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At least 1,171 records · Page 65

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NASA NTRS1984

A comparison of flow rates and pressure profiles for N-sequential inlets and three related seal configurations

Experimental and analytical results are presented for choked flows of fluid nitrogen over a range of reduced inlet stagnation temperatures (from 0.67 to ambient) and reduced inlet stagnation pressures to 2. Flow rate and pressure profile comparisons are made between N aligned sequential orifice inlets, a 33-tooth labyrinth seal, a 3-step seal, a cylindrical seal and the classic venturi. Seal effectiveness appears strongly dependent on upstream losses and geometry configuration.

Hendricks, R. C.↗

NASA NTRS1985

IUE and optical spectral scans of U Sagittae - An analysis and comparison with U Cephei

Recent optical and ultraviolet observations of U Sge are presented, and the results are compared with observations of U Cephei. The observations were carried out with: the International Ultraviolet Explorer (IUE) satellite; with the ITS scanner of the Lick Observatory; and with a Varo image-tube camera attached to a coude spectrograph. Comparison with data for U Ceph showed that U Sge is of the B7.5 V spectral type with an effective temperature of 12,250 + or 250 K, and a surface gravity of 3.9 + or - 0.1 log g. The secondary component of U Sge appears to be of the G4 III-IV spectral type. The best estimate for the distance of U Sge was 295 + or - 20 pc. Emission lines of the W Serpentis type were found in the IUE spectrum for U Sge. Although the observed fluxes for the lines were low, the powers were half as strong as those observed in U Cep. Selected emission lines of Fe II, Si II, and Si III were also found assuming solar abundances. A complete summary of the IUE and optical data is provided in a series of graphs and tables.

Dobias, J. J.↗

NASA NTRS1985

A comparison of precipitating electron energy flux on March 22, 1979 with an empirical model - CDAW 6

Data recorded by Defense Meteorological Satellite Program, Tiros and P-78-1 satellites for the CDAW 6 event on March 22, 1979, have been compared with a statistical model of precipitating electron fluxes. Comparisons have been made on both an orbit-by-orbit basis and on a global basis by sorting and binning the data by AE index, invariant latitude, and magnetic local time in a manner similar to which the model was generated. It is concluded that the model flux agrees with the data to within a factor of two, although small features and the exact locations of features are not consistently reproduced. In addition, the latitude of highest electron precipitation usually occurs about 3 deg more poleward in the model than in the data. This discrepancy is attributed to ring current inflation of the storm time magnetosphere.

Simons, S. L., Jr.↗

NASA NTRS1985

Satellite-derived sea surface temperature - Workshop comparisons

A series of three workshops was held between January 1983 and February 1984 to assess the current status of global sea surface temperature (SST) measurement from space. Workshop participants included sensor scientists, radiative transfer specialists, and users of SST data in the disciplines of oceanography and climate. Data from four satellite sensors (three infrared and one microwave) were evaluated by direct comparison with each other and with data from ships, XBTs, and buoys. The satellite data showed good agreement in a global rms sense (about 0.5-1.0 C), but several anomalous regional biases were also observed. The nature of these biases and techniques for their removal require further study.

Njoku, E. G.↗

NASA NTRS1985

Comparison of horizontal winds from the LIMS satellite instrument with rocket measurements

Statistical results are given for a comparison between horizontal geostrophic winds computed from satellite height data and all available in situ rocket wind soundings during a 7-month period. The satellite data are the daily mapped fields from the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument, which extend from 100 to 0.1 mbar. Results indicate that in both the tropics and the extratropical Northern Hemisphere, the average zonal and meridional wind speeds agree to within 2-4 m/s throughout the stratosphere. The rms differences are much larger, with values of 5-10 m/s in the lower stratosphere, increasing to 20-40 m/s in the lower mesosphere. Time series show that LIMS and rocketsonde zonal wind speeds show coherent variations with temporal periods of 1-2 weeks and more, and both exhibit irregular variations on time scales of less than one week.

Smith, A. K.↗

NASA NTRS1984

Comparison of noise prediction for the X-wing system and a conventional rotor in hover

Analytic predictions of X-wing rotor noise levels in hover without circulation control are presented and compared with measured data at two observer locations. Agreement of predictions and data is best in the rotor plane, due to the dominance of thickness noise terms. Predictions are made for the X-wing and a conventional type rotor system and are compared at two locations at the same tip speed and at each rotor's design tip speed. The acoustic signal of the X-wing is more heavily influenced by thickness noise terms than the conventional rotor. The comparison of each rotor's noise levels depends on the observer location and the amount of circulation control blowing employed.

Martin, R. M.↗

NASA NTRS1985

Cost comparisons of solar power satellites versus lunar based power systems

A comparison is made between projected electricity costs of an optimized space solar power station (SPS) in GEO and a moon-based SPS (LPS). A single SPS would receive sunlight on an almost uninterruptible basis. The LPS would be illumined 50 percent of the time, thus requiring two stations on opposite sides of the moon as well as three terrestrial rectennas spaced 120 deg apart. The 5 percent efficient LPS cells would be manufactured from lunar materials and built into arrays mounted on tall mounds. The steerable GEO SPS would have 15 percent efficient cells. Construction costs would be significantly lower on the moon, but the total antenna area would need to be two orders of magnitude larger to produce the same output as the SPS. It is estimated that the LPS would therefore deliver 5 GW electricity to earth stations at a cost of 511.3 mills/kW, compared to 46.8 mills/kW from the SPS. It is concluded that lunar materials are suitable for building an SPS, not a LPS.

Kerwin, E. M.↗

NASA NTRS1985

Numerical simulation and comparison with experiment for self-excited oscillations in a diffuser flow

This paper describes numerical simulations of self-excited oscillations in a two-dimensional transonic diffuser flow obtained by solving the Navier-Stokes equations with a two-equation turbulence model. Comparisons were made between the computational results and experimental data. For the mean flowfields, the agreement between computation and experiment is good for the wall pressures, shock location, and the separation and reattachment points. However, the thickness of the computed recirculation zone is about 50 percent of the measured thickness. For the fluctuating flowfields, a great deal of qualitative similarity exists between the computation and experiment; however, the predicted oscillation frequency is about 50 percent higher than the measured value. The formation of a succession of downstream-traveling counter-rotating vortices, as seen experimentally, is also vividly displayed in the numerical results.

Hsieh, T.↗

NASA NTRS1985

A comparison of SAGE I data during the stratospheric warming of February-March, 1979

The fine scale vertical structure of SAGE I ozone and aerosol data during a stratospheric warming is investigated using meteorological and SBUV ozone data. By stratifying the ozone and aerosol data for a limited time period, a comparison of the structure of profiles becomes possible under different meteorological conditions. For example, the cold air region shows more laminated structures than the other regions. In addition, vertical motions calculated at the same locations as the SAGE profiles show that they are consistent with variances found in the ozone and aerosol data.

Nagatani, R. M.↗

NASA NTRS1985

Comparison of band model calculations of upper atmospheric cooling rates for the 15-micrometer carbon dioxide band

Within the atmosphere of the earth, absorption and emission of thermal radiation by the 15-micron CO2 bands are the largest contributors to infrared cooling rates in the stratosphere. Various techniques for calculating cooling rates due to these bands have been described. These techniques can be classified into one of two categories, including 'exact' or line-by-line calculations and other methods. The latter methods are based on broad band emissivity and band absorptance formulations. The present paper has the objective to present comparisons of the considered computational approaches. It was found that the best agreement with the exact line-by-line calculations of Fels and Schwarzkopf (1981) could be obtained by making use of a new Doppler band model which is described in the appendix of the paper.

Boughner, R. E.↗

NASA NTRS1984

A 37.5-kW point design comparison of the nickel-cadmium battery, bipolar nickel-hydrogen battery, and regenerative hydrogen-oxygen fuel cell energy storage subsystems for low earth orbit

Nickel-cadmium batteries, bipolar nickel-hydrogen batteries, and regenerative fuel cell storage subsystems were evaluated for use as the storage subsystem in a 37.5 kW power system for Space Station. Design requirements were set in order to establish a common baseline for comparison purposes. The storage subsystems were compared on the basis of effective energy density, round trip electrical efficiency, total subsystem weight and volume, and life.

Manzo, M. A.↗

NASA NTRS1984

Laser and solar-photovoltaic space power systems comparison. II.

A comparison of total system cost is made between solar photovoltaic and laser/receiver systems. The laser systems assume either a solar-pumped CO2 blackbody transfer laser with MHD receiver or a solar pumped liquid neodymium laser with a photovoltaic receiver. Total system costs are less for the laser systems below 300 km where drag is significant. System costs are highly dependent on altitude.

De Young, R. J.↗

NASA NTRS1985

Experimental aerodynamic coefficients on a Shuttle-like vehicle at Mach 6 and 10 and comparison to prediction

Aerodynamic coefficients measured for an Orbiter-like configuration are presented for a range of angle of attack from 15 deg to 45 deg at Mach 6 and 10. The low-gamma aspect of a real gas on aerodynamic characteristics and shock detachment distance were simulated by testing this configuration in Mach 6 air (freestream gamma equal to 1.4) and Mach 6 CF4 (freestream gamma equal to 1.17). The effects of Mach number, Reynolds number, and gamma on these measurements are examined and comparisons made to an inviscid flowfield computer code known as HALIS. Pitching-moment coefficients measured in CF4 revealed a nose-up increment when compared with measurements in perfect air, indicative of real-gas effects. In general, the HALIS code accurately predicted the measured aerodynamic coefficients in air and CF4.

Micol, J. R.↗

NASA NTRS1985

A comparison between active and passive sensing of soil moisture from vegetated terrains

A comparison between active and passive sensing of soil moisture over vegetated areas is studied via scattering models. In active sensing three contributing terms to radar backscattering can be identified: (1) the ground surface scatter term; (2) the volume scatter term representing scattering from the vegetation layer; and (3) the surface volume scatter term accounting for scattering from both surface and volume. In emission three sources of contribution can also be identified: (1) surface emission; (2) upward volume emission from the vegetation layer; and (3) downward volume emission scattered upward by the ground surface. As ground moisture increases, terms (1) and (3) increase due to increase in permittivity in the active case. However, in passive sensing, term (1) decreases but term (3) increases for the same reason. This self compensating effect produces a loss in sensitivity to change in ground moisture. Furthermore, emission from vegetation may be larger than that from the ground. Hence, the presence of vegetation layer causes a much greater loss of sensitivity to passive than active sensing of soil moisture.

Fung, A. K.↗

NASA NTRS1985

Comparison of mesospheric ozone measurements using the LRIR and UVMCS satellite instruments

A comparison between mesospheric ozone profiles determined by two radically different satellite-borne instruments is presented for the period of July to November, 1975. The Limb Radiance Inversion Radiometer measured 9.6-micron O3 emission, while the Ultraviolet Multiple Channel Spectrometer measured the atmospheric attenuation of solar ultraviolet radiation during passage of the OSO-8 satellite across the terminator. Only nine near coincident measurements were found. The individual instruments have estimated precision errors of + or - 10 to 15 percent. Agreement between ozone values as measured by the two techniques for specific cases varies between 10 and 20 percent. The statistical correlation is positive and significant at all altitudes where both instruments had reasonable signal-to-noise ratio. A maximum correlation of 0.76 occurred at 0.3 mb (about 59 km).

Millier, F.↗

NASA NTRS1986

Economic Comparison of Processes Using Spreadsheet Programs

Inexpensive approach aids plant-design decisions. Commercially available electronic spreadsheet programs aid economic comparison of different processes for producing particular end products. Facilitates plantdesign decisions without requiring large expenditures for powerful mainframe computers.

Ferrall, J. F.↗

NASA NTRS1985

Photographic catalog of selected planetary size comparisons

Photographs taken by NASA spacecraft, and cartographic products based on these photos, are used to illustrate size comparisons of the planets and moons of the solar system. Global views and prominent geographical features are depicted at the same scale, allowing size relationships to be studied visually.

Meszaros, S. P.↗

NASA NTRS1985

A comparison of measured and calculated thermal stresses in a hybrid metal matrix composite spar cap element

A hybrid spar of titanium with an integrally brazed composite, consisting of an aluminum matrix reinforced with boron-carbide-coated fibers, was heated in an oven and the resulting thermal stresses were measured. Uniform heating of the spar in an oven resulted in thermal stresses arising from the effects of dissimilar materials and anisotropy of the metal matrix composite. Thermal stresses were calculated from a finite element structural model using anisotropic material properties deduced from constituent properties and rules of mixtures. Comparisons of calculated thermal stresses with measured thermal stresses on the spar are presented. It was shown that failure to account for anisotropy in the metal matrix composite elements would result in large errors in correlating measured and calculated thermal stresses. It was concluded that very strong material characterization efforts are required to predict accurate thermal stresses in anisotropic composite structures.

Jenkins, J. M.↗