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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Current Sheet Magnetic Model for the Solar Corona

A new magnetic model is developed and compared with previous models and the observed solar corona. An attempt is made to more accurately compute the three-dimensional currents flowing in the solar corona. Physical reasons are given that require most of the large scale currents flowing in the solar corona to lie near thin sheets. The current sheets are not constrained into any particular geometry or symmetry as in the previous models of Altschuler and Newkirk (1969) and Schatten et al. (1969). A comparison with the axisymmetric, isothermal MHD solution of Pneuman and Kopp (1970) suggests that the model is able to simulate to high accuracy an isothermal corona. A comparison of the model with the May 30, 1965, solar eclipse and the November 12, 1966, solar eclipse shows the model is capable of computing many features including the polar plume orientations as well as radial and nonradial streamers in the solar corona.

Schatten, K. H.↗
NASA NTRS1972

Development of a model and test equipment for cold flow tests at 500 atm of small nuclear light bulb configurations

A model and test equipment were developed and cold-flow-tested at greater than 500 atm in preparation for future high-pressure rf plasma experiments and in-reactor tests with small nuclear light bulb configurations. With minor exceptions, the model chamber is similar in design and dimensions to a proposed in-reactor geometry for tests with fissioning uranium plasmas in the nuclear furnace. The model and the equipment were designed for use with the UARL 1.2-MW rf induction heater in tests with rf plasmas at pressures up to 500 atm. A series of cold-flow tests of the model was then conducted at pressures up to about 510 atm. At 504 atm, the flow rates of argon and cooling water were 3.35 liter/sec (STP) and 26 gal/min, respectively. It was demonstrated that the model is capable of being operated for extended periods at the 500-atm pressure level and is, therefore, ready for use in initial high-pressure rf plasma experiments.

Jaminet, J. F.↗
NASA NTRS1972

A Limited Survey of General Purpose Finite Element Computer Programs

Ten representative programs are compared. A listing of additional programs encountered during the course of this effort is also included. Tables are presented to show the structural analysis, material, load, and modeling element capability for the ten selected programs.

Glaser, J. C.↗
NASA NTRS1974

Electrochemical carbon dioxide concentrator subsystem math model

A steady state computer simulation model has been developed to describe the performance of a total six man, self-contained electrochemical carbon dioxide concentrator subsystem built for the space station prototype. The math model combines expressions describing the performance of the electrochemical depolarized carbon dioxide concentrator cells and modules previously developed with expressions describing the performance of the other major CS-6 components. The model is capable of accurately predicting CS-6 performance over EDC operating ranges and the computer simulation results agree with experimental data obtained over the prediction range.

Marshall, R. D.↗
NASA NTRS1971

Acoustic radiation from lined, unflanged ducts: Acoustic source distribution program

An acoustic radiation analysis was developed to predict the far-field characteristics of fan noise radiated from an acoustically lined unflanged duct. This analysis is comprised of three modular digital computer programs which together provide a capability of accounting for the impedance mismatch at the duct exit plane. Admissible duct configurations include circular or annular, with or without an extended centerbody. This variation in duct configurations provides a capability of modeling inlet and fan duct noise radiation. The computer programs are described in detail.

Beckemeyer, R. J.↗
NASA NTRS1974

Model calculations for diffuse molecular clouds

A local steady-state isobaric model of the interstellar clouds is developed and applied to the OAO-3 observations. The model allows for cooling by C II fine-structure transitions and for inhomogeneities resulting from attenuations in the external radiations which heat the cloud constituents. Factors affecting the thermal properties of the clouds are emphasized; these include H and H2 balance, interstellar grain heating, electron density, and calcium equilibrium. The thermodynamic consequences of the attenuation of the ultraviolet interstellar radiation field are studied. The effect of varying the most important parameters and their allowed ranges is considered. Results indicate that the model is capable of reproducing the H2 fractional abundances and kinetic temperatures observed by OAO-3.

Glassgold, A. E.↗
NASA NTRS1975

Example of input-output analysis

The thirty sectors included in the ECASTAR energy input-output model were listed. Five of these belong to energy producing sectors, fifteen to manufacturing industries, two to residential and commercial sectors, and eight to service industries. The model is capable of tracing impacts of an action in three dimensions: dollars, BTU's of energy, and labor. Four conservation actions considered were listed and then discussed separately, dealing with the following areas: increase in fuel efficiency, reduction in fuel used by the transportation and warehousing group, manufacturing of smaller automobiles, and a communications/transportation trade-off.

Source record↗
NASA NTRS1978

The data system dynamic simulation /DSDS/

The paper describes the development by NASA of the data system dynamic simulation (DSDS) which provides a data system simulation capability for a broad range of programs, with the capability to model and simulate all or any portion of an end-to-end data system to multiple levels of fidelity. Versatility is achieved by specifying parameters which define the performance characteristics of data system components, and by specifying control and data paths in a data system. DSDS helps reduce overall simulation cost and the time required for obtaining a data systems analysis, and helps provide both early realistic representations of data systems and the flexibility to study design changes and operating strategies.

Hooper, J. W.↗
NASA NTRS1978

A steady-state stratospheric aerosol model

This paper deals with the development of a one-dimensional steady-state stratospheric aerosol model and the subsequent perturbations caused by including the expected Space Shuttle particulate effluents in the model. Two approaches to the basic modeling effort have been made: in one, enough simplifying assumptions were introduced so that a more or less exact solution to the descriptive equations could be obtained; in the other, very few simplifications were made and a computer technique was used to solve the equations. The most complete form of the model contains the effects of sedimentation, diffusion, particle growth and coagulation. The results indicate that the model is capable of describing many aspects of the stratospheric aerosol layer, such as size distribution and the vertical profile of particles greater than 0.3 micron diameter.

Rosen, J. M.↗
NASA NTRS1977

Severe weather prediction studies

A numerical forecast model is described which uses three-dimensional primitive equations to predict the evolution of the wind, temperature and moisture fields along with the subsynoptic-scale convective activity. There are 15 vertical levels set on a longitude-latitude horizontal grid. In this study, the horizontal grid distance is 70 km (0.625 deg latitude and 0.816 deg longitude at 40 deg N) and the time step is 90 sec. Orography is included and terrain coordinates are adopted. The forecast model is used to test two tornado-producing storms with very different synoptic structures. A 12 hr forecast is carried out for both cases. The rms errors of the forecast indicate much smaller errors in the middle troposphere than in the lower troposphere. The results demonstrate that a rather fine-mesh limited-area numerical model is capable of providing a valuable short-range forecast of the circulation and the mesoscale precipitation features.

Chang, C.-B.↗
NASA NTRS1980

Assessment of space sensors for ocean pollution monitoring

Several passive and active microwave, as well as passive optical remote sensors, applicable to the monitoring of oil spills and waste discharges at sea, are considered. The discussed types of measurements relate to: (1) spatial distribution and properties of the pollutant, and (2) oceanic parameters needed to predict the movement of the pollutants and their impact upon land. The sensors, operating from satellite platforms at 700-900 km altitudes, are found to be useful in mapping the spread of oil in major oil spills and in addition, can be effective in producing wind and ocean parameters as inputs to oil trajectory and dispersion models. These capabilities can be used in countermeasures.

Alvarado, U. R.↗
NASA NTRS1981

A split explicit reformulation of the regional numerical weather prediction model of the Japan Meteorological Agency

The split explicit integration scheme for numerical weather prediction models is employed in a version of the regional numerical weather prediction model of the Japan Meteorological Agency. The finite-difference scheme of the model is designed in the manner proposed by Okamura (1975). The horizontal advection terms in the governing equations are integrated with a time step limited by the wind speed while the terms which describe inertial-gravity oscillations are integrated in a succession of shorter time steps. The physical processes included within the model are precipitation, small-scale convection, surface exchanges of sensible and latent heat, and radiative heating and cooling. An example of a surface pressure forecast over Europe is shown for initial data observed at 0000 GMT 29 December 1979. Quantitative precipitation forecasts over Europe and North America for the 24 h period beginning at 0000 GMT 30 December 1979 are also shown. It is concluded that the model is capable of realistically depicting the evolution of synoptic-scale systems.

Duffy, D. G.↗
NASA NTRS1982

The effects of microcracking on the thermal expansion of graphite-epoxy composites

A study of the effects of thermal environment and microcracking in graphite epoxy composites was made. Research indicates that microcracking does affect the thermal expansion of composite laminates. The amount of reduction in thermal expansion was a function of the crack density. A maximum reduction of approximately 25% occurred in a quasi-isotropic specimen with a crack density of 2.05 mm 1 in the 90 deg plies. Laminate analysis with appropriate reductions in E sub 2 and Alpha sub 2 of the damaged plies appears to be capable of modeling the observed

Bowles, D. E.↗
NASA NTRS1982

VLF wave growth and discrete emission triggering in the magnetosphere - A feedback model

A simple nonlinear feedback model is presented to explain VLF wave growth and emission triggering observed in VLF transmission experiments. The model is formulated in terms of the interaction of electrons with a slowly varying wave in an inhomogeneous medium as in an unstable feedback amplifier with a delay line; constant frequency oscillations are generated on the magnetic equator, while risers and fallers are generated on the downstream and upstream sides of the equator, respectively. Quantitative expressions are obtained for the stimulated radiation produced by energy exchanged between energetic electrons and waves by Doppler-shifted cyclotron resonance, and feedback between the stimulated radiation and the phase bunched currents is incorporated in terms of a two-port discrete time model. The resulting model is capable of explaining the observed temporal growth and saturation effects, phase advance, retardation or frequency shift during growth in the context of a single parameter depending on the energetic particle distribution function, as well as pretermination triggering.

Helliwell, R. A.↗
NASA NTRS1983

Identification of radio emission from the Io flux tube

The identification of a specific Jovian decametric emission with the particular flux tube near the orbit of Io giving rise to it would substantially improve theoretical understandings of the relation of the Io flux tubes with the arc-like structures seen on time vs. frequency plots of decametric emissions observed by the Voyager spacecraft. The present paper shows how the instantaneous Io flux tube may be identified with particular emission features. It is demonstrated that the emissions designated Io caused emission (ICE) may be interpreted as representing sections of arc structures emitted by the interaction of Io with successive flux tubes. The model is capable of accounting for the change of displacement angle of the ICE structures as the sub-observed Jovian longitude changes. The identification permits the mapping of emissions onto the causative flux tubes for Jovian longitudes from 240 to 360 deg.

Riddle, A. C.↗
NASA NTRS1983

Infrared photometry of O stars

The results of a survey of 50 O stars in the J, H, K, L, and M bands are described. The observations are described, and the fitting of reddening relations to them is discussed. The zero points in the reddening relations are related to the intrinsic colors of the samples of normal stars, and these are compared with theoretical colors. The comparison reveals anomalies at L and M, which are discussed. The residuals for an individual star from the reddening relations are a measure of its infrared excesses, if indeed it has any. How the excesses can be fitted to a stellar wind model to derive a parameter that involves the rate of mass loss in the wind, the stellar radius and temperature, and wind terminal velocity is considered. The results for a number of individual stars are discussed and compared with other mass loss measurements, and it is concluded that no single model is capable of reconciling the IR, UV, radio, and H-alpha observations for the stars.

Castor, J. I.↗
NASA NTRS1984

Aeroelastic effects in multi-rotor vehicles with application to a hybrid heavy lift system. Part 1: Formulation of equations of motion

This report presents a set of governing coupled differential equations for a model of a hybrid aircraft. The model consists of multiple rotor systems connected by an elastic interconnecting structure, with options to add any combination of or all of the following components; i.e., thrusters, a buoyant hull, and an underslung weight. The dynamic equations are written for the individual blade with hub motions, for the rigid body motions of the whole model, and also for the flexible modes of the interconnecting structure. One of the purposes of this study is to serve as the basis of a numerical study aimed at determining the aeroelastic stability and structural response characteristics of a Hybrid Heavy Lift Airship (HHLA). It is also expected that the formulation may be applicable to analyzing stability and responses of dual rotor helicopters such as a Heavy Lift Helicopter (HLH). Futhermore, the model is capable of representing coupled rotor/body aeromechanical problems of single rotor helicopters.

Venkatesan, C.↗
NASA NTRS1984

Finite Element Prediction of Acoustic Scattering and Radiation from Submerged Elastic Structures

A finite element formulation is derived for the scattering and radiation of acoustic waves from submerged elastic structures. The formulation uses as fundamental unknowns the displacement in the structure and a velocity potential in the field. Symmetric coefficient matrices result. The outer boundary of the fluid region is terminated with an approximate local wave-absorbing boundary condition which assumes that outgoing waves are locally planar. The finite element model is capable of predicting only the near-field acoustic pressures. Far-field sound pressure levels may be determined by integrating the surface pressures and velocities over the wet boundary of the structure using the Helmholtz integral. Comparison of finite element results with analytic results show excellent agreement. The coupled fluid-structure problem may be solved with general purpose finite element codes by using an analogy between the equations of elasticity and the wave equation of linear acoustics.

Everstine, G. C.↗