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  • 1
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    Frequency domain stress intensity calibration of damped cracked panels (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: This paper discusses two schemes for doing finite element K calibration in the frequency domain. The baseline scheme uses the definition of K as a limit toward the crack tip. The limiting process requires using a very fine mesh around the crack tip making the scheme computationally very expensive. It is shown that the behavior of K as a function of frequency is very similar to a modal response. Taking advantage of this, a more efficient scheme involves a modal analysis of the cracked sheet and scaling the response to that of the static stress intensity. In this way, only a static K calibration need be performed. All the examples shown are for a frequency range spanning multiple resonances and with two levels of damping.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture (ISSN 0376-9429); 61; 2; p. 123-130.
    Format: text
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  • 2
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    Spectral analysis of wave motion in plane solids with boundaries (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A spectral formulation is employed whereby in-plane stress waves are synthesized from the superposition of components at discrete frequencies and wavenumbers. The summations are performed using the fast Fourier transform and the Fourier series, respectively. Because the components are discrete, the solution to problems (over the entire field) with completely arbitrary loading, both in time and space, is made tractable. Waves generated from a line load acting on an infinite and semiinfinite plane are first considered. A cascade approach is then adopted for the treatment of these waves incident on a free, fixed, and elastic boundary. At each stage, the results are compared with those obtained from the available classical solutions and/or finite element results. These studies will form the basis for the investigation of in-plane stress waves in multiply layered media.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME, Transactions, Journal of Vibration and Acoustics (ISSN 0739-3717); 114; 2, Ap
    Format: text
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  • 3
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    A spectral element approach to wave motion in layered solids (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A matrix methodology similar to that of the finite element method is developed for the analysis of stress waves in layered solids. Because the mass distribution is modeled exactly, the approach gives the exact frequency response of each layer. The fast Fourier transform and Fourier series are used for inversion to the time/space domain. The impact of a structured medium with multiple layers is used to demonstrate the method. Comparison with existing propagator and direct global matrix methods show the present approach to be computationally more efficient.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME, Transactions, Journal of Vibration and Acoustics (ISSN 0739-3717); 114; 4; p. 569-577.
    Format: text
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  • 4
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    Dynamic programming and direct interaction for the optimum design of skeletal towers (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A computer technique is proposed for automatically designing tower structures. Dynamic programming was used to find the optimum geometric configuration of the structural members, while the member sizes were proportioned by direct iteration. Tower structures are particularly suited to this method of automatic design since the rapidity of the analysis and design depends primarily upon substructuring. Substructuring of towers was comparatively simple because interaction between adjacent substructures is simulated with reasonable accuracy. Typical examples are presented to illustrate the method.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Res. in Computerized Structural Analysis and Syn.,; p 101-118
    Format: application/pdf
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  • 5
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    Computer program for the load and trajectory analysis of two DOF bodies connected by an elastic tether: Users manual (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The derivation of the differential equations of motion of a 3 Degrees of Freedom body joined to a 3 Degrees of Freedom body by an elastic tether. The tether is represented by a spring and dashpot in parallel. A computer program which integrates the equations of motion is also described. Although the derivation of the equations of motions are for a general system, the computer program is written for defining loads in large boosters recovered by parachutes.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-124259 , GER-15853
    Format: application/pdf
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  • 6
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    Users manual: Dynamics of two bodies connected by an elastic tether, six degrees of freedom forebody and five degrees of freedom decelerator (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The equations of motion and a computer program for the dynamics of a six degree of freedom body joined to a five degree of freedom body by a quasilinear elastic tether are presented. The forebody is assumed to be a completely general rigid body with six degrees of freedom; the decelerator is also assumed to be rigid, but with only five degrees of freedom (symmetric about its longitudinal axis). The tether is represented by a spring and dashpot in parallel, where the spring constant is a function of tether elongation. Lagrange's equation is used to derive the equations of motion with the Lagrange multiplier technique used to express the constraint provided by the tether. A computer program is included which provides a time history of the dynamics of both bodies and the tension in the tether.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120261 , GER-16047
    Format: application/pdf
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  • 7
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    Frequency domain analysis of the random loading of cracked panels (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The primary effort concerned the development of analytical methods for the accurate prediction of the effect of random loading on a panel with a crack. Of particular concern was the influence of frequency on the stress intensity factor behavior. Many modern structures, such as those found in advanced aircraft, are lightweight and susceptible to critical vibrations, and consequently dynamic response plays a very important role in their analysis. The presence of flaws and cracks can have catastrophic consequences. The stress intensity factor, K, emerges as a very significant parameter that characterizes the crack behavior. In analyzing the dynamic response of panels that contain cracks, the finite element method is used, but because this type of problem is inherently computationally intensive, a number of ways of calculating K more efficiently are explored.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-196021 , NAS 1.26:196021
    Format: application/pdf
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  • 8
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    Dangers on the Ramp: Aviation Safety Reporting System (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: The Aviation Safety Reporting System (ASRS) in a partnership between the National Aeronautics and Space Administration (NASA), the Federal Aviation Administration (FAA), participating carriers, and labor organizations. It is designed to improve the National Airspace System by collecting and studying reports detailing unsafe conditions and events in the aviation industry. Employees are able to report safety issues or concerns with confidentiality and without fear of discipline.
    Keywords: Air Transportation and Safety
    Type: ARC-E-DAA-TN13824 , Aviation Safety InfoShare; Mar 04, 2014; Seattle, WA; United States
    Format: application/pdf
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  • 9
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    Ground Related Safety Issues Through the Eyes of Flight Crews (2019)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: This presentation reviews voluntary safety reports received by NASA's Aviation Safety Reporting System pertaining to safety issues related to Ground Operations.
    Keywords: Air Transportation and Safety
    Type: ARC-E-DAA-TN67495 , Aviation Safety InfoShare; Apr 17, 2019; Dallas, TX; United States
    Format: application/pdf
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  • 10
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    Aircraft Taxi, Tow, or Pushback Gone Wrong ASRS Review of Maintenance Reports with Unintended Aircraft Movement Outcome (2018)
    In:  CASI
    Details
    Publication Date: 2019-08-16
    Description: This presentation reviews voluntary safety reports received by NASA's Aviation Safety Reporting System pertaining to aircraft taxi, tow, or pushback incidents during maintenance operations.
    Keywords: Air Transportation and Safety
    Type: ARC-E-DAA-TN54168
    Format: application/pdf
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