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  • 1
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    In-service health monitoring of composite structures (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The aerospace industry is witnessing a vast utilization of composites in critical structural applications and anticipates even more use of them in future aircraft. Therefore, a definite need exists for a composite health monitoring expert system to meet today's current needs and tomorrow's future demands. The primary goal for this conceptual health monitoring system is functional reliably for in-service operation in the environments of various composite structures. The underlying philosophy of this system is to utilize proven vibration techniques to assess the structural integrity of a fibrous composite. Statistical methods are used to determine if the variances in the measured data are acceptable for making a reliable decision on the health status of the composite. The flexible system allows for algorithms describing any composite fatigue or damage behavior characteristic to be provided as an input to the system. Alert thresholds and variances can also be provided as an input to this system and may be updated to allow for future changes/refinements in the composite's structural integrity behavior.
    Keywords: QUALITY ASSURANCE AND RELIABILITY
    Format: text
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  • 2
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    Derivation of aerodynamic kernel functions (1973)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The method of Fourier transforms is used to determine the kernel function which relates the pressure on a lifting surface to the prescribed downwash within the framework of Dowell's (1971) shear flow model. This model is intended to improve upon the potential flow aerodynamic model by allowing for the aerodynamic boundary layer effects neglected in the potential flow model. For simplicity, incompressible, steady flow is considered. The proposed method is illustrated by deriving known results from potential flow theory.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 11; Nov. 197
    Format: text
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  • 3
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    Turbofan noise generation. Volume 2: Computer programs (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The use of a package of computer programs developed to calculate the in duct acoustic mods excited by a fan/stator stage operating at subsonic tip speed is described. The following three noise source mechanisms are included: (1) sound generated by the rotor blades interacting with turbulence ingested into, or generated within, the inlet duct; (2) sound generated by the stator vanes interacting with the turbulent wakes of the rotor blades; and (3) sound generated by the stator vanes interacting with the velocity deficits in the mean wakes of the rotor blades. The computations for three different noise mechanisms are coded as three separate computer program packages. The computer codes are described by means of block diagrams, tables of data and variables, and example program executions; FORTRAN listings are included.
    Keywords: ACOUSTICS
    Type: NASA-CR-167952 , NAS 1.26:167952 , BBN-4770
    Format: application/pdf
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  • 4
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    The SRB heat shield: Aeroelastic stability during reentry (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Wind tunnel tests of a 3% scale model of the aft portion of the SRB equipped with partially scaled heat shields were conducted for the purpose of measuring fluctuating pressure levels in the aft skirt region. During these tests, the heat shields were observed to oscillate violently, the oscillations in some instances causing the heat shields to fail. High speed films taken during the tests reveal a regular pattern of waves in the fabric starting near the flow stagnation point and progressing around both sides of the annulus. The amplitude of the waves was too great, and their pattern too regular, for them to be attributed to the fluctuating pressure levels measured during the tests. The cause of the oscillations observed in the model heat shields, and whether or not similar oscillations will occur in the full scale SRB heat shield during reentry were investigated. Suggestions for modifying the heat shield so as to avoid the oscillations are provided, and recommendations are made for a program of vibration and wind tunnel tests of reduced-scale aeroelastic models of the heat shield.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-150479 , BBN-3532
    Format: application/pdf
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  • 5
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    Large amplitude flutter of a low aspect ratio panel at low supersonic speeds comparison of theory and experiment (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Flutter boundaries, as well as flutter limit cycle amplitudes, frequencies and stresses were computed for a panel of length-width ratio 4.48 exposed to applied in-plane and transverse loads. The Mach number range was 1.1 to 1.4. The method used involved direct numerical integration of modal equations of motion derived from the nonlinear plate equations of von Karman, coupled with linearized potential flow aerodynamic theory. The flutter boundaries agreed reasonably well with experiment, except when the in-plane loading approached the buckling load. Structural damping had to be introduced, to produce frequencies comparable to the experimental values. Attempts to compute panel deflections or stress at a given point met with limited success. There is some evidence, however, that deflection and stress maxima can be estimated with somewhat greater accuracy.
    Keywords: AERODYNAMICS
    Type: NASA-CR-120105 , AMS-1116
    Format: application/pdf
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  • 6
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    Shear flow aerodynamics - Lifting surface theory (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A lifting surface theory based on a parallel shear flow model is presented for steady, incompressible flows. The theory is intended to account approximately for the presence of a boundary layer. The method of Fourier transforms is used to calculate the pressure on a surface of infinite extent and arbitrary contour. Immediately above the surface is a region of sheared flow (the boundary layer), outside of which the flow velocity is constant. The Fourier transform of the pressure on this surface is used to derive the shear flow equivalent to the kernel function of classical potential flow lifting surface theory. The kernel function provides an integral relation between the upwash at a given point on the surface and the pressure everywhere on the surface. This relation is treated as an integral equation for the pressure, and is solved numerically. Computations are presented for the lift and pitching moment on a flat plate in two-dimensional flow, and for flat, rectangular wings of aspect ratio 1, 2, and 5. As expected, the shear layer decreases the lift curve slope; however, the shear layer (whose thickness is constant along the wing chord) has little effect on the center of pressure.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 13; Sept
    Format: text
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  • 7
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    Influence of in-plane edge support flexibility on the nonlinear flutter of loaded plates. (1969)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Flutter analysis of plates with inplane boundary support flexibility exposed to transverse pressure loading or buckled by uniform thermal expansion
    Keywords: STRUCTURAL MECHANICS
    Type: AMERICAN INST. OF AERONAUTICS AND ASTRONAUTICS, STRUCTURAL DYNAMICS AND AEROELASTICITY SPECIALIST CONFERENCE; APRIL 16, 17, 1969; NEW ORLEANS, LA.
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  • 8
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    Influence of in-plane support flexibility on the nonlinear flutter of loaded plates (1968)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Flutter behavior of plates exposed to supersonic flow with concurrent transverse and plane loadings
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-97255
    Format: application/pdf
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  • 9
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    Flutter of low aspect ratio plates (1970)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Low aspect ratio plates flutter analysis for subsonic and supersonic models
    Keywords: STRUCTURAL MECHANICS
    Type: ; ADEMIE DES SCIENCES
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  • 10
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    Nonlinear panel response by a Monte Carlo approach (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The vibration of clamped and simply supported elastic panels due to subsonic and supersonic turbulent boundary-layer flows is investigated by a Monte Carlo technique. The resulting generalized random forces are simulated numerically from boundary-layer turbulence spectra, and the response analysis is performed in the time domain. The mutual interaction between panel motion and external and/or internal airflow is included. Response studies are performed with respect to rms response, probability structure, peak distribution, threshold crossing and spectral density. The effect on the response statistics of in-plane loading, static pressure differential, and cavity pressure is investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 12; May 1974
    Format: text
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