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  • Other Sources  (5,351)
  • STRUCTURAL MECHANICS  (3,500)
  • CYBERNETICS  (1,851)
  • 1990-1994  (3,821)
  • 1970-1974  (1,530)
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  • Other Sources  (5,351)
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  • 1
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    Fuel-optimal slewing of an experimental hinged-free beam (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: With the recent development of numerical methods for exactly solving larger order fuel-optlmal control problems, the implementation of exact real-time fuel-optimal control becomes possible. This paper describes a physical experiment in which a hinged-free beam is slewed in a fuel-optimal manner. A comparison between experimental results and the analytical predictions highlights the sources of errors typical of this class of problems.
    Keywords: CYBERNETICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 6; p. 1162-1168.
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  • 2
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    Terrestrial applications of NASA space telerobotics technologies (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: In 1985 the National Aeronautics and Space Administration (NASA) instituted a research program in telerobotics to develop and provide the technology for applications of telerobotics to the United States space program. The activities of the program are intended to most effectively utilize limited astronaut time by facilitating tasks such as inspection, assembly, repair, and servicing, as well as providing extended capability for remotely conducting planetary surface operations. As the program matured, it also developed a strong heritage of working with government and industry to directly transfer the developed technology into industrial applications.
    Keywords: CYBERNETICS
    Type: AIAA PAPER 94-1235-CP , NASA. Johnson Space Center, Conference on Intelligent Robotics in Field, Factory, Service, and Space (CIRFFSS 1994), Volume 1; p 434-440
    Format: application/pdf
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  • 3
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    Decision boundary feature selection for non-parametric classifier (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Feature selection has been one of the most important topics in pattern recognition. Although many authors have studied feature selection for parametric classifiers, few algorithms are available for feature selection for nonparametric classifiers. In this paper we propose a new feature selection algorithm based on decision boundaries for nonparametric classifiers. We first note that feature selection for pattern recognition is equivalent to retaining 'discriminantly informative features', and a discriminantly informative feature is related to the decision boundary. A procedure to extract discriminantly informative features based on a decision boundary for nonparametric classification is proposed. Experiments show that the proposed algorithm finds effective features for the nonparametric classifier with Parzen density estimation.
    Keywords: CYBERNETICS
    Type: Society for Imaging Science and Technology, Annual Conference; May 12, 1991 - May 17, 1991; Saint Paul, MN; United States|; 4 p.
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  • 4
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    Transverse cracking and stiffness reduction in composite laminates (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A study of transverse cracking mechanism in composite laminates is presented using a singular hybrid finite element model. The model provides the global structural response as well as the precise local crack-tip stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eigenfunction expansion. Stress singularities associated with the transverse crack are obtained by decomposing the deformation into the symmetric and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principle of a modified hybrid functional to incorporate local crack singularities. Axial stiffness reduction due to transverse cracking is studied. The results are shown to be in very good agreement with the existing experimental data. Comparison with simple shear lag analysis is also given. The effects of stress intensity factors and strain energy density on the increase of crack density are analyzed. The results reveal that the parameters approach definite limits when crack densities are saturated, an evidence of the existence of characteristic damage state.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Reinforced Plastics and Composites (ISSN 0731-6844); 12; 9; p. 987-1015.
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  • 5
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    Thermal stresses in thick laminated composite shells (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The paper provides an analytical formulation to investigate the thermomechanical behavior of thick composite shells subjected to a temperature distribution which varies arbitrarily in the radial direction. For illustrative purposes, shells under uniform temperature change are presented. It is found that thermal twist would occur even for symmetric laminated shells. Under uniform temperature rise, results for off-axis graphite/epoxy shells show that extensional-shear coupling can cause tensile radial stress throughout the shell and tensile hoop stress in the inner region. Laminated graphite/epoxy shells can exhibit negative effective thermal expansion coefficients in the longitudinal and transverse directions. Finally, the stacking sequence has a strong influence on the thermal stress distributions.
    Keywords: STRUCTURAL MECHANICS
    Type: Composite Structures (ISSN 0263-8223); 26; 2-Jan; p. 63-75.
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  • 6
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    Recent advances in approximation concepts for optimum structural design (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The basic approximation concepts used in structural optimization are reviewed. Some of the most recent developments in that area since the introduction of the concept in the mid-seventies are discussed. The paper distinguishes between local, medium-range, and global approximations; it covers functions approximations and problem approximations. It shows that, although the lack of comparative data established on reference test cases prevents an accurate assessment, there have been significant improvements. The largest number of developments have been in the areas of local function approximations and use of intermediate variable and response quantities. It also appears that some new methodologies are emerging which could greatly benefit from the introduction of new computer architecture.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Optimization of large structural systems; Proceedings of the NATO(DFG Advanced Study Institute, Berchtesgaden, Germany, Sept. 23-Oct. 4, 1991. Vol. 1 (A93-54501 24-39); p. 235-256.
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  • 7
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    Practical model reduction for flexible structures (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: CYBERNETICS
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 41; 2; p. 227-247.
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  • 8
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    Material selection and evaluation aimed at resolving deficiencies of a space technology material (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: NASA-Kennedy Space Center propellant handlers' visors are undergoing conversion from Plexiglass G to a Surlyn 8920-based material; various Surlyn compositions are here subjected to a battery of environmental and mechanical-properties tests under the relevant conditions. Specially-molded Surlyn samples have exhibited much higher impact strengths than either Plexiglass G or Lexan, and passed the ANSI weight-drop test. DSC results show that Surlyn and Plexiglass G exhibit strikingly different thermal transitions.
    Keywords: STRUCTURAL MECHANICS
    Type: In: International SAMPE Technical Conference, 24th and International SAMPE Metals and Metals Processing Conference, 3rd, Toronto, Canada, Oct. 20-22, 1992, Proceedings. Vol. 24 (A93-53376 23-23); p. T724-T734.
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  • 9
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    Transverse shear deformation in exact buckling and vibration of composite plate assemblies (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 10; p. 1963-1965. Abridg
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  • 10
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    Strain energy of thermally stressed multilayer panels and its sensitivity coefficients (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A study is made of the effect of lamination and material parameters of thermally stressed multilayer composite panels on the strain energy and its sensitivity coefficients obtained by the three-dimensional thermoelasticity model. The sensitivity coefficients measure the sensitivity of the strain energy to variations in the different lamination and material parameters of the panel. The strain energy and sensitivity coefficients obtained by the three-dimensional model are used as the basis for assessing the accuracy of the corresponding quantities obtained by two-dimensional first-order shear deformation theory. Numerical results are presented for antisymmetrically laminated angle-ply panels subjected to linear temperature variation through the thickness. The numerical results demonstrate the accuracy of the strain energy and its sensitivity coefficients obtained by the first-order shear deformation theory, for the range of parameters considered, and the importance of the particular terms in the strain energy, which vanish for single-layer panels.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 10; p. 1946-1952.
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