Large strain, elasto-plastic finite element analysis
Two dimensional structures large strain elastoplastic analysis by finite element method, using variational principles to derive equilibrium equations
Evensen, D. A.↗
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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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Ring current particle distributions during the magnetic storms of December 16-18, 1971.
Proton density energy distributions during two magnetic storms on Dec. 16 and 18, 1971, are derived from proton detector data of the S3-A satellite and are analyzed to show the contrast in the ring current developments during the two events. Ground magnetograms are also used in the analysis to show the magnetic field variations during the storms. Satellite orbits 97 through 103 are covered.
Smith, P. H.↗
Relation between near field and far field acoustic measurements
Several approaches to the problem of determining the far field directivity of an acoustic source located in a reverberant environment, such as a wind tunnel, are investigated analytically and experimentally. The decrease of sound pressure level with distance is illustrated; and the spatial extent of the hydrodynamic and geometric near fields, the far field, and the reverberant field are described. A previously-prosposed analytical technique for predicting the far field directivity of the acoustic source on the basis of near field data is investigated. Experiments are conducted with small acoustic sources and an analysis is performed to determine the variation with distance from the source of the directionality of the sound field. A novel experiment is conducted in which the sound pressure measured at various distances from an acoustic driver located in the NASA Ames 40 x 80 ft wind tunnel is crosscorrelated with the driver excitation voltage.
Bies, D. A.↗
Selected reliability studies for the NERVA program
An investigation was made into certain methods of reliability analysis that are particularly suitable for complex mechanisms or systems in which there are many interactions. The methods developed were intended to assist in the design of such mechanisms, especially for analysis of failure sensitivity to parameter variations and for estimating reliability where extensive and meaningful life testing is not feasible. The system is modeled by a network of interconnected nodes. Each node is a state or mode of operation, or is an input or output node, and the branches are interactions. The network, with its probabilistic and time-dependent paths is also analyzed for reliability and failure modes by a Monte Carlo, computerized simulation of system performance.
Hoover, S. V.↗
A second-order theory of an artificial satellite under the influence of the oblateness of the earth
The general theory of the method of averaging is used to study the effect of the oblateness of the earth on the motion of an artificial satellite. The first-order harmonic J2 and the second-order harmonics J3 and J4 are included in the analysis. The first-order, periodic variations together with the second-order, averaged and secular variations are derived for all the six orbital elements. Alternative orbital elements and necessary relations are introduced to deal with circular orbits, orbits at critical inclination and equatorial orbits. Essential transformations and initialization procedures are also outlined.
Liu, J. J. F.↗
Convection effects on Skylab experiments M551, M552, and M553, phase C report
This report described an analysis of Skylab Experiments M551 (Metals Melting), M552 (Exothermic Brazing), and M553 (Sphere Forming). The primary objective is the study of convection in the molten metals and their attendant solidification theory. Particular attention is given to clarifying the effects of reduced gravity on molten metal flow and solidification. Based on an analysis of physical forces and solidification theory expected for ground-based and Skylab processing, low-g variations were predicted for each experiment. A comparison was then made with the Skylab results available to date. Both metallurgical analyses of other investigators and movies of ground-based and Skylab samples were utilized. Several low-g variations in Skylab processed materials were successfully predicted based on expected variations in physical forces and fluid convection. The same analysis also successfully predicted several features in the Skylab-processed materials which were identical to terrestrially-processed materials. These results are summarized in the conclusion section for each experiment.
Bourgeois, S. V.↗
A determination of the lunar moment of inertia
An estimate of the second zonal coefficient of the spherical-harmonic representation of the lunar gravitational field has been obtained from an analysis of particular orbital-element variations of the Explorer 35 and Explorer 49 spacecraft. Data from these spacecraft were used because the orbital configurations resulted in variations of the longitude of periapse and node which were, to first order, dependent only on the even zonal harmonics. The data time span for each satellite was extremely long: 2138 days for Explorer 35 and 230 days for Explorer 49. The value of the harmonic coefficient is determined and used to obtain a value of the lunar moment of inertia.
Gapcynski, J. P.↗
A search for periodic variations of solar radio emission at 3.7- and 11.1-cm wavelengths
Periodic time variations in the emission of quiet solar regions were sought with the NRAO three-element interferometer at 3.7 and 11.1 cm. The visibility function of a source as obtained with a tracking interferometer is an implicit function of time, because of projected baseline changes, and therefore only observations taken when the baseline changes vary slowly with time were used. The visibility function shows significant time variations, but a power-spectrum analysis of the data revealed no unique periodicity.
Kundu, M. R.↗
Mariner 10 data analysis. 1: Scarps, ridges, troughs, and other lineaments on Mercury. 2: Geologic significance of photometric variations on Mercury
Volcanic and tectonic implications of the surface morphology of Mercury are discussed. Mercurian scarps, ridges, troughs, and other lineaments are described and classified as planimetrically linear, arcuate, lobate, or irregular. A global pattern of lineaments is interpreted to reflect modification of linear crustal joints formed in response to stresses induced by tidal spindown. Large arcuate scarps on Mercury most likely record a period of compressional tectonism near the end of heavy bombardment. Shrinkage owing to planetary cooling is the mechanism preferred for their production. Measurements of local normal albedo are combined with computer-generated photometric maps of Mercury to provide constraints on the nature of surface materials and processes. If the mercurian surface obeys the average lunar photometric function, its normal albedo at 554 nm is .16 + or - .03.
Dzurisin, D.↗
Automated array assembly task, phase 1
Various aspects of a sensitivity analysis, in particular, the impact of variations in metal sheet resistivity, metal line width, diffused layer sheet resistance, junction depth, base layer lifetime, optical coating thickness and optical coating refractive index and on process reproducibility for A's diffusion from a polymer dopant source and on module fabrication were studied. Model calculations show that acceptable process windows exist for each of these parameters.
Carbajal, B. G.↗
Spatially resolved excitation temperature measurements in a hypersonic flow using the hook method
Following an analysis of the hook equations for variation of refractivity along a spectrograph slit a series of experiments is reported, in which CO2 was used as the test gas, and the flow variations were spatially resolved. The hooked spectra were used to measure the ground state number densities of the impurity atom of CrI present in the flow. The excitation temperature of the CrI 1-eV level was obtained from the separation of the hooks of the CrI 425.4-nm transition resonance line and simultaneously the 434.4-nm CrI eV lower level line, from the shock to the body of the hypersonic shock tunnel flow. This excitation temperature is compared with theoretical calculations of the CO2 gas temperature. Some further applications of the hook type methods to gas diagnostics are discussed.
Sandeman, R. J.↗
Evaluation and modeling of the topographic effect on the spectral response from NADIR pointing sensors
A field experiment, using a hand-held radiometer, was designed and conducted to assess a simple theoretical incidence model for simulating the topographic effect of a uniform sand surface. Seven data sets were taken to compare effects of solar elevation and azimuth encountered at different times of year. Analysis of these data showed considerable variation in radiance values for different slope angles and aspects and that these values varied considerably with changes in solar elevation and azimuth. The field measured variations in spectral response were found to have generally strong correlations with the theoretical model. The reason for the occurrence of lower correlations are given and methods for improving the model are suggested. A model to simulate LANDSAT sensor response was applied to two subsets of the field data to establish the magnitude of the topographic effect on satellite data.
Holben, B. N.↗
An internal velocity study of the Rosette Nebula
Emission-line profiles of H-alpha were studied at about 700 points in the Rosette Nebula by using a multislit echelle spectrograph. Numerical analysis of the profiles indicates that variations in the line-of-sight velocity occur within the nebula, reaching about + or - 20 km/s in the inner regions. Evidence is presented that these highest velocities are more probably inward, favoring a model where the central cavity is due to a depletion resulting from rapid star formation
Fountain, W. F.↗
Titan aerosols - Optical properties and vertical distribution
An analysis of Titan's solar phase variation as a function of wavelength together with the continuum geometric albedo makes it possible to set limits on the real part of the refractive index and on the average particle size of the aerosol component of Titan's atmosphere of between about 1.5 and 2.0 and between 0.20 microns and about 0.35 microns, respectively. If the real part of the refractive index is known the average particle size can be determined to within a few percent, and varies inversely with the real part of the refractive index. Using this information in a two-layer model of a methane-aerosol atmosphere and comparing the result with Titan's visible and near-infrared methane spectrum leads to the conclusion that the top layer of Titan's atmosphere contains 0.01 km atm of methane and 2.5 extinction optical depths of aerosol, while the data are consistent with a bottom layer containing 2.2 km atm of methane and about 7.5 aerosol optical depths for a real part of the refractive index equal to 1.7 and an average particle size of 0.25 microns.
Rages, K.↗
Rectenna session: Micro aspects
Two micro aspects of the rectenna design are addressed: evaluation of the degradation in net rectenna RF to DC conversion efficiency due to power density variations across the rectenna (power combining analysis) and design of Yagi-Uda receiving elements to reduce rectenna cost by decreasing the number of conversion circuits (directional receiving elements). The first of these micro aspects involves resolving a fundamental question of efficiency potential with a rectenna, while the second involves a design modification with a large potential cost saving.
Gutmann, R. J.↗
Rectenna session: Micro aspects
Two micro aspects of rectenna design are discussed: evaluation of the degradation in net rectenna RF to DC conversion efficiency due to power density variations across the rectenna (power combining analysis) and design of Yagi-Uda receiving elements to reduce rectenna cost by decreasing the number of conversion circuits (directional receiving elements). The first of these involves resolving a fundamental question of efficiency potential with a rectenna, while the second involves a design modification with a large potential cost saving.
Gutmann, R. J.↗
A theoretical interpretation of Forbush decreases
An analysis is presented of the intensity variations of relativistic cosmic rays, at 1 AU, which are associated with the passage of a flare shock wave. The magnitude and time profile obtained is similar to that observed in flare-induced Forbush decreases, and the principal cause of the energy reduction is an increase in adiabatic cooling of the arriving particles due to prolonged containment behind the compressed field of the flare shock wave. The large decreases calculated for the smaller diffusion coefficients are inconsistent with observation, implying larger mean free paths than those traditionally assumed at these rigidities. The method presented may be used to study intensity variations associated with other large-scale structures of the interplanetary field, such as corotating interaction regions.
Gall, R.↗
A time Fourier analysis of zonal averaged ozone heating rates
A time-Fourier analysis is presented for the yearly variation of the zonal averaged ozone heating rates in the middle atmosphere based on a model study. The ozone heating rates are determined by utilizing two-dimensional ozone distributions, the altitude and latitude, and by including the effect of the curved earth's atmosphere. In addition, assumptions are introduced to the yearly variations of the ozone distributions due to the lack of sufficient existing ozone data. Among other results, it is shown that the first harmonic component indicates that the heating rates are completely out of phase between the northern and southern hemispheres. The second Fourier component shows a symmetric pattern with respect to the equator, as well as five distinct local extreme values of the ozone heating rate. The third harmonic component shows a pattern close to that of the first component except in the regions above 70 deg between 45-95 km in both hemispheres.
Wang, P.-H.↗