supercirculation effects from thrust vectoring have indicated a potential for not only increasing maneuverability of fighter aircraft but also as a means of improving cruise performance. The current study investigated a partial-span rectangular jet-exhaust nozzle located at the wing trailing edge that acts similar to a jet flap by increasing lift due to supercirculation. This paper summarizes experimental studies including the effects of nozzle deflection angle, wing camber, and nozzle shape and exit location on lift, drag and load distributions. The results indicate that significant increases in thrust-induced lift along with substantial decreases in drag are possible.

Capone, F. J.↗
NASA NTRS1974

Results of induced atmosphere measurements from the Apollo program

Experiments on Apollo missions 15, 16, and 17 were utilized in an attempt to learn about the induced environment in the vicinity of manned spacecraft. Photographic sequences were examined to obtain scattered light data from the spacecraft-generated particulates during quiescence periods and after liquid dumps. The results allowed estimates of the obscuration factor and the clearing times after dumps. It was found that the clearing times were substantially longer than anticipated. The mass spectrometer detected a high molecular flux in lunar orbit which was induced by the spacecraft. It is shown that this is most likely caused by small ice crystals being continually produced in lunar orbit. Other data from the ultraviolet spectrometer and the stellar camera are also analyzed, and estimated values or upper limits are placed on the total scattering background, the size and number of particles generated, the velocity range, and the column density.

Naumann, R. J.↗
NASA NTRS1975

Application of monochromatic ocean wave forecasts to prediction of wave-induced currents

The use of monochromatic wind-wave forecasts in prediction of wind-wave-induced currents was assessed. Currents were computed for selected combinations of wind conditions by using a spectrum approach which was developed by using the Bretschneider wave spectrum for partially developed wind seas. These currents were compared with currents computed by using the significant and average monochromatic wave parameters related to the Bretschneider spectrum. Results indicate that forecasts of significant wave parameters can be used to predict surface wind-wave-induced currents. Conversion of these parameters to average wave parameters can furnish reasonable estimates of subsurface current values.

Poole, L. R.↗
NASA NTRS1975

A flight test investigation of the rolling moments induced on a T-37B airplane in the wake of a B-747 airplane

A flight test investigation of the B-747 vortex wake characteristics was conducted using a T-37B as a probe aircraft. The primary purpose of the program was the validation of the results of B-747 model tests which predicted significant alleviation of the vortex strength when only the inboard flaps were deflected. Measurements of the vortex-induced rolling moments of the probe aircraft showed that the predicted alleviation did occur. The effects of landing gear extension, increased lift coefficient, idle thrust, and sideslip were investigated, and all had an adverse effect on the alleviated condition as evidenced by increased induced rolling moments of the T-37B probe aircraft. Idle thrust also increased the strength of the B-747 wake vortexes with both inboard and outboard flaps extended.

Smith, H. J.↗
NASA NTRS1975

A static air flow visualization method to obtain a time history of the lift-induced vortex and circulation

A recently proposed method of flow visualization was investigated at the National Aeronautics and Space Administration's Langley Research Center. This method of flow visualization is particularly applicable to the study of lift-induced wing tip vortices through which it is possible to record the entire life span of the vortex. To accomplish this, a vertical screen of smoke was produced perpendicular to the flight path and allowed to become stationary. A model was then driven through the screen of smoke producing the circular vortex motion made visible as the smoke was induced along the path taken by the flow and was recorded by highspeed motion pictures.

Patterson, J. C., Jr.↗
NASA NTRS1974

Lunar magnetic field - Permanent and induced dipole moments

Apollo 15 subsatellite magnetic field observations have been used to measure both the permanent and the induced lunar dipole moments. Although only an upper limit of 1.3 x 10 to the 18th gauss-cubic centimeters has been determined for the permanent dipole moment in the orbital plane, there is a significant induced dipole moment which opposes the applied field, indicating the existence of a weak lunar ionosphere.

Russell, C. T.↗
NASA NTRS1975

Ambient and induced pressure fluctuations in supersonic jet flows

An experimental investigation of the ambient static pressure fluctuations and induced acoustic fields in supersonic jet flows has been undertaken to identify possible noise sources and the mechanisms involved in the propagation of disturbances within the flows. The axisymmetric cold air jet under investigation exhausted from a 7-in. exit diameter C-D nozzle run in two conditions: one yielding a fully expanded flow and the other an overexpanded flow. The survey of static pressure fluctuations consisted of measurements of the overall levels and spectra of the fluctuations along the centerline of the two flows and the variation in level across various transverse sections. The second aspect of the study involved the development of a procedure for tracing the propagation of externally induced periodic pressure disturbances inside the jet.

Barra, V.↗