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  • Other Sources  (4,813)
  • AERODYNAMICS  (2,823)
  • STRUCTURAL MECHANICS  (1,990)
  • Life and Medical Sciences
  • 1990-1994  (4,813)
  • 1910-1914
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  • 1
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    Overview of supersonic laminar flow control research on the F-16XL ships 1 and 2 (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: NASA is directing research to develop technology for a high-speed civil transport. Supersonic laminar flow control has been identified as a program element, since it offers significant drag-reduction benefits and is one of the more promising technologies for producing an economically viable aircraft design. NASA is using two prototype F-16XL aircraft to research supersonic laminar flow control. The F-16XL planform is similar to design planforms of high-speed civil transports. The planform makes the aircraft ideally suited for developing technology pertinent to high-speed transports. The supersonic laminar flow control research programs for both aircraft are described. Some general results of the ship-1 program demonstrate that significant laminar flow was obtained using laminar flow control on a highly swept wing at supersonic speeds.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 921994 , ; 14 p.|SAE, Aerotech ''92 Conference; Oct 05, 1992 - Oct 08, 1992; Anaheim, CA; United States
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  • 2
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    Perspectives on hypersonic viscous flow research (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Issues and advances in current hypersonic flow research perceived to be of interest in theoretical fluid/gas dynamics are reviewed. Particular attention is given to the hypersonic aircraft as waverider, computational methods and theoretical development in the study of viscous interaction, and boundary-layer instability and transition studies. In the present framework the study of viscous hypersonic flow faces transition problems of two kinds which represent the two major areas of current research: the turbulence transition in the high Re range and the transition to the free-molecule limit.
    Keywords: AERODYNAMICS
    Type: In: Annual review of fluid mechanics. Vol. 25 (A94-10885 01-34); p. 455-484.
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  • 3
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    Identification of aerodynamic coefficients using computational neural networks (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: AERODYNAMICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 6; p. 1018-1025.
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  • 4
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    Development of the wake behind a circular cylinder impulsively started into rotatory and rectilinear motion (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The temporal development of a 2D viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law. Results are presented for a Reynolds number of 200 (based on the cylinder diameter 2a and the magnitude U of the rectilinear velocity) for several values of the angular/rectilinear speed ratio alpha = omega(a)/U (where omega is the angular speed) up to 3.25. Several aspects of the kinematics and dynamics of the flow not considered earlier are discussed. For higher values of alpha, the results indicate that for Re = 200, vortex shedding does indeed occur for alpha = 3.25. However, consecutive vortices shed by the body can be shed from the same side and be of the same sense, in contrast to the nonrotating case, in which mirror-image vortices of opposite sense are shed alternately on opposite sides of the body. The implications of the results are discussed in relation to the possibility of suppressing vortex shedding by open or closed-loop control of the rotation rate.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 449-484.
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  • 5
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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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  • 6
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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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  • 7
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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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  • 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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