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  • 1
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    Recent advances in thermal-structural analysis and design (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A continuing effort to develop a comprehensive capability for thermal-structural analysis and automated design (sizing) is reviewed. A principal role in the activity is played by the finite element program SPAR which contains both an efficient structural and thermal analysis capability. The benefit of having thermal and structural analyses in the same finite element program is illustrated by the application of SPAR to design calculations for the National Transonic Facility - a cryogenic wind tunnel under construction at Langley. Some experience with large-scale thermal structural analysis problems, particularly the space shuttle orbiter, has led to the identification of some analysis needs. Those needs include automated model generation and data output for lumped parameter thermal analysis, faster solution methods for nonlinear transient heat transfer, automated interpolation of temperature data from a thermal finite element model to a dissimilar structural finite model, and automated techniques to identify the times at which the critical combinations of transient heating and loads occur on a structure.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Advan. in Structures for Hypersonic Flight, Pt.2; p 897-941
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  • 2
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    Sensitivity analysis of discrete structural systems (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Methods for calculating sensitivity derivatives for discrete structural systems are surveyed, primarily covering literature published during the past two decades. Methods are described for calculating derivatives of static displacements and stresses, eigenvalues and eigenvectors, transient structural response, and derivatives of optimum structural designs with respect to problem parameters. The survey is focused on publications developed in nonstructural fields such as electronics, controls, and physical chemistry which are directly applicable to structural problems. Most notable among the nonstructural-based methods are the adjoint variable technique from control theory, and the Green's function and FAST methods from physical chemistry.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 24; 823-832
    Format: text
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  • 3
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    Sensitivity analysis and optimization of nodal point placement for vibration reduction (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location - for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 119; 277-289
    Format: text
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  • 4
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    Inclusion of transverse shear deformation in finite element displacement formulations (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A stiffness matrix is derived for a beam element with transverse shear deformation. It is shown that straightforward energy minimization yields the correct stiffness matrix in displacement formulations when transverse shear effects are considered. Since the TIM4 beam element does not represent the geometric boundary conditions for a cantilever beam the rotation of the normal must be retained as a grid point degree of freedom.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 12; Nov. 197
    Format: text
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  • 5
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    Resizing procedure for structures under combined mechanical and thermal loading (1976)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The fully-stressed design (FSD) appears to be the most widely used approach for sizing of flight structures under strength and minimum-gage constraints. Almost all of the experience with FSD has been with structures primarily under mechanical loading as opposed to thermal loading. In this method the structural sizes are iterated with the step size, depending on the ratio of the total stress to the allowable stress. In this paper, the thermal fully-stressed design (TFSD) procedure developed for problems involving substantial thermal stress is extended to biaxial stress members using a Von Mises failure criterion. The TFSD resizing procedure for uniaxial stress is restated and the new procedure for biaxial stress members is developed. Results are presented for an application of the two procedures to size a simplified wing structure.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 14; Oct. 197
    Format: text
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  • 6
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    Structural sensitivity analysis: Methods, applications, and needs (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some innovative techniques applicable to sensitivity analysis of discretized structural systems are reviewed. These techniques include a finite-difference step-size selection algorithm, a method for derivatives of iterative solutions, a Green's function technique for derivatives of transient response, a simultaneous calculation of temperatures and their derivatives, derivatives with respect to shape, and derivatives of optimum designs with respect to problem parameters. Computerized implementations of sensitivity analysis and applications of sensitivity derivatives are also discussed. Finally, some of the critical needs in the structural sensitivity area are indicated along with Langley plans for dealing with some of these needs.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Experiences in Multidisciplinary Analysis and Optimization, Part 1; 18 p
    Format: application/pdf
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  • 7
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    An isoparametric quadrilateral membrane element for NASTRAN (1972)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The geometric and kinematic properties of the element are described, along with development of the matrices and vectors which characterize the element. The necessity for considering small deviations from element planeness is discussed, and the approach taken to account for these deviations is described. The improved accuracy over the existing quadrilateral membrane is indicated by a sample calculation for which an analytical solution is available from beam theory. For the same finite element idealization, the errors in maximum displacement and stress were significantly reduced.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences e; p 315-336
    Format: application/pdf
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  • 8
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    A comparison of several methods for the calculation of vibration mode shape derivatives (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Four methods for the calculation of derivatives of vibration mode shapes (eigenvectors) with respect to design parameters are reviewed and compared. These methods (finite difference method, Nelson's method, modal method and a modified modal method) are implemented in a general-purpose commercial finite element program and applied to a cantilever beam and a stiffened cylinder with a cutout. A beam tip mass, a beam root height and specific dimensions of the cylinder model comprise the design variables. Data are presented showing the amount of central processor time used to compute the first four eigenvector derivatives for each example problem; errors and rapidity of convergence of the approximate derivative to the exact derivative are taken into account. Nelson's method proved to be most reliable and efficient.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 86-0873
    Format: text
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  • 9
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    Senstitivty analysis and optimization of nodal point placement for vibration reduction (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location - for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-87763 , NAS 1.15:87763
    Format: application/pdf
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  • 10
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    Analysis of a Hot Elevon Structure (1971)
    In:  CASI
    Details
    Publication Date: 2014-09-03
    Description: Comparison of ASKA and NASTRAN programs analyses of space shuttle hot elevon test article deformed under thermal and mechanical loads
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users Experiences; p 163-180
    Format: text
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