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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 901 records · Page 50
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NASA NTRS1976

Meteorological adjustment of yearly mean values for air pollutant concentration comparison

Using multiple linear regression analysis, models which estimate mean concentrations of Total Suspended Particulate (TSP), sulfur dioxide, and nitrogen dioxide as a function of several meteorologic variables, two rough economic indicators, and a simple trend in time are studied. Meteorologic data were obtained and do not include inversion heights. The goodness of fit of the estimated models is partially reflected by the squared coefficient of multiple correlation which indicates that, at the various sampling stations, the models accounted for about 23 to 47 percent of the total variance of the observed TSP concentrations. If the resulting model equations are used in place of simple overall means of the observed concentrations, there is about a 20 percent improvement in either: (1) predicting mean concentrations for specified meteorological conditions; or (2) adjusting successive yearly averages to allow for comparisons devoid of meteorological effects. An application to source identification is presented using regression coefficients of wind velocity predictor variables.

Sidik, S. M.↗
NASA NTRS1975

Comparison theorems, numerical integration and satellite orbits

A comparison theorem estimating the difference between solutions of a perturbed and unperturbed equation is obtained. This is then applied to obtain error estimates in numerical integration problems, in particular, those problems involving computation of satellite orbits. The main result is a proof of the intuitive notion that the error in numerically integrating a stable equation grows less rapidly than for an unstable equation.

Stokes, A.↗
NASA NTRS1976

Comparison of the San Marco 3 Nace neutral composition data with the extrapolated Ogo 6 empirical model

An investigation is conducted concerning the feasibility to extrapolate the data of the Ogo 6 empirical composition model to altitudes which are lower than 450 km. Extrapolated Ogo 6 model densities are, therefore, compared with data obtained in the Neutral Atmospheric Composition Experiment (Nace) carried out during the time from April to November 1971. The results of the investigation support the conclusions of an earlier comparison of Ogo 6 and Nace data conducted by Newton et al. (1973).

Kasprzak, W. T.↗
NASA NTRS1976

Weight comparisons of optimized stiffened, unstiffened, and sandwich cylindrical shells made from composite or aluminum materials

This work presents optimum designs for unstiffened, hat stringer-stiffened and honeycomb sandwich cylinders under axial compression. Optimization results for graphite-epoxy cylinders show about a 50 percent weight savings over corresponding optimized aluminum cylinders for a wide loading range. The inclusion of minimum gage considerations results in a significant weight penalty, especially for a lightly loaded cylinder. Effects of employing a smeared stiffener buckling theory in the optimization program are investigated through comparison of results obtained from a more accurate branched shell buckling computer code. It was found that the stiffener cross-sectional deformations, which are usually ignored in smeared stiffener theory, result in about a 30 percent lower buckling load for the graphite-epoxy hat stiffened cylinder.

Agarwal, B. L.↗
NASA NTRS1976

Comparisons of measured and theoretical thermospheric daily composition variations

A comparison of the diurnal component of the daily variation in the neutral composition data from the San Marco 3 Nace (Neutral Atmospheric Composition Experiment) mass spectrometer at 220, 250, and 280 km, the OGO-6 model data at 450 km, rocket measurements of nitrogen between 140 and 300 km, and the two-constituent theoretical model of Mayr and Volland (1973) gives good agreement for molecular nitrogen and atomic oxygen. The Nace and rocket measurements overlap in altitude, and there is good agreement in the amplitude and phase of the diurnal and semidiurnal components for molecular nitrogen. The helium diurnal amplitude and phase of the theoretical model are in fair agreement with the Nace results, while the amplitude from the OGO-6 model at 450 km is much larger than the model predicts, a result suggesting that the OGO-6 model diurnal amplitude may be overestimated as the result of an incomplete separation of local-time and seasonal effects.

Kasprzak, W. T.↗
NASA NTRS1975

A cost-effectiveness comparison of existing and Landsat-aided snow water content estimation systems

This study describes how Landsat imagery can be cost-effectively employed to augment an operational hydrologic model. Attention is directed toward the estimation of snow water content, a major predictor variable in the volumetric runoff forecasting model presently used by the California Department of Water Resources. A stratified double sampling scheme is supplemented with qualitative and quantitative analyses of existing operations to develop a comparison between the existing and satellite-aided approaches to snow water content estimation. Results show a decided advantage for the Landsat-aided approach.

Sharp, J. M.↗
NASA NTRS1976

A comparison of the computed and experimental three dimensional flow in a transonic compressor rotor

The three dimensional inviscid flow in a transonic compressor rotor; total pressure ratio of 1.65, has been numerically computed using MacCormack's time-marching method. This solution is compared to intra-blade static density measurements obtained by gas fluorescence. These results and comparisons illustrate the importance of three dimensional flow phenomena in determining the rotor flow field and show that while the viscous phenomena have an important influence, particularly on the outflow, the inviscid computation properly models the flow in the inlet portion of the rotor passages.

Thompkins, W. T., Jr.↗
NASA NTRS1976

Tests and comparisons of satellite-derived geoids with Skylab altimeter data

During the Skylab 4 mission, the S-193 radar altimeter was operated nearly continuously for a revolution around the world on Jan. 31, 1974. This direct measurement to the sea surface has provided an independent basis for the evaluation of the precision of global geoids computed from satellite-derived earth gravity models. This paper presents comparisons between the Skylab data and several recent gravity models published by Goddard Space Flight Center, the Smithsonian Astrophysical Observatory, and the National Oceanic and Atmospheric Administration. The differences between the altimeter geoid and the satellite geoids were as large as 20 m, rms values ranging from 8 to 10 m. These differences also indicated a systematic long-wavelength variation (about 100 deg) not related to error in the Skylab orbits. Truncation of the models to degree and order 8 did not eliminate the long-wavelength variation, but in every case the rms agreement between the satellite geoids and the altimeter geoid was slightly improved. Orbits computed with the truncated models were found to be inferior to those computed with the complete models.

Marsh, J. G.↗
NASA NTRS1976

Outline and comparison of the possible effects present in a metal-thin-film-insulator-semiconductor solar cell

The advantages possible with the insertion of a thin-film insulating or semi-insulating layer between a metal and a semiconductor to form the MIS photovoltaic device have been presented previously in the literature. This MIS configuration may be considered as a specific example of a more general class of photovoltaic devices: electrode-thin-film-insulator-semiconductor devices. Since the advantages of the configuration were pointed out, there has been considerable experimental interest in these photovoltaic devices. Because the previous analysis showed that the introduction of the insulator layer could produce several different but advantageous effects, this paper presents a further outline giving a comparison of these effects together with their ramifications.

Fonash, S. J.↗
NASA NTRS1976

Comparison of ozone determinations by ultraviolet photometry and gas-phase titration

A comparison of ozone determinations based on ultraviolet absorption photometry and gas-phase titration (GPT) shows good agreement between the two methods. Together with other results, these findings indicate that three candidate reference methods for ozone, UV photometry, IR photometry, and GPT are in substantial agreement. However, the GPT method is not recommended for routine use by air pollution agencies for calibration of ozone monitors because of susceptibility to experimental error.

Demore, W. B.↗
NASA NTRS1976

A comparison of GaAs and Si hybrid solar power systems

An analytical comparison of energy output from various silicon and gallium arsenide hybrid solar power systems, producing electric power and also thermal power for heating or cooling, is made. System performance indices in terms of capital cost, peak power, total power output, and electric power were evaluated. Limiting values for annual energy production from GaAs and Si solar concentrator systems were estimated to be 2 cents and 6.8 cents per kWh for GaAs concentrator systems and between 2.5 cents and 11 cents per kWh for Si concentrator systems.

Heinbockel, J. H.↗
NASA NTRS1976

A model for the pyrolysis of unfilled and filled polymers and comparisons with NBS smoke-density chamber data

This paper considers a model for the pyrolysis of polymers for use in mass loss and smoke density predictions in a fire situation. It is based on the fundamental postulate that the overall rate-limiting reactions are in the relatively low temperature condensed phase; the rate limiting step is the polymer degradation to a vaporizable state. The state of the polymer (chain length) at the surface is specified by the vapor pressure equilibrium criterion. For the case of polymers with inert fillers, like alumina trihydrate, the further assumption is made that the linear regression rate of the material is identical to the unfilled material's at the same surface temperature. The fraction of polymer mass loss converted to smoke is inferred from the literature. The smoke density in the NBS-smoke density chamber is predicted for a polyester and the same polyester with two different loads of alumina trihydrate filler. Diffusional effects in the smoke spreading are considered in an elementary manner. The comparisons with experimental data are encouraging. The overall fire characteristics are predicted using only the fundamental physicochemical property values of ingredients.

Kumar, R. N.↗
NASA NTRS1976

Comparisons of several aerodynamic methods for application to dynamic loads analyses

The results of a study are presented in which the applicability at subsonic speeds of several aerodynamic methods for predicting dynamic gust loads on aircraft, including active control systems, was examined and compared. These aerodynamic methods varied from steady state to an advanced unsteady aerodynamic formulation. Brief descriptions of the structural and aerodynamic representations and of the motion and load equations are presented. Comparisons of numerical results achieved using the various aerodynamic methods are shown in detail. From these results, aerodynamic representations for dynamic gust analyses are identified. It was concluded that several aerodynamic methods are satisfactory for dynamic gust analyses of configurations having either controls fixed or active control systems that primarily affect the low frequency rigid body aircraft response.

Kroll, R. I.↗
NASA NTRS1976

Comparison of the nonlinear dynamic characteristics of Barber S-2 and ASF ride control freight trucks

The results of an experimental and analytical program to define the load deflection characteristics of a Barber S-2 freight truck and to compare these characteristics to those of an ASF freight truck of the same load capacity are presented. The comparison of the two trucks is made on a parameter basis and on the basis of the wheel/rail loads induced by track misalignment. The results indicate there is very little difference in the parameters and the response of the two trucks. This is of course qualified by the assumptions required in the development of the mathematical models.

Abbott, P.↗
NASA NTRS1977

A comparison of a laboratory and field study of annoyance and acceptability of aircraft noise exposures

Residents living in close, middle and distant areas from JFK Airport were included in a field interview and laboratory study. Judgments were made of simulated aircraft noise exposures of comparable community indoor noise levels and mixes of aircraft. Each group of subjects judged the levels of noise typical for its distance area. Four different numbers of flyovers were tested: less than average for each area, the approximate average, the peak number, or worst day, and above peak number. The major findings are: (1) the reported integrated field annoyance is best related to the annoyance reported for the simulated approximate worst day exposure in the laboratory; (2) annoyance is generally less when there are fewer aircraft flyovers, and the subject has less fear of crashes and more favorable attitudes toward airplanes; (3) beliefs in harmful health effects and misfeasance by operators of aircraft are also highly correlated with fear and noise annoyance; (4) in direct retrospective comparisons of number of flights, noise levels and annoyance, subjects more often said the worst day laboratory exposured more like their usual home environments; and (5) subjects do not expect an annoyance-free environment. Half of the subjects can accept an annoyance level of 5 to 6 from a possible annoyance range of 0 to 9, 28% can live with an annoyance intensity of 7, and only 5% can accept the top scores of 8 to 9.

Borsky, P. N.↗
NASA NTRS1977

Comparison of thermal analytic model with experimental test results for 30-sentimeter-diameter engineering model mercury ion thruster

A thermal analytic model for a 30-cm engineering model mercury-ion thruster was developed and calibrated using the experimental test results of tests of a pre-engineering model 30-cm thruster. A series of tests, performed later, simulated a wide range of thermal environments on an operating 30-cm engineering model thruster, which was instrumented to measure the temperature distribution within it. The modified analytic model is described and analytic and experimental results compared for various operating conditions. Based on the comparisons, it is concluded that the analytic model can be used as a preliminary design tool to predict thruster steady-state temperature distributions for stage and mission studies and to define the thermal interface bewteen the thruster and other elements of a spacecraft.

Oglebay, J. C.↗
NASA NTRS1977

Comparison of effects of unsteady lift and spanwise averaging in flight through turbulence

Gust loads on aircraft flying through random atmospheric turbulence are attenuated at high frequencies by the effects of unsteady lift and spanwise averaging. Previously derived theoretical results for these two effects are placed in a form which makes direct comparison possible. The attenuation effects from each cause are found to be of approximately equal magnitude for unswept wings of moderate aspect ratio. For small values of the ratio of wingspan to scale of turbulence, the attenuation due to spanwise averaging is a function only of reduced frequency based on wingspan and is independent of the ratio of wingspan to scale of turbulence.

Phillips, W. H.↗