Multidisciplinary design optimization is a field of research that studies the application of numerical optimization techniques to the design of engineering systems involving multiple disciplines or components. Since the inception of multidisciplinary design optimization, various methods (architectures) have been developed and applied to solve multidisciplinary design-optimization problems. This paper provides a survey of all the architectures that have been presented in the literature so far. All architectures are explained in detail using a unified description that includes optimization problem statements, diagrams, and detailed algorithms. The diagrams show both data and process flow through the multidisciplinary system and computational elements, which facilitate the understanding of the various architectures, and how they relate to each other. A classification of the multidisciplinary design-optimization architectures based on their problem formulations and decomposition strategies is also provided, a...

Multidisciplinary design optimization: A survey of architectures

An efficient automated minimum weight design procedure is presented which is applicable to sizing structural systems that can be idealized by truss, shear panel, and constant strain triangles. Static stress and displacement constraints under alternative loading conditions are considered. The optimization algorithm is an adaptation of the method of inscribed hyperspheres and high efficiency is achieved by using several approximation concepts including temporary deletion of noncritical constraints, design variable linking, and Taylor series expansions for response variables in terms of design variables. Optimum designs for several planar and space truss examples problems are presented. The results reported support the contention that the innovative use of approximation concepts in structural synthesis can produce significant improvements in efficiency.

Some Approximation Concepts for Structural Synthesis

An historical account is given of the development, from its conception in 1960, of the structural synthesis method. While synthesis techniques lag behind analytical ones in both sophistication and application, the structural design procedures created by combining finite element analysis and mathematical programming algorithms have progressed to the point of maturity. As in the case of finite element analysis, use and acceptance of structural synthesis methodology depends on the development and distribution of easily used and well-documented, production-quality computer programs. Attention is given such elementary applications of synthesis methods as the three-bar truss, an integrally stiffened waffle plate, a stiffened cylindrical shell, aircraft fuselage window panels, the structural efficiency of graphite-epoxy hat-stiffened panels, and an idealized delta wing.

Structural synthesis - Its genesis and development

The general characteristics of panel flutter at high supersonic Mach numbers are examined theoretically. Linear plate theory and two-dimensional first-order aerodynamics are used. The paper attempts to clarify the important role of damping, the relationship between traveling and standing wave theories of panel flutter, and the effects of edge conditions. The solution procedures and general mathematical behavior may be of interest in other stability problems characterized by the appearance of complex eigenvalues.

Theoretical considerations of panel flutter at high supersonic Mach numbers.

Recent advances in structural analysis and design technology for buckling-critical shell structures are discussed. These advances include a hierarchical analysis strategy that includes analyses that range from classical analysis methods to high-fidelity nonlinear finite element analysis methods, reliability based design methods, the development of imperfection data bases, and the identification of traditional and nontraditional initial imperfections for composite shell structures. When used judiciously, these advances provide the basis for a viable alternative to the traditional and conservative lower-bound design philosophy of the 1960s. These advances also help answer the question of why, after so many years of concentrated research effort to understand the behavior of buckling-critical thin-walled shells, one has not been able to improve on this conservative lower- bound design philosophy in the past.

Future directions and challenges in shell stability analysis

Hypersonic vehicles are envisioned to require, in addition to carbon-carbon and ceramic-matrix composities for leading edges heated to above 2000 F, such 600 to 1800 F operating temperature materials as advanced Ti alloys, nickel aluminides, and metal-matrix composited; These possess the necessary low density and high strength and stiffness. The primary design drivers are maximum vehicle heating rate, total heat load, flight envelope, propulsion system type, mission life requirements and liquid hydrogen containment systems. Attention is presently given to aspects of these materials and structures requiring more intensive development.

Materials and structures for hypersonic vehicles

The accuracy of the two-dimensional static aerodynamic approximation for flutter analyses is investigated by comparison with results obtained on the basis of exact linearized threedimensional potential flow theory. For unstressed panels, these results indicate that, for Mach numbers greater than 1.3, two-dimensional static aerodynamics is applicable over the whole range of length-width ratios greater than 1. The theoretical boundaries are also in good agreement with experimental data obtained from stress-free isotropic panels with length-width ratios from 1 to 10. For stressed panels, results using the approximate aerodynamics differ widely from the trends indicated by experiment; use of more exact aerodynamics does not alter this comparison, but inclusion of structural damping improves the correlation of theory and experiment. Experimental results for unstressed corrugationstiffened panels are also presented and compared with theory. In some cases flutter occurred at dynamic pressures as low as 2% of the predicted value. An analysis of the effect of panel boundary conditions shows that such highly unconservative predictions may result from failure to account for the deflectional stiffness of the panel supports. Application of this analysis to the test panels results in marked improvement in the flutter predictions.

Some recent developments in flutter of flat panels

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Results from a continuing effort to develop automated methods for structural design are described. A system of computer programs presently under development called SAVES is intended to automate the preliminary structural design of a complete aerospace vehicle. Each step in the automated design process of the SAVES system of programs is discussed, with emphasis placed on use of automated routines for generation of finite-element models. The versatility of these routines is demonstrated by structural models generated for a space shuttle orbiter, an advanced technology transport,n hydrogen fueled Mach 3 transport. Illustrative numerical results are presented for the Mach 3 transport wing.

Automated procedures for sizing aerospace vehicle structures /SAVES/

A comparison is made of results obtained from mathematical programing and optimality criteria procedures for the minimum-mass design of typical aircraft wing structures to satisfy prescribed flutter requirements The mathematical programing method is based on an interior penalty function approach A Langrangian optimality criterion and an intuitive optimality criterion based on uniform strain energy density are considered An intuitive resizing procedure is used for both optimality criterion solutions All results are calculated using the same computer program, changing only the optimization procedure Both high- and low-aspect-ratio wings are examined Finite elements are used for structural modeling, and the generalized coordinates for the flutter solution are based on the natural vibration modes of the structure Second-order piston theory aerodynamics is used for supersonic conditions and kernel function aerodynamics for subsonic conditions Convergence of the optimality criteria procedures with respect to the number of natural modes is considered [A ] [B] [Bti] Nomenclature

Sidney C. Dixon

Papers

Materials and structures for hypersonic vehicles

Some recent developments in flutter of flat panels

Materials and structures for hypersonic vehicles

Automated procedures for sizing aerospace vehicle structures /SAVES/

Comparison of Two Types of Structural Optimization Procedures for Flutter Requirements