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  • 1995-1999  (3)
  • 1985-1989  (9)
  • 1
    Publication Date: 1988-07-01
    Print ISSN: 0002-1962
    Electronic ISSN: 1435-0645
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 2
    Publication Date: 1996-01-01
    Print ISSN: 0011-183X
    Electronic ISSN: 1435-0653
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 3
    Publication Date: 1995-05-01
    Print ISSN: 0011-183X
    Electronic ISSN: 1435-0653
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 4
    Publication Date: 2019-06-28
    Description: The sensitivity of the predicted synchrophasing (SP) effectiveness trends to the propeller source model issued is investigated with reference to the development of advanced turboprop engines for transport aircraft. SP effectiveness is shown to be sensitive to the type of source model used. For the virtually rotating dipole source model, the SP effectiveness is sensitive to the direction of rotation at some frequencies but not at others. The SP effectiveness obtained from the virtually rotating dipole model is not very sensitive to the radial location of the source distribution within reasonable limits. Finally, the predicted SP effectiveness is shown to be more sensitive to the details of the source model used for the case of corotation than for the case of counterrotation.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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  • 5
    Publication Date: 2019-06-28
    Description: There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise levels. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significantly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.
    Keywords: ACOUSTICS
    Type: NASA-CR-172517 , NAS 1.26:172517
    Format: application/pdf
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  • 6
    Publication Date: 2019-07-12
    Description: The residence time of the combustible mixture in the combustion chamber of a scramjet engine is much less than the time normally required for complete combustion. Hydrogen and hydrocarbon fuels require an ignition source under conditions typically found in a scramjet combustor. Analytical studies indicate that the presence of hydrogen atoms should greatly reduce the ignition delay in this environment. Because hydrogen plasmas are prolific sources of hydrogen atoms, a low-power, uncooled hydrogen plasma torch has been built and tested to evaluate its potential as a possible flame holder for supersonic combustion. The torch was found to be unstable when operated on pure hydrogen; however, stable operation could be obtained by using argon as a body gas and mixing in the desired amount of hydrogen. The stability limits of the torch are delineated and its electrical and thermal behavior documented. An average torch thermal efficiency of around 88 percent is demonstrated.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 5; 129-133
    Format: text
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  • 7
    Publication Date: 2019-07-13
    Description: There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise level. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significnatly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 85-0787 , Structures, Structural Dynamics, and Materials Conference; Apr 15, 1985 - Apr 17, 1985; Orlando, FL
    Format: text
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  • 8
    Publication Date: 2019-07-10
    Description: The current effort addresses two issues important to the research conducted by the Thermal Radiation Group at Virginia Tech. The first research topic involves the development of a method which can properly model the diffraction of radiation as it enters an instrument aperture. The second topic involves the study of a potential next-generation space-borne radiometric instrument concept. Presented are multiple modeling efforts to describe the diffraction of monochromatic radiant energy passing through an aperture for use in the Monte-Carlo ray-trace environment. Described in detail is a deterministic model based upon Heisenberg's uncertainty principle and the particle theory of light. This method is applicable to either Fraunhofer or Fresnel diffraction situations, but is incapable of predicting the secondary fringes in a diffraction pattern. Also presented is a second diffraction model, based on the Huygens-Fresnel principle with a correcting obliquity factor. This model is useful for predicting Fraunhofer diffraction, and can predict the secondary fringes because it keeps track of phase. NASA is planning for the next-generation of instruments to follow CERES (Clouds and the Earth's Radiant Energy System), an instrument which measures components of the Earth's radiant energy budget in three spectral bands. A potential next-generation concept involves modification of the current CERES instrument to measure in a larger number of wavelength bands. This increased spectral partitioning would be achieved by the addition of filters and detectors to the current CERES geometry. The capacity of the CERES telescope to serve for this purpose is addressed in this thesis.
    Keywords: Environment Pollution
    Format: application/pdf
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  • 9
    Publication Date: 2019-07-12
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 23; 142-147
    Format: text
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  • 10
    Publication Date: 2019-07-12
    Description: The Earth Radiation Budget Experiment consists of an array of radiometric instruments placed in earth orbit by the National Aeronautics and Space Administration to monitor the longwave and visible components of the earth's radiation budget. Presented is a dynamic electrothermal model of the active cavity radiometer used to measure the earth's total radiative exitance. Radiative exchange is modeled using the Monte Carlo method and transient conduction is treated using the finite element method. Also included is the feedback circuit which controls electrical substitution heating of the cavity. The model is shown to accurately predict the dynamic response of the instrument during solar calibration.
    Keywords: GEOPHYSICS
    Type: Applied Optics (ISSN 0003-6935); 28; 1327-133
    Format: text
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