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  • 1
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    Iterative methods for design sensitivity analysis (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A numerical method is presented for design sensitivity analysis, using an iterative-method reanalysis of the structure generated by a small perturbation in the design variable; a forward-difference scheme is then employed to obtain the approximate sensitivity. Algorithms are developed for displacement and stress sensitivity, as well as for eignevalues and eigenvector sensitivity, and the iterative schemes are modified so that the coefficient matrices are constant and therefore decomposed only once.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, Recent Advances in Multidisciplinary Analysis and Optimization, Part 2; p 713-726
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Exponential approximations in optimal design (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: One-point and two-point exponential functions have been developed and proved to be very effective approximations of structural response. The exponential has been compared to the linear, reciprocal and quadratic fit methods. Four test problems in structural analysis have been selected. The use of such approximations is attractive in structural optimization to reduce the numbers of exact analyses which involve computationally expensive finite element analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Langley Research Center, Research in Structures, Structural Dynamics and Materials, 1990; p 137-150
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  • 3
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    Problems in large-scale structural optimization (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A general design optimization model for large complex systems is defined. Major features of the model that challenge various optimization algorithms are discussed. Requirements of a model optimization algorithm are identified. Objectives of the study of various algorithms are defined and a basis for conducting such a study is developed. Primal as well as transformation methods are analytically studied and a unified viewpoint of various methods is presented. Several numerical examples are solved using different methods to study their performance. Conclusions drawn from the study are presented and discussed. Areas of future research in nonlinear programming as well as structural optimization are identified and discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Recent Experiences in Multidisciplinary Analysis and Optimization, Part 2; 26 p
    Format: text
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  • 4
    Electronic Resource
    Electronic Resource
    A systematic approach for generating velocity fields in shape optimization (1992)
    Springer
    Structural and multidisciplinary optimization 5 (1992), S. 84-94 
    Details
    ISSN: 1615-1488
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Design velocity fields affect every stage of the shape optimization process. The progress of the optimization process, distortion of the finite element mesh, and final shape are sensitive to the quality of velocity fields. It is important to identify and generate effective velocity fields at the beginning of the process. This paper provides several criteria to determine the effectiveness of velocity fields. A systematic approach for generating these velocity fields using deformation fields is developed. The use of interactive procedures is shown to be indispensable for ensuring the effectiveness and quality of design velocity fields. General strategies and guidelines for generating velocity fields are given. Concepts of weight-reducing, stress-reducing, form-preserving, and smooth basis shapes are presented. Normalization of velocity fields is discussed. A method for controlling mesh distortion during the shape optimization process is given based on an explicit limit on the design change to prevent the Jacobian from vanishing. Two- and three-dimensional design problems are solved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01744700
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    A general optimization strategy for sound power minimization (1994)
    Springer
    Structural and multidisciplinary optimization 8 (1994), S. 113-119 
    Details
    ISSN: 1615-1488
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A general approach for minimizing radiated acoustic power of a baffled plate excited by broad band harmonic excitation is given. The steps involve a finite element discretization for expressing acoustic power and vibration analysis, analytical design sensitivity analysis, and the use of gradient-based optimization algorithms. Acoustic power expressions are derived from the Rayleigh integral for plates. A general methodology is developed for computing design sensitivities using analytical expressions. Results show that analytical sensitivity analysis is important from both computational time and accuracy considerations. Applications of the optimization strategy to rectangular plates and an engine cover plate are presented. Thicknesses are chosen as design variables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01743306
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  • 6
    Electronic Resource
    Electronic Resource
    An optimization algorithm based on the method of feasible directions (1995)
    Springer
    Structural and multidisciplinary optimization 9 (1995), S. 83-88 
    Details
    ISSN: 1615-1488
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The theory and implementation of an optimization algorithm code based on the method of feasible directions are presented. Although the method of feasible directions was developed during the 1960's, the present implementation of the algorithm includes several modifications to improve its robustness. In particular, the search direction is generated by solving a quadratic program which uses an interior method based on a variation of Karmarkar's algorithm. The constraint thickness parameter is dynamically adjusted to yield usable-feasible directions. The theory is discussed with emphasis on the important and often overlooked role played by the various parameters guiding the iterations within the program. Also discussed is a robust approach for handling infeasible starting points. The code was validated by solving a variety of structural optimization test problems that have known solutions (obtained by other optimization codes). A variety of problems from different infeasible starting points has been solved successfully. It is observed that this code is robust and accurate. Further research is required to improve its numerical efficiency while retaining its robustness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01758824
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  • 7
    Electronic Resource
    Electronic Resource
    Trust region methods for structural optimization using exact second order sensitivity (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 32 (1991), S. 275-293 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The performance of multiplier algorithms for structural optimization has been significantly improved by using trust regions. The trust regions are constructed using analytical second order sensitivity, and within this region, the augmented Lagrangian φ is minimized subject to bounds. Evaluation of first and second derivatives of φ by the adjoint method does not require derivations of individual (implicit) constraint functions, which makes the method economical. Eight test problems are considered and a vast improvement over previously used multiplier algorithms has been noted. Also, the algorithm is robust with respect to scaling, input parameters and starting designs.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620320204
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