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  • Other Sources  (65)
  • STRUCTURAL MECHANICS  (65)
  • Cell & Developmental Biology
  • 1980-1984
  • 1975-1979  (20)
  • 1970-1974  (45)
  • 1960-1964
  • 1950-1954
  • 1977  (20)
  • 1972  (45)
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  • 1980-1984
  • 1975-1979  (20)
  • 1970-1974  (45)
  • 1960-1964
  • 1950-1954
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  • 1
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    A non-linear dynamic lumped-parameter model of a rectangular plate. (1972)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A lumped-parameter model of a rectangular plate is developed by assuming fundamental mode solutions and using Hamilton's Principle and the Euler equations to set up the differential equation of motion for the system. The plate theory used may be described as the dynamic analogue of the von Karman large-deflection theory. Four sets of symmetrical boundary conditions are considered with the restriction of uniform pressure dynamic loads. The model takes the form of a mass on a cubic-hardening spring with each term defined by algebraic expressions of the plate parameters. The results for some specific problems are compared with two previous solutions. This method is less accurate but simpler to develop and apply.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 21; Apr. 8
    Format: text
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  • 2
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    A comparison of the capabilities of three finite element programs (1972)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Three finite element programs are compared to assess their capabilities as an analysis tool in a structural design process. Because of the need for repetitive analyses as an integral part of a design loop, a candidate program must be capable of handling large problems, operate efficiently, and be readily adaptable for use in computer-aided design. The three programs considered in the study, ELAS,SNAP, and NASTRAN, range from a relatively small finite element program limited to static structural analysis (ELAS) to a large complex general analysis system (NASTRAN). Results are given for comparative speeds and computer resources required for each program in the analysis of sample fuselage problems representative of practical aircraft design.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 277-287
    Format: application/pdf
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  • 3
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    Experiences in interfacing NASTRAN with another finite element program (1972)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The coupling of NASTRAN to another finite element program developed for the static analysis of automotive structures is discussed. The two programs were coupled together to use the substructuring capability of the in-house program and the normal mode analysis capability of NASTRAN. Modifications were made to the NASTRAN program in order to make the coupling feasible.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 111-119
    Format: application/pdf
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  • 4
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    A 3-D hydroelastic analysis in NASTRAN with general fluid and structure geometry (1977)
    In:  Other Sources
    Details
    Publication Date: 2016-06-07
    Description: The implementation of a general three dimensional hydroelastic mode analysis capability in NASTRAN is presented. Finite elements with polyhedral shapes define the fluid; existing NASTRAN plate elements define the fluid/structure interface. Efficient solution methods were implemented to allow a separate structural matrix reduction and to allow connection of the fluid mass directly to a small set of grid points or modal coordinates representing the structure. Test case results for the various solution options are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Washington 6th NASTRAN (R) Users' Colloq.; p 3-23
    Format: text
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  • 5
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    Coupling between structure and liquids in a parallel stage space shuttle design (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A study was conducted to determine the influence of liquid propellants on the dynamic loads for space shuttle vehicles. A parallel-stage configuration model was designed and tested to determine the influence of liquid propellants on coupled natural modes. A forty degree-of-freedom analytical model was also developed for predicting these modes. Currently available analytical models were used to represent the liquid contributions, even though coupled longitudinal and lateral motions are present in such a complex structure. Agreement between the results was found in the lower few modes.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-127631 , AIAA PAPER 72-347-REV
    Format: application/pdf
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  • 6
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    Multimaterial lamination as a means of retarding penetration and spallation failures in plates (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Experimental data are presented which show that hypervelocity impact spallation and penetration failures of a single solid aluminum plate and of a solid aluminum plate spaced a distance behind a Whipple meteor bumper may be retarded by replacing the solid aluminum plate with a laminated plate. Four sets of experiments were conducted. The first set of experiments was conducted with projectile mass and velocity held constant and with polycarbonate cylinders impacted into single plates of different construction. The second set of experiments was done with single plates of various construction and aluminum spherical projectiles of similar mass but different velocities. These two experiments showed that a laminated plate of aluminum and polycarbonate or aluminum and methyl methacrylate could prevent spallation and penetration failures with a lower areal density than either an all-aluminum laminated plate or a solid aluminum plate. The aluminum laminated plate was in turn superior to the solid aluminum plate in resisting spallation and penetration failures. In addition, through an example of 6061-T6 aluminum and methyl methacrylate, it is shown that a laminated structure ballistically superior to its parent materials may be built. The last two sets of experiments were conducted using bumper-protected main walls of solid aluminum and of laminated aluminum and polycarbonate. Again, under hypervelocity impact conditions, the laminated main walls were superior to the solid aluminum main walls in retarding spallation and penetration failures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-6989 , L-8444
    Format: application/pdf
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  • 7
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    Fatigue flaw growth and NDI evaluation for preventing through cracks in spacecraft tankage structures (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A program was conducted to determine the fatigue-crack propagation behavior of parent and welded 2219-T87 aluminum alloy sheet under controlled cyclic stress conditions in room temperature air and 300 F air. Specimens possessing an initial surface defect of controlled dimensions were cycled under constant load amplitude until the propagating fatigue crack penetrated the back surface of the specimen. A series of precracked specimens were prepared to determine optimum penetrant, X-ray, ultrasonic, and eddy current nondestructive inspection procedures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-128600 , LR-25387
    Format: application/pdf
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  • 8
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    Lumped parameter analysis of a stringer reinforced plate excited by band limited noise (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The maximum root-mean-square response of a square clamped plate, subjected to a stationary random excitation, was determined both theoretically and empirically. For the tests, a 40 x 40 x 1/4 aluminum sheet was milled out to provide a thin waffle plate with 9 panels. The plate was acoustically excited, with the frequency range limited between 25 Hz and 500 Hz. The root-mean-square power of the random excitations, 149 decibels, was nearly constant for all natural frequencies of the plate system. Strain gage readings at 14 points were plotted as power spectral densities and root-mean-square displacements. A modal damping ratio matrix was determined from the response curves. Damping ratios were found to be a function of frequency, but not of location on the plate. For comparisons with the theoretical response, the plate was subdivided into 14 modes and anlayzed as a damped, lumped parameter system by use of an approximate normal-mode method. This method gave the best predictions of the power spectral densities for the lower frequencies. That prediction errors increased for the higher frequencies is attributed to improper assumptions for mass distribution and the insufficient number of lumped mass points.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-129301
    Format: application/pdf
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  • 9
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    Non-linear analysis of vibrations of irregular plates (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A numerical perturbation method is used to investigate the forced vibrations of irregular plates. Nonlinear terms associated with the midplane stretching are retained in the analysis. The numerical part of the method involves the use of linear, finite element techniques to determine the free oscillation mode shapes and frequencies and to obtain the linear midplane stress resultants caused by the midplane stretching. Representing the solution as an expansion in terms of these linear mode shapes, these modes and the resultants are used to determine the equations governing the time-dependent coefficients of this expansion. These equations are solved by using the method of multiple scales. Specific solutions are given for the main-resonant vibrations of an elliptical plate in the presence of internal resonances. The results indicate that modes other than the driven mode can be drawn into the steady state response. Though the excitation is composed of a single harmonic, the response may not be periodic. Moreover, the particular types of responses that can occur are highly dependent on the mode being excited and are sensitive to small geometrical changes.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 50; Jan. 22
    Format: text
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  • 10
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    Transient excitation and mechanical admittance test techniques for prediction of payload vibration environments (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Transient excitation forces were applied separately to simple beam-and-mass launch vehicle and payload models to develop complex admittance functions for the interface and other appropriate points on the structures. These measured admittances were then analytically combined by a matrix representation to obtain a description of the coupled system dynamic characteristics. Response of the payload model to excitation of the launch vehicle model was predicted and compared with results measured on the combined models. These results are also compared with results of earlier work in which a similar procedure was employed except that steady-state sinusoidal excitation techniques were included. It is found that the method employing transient tests produces results that are better overall than the steady state methods. Furthermore, the transient method requires far less time to implement, and provides far better resolution in the data. However, the data acquisition and handling problem is more complex for this method. It is concluded that the transient test and admittance matrix prediction method can be a valuable tool for development of payload vibration tests.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2787 , SWRI-02-4202
    Format: application/pdf
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