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  • STRUCTURAL MECHANICS  (17)
  • 2015-2019
  • 1990-1994  (2)
  • 1985-1989  (11)
  • 1965-1969  (4)
  • 1935-1939
  • 1
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    Sublaminate- or ply-level analysis of composites and strain energy release rates of end-notch and mixed-mode fracture specimens (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The sublaminate or ply-level analysis of composite structures is presently undertaken by a computational procedure yielding the stresses in regions affected by delaminations, transverse cracks, and discontinuities that are related to material properties, geometries, and loads. Attention is given to layers or groups of layers that are immediately affected by flaws; these are analyzed as if they were homogeneous bodies in equilibrium, in isolation from the rest of the laminate. Computed stresses agree with those from a three-dimensional FEM analysis.
    Keywords: STRUCTURAL MECHANICS
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    NASA TECHNICAL REPORTS
  • 2
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    Method of calculation of frequencies of partially fixed beams carrying masses. (1966)
    In:  Other Sources
    Details
    Publication Date: 2011-08-11
    Description: Finite Fourier sine transform method of obtaining closed-form solution, calculating eigenfrequencies for free vibrations of partially fixed beam carrying concentrated masses
    Keywords: STRUCTURAL MECHANICS
    Type: ACOUSTICAL SOCIETY OF AMERICA
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    On the glitches in the force transmitted by an electrodynamic exciter to a structure (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Around resonance, the force transmitted by an exciter into a structure will be smaller or greater than a reference force generated by its coils due to electromechanical interaction. A simple analysis is presented which reveals how this phenomenon of force drop-off is controlled by three factors. The first factor, called Armature Mass Factor, describes a purely mechanical interaction between the structure and the exciter. The electromechanical energy conversion and its interaction with the structure yields two additional factors, called Electrical Resistance and Electrical Inductance Factors. They describe the effects of coil resistance, inductance and magnetic field strength relative to structural damping and stiffness. Present analysis indicates that, under proper circumstances, more than 90 percent of the force drop-off can be eliminated if armature-to-structure mass ratio is smaller or equal to half of modal loss factor.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 245-255
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Development of aeroelastic analysis methods for turborotors and propfans, including mistuning (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The NASA Lewis aeroelastic research program is focused on unstalled and stalled flutter, forced response, and whirl flutter of turborotors and propfans. The objectives are to understand the physical phenomena of cascade flutter and response including blade mistuning.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Lewis Structures Technology, 1988. Volume 1: Structural Dynamics; p 247-262
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  • 5
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    A computational procedure for automated flutter analysis (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A direct solution procedure for computing the flutter Mach number and the flutter frequency is applied to the aeroelastic analysis of propfans using a finite element structural model and an unsteady aerodynamic model based on a three-dimensional subsonic compressible lifting surface theory. An approximation to the Jacobian matrix that improves the efficiency of the iterative process is presented. The Jacobian matrix is indirectly approximated from approximate derivatives of the flutter matrix, which are updated only in the direction of the last move. Examples are used to illustrate the convergence properties. The direct solution procedure facilitates the automated flutter analysis in addition to contributing to the efficient use of computer time as well as the analyst's time.
    Keywords: STRUCTURAL MECHANICS
    Type: Communications in Applied Numerical Methods (ISSN 0748-8025); 5; 29-37
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  • 6
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    Analytical and experimental investigation of mistuning in propfan flutter (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An analytical and experimental investigation of the effects of mistuning on propfan subsonic flutter was performed. The analytical model is based on the normal modes of a rotating composite blade and a three-dimensinal subsonic unsteady lifting surface aerodynamic theory. Theoretical and experimental results are compared for selected cases at different blade pitch angles, rotational speeds, and free-stream Mach numbers. The comparison shows a reasonably good agreement between theory and experiment. Both theory and experiment showed that combined mode shape, frequency, and aerodynamic mistuning can have a beneficial or adverse effect on blade damping depending on Mach number. Additional parametric results showed that alternative blade frequency mistuning does not have enough potential for it to be used as a passive flutter control in propfans similar to the one studied. It can be inferred from the results that a laminated composite propfan blade can be tailored to optimize its flutter speed by selecting the proper ply angles.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-88959 , E-3412 , NAS 1.15:88959 , AIAA PAPER 87-0739
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  • 7
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    A computational procedure for automated flutter analysis (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A direct solution procedure for computing the flutter Mach number and the flutter frequency is applied to the aeroelastic analysis of propfans using a finite element structural model and an unsteady aerodynamic model based on a three-dimensional subsonic compressible lifting surface theory. An approximation to the Jacobian matrix that improves the efficiency of the iterative process is presented. The Jacobian matrix is indirectly approximated from approximate derivatives of the flutter matrix. Examples are used to illustrate the convergence properties. The direct solution procedure facilitates the automated flutter analysis in addition to contributing to the efficient use of computer time as well as the analyst's time.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-100171 , E-3736 , NAS 1.15:100171
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  • 8
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    A semianalytical technique for sensitivity analysis of unsteady aerodynamic computations (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A semianalytical approach is developed for the sensitivity analysis of linear unsteady aerodynamic loads. The semianalytical approach is easier to implement than the analytical approach. It is also computationally less expensive than the finite difference approach when used with panel methods, which require a large number of panels. The semianalytical approach is applied to an isolated airfoil in a 2-D flow and rotating propfan blades in 3-D flow. Sensitivity coefficients with respect to non-shape-dependent variables are shown for some cases. It is expected that the semianalytical approach will be useful in aeroelastic design procedures particularly when mistuning is present, and that it is potentially useful for shape sensitivity analysis of linear unsteady aerodynamics.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-100810 , E-3990 , NAS 1.15:100810 , AIAA PAPER 88-2377
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  • 9
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    Vibration and flutter characteristics of the SR7L large-scale propfan (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An investigation of the vibration characteristics and aeroelastic stability of the SR7L Large-Scale Advanced Propfan was performed using a finite element blade model and an improved aeroelasticity code. Analyses were conducted for different blade pitch angles, blade support conditions, number of blades, rotational speeds, and freestream Mach numbers. A finite element model of the blade was used to determine the blade's vibration behavior and sensitivity to support stiffness. The calculated frequencies and mode shape obtained with this model agreed well with the published experimental data. A computer code recently developed at NASA Lewis Research Center and based on three-dimensional, unsteady, lifting surface aerodynamic theory was used for the aeroelastic analysis to examine the blade's stability at a cruise condition of Mach 0.8 at 1700 rpm. The results showed that the blade is stable for that operating point. However, a flutter condition was predicted if the cruise Mach number was increased to 0.9.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-100272 , E-3908 , NAS 1.15:100272
    Format: application/pdf
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  • 10
    facet.materialart.
    Unknown
    Analytical and experimental investigation of mistuning in propfan flutter (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An analytical and experimental investigation of the effects of mistuning on propfan subsonic flutter was performed. The analytical model is based on the normal modes of a rotating composite blade and a three-dimensional subsonic unsteady lifting surface aerodynamic theory. Theoretical and experimental results are compared for selected cases at different blade pitch angles, rotational speeds, and free-stream Mach numbers. The comparison shows a reasonably good agreement between theory and experiment. Both theory and experiment showed that combined mode shape, frequency, and aerodynamic mistuning can have a beneficial or adverse effect on blade damping depending on Mach number. Additional parametric results showed that alternative blade frequency mistuning does not have enough potential for it to be used as a passive flutter control in propfans similar to the one studied. It can be inferred from the results that a laminated composite propfan blade can be tailored to optimize its flutter speed by selecting the proper ply angles.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 87-0739
    Format: text
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