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  • 1
    Electronic Resource
    Electronic Resource
    Partial match retrieval using recursive linear hashing (1985)
    Springer
    BIT 25 (1985), S. 477-484 
    Details
    ISSN: 1572-9125
    Keywords: partial match retrieval ; linear hashing ; dynamic files ; 3.74 ; 4.33 ; 4.34
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Recursive linear hashing is a hashing technique proposed for files which can grow and shrink dynamically. The scheme is an extension of linear hashing, a method originally proposed by Litwin, but unlike Litwin's scheme, it does not require conventional overflow pages. In this paper, we investigate the application of recursive linear hashing to partial match retrieval problems. Consistent with the results for primary key retrieval, recursive linear hashing performs better than the conventional scheme on these problems, especially at high load factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01935368
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    Paper (German National Licenses)
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  • 2
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    Unknown
    Flight and analytical investigations of a structural mode excitation system on the YF-12A airplane (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A structural excitation system, using an oscillating canard vane to generate force, was mounted on the forebody of the YF-12A airplane. The canard vane was used to excite the airframe structural modes during flight in the subsonic, transonic, and supersonic regimes. Structural modal responses generated by the canard vane forces were measured at the flight test conditions by airframe-mounted accelerometers. Correlations of analytical and experimental aeroelastic results were made. Doublet lattice, steady state double lattice with uniform lag, Mach box, and piston theory all produced acceptable analytical aerodynamic results within the restrictions that apply to each. In general, the aerodynamic theory methods, carefully applied, were found to predict the dynamic behavior of the YF-12A aircraft adequately.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-166623 , H-1361 , NAS 1.26:166623
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Computational fluid dynamics study of the variable-pitch split-blade fan concept (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A computational fluid dynamics study was conducted to evaluate the feasibility of the variable-pitch split-blade supersonic fan concept. This fan configuration was conceived as a means to enable a supersonic fan to switch from the supersonic through-flow type of operation at high speeds to a conventional fan with subsonic inflow and outflow at low speeds. During this off-design, low-speed mode of operation, the fan would operate with a substantial static pressure rise across the blade row like a conventional transonic fan; the front (variable-pitch) blade would be aligned with the incoming flow, and the aft blade would remain fixed in the position set by the supersonic design conditions. Because of these geometrical features, this low speed configuration would inherently have a large amount of turning and, thereby, would have the potential for a large total pressure increase in a single stage. Such a high-turning blade configuration is prone to flow separation; it was hoped that the channeling of the flow between the blades would act like a slotted wing and help alleviate this problem. A total of 20 blade configurations representing various supersonic and transonic configurations were evaluated using a Navier Stokes CFD program called ADAPTNS because of its adaptive grid features. The flow fields generated by this computational procedure were processed by another data reduction program which calculated average flow properties and simulated fan performance. These results were employed to make quantitative comparisons and evaluations of blade performance. The supersonic split-blade configurations generated performance comparable to a single-blade supersonic, through-flow fan configuration. Simulated rotor total pressure ratios of the order of 2.5 or better were achieved for Mach 2.0 inflow conditions. The corresponding fan efficiencies were approximately 75 percent or better. The transonic split-blade configurations having large amounts of turning were able to generate large amounts of total turning and achieve simulated total pressure ratios of 3.0 or better with subsonic inflow conditions. These configurations had large losses and low fan efficiencies in the 70's percent. They had large separated regions and low velocity wakes. Additional turning and diffusion of this flow in a subsequent stator row would probably be very inefficient. The high total pressure ratios indicated by the rotor performance would be substantially reduced by the stators, and the stage efficiency would be substantially lower. Such performance leaves this dual-mode fan concept less attractive than originally postulated.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-189206 , NAS 1.26:189206 , UTRC-R91-254576-20
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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