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  • 1
    ISSN: 1573-269X
    Keywords: Periodic solutions ; stability ; local bifurcations ; Fourier series
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper explores the application of the method of variable-coefficient harmonic balance to nonautonomous nonlinear equations of the form XsF(X, t:λ), and in particular, a one-degree-of-freedom nonlinear oscillator equation describing escape from a cubic potential well. Each component of the solution, X(t), is expressed as a truncated Fourier series of superharmonics, subharmonics and ultrasubharmonics. Use is then made of symbolic manipulation in order to arrange the oscillator equation as a Fourier series and its coefficient are evaluated in the traditional way. The time-dependent coefficients permit the construction of a set of amplitude evolution equations with corresponding stability criteria. The technique enables detection of local bifurcations, such as saddle-node folds, period doubling flips, and parts of the Feigenbaum cascade. This representation of the periodic solution leads to local bifurcations being associated with a term in the Fourier series and, in particular, the onset of a period doubled solution can be detected by a series of superharmonics only. Its validity is such that control space bifurcation diagrams can be obtained with reasonable accuracy and large reductions in computational expense.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Two industrially important free surface flows arising in polymer processing and thin film coating applications are modelled as lid-driven cavity problems to which a creeping flow analysis is applied. Each is formulated as a biharmonic boundary-value problem and solved both analytically and numerically. The analytical solutions take the form of a truncated biharmonic series of eigenfunctions for the streamfunction, while numerical results are obtained using a linear, finite-element formulation of the governing equations written in terms of both the streamfunction and vorticity. A key feature of the latter is that problems associated with singularities are alleviated by expanding the solution there in a series of separated eigenfunctions. Both sets of results are found to be in extremely good agreement and reveal distinctive flow transformations that occur as the operating parameters are varied. They also compare well with other published work and experimental observation.
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  • 3
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. Two industrially important free surface flows arising in polymer processing and thin film coating applications are modelled as lid-driven cavity problems to which a creeping flow analysis is applied. Each is formulated as a biharmonic boundary-value problem and solved both analytically and numerically. The analytical solutions take the form of a truncated biharmonic series of eigenfunctions for the streamfunction, while numerical results are obtained using a linear, finite-element formulation of the governing equations written in terms of both the streamfunction and vorticity. A key feature of the latter is that problems associated with singularities are alleviated by expanding the solution there in a series of separated eigenfunctions. Both sets of results are found to be in extremely good agreement and reveal distinctive flow transformations that occur as the operating parameters are varied. They also compare well with other published work and experimental observation.
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  • 4
    Publication Date: 2011-10-14
    Description: Impact performance of composite spacecraft structures
    Keywords: STRUCTURAL MECHANICS
    Format: text
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  • 5
    Publication Date: 2019-05-23
    Description: Effect of material properties on threshold penetration
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-54786
    Format: application/pdf
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  • 6
    Publication Date: 2019-06-27
    Description: Projectile size effects on hypervelocity impact craters in aluminum
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-4067
    Format: application/pdf
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  • 7
    Publication Date: 2019-06-27
    Description: An experimental investigation was conducted in an 11- by 11-foot transonic wind tunnel to study the lift, drag and stability characteristics of a 0.087-scale model of an operational airplane fitted with an oblique wing. The model wing was of elliptical planform with an unswept aspect ratio of 12.7 and a thickness of 10 percent. All other external geometric features of the model were scaled to the basic full size operational airplane with the engine inlet faired closed. Longitudinal and lateral-directional stability data were obtained with the wing at sweep angles of 0 deg, 45 deg and 60 deg Test Mach numbers ranged from 0.6 to 1.4 deg Angles of attack were between minus 4 deg and 8 deg at zero sideslip. Angles of sideslip were between plus and minus 4 degrees for two angles of attack depending upon the wing configuration. Tests were conducted at a Reynolds number of 6 million per foot except for a few runs when balance capacity limited the Reynolds number to 4 million per foot.
    Keywords: AIRCRAFT
    Type: NASA-TM-X-62273
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  • 8
    Publication Date: 2018-12-01
    Description: Impact resistance of spacecraft structures indicate performance criterion effect on final structural configuration and importance of hypervelocity of realistic hypervelocity test specimens
    Keywords: SPACE VEHICLES
    Format: text
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  • 9
    Publication Date: 2019-06-27
    Description: An experimental investigation was conducted in the Ames 14-foot transonic wind tunnel to study the aerodynamic performance and stability characteristics of a 0.087-scale model of an F-8 airplane fitted with an oblique wing. Two elliptical planform (axis ratio = 8:1) wings, each having a maximum thickness of 12 and 14 percent, were tested. Longitudinal stability data were obtained with no wing and with each of the two wings set at sweep angles of 0, 45, and 60 deg. Lateral directional stability data were obtained for the 12 percent wing only. Test Mach numbers ranged from 0.6 to 1.2 in the unit Reynolds number range from 11.2 to 13.1 million per meter. Angles of attack were between -6 and 22 deg at zero sideslip. Angles of sideslip were between -6 and +6 deg for two angles of attack, depending upon the wing configuration.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-X-62478 , A-6259
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  • 10
    Publication Date: 2019-06-27
    Description: The aerodynamic stability and control characteristics of a 0.087-scale model of an F-8 airplane fitted with an oblique wing was studied. The wing had an elliptical planform (axis ratio = 8:1), a maximum thickness of 12 percent, and was tested at three sweep angles, 0, 45, and 60 deg. Six-component force and moment data were measured at zero sideslip for angles of attack between -6 and +16 deg, with the left and right ailerons deflected one at a time at angles between -14 deg and +14. Further tests were made with the horizontal tail deflected -5 and +2.5 deg. Test Mach numbers ranged from 0.6 to 1.4 at a Reynolds number of 20 million/m.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-X-73103 , A-6434
    Format: application/pdf
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