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  • Other Sources  (27)
  • 1990-1994  (27)
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  • 1
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    Multi-use lunar telescopes (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The objective of multi-use telescopes is to reduce the initial and operational costs of space telescopes to the point where a fair number of telescopes, a dozen or so, would be affordable. The basic approach is to develop a common telescope, control system, and power and communications subsystem that can be used with a wide variety of instrument payloads, i.e., imaging CCD cameras, photometers, spectrographs, etc. By having such a multi-use and multi-user telescope, a common practice for earth-based telescopes, development cost can be shared across many telescopes, and the telescopes can be produced in economical batches.
    Keywords: ASTRONOMY
    Type: In: Robotic telescopes in the 1990s; Proceedings of the Symposium, 103rd Annual Meeting of the Astronomical Society of the Pacific, Univ. of Wyoming, Laramie, June 22-24, 1991, 1991 (A93-36457 14-89); p. 289-303.
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  • 2
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    The use of robotic telescopes for detecting planetary systems (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It is argued that increases in the precision of photometric measurements and the development of fully automatic photometric telescopes (APTs) now make possible the detection of Jupiter-size objects around other stars. The two most promising approaches are to monitor binary stars that have their orbital plane nearly in our line of sight and to measure the rotation periods of stars that are known to have dark companions and have very accurate values for Vsini. Differential photometry with APTs, based on a rapid comparison among a group of stars, provides a precision of 2 parts in 1000. Transits of solar-type stars by planets or brown dwarfs the size of Jupiter or Saturn will produce brightness variations of about 10 parts per 1000.
    Keywords: ASTRONOMY
    Type: In: Robotic telescopes in the 1990s; Proceedings of the Symposium, 103rd Annual Meeting of the Astronomical Society of the Pacific, Univ. of Wyoming, Laramie, June 22-24, 1991, 1991 (A93-36457 14-89); p. 153-169.
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  • 3
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    Navier-Stokes predictions for the F-18 wing and fuselage at large incidence (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 29; 4, Ju; 565-574
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  • 4
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    Numerical simulation of high-incidence flow over the F-18 fuselage forebody (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 609-617
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  • 5
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    Computational analysis of forebody tangential slot blowing (1994)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An overview of the computational effort to analyze forebody tangential slot blowing is presented. Tangential slot blowing generates side force and yawing moment which may be used to control an aircraft flying at high-angle-of-attack. Two different geometries are used in the analysis: (1) The High Alpha Research Vehicle; and (2) a generic chined forebody. Computations using the isolated F/A-18 forebody are obtained at full-scale wind tunnel test conditions for direct comparison with available experimental data. The effects of over- and under-blowing on force and moment production are analyzed. Time-accurate solutions using the isolated forebody are obtained to study the force onset timelag of tangential slot blowing. Computations using the generic chined forebody are obtained at experimental wind tunnel conditions, and the results compared with available experimental data. This computational analysis compliments the experimental results and provides a detailed understanding of the effects of tangential slot blowing on the flow field about simple and complex geometries.
    Keywords: AERODYNAMICS
    Type: NASA. Dryden Flight Research Center, Fourth High Alpha Conference, Volume 3; 22 p
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  • 6
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    Computation of three-dimensional turbulent vortical flows on bodies at high incidence (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 689-699
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  • 7
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    Blocking reduction of Landsat Thematic Mapper JPEG browse images using optimal PSNR estimated spectra adaptive postfiltering (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Two representative sample images of Band 4 of the Landsat Thematic Mapper are compressed with the JPEG algorithm at 8:1, 16:1 and 24:1 Compression Ratios for experimental browsing purposes. We then apply the Optimal PSNR Estimated Spectra Adaptive Postfiltering (ESAP) algorithm to reduce the DCT blocking distortion. ESAP reduces the blocking distortion while preserving most of the image's edge information by adaptively postfiltering the decoded image using the block's spectral information already obtainable from each block's DCT coefficients. The algorithm iteratively applied a one dimensional log-sigmoid weighting function to the separable interpolated local block estimated spectra of the decoded image until it converges to the optimal PSNR with respect to the original using a 2-D steepest ascent search. Convergence is obtained in a few iterations for integer parameters. The optimal logsig parameters are transmitted to the decoder as a negligible byte of overhead data. A unique maxima is guaranteed due to the 2-D asymptotic exponential overshoot shape of the surface generated by the algorithm. ESAP is based on a DFT analysis of the DCT basis functions. It is implemented with pixel-by-pixel spatially adaptive separable FIR postfilters. PSNR objective improvements between 0.4 to 0.8 dB are shown together with their corresponding optimal PSNR adaptive postfiltered images.
    Keywords: COMPUTER SYSTEMS
    Type: NASA. Goddard Space Flight Center, 1994 Science Information Management and Data Compression Workshop; p 41
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  • 8
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    Numerical investigation of multi-element airfoils (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The flow over multi-element airfoils with flat-plate lift-enhancing tabs was numerically investigated. Tabs ranging in height from 0.25 percent to 1.25 percent of the reference airfoil chord were studied near the trailing edge of the main-element. This two-dimensional numerical simulation employed an incompressible Navier-Stokes solver on a structured, embedded grid topology. New grid refinements were used to improve the accuracy of the solution near the overlapping grid boundaries. The effects of various tabs were studied at a constant Reynolds number on a two-element airfoil with a slotted flap. Both computed and measured results indicated that a tab in the main-element cove improved the maximum lift and lift-to-drag ratio relative to the baseline airfoil without a tab. Computed streamlines revealed that the additional turning caused by the tab may reduce the amount of separated flow on the flap. A three-element airfoil was also studied over a range of Reynolds numbers. For the optimized flap rigging, the computed and measured Reynolds number effects were similar. When the flap was moved from the optimum position, numerical results indicated that a tab may help to reoptimize the airfoil to within 1 percent of the optimum flap case.
    Keywords: AERODYNAMICS
    Type: NASA-CR-194592 , NAS 1.26:194592
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  • 9
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    Computation of three-dimensional effects on two dimensional wings (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A 2-D numerical investigation was performed to determine the effect of a Gurney flap on a NACA 4412 airfoil. A Gurney flap is a flat plate on the order of 1 to 3 percent of the airfoil chord length, oriented perpendicular to the airfoil chord line and located at the trailing edge of the airfoil. An incompressible Navier Stokes code, INS2D, was used to calculate the flow field about the airfoil. The fully turbulent results were obtained using the Baldwin-Barth one-equation turbulence model. Gurney flap sizes of 0.5, 1, 1.25, 1.5, 2, and 3 percent of the airfoil chord were studied. Computational results were compared with experimental results where possible. The numerical solutions show that the Gurney flap increases airfoil lift coefficient with only a slight increase in drag coefficient. Use of a 1.5 percent chord Gurney flap increases the maximum lift coefficient by approximately 0.3 and decreases the angle of attack for a given lift coefficient by more than 3 degrees. The numerical solutions exhibit detailed flow structures at the trailing edge and provide a possible explanation for the increased aerodynamic performance.
    Keywords: AERODYNAMICS
    Type: NASA-CR-190576 , NAS 1.26:190576
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  • 10
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    Pneumatic vortical flow control at high angles of attack (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The injection of thin, high-momentum jets of air into the fuselage forebody boundary layers of the F-18 aircraft is explored numerically as a means of controlling the onset of fuselage vortices and of generating yaw control forces. The study was carried out for an angle of attack of 30 deg with symmetrical and asymmetrical blowing configurations. One-sided blowing results in a strongly asymmetrical flow pattern in the fore portion of the fuselage, leading to a net lateral force.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 90-0098
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