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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The line-locking hypothesis, absorption by intervening galaxies, and the z = 1.95 peak in redshifts

The controversy over whether the absorption spectrum in QSOs is intrinsic or extrinsic is approached with attention to the peak of redshifts at z = 1.95. Also considered are the line-locking and the intervening galaxy hypotheses. The line locking hypothesis is based on observations that certain ratios found in absorption line QSOs are preferred, and leads inevitably to the conclusion that the absorption line systems are intrinsic. The intervening galaxy hypothesis is based on absorption redshifts resulting from given absorption cross-sections of galactic clusters and the intergalactic medium, and would lead to the theoretical conclusion that most QSOs show strong absorption, a conclusion which is not supported by empirical data. The 1.95 peak, on the other hand, is most probably an intrinsic property of QSOs. The peak is enhanced by redshift, and it is noted that both an emission and an absorption redshift peak are seen at 1.95.

Burbidge, G.↗
NASA NTRS1978

Observations of a double-layer in a hot-cathode discharge

The meniscus region of a hot cathode discharge was selected for an analysis of the nonlinear interaction of a convectively amplifying wave with a background plasma. A potential step, resulting from rectification of the wave fields is observed, and it is noted that predicted values for the step are in good agreement with empirical data. Attention is given to the determination of plasma parameters (using a Langmuir probe placed in front of the cathode) in terms of their relation to the pondermotive force.

Levine, J. S.↗
NASA NTRS1978

Methods used for Space Shuttle SRB thrust shape design

Optimization of the Space Shuttle trajectory is discussed with reference to the low acceleration profile required for Shuttle missions. Static tests of the nominal flight curve are described in terms of impulse requirements, vacuum thrust, and burn time. Attention is given to BARF (Burning Anomaly Rate Factor), and it is noted that mandrel fabrication is intended to include the flexibility to counter BARF, should it occur. Test results are presented in which both BARF and specific impulse are considered as independent variables. It was found that no erosive burning occurred, BARF did not occur, specific impulse was on the order of 265 sec, and flow anomalies in the star region produced head-to-aft stagnation pressure drops in excess of theoretical predictions. In other areas, good agreement is noted between theoretical prediction and empirical data.

Baker, J.↗
NASA NTRS1979

Time optimal control of a jet engine using a quasi-Hermite interpolation model

This work made preliminary efforts to generate nonlinear numerical models of a two-spooled turbofan jet engine, and subject these models to a known method of generating global, nonlinear, time optimal control laws. The models were derived numerically, directly from empirical data, as a first step in developing an automatic modelling procedure.

Comiskey, J. G.↗
NASA NTRS1979

Analytical core loss calculations for magnetic materials used in high frequency high power converter applications

The basic magnetic properties under various operating conditions encountered in the state-of-the-art DC-AC/DC converters are examined. Using a novel core excitation circuit, the basic B-H and loss characteristics of various core materials may be observed as a function of circuit configuration, frequency of operation, input voltage, and pulse-width modulation conditions. From this empirical data, a mathematical loss characteristics equation is developed to analytically predict the specific core loss of several magnetic materials under various waveform excitation conditions.

Triner, J. E.↗
NASA NTRS1979

NASA overview

The history of NASA efforts at Ames Research Center in researching the performance and application of thrusting augmentors is reviewed. Current objectives include: (1) parametric description of thrust augmentor application to STOL and V/STOL; (2) the use of theoretical and empirical data; (3) aircraft-augmentor integration; and (4) key design considerations for STOL transport and V/STOL fighter aircraft. Test facilities are described and ejector development and performance are assessed.

Koenig, D. G.↗
NASA NTRS1980

Detonation-flame arrester devices for gasoline cargo vapor recovery systems

Empirical data on the deflagration-to-detonation run-up distance for flowing mixtures of gasoline and air in 15.2-cm- (6.0-in.-) diameter piping simulating a vapor recovery system are presented. The quenching capability of eight selected flame control devices subjected to repeated stable detonations was evaluated. The successful detonation-flame arresters were: (1) spiral-wound, crimped aluminum ribbon, (2) foamed nickel-chrome metal, (3) vertically packed bed of aluminum Ballast rings, and (4) water-trap or hydraulic back-pressure valve. Installation configurations for two of the more applicable arresters, the spiral-wound, crimped stainless-steel ribbon and the vertically packed bed of aluminum Ballast rings, were further optimized by a series of parametric tests. The final configuration of these two arresters was demonstrated with repeated detonation tests at conditions that simulated vapor recovery system operation. On these tests, the combustible mixture of gasoline and air continued to flow through the piping for periods up to 120 seconds after the initial detonation had been arrested. There was no indication of continuous burning or reignition occurring on either side of the test arresters.

Bjorklund, R. A.↗
NASA NTRS1980

Analysis and calculation of macrosegregation in a casting ingot. MPS solidification model. Volume 1: Formulation and analysis

The physical and numerical formulation of a model for the horizontal solidification of a binary alloy is described. It can be applied in an ingot. The major purpose of the model is to calculate macrosegregation in a casting ingot which results from flow of interdendritic liquid during solidification. The flow, driven by solidification contractions and by gravity acting on density gradients in the interdendritic liquid, was modeled as flow through a porous medium. The symbols used are defined. The physical formulation of the problem leading to a set of equations which can be used to obtain: (1) the pressure field; (2) the velocity field: (3) mass flow and (4) solute flow in the solid plus liquid zone during solidification is presented. With these established, the model calculates macrosegregation after solidification is complete. The numerical techniques used to obtain solution on a computational grid are presented. Results, evaluation of the results, and recommendations for future development of the model are given. The macrosegregation and flow field predictions for tin-lead, aluminum-copper, and tin-bismuth alloys are included as well as comparisons of some of the predictions with published predictions or with empirical data.

Maples, A. L.↗
NASA NTRS1981

Two-dimensional analytical model of twin jet shielding

Estimation of the impact of jet noise requires analytical modeling not only of the noise source mechanism, but also of the propagation of noise from the source to receiver. One factor which influences the jet noise path is shielding of one jet by another in a twin jet configuration. An analytical model is developed to investigate the shielding phenomenon. The two-dimensional wave equation is solved for a stationary line source impinging upon a cylinder of heated flow. The solution estimates the diffraction and scattering of the incident sound wave by the shielding jet in a plane normal to the jet axis. The frequency dependence of the normalized sound pressure estimated by the model is found to agree in form with empirical data. The azimuthal redistribution of the incident sound shows that, as the frequency of maximum shielding is approached, the scattered sound becomes more highly concentrated into lobes adjacent to the shielding zone.

Gerhold, C. H.↗
NASA NTRS1981

The technical report as an effective medium for information transmittal

The NASA technical report is evaluated to determine its effectiveness as a medium for information transmittal. Empirical data was compiled through a survey of report producers and through an assessment of report components, format, and organization found in current style manuals. It was found that little documented research exists to support or suggest criteria for assessing the effectiveness of a technical report. The survey showed that wide variances in the technical report exist: ninety-nine report producers generated ninety-eight different structural components, only five of which were used by 50% or more of the respondents. Moreover, 33% of the respondents claimed to use no style manual at all. Future research is planned to assess the adequacy of a reduced set of report components, clearly defining the purpose and evaluating the criteria for each component.

Stohrer, F. F.↗
NASA NTRS1983

Semiempirical Estimate of Aircraft Wing Weight

Computational method estimates weight of aircraft wings from theoretical relationships and empirical data. Permits comparison of alternative materials, methods of construction, and design philosophies. Method used to make tradeoffs in preliminary design phases on basis of simple input data and for more accurate calculations in later phases when more data are available.

York, P.↗
NASA NTRS1981

Measurement of fault latency in a digital avionic miniprocessor

The results of fault injection experiments utilizing a gate-level emulation of the central processor unit of the Bendix BDX-930 digital computer are presented. The failure detection coverage of comparison-monitoring and a typical avionics CPU self-test program was determined. The specific tasks and experiments included: (1) inject randomly selected gate-level and pin-level faults and emulate six software programs using comparison-monitoring to detect the faults; (2) based upon the derived empirical data develop and validate a model of fault latency that will forecast a software program's detecting ability; (3) given a typical avionics self-test program, inject randomly selected faults at both the gate-level and pin-level and determine the proportion of faults detected; (4) determine why faults were undetected; (5) recommend how the emulation can be extended to multiprocessor systems such as SIFT; and (6) determine the proportion of faults detected by a uniprocessor BIT (built-in-test) irrespective of self-test.

Mcgough, J. G.↗
NASA NTRS1982

The modeling and prediction of multiple jet VTOL aircraft flow fields in ground effect

An engineering methodology based on an empirical data base and analytical fluid dynamic models was developed for the prediction of propulsive lift system induced aerodynamic effects for multiple lift jet VTOL aircraft operating in the hover mode in and out of ground effect. The effects of aircraft geometry, aircraft orientation (pitch, roll) as well as height above ground are considered. Lift jet vector and splay directions fit the airframe, lift jet exit flow conditions, and both axisymmetric and rectangular nozzle exit geometry are also accommodated. The induced suckdown flows are computed from the potential flowfield induced by the turbulent entrainment of both the free jets and wall jets in ground effect and from the free jets alone out of ground effect. The methodology emphasized geometric considerations, computation of stagnation lines and fountain upwash inclination, fountain upwash formation and development, and fountain impingement on the airframe.

Kotansky, D. R.↗
NASA NTRS1981

Geological and geothermal investigations for HCMM-derived data

An attempt was made to match HCMM- and U2HCMR-derived temperature data over two test sites of very local size to similar data collected in the field at nearly the same times. Results indicate that HCMM investigations using resolutions cells of 500 m or so are best conducted with areally-extensive sites, rather than point observations. The excellent quality day-VIS imagery is particularly useful for lineament studies, as is the DELTA-T imagery. Attempts to register the ground observed temperatures (even for 0.5 sq mile targets) were unsuccessful due to excessive pixel-to-pixel noise on the HCMM data. Several computer models were explored and related to thermal parameter value changes with observed data. Unless quite complex models, with many parameters which can be observed (perhaps not even measured (perhaps not even measured) only under remote sensing conditions (e.g., roughness, wind shear, etc) are used, the model outputs do not match the observed data. Empirical relationship may be most readily studied.

Lyon, R. J. P.↗
NASA NTRS1982

A review of depolarization modeling for earth-space radio paths at frequencies above 10 GHz

A review is presented of models for the depolarization, caused by scattering from raindrops and ice crystals, that limits the performance of dual-polarized satellite communication systems at frequencies above 10 GHz. The physical mechanisms of depolarization as well as theoretical formulations and empirical data are examined. Three theoretical models, the transmission, attenuation-derived, and scaling models, are described and their relative merits are considered.

Bostian, C. W.↗
NASA NTRS1982

Advances in core loss calculations for magnetic materials

A new analytical technique which predicts the basic magnetic properties under various operating conditions encountered in state-of-the-art dc-ac/dc converters is discussed. Using a new flux-controlled core excitation circuit, magnetic core characteristics were developed for constant values of ramp flux (square wave voltage excitation) and frequency. From this empirical data, a mathematical loss characteristics equation is developed to analytically predict the specific core loss of several magnetic materials under various waveform excitation conditions. In addition, these characteristics show the circuit designer for the first time the direct functional relatonships between induction level and specific core loss as a function of the two key dc-dc converter operating parameters of input voltage and duty cycle.

Triner, J. E.↗
NASA NTRS1983

Simulation of a weather radar display for over-water airborne radar approaches

Airborne radar approach (ARA) concepts are being investigated as a part of NASA's Rotorcraft All-Weather Operations Research Program on advanced guidance and navigation methods. This research is being conducted using both piloted simulations and flight test evaluations. For the piloted simulations, a mathematical model of the airborne radar was developed for over-water ARAs to offshore platforms. This simulated flight scenario requires radar simulation of point targets, such as oil rigs and ships, distributed sea clutter, and transponder beacon replies. Radar theory, weather radar characteristics, and empirical data derived from in-flight radar photographs are combined to model a civil weather/mapping radar typical of those used in offshore rotorcraft operations. The resulting radar simulation is realistic and provides the needed simulation capability for ongoing ARA research.

Clary, G. R.↗
NASA NTRS1983

Cyclic oxidation of superalloys

The development of mathematical/computer models of cyclic oxidation in high-temperature alloys is described. The acceleration of oxidation attack caused by the spalling of protective oxide scales is discussed. The COREST paralinear model based on empirical data, designed by Barrett and Pressler, is found to be of limited value. Basic research on the spalling process in different alloy systems is reviewed, and the phenomenon is characterized: occurring mainly within the oxide, it is caused by the different thermal expansion coefficients of oxide and metal and is a linear function of the total retained oxide. This information has been used in the development of the discrete oxide-spall model COSP and in its modification by addition of a diffusion-zone-profile model to predict the failure of components (Heckel and Nesbitt, unpublished). The COSP model is shown to produce good predictions of cyclic oxidation under a variety of conditions, using data from simple isothermic tests.

Lowell, C. E.↗