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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The Strength and Characteristics of VPPA Welded 2219-T87 Aluminum Alloy

A study of the variable polarity plasma arc (VPPA) welding process and those factors that control the structure and properties of VPPA welded aluminum alloy 2219-T87 was conducted. The importance of joint preparation, alignment of parts and welding process variables are already established. Internal weld defects have been eliminated. However, a variation of properties was found to be due to the size variation of interdendritic particles in the fusion zone. These particles contribute to the void formation process, which controls the ultimate tensile strength of the welded alloy. A variation of 150 microns in particle size correlated with a 10 ksi variation of ultimate tensile strength. It was found that all fracture surfaces were of the dimple rupture type, with fracture initiating within the fusion zone.

Jemian, W. A.↗
NASA NTRS1985

Energy Sources of the Dominant Frequency Dependent 3-dimensional Atmospheric Modes

The energy sources and sinks associated with the zonally asymmetric winter mean flow are investigated as part of an on-going study of atmospheric variability. Distinctly different horizontal structures for the long, intermediate and short time scale atmospheric variations were noted. In previous observations, the 3-dimensional structure of the fluctuations is investigated and the relative roles of barotropic and baroclinic terms are assessed.

Schubert, S.↗
NASA NTRS1985

The solar spectral irradiance between 150 and 200 nm

The absorption of solar photons controls the composition of the middle atmosphere. Concern about the effects of man's industrial activities on his environment has led to a number of long-term programs related to stratospheric photochemistry. An important part of these programs represents studies of the variability of the sun's solar spectral irradiance. A program to measure the solar ultraviolet flux, both within and outside the earth's atmosphere, has been in progress for a number of years. This program has the objective to develop techniques which would provide an absolute accuracy of at least 5 percent. The amount of satellite instrument degradation is determined on the basis of a comparison of data provided by these instruments with data obtained in connection with rocket flights. It was found that a significant decrease in the solar irradiance below 190 nm occurred between 1980 and 1981.

Mentall, J. E.↗
NASA NTRS1985

Sea surface temperature from satellites: The impact of FGGE

Spacecraft instruments first launched at the beginning of the FGGE year are now producing sea surface temperature data accurate to about 1 C. At larger scales, the errors are dominated by systematic effects, some of which are instrumental, but most are geophysical, i.e., correlated with volcanic aerosols, atmospheric water vapor, clouds, and surface wind. Progress is being made to identify and eliminate such errors and thereby provide sea surface temperature data on a global basis consistently accurate to 0.5 C, which will be needed for studies of climate variability.

Bernstein, R. L.↗
NASA NTRS1986

Predicting earth's dynamic changes

Given a suitable strategy for conducting measurements, satellite-based remote sensing of the earth can furnish valuable information on the dynamic changes of such planetary characteristics as ocean surface temperatures and atmospheric CO2. Observations must be global and synoptic, quantitatively validated, and consistent over the long term. A program spanning 20 years will study such critical variables as solar flux, stratospheric temperature, aerosols and ozone, cloud cover, tropospheric gases and aerosols, radiation balance, surface temperature, albedo, precipitation, vegetation cover, moisture, snow and ice, as well as oceanic color, topography, and wind stress.

Rasool, S. I.↗
NASA NTRS1986

The effects of gravity level during directional solidification on the microstructure of hypermonotectic Al-In-Sn alloys

Five hypermonotectic Al-In-Sn compositions were directionally solidified in a Bridgman-type furnace at normal gravity and during aircraft low-gravity maneuvers. The tendency of the Al-30In alloy to form an indium-rich band at the start of unidirectional growth (SUG) made it difficult to study the integration of L sub 2 into the solidification interface. Hypermonotectic compositions closer to monotectic slightly hypermonotectic caused only a partial band on L sub 2 to form at SUG and allowed the study of such variables as gravity, composition, and monotectic dome height on integration of excess L sub 2 into the solid plus L sub 2 interface. It was found that formation of aligned composite structures for the Al-In-Sn system is not only a function of G and R but also of the degree to which the composition varies from monotectic. Most of the aligned fibrous structures formed from hypermonotectic Al-In-Sn had spacings that were of the order of irregular fibrous structures reported for on monotectic Al-In-Sn. The spacings for the large fibers and aligned globules found for ground and low-gravity processed Al-In-18-Sn-22, respectively, were significantly larger than the others measured and were of the order expected for cell spacings under the growth conditions utilized. It was found that the integration into the solidification front of excess L sub 2 in low gravity was a function of the Sn composition of the alloy.

Curreri, P. A.↗
NASA NTRS1988

Sensitivity study of the monogroove with screen heat pipe design

The present sensitivity study of design variable effects on the performance of a monogroove-with-screen heat pipe obtains performance curves for maximum heat-transfer rates vs. operating temperatures by means of a computer code; performance projections for both 1-g and zero-g conditions are obtainable. The variables in question were liquid and vapor channel design, wall groove design, and the number of feed lines in the evaporator and condenser. The effect on performance of three different working fluids, namely ammonia, methanol, and water, were also determined. Greatest sensitivity was to changes in liquid and vapor channel diameters.

Evans, Austin L.↗
NASA NTRS1989

The art of spacecraft design: A multidisciplinary challenge

Actual design turn-around time has become shorter due to the use of optimization techniques which have been introduced into the design process. It seems that what, how and when to use these optimization techniques may be the key factor for future aircraft engineering operations. Another important aspect of this technique is that complex physical phenomena can be modeled by a simple mathematical equation. The new powerful multilevel methodology reduces time-consuming analysis significantly while maintaining the coupling effects. This simultaneous analysis method stems from the implicit function theorem and system sensitivity derivatives of input variables. Use of the Taylor's series expansion and finite differencing technique for sensitivity derivatives in each discipline makes this approach unique for screening dominant variables from nondominant variables. In this study, the current Computational Fluid Dynamics (CFD) aerodynamic and sensitivity derivative/optimization techniques are applied for a simple cone-type forebody of a high-speed vehicle configuration to understand basic aerodynamic/structure interaction in a hypersonic flight condition.

Abdi, F.↗
NASA NTRS1989

A ten-year monthly data set of outgoing longwave radiation from Nimbus-6 and Nimbus-7 satellites

Monthly mean outgoing longwave radiation (OLR) measurements in the form of global contour maps and coefficients of spherical-harmonic functions for each month of the 10-year period, July 1975 through October 1985, have recently been completed. One data set contains three years (July 1975 to June 1978) of 'continuous' data from the wide field-of-view sensor of the Earth Radiation Budget experiment (ERB) aboard the Nimbus-6 satellite. The other data set contains seven years (November 1978 to October 1985) of 'continuous' data from the ERB experiment aboard the Nimbus-7 satellite. The OLR broadband time series could be used, for example, to study the interannual variability of OLR. An example is given of two El Ninos that occurred in the 10-year timeframe.

Bess, T. Dale↗
NASA NTRS1990

The CFL condition for spectral approximations to hyperbolic initial-boundary value problems

The stability of spectral approximations to scalar hyperbolic initial-boundary value problems with variable coefficients are studied. Time is discretized by explicit multi-level or Runge-Kutta methods of order less than or equal to 3 (forward Euler time differencing is included), and spatial discretizations are studied by spectral and pseudospectral approximations associated with the general family of Jacobi polynomials. It is proved that these fully explicit spectral approximations are stable provided their time-step, delta t, is restricted by the CFL-like condition, delta t less than Const. N(exp-2), where N equals the spatial number of degrees of freedom. We give two independent proofs of this result, depending on two different choices of approximate L(exp 2)-weighted norms. In both approaches, the proofs hinge on a certain inverse inequality interesting for its own sake. The result confirms the commonly held belief that the above CFL stability restriction, which is extensively used in practical implementations, guarantees the stability (and hence the convergence) of fully-explicit spectral approximations in the nonperiodic case.

Gottlieb, David↗
NASA NTRS1989

Measurement of strains at high temperatures by means of a portable holographic moire camera

Electronic holographic moire is utilized to measure strains at temperatures up to 1000 C. A CW laser operating at 50 mW and at the wavelength of 632.8 nm is used to illuminate the objects under study. The main variables influencing the fringe patterns visibility are discussed and measurements are performed to obtain the values of these variables in the performed experiments. The coefficient of expansion of an alloy is measured at temperatures ranging from 797 C to 986 C. Excellent agreement is found between the measured values and those provided by the manufacturer.

Sciammarella, C. A.↗
NASA NTRS1991

The CFL condition for spectral approximations to hyperbolic initial-boundary value problems

The stability of spectral approximations to scalar hyperbolic initial-boundary value problems with variable coefficients are studied. Time is discretized by explicit multi-level or Runge-Kutta methods of order less than or equal to 3 (forward Euler time differencing is included), and spatial discretizations are studied by spectral and pseudospectral approximations associated with the general family of Jacobi polynomials. It is proved that these fully explicit spectral approximations are stable provided their time-step, delta t, is restricted by the CFL-like condition, delta t less than Const. N(exp-2), where N equals the spatial number of degrees of freedom. We give two independent proofs of this result, depending on two different choices of approximate L(exp 2)-weighted norms. In both approaches, the proofs hinge on a certain inverse inequality interesting for its own sake. The result confirms the commonly held belief that the above CFL stability restriction, which is extensively used in practical implementations, guarantees the stability (and hence the convergence) of fully-explicit spectral approximations in the nonperiodic case.

Gottlieb, David↗
NASA NTRS1991

Comparison of aerosol extinction profiles from lidar and SAGE II data at a tropical station

Aerosol extinction profiles obtained from lidar data at Trivandrum (8.6 deg N, 77 deg E) are compared with corresponding Stratospheric Aerosol and Gas Experiment II extinction profiles. The agreement between the two is found to be satisfactory. The extinction profiles obtained by both the experiments showed a prominent peak at 23-24 km altitude in the stratosphere. The study revealed large variability in upper tropospheric extinction with location (latitude).

Parameswaran, K.↗
NASA NTRS1991

Results from computational analysis of a mixed compression supersonic inlet

A numerical study was performed to simulate the critical flow through a supersonic inlet. This flowfield has many phenomena such as shock waves, strong viscous effects, turbulent boundary layer development, boundary layer separations and mass flow suction through the walls (bleed). The computational tools used in this study were two full Navier-Stokes (FNS) codes. The supersonic inlet that was analyzed in this study is the Variable Diameter Centerbody (VDC), inlet. This inlet is a candidate concept for the next generation supersonic transport. Application of the code to the inlet geometry involved effort in generating an efficient grid geometry and specifying boundary conditions, particularly in the bleed region and at the outflow boundary. Results for a critical inlet operation compare favorably to Method of Characteristics predictions and experimental data.

Saunders, J. D.↗
NASA NTRS1991

Display format, highlight validity, and highlight method: Their effects on search performance

Display format and highlight validity were shown to affect visual display search performance; however, these studies were conducted on small, artificial displays of alphanumeric stimuli. A study manipulating these variables was conducted using realistic, complex Space Shuttle information displays. A 2x2x3 within-subjects analysis of variance found that search times were faster for items in reformatted displays than for current displays. Responses to valid applications of highlight were significantly faster than responses to non or invalidly highlighted applications. The significant format by highlight validity interaction showed that there was little difference in response time to both current and reformatted displays when the highlight validity was applied; however, under the non or invalid highlight conditions, search times were faster with reformatted displays. A separate within-subject analysis of variance of display format, highlight validity, and several highlight methods did not reveal a main effect of highlight method. In addition, observed display search times were compared to search time predicted by Tullis' Display Analysis Program. Benefits of highlighting and reformatting displays to enhance search and the necessity to consider highlight validity and format characteristics in tandem for predicting search performance are discussed.

Donner, Kimberly A.↗
NASA NTRS1992

Simulation of the 1979 spring bloom in the Mid-Atlantic Bight - A coupled physical/biological/optical model

A coupled physical/biological/optical model is developed for studies of phytoplankton variability in the spring 1979 Mid-Atlantic Bight, as observed by CZCS imagery. The model incorporates advection, mixing, sinking, growth as a function of light, temperature, nutrient availability, and death as a function of ingestion. It produced chlorophyll concentrations within the first attenuated depth within 1 standard deviation of CZCS imagery on large scale. The primary production estimates obtained using this model were within reasonable agreement with those measured in situ.

Gregg, Watson W.↗
NASA NTRS1992

The Composite Infrared Spectrometer

The Composite Infrared Spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. It contains two Fourier transform spectrometers covering wavelengths of 7-1000 microns. The instrument is expected to have higher spectral resolution, smaller field of view, and better signal-to-noise performance than its counterpart, IRIS, on the Voyager missions. These improvements allow the study of the variability of the composition and temperature of the atmospheres of both Saturn and Titan with latitude, longitude and height, as well as allowing the possibility of discovery of previously undetected chemical species in these atmospheres. The long wavelengths accessible to CIRS allow sounding deeper into both atmospheres than was possible with IRIS.

Calcutt, Simon↗
NASA NTRS1992

Analysis of precracking parameters and fracture toughness for ceramic single-edge-precracked-beam specimens

The single-edge-precracked-beam (SEPB) method involves creation of a straight-through crack from an indentation crack. The straight-through crack is developed by applying a controlled bending load to a specimen via a precracking fixture. The fixture induces the following sequence: (1) stable growth of the indentation crack; (2) pop-in; and finally, (3) arrest-thereby forming a straight-through precrack. The effects of indentation load on precracking load as well as precrack size were studied for experimental variables such as specimen width, fixture span, and material. Finite element analysis was used to obtain the stress distribution and stress intensity factor, thus providing a quantitative prediction of the precracking load and precrack size for silicon nitride, alumina, silicon cabide, and two SiC whisker-reinforced silicon nitrides. Fracture toughness values obtained from the SEPB method were compared with those obtained from other methods.

Choi, Sung R.↗