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Optimum stacking sequence design of composite materials Part II: Variable stiffness design

Optimum design of composite structures with curved fiber courses

The drive for ever more efficient aircraft structures stimulates the research to use the full potential of anisotropy of composite materials. The stiffness optimization of the upper and lower skins...

Stiffness Optimization of Composite Wings with Aeroelastic Constraints

Improved aeroelastic tailoring using tow-steered composites

Optimum structural design with stability constraints

A wing-design optimization study is conducted on a composite wing. The objective is to evaluate the effect of the compositelayup orientation on theoptimized weight while satisfying constraints on strength, roll-reversalvelocity, and e utter velocity. The wing optimization studies are presented with the composite layups oriented at 5-deg increments up to § 20 deg from the midspar of the wing. The multidisciplinary optimization system, ASTROS, was used in the design study. This study, although not conclusive, indicates that optimal designs when subjected to multiple structural constraints are relatively insensitive to the orientation of the laminate layup. I. Introduction M ULTIDISCIPLINARYdesign optimization (MDO)hasbeen the subject of numerous investigations in recent years. This technology push is primarily attributed to the rapid growth in speed, data transfer,and storage capabilities of modern computers. Itis anticipated that in a few years the speed of computation may surpass the Ge ops/s range with similar improvements in memory devices. The computer’ s capabilities are doubling or tripling in a relatively short time, while the cost of computation and information processing is reducing by similar factors. These far-reaching developments in computers are the propelling force behind the rapid evolution of the so-called information highway . The information explosion is already affecting almost every facet of life in industrialized countrieswhilepushing industrializationofthe remainingcountries.The world is a very competitive market place for products. It is expected to be even better for the consumer. Cost, quality, and innovation are the key ingredients for success in such an environment. A wellorchestrated MDO strategy is the best means for improvement in all three areas. It is often the mistakes made in early design that haunt the bad performance of the products. MDO systems on modern computers allow the rapid evaluation of the operation scenarios of the products. The rapid strides in computers are the catalyst in promoting sophisticated computer architectures, database technology, and numerical methods. These developments, in turn, are providing the necessary infrastructure for integration of both disciplines and the designstages.Forexample,inairframedevelopment,aerodynamics, structures, and controls are the main disciplines; whereas in design, manufacture, operation, and maintenance are the stages of development. Each of these stages is further divided into manageable tasks that are appropriate to available resources. For example, the design task is traditionally conducted in conceptual, preliminary, and detail design stages. If we couple this view of design with the task of integration of the disciplines (such as aerodynamics, structures, and controls ), we have an almost intractable optimization problem, where the overall minimum cost is the primary driver. It is under

Aeroelastic Tailoring of Composite Structures

Optimization of fiber reinforced composite structures

The influence of a wing tip missile on the design optimization of a wing structure is studied. Finite element models of a realistic built-up wing structure are used to represent stiffness and mass properties. The store location and the effect of the store aerodynamics and mass are the variables included. A multidisciplinary optimization technique is used to compensate/restore the lost aeroelastic performance due to the presence of the store. Missile locations are the only configuration variables addressed besides the structural variables. The built-up wing box structure is optimized with constraints on the static strength and flutter speed. The thickness and the cross-sectional areas of the structural elements are the primary variables in the optimization. The aerodynamics of the tip missile has a significant effect on the flutter characteristics. In addition, the flutter behavior of the optimized structure is very sensitive to the tip missile movement along the tip chord. The results indicate that the effect of the tip missile aft movement must be examined in conjunction with the store aerodynamics. ASTROS is the primary tool used.

Multidisciplinary Design Optimization of a Built-Up Wing Structure with Tip Missile

Vibration control as applied to large space structures is the subject or this study. A number of computational issues have to be resolved before integrating the disciplines of optimal structural design and modern control theory. Control of free-free structures and the effects of model order reduction are the two issues addressed in this paper. Results are presented for a two dimensional truss structure.

Dynamics and control of space structures

The objective of the paper is to demonstrate the validity of e utter predictions obtained using eigenvector orientations (EVO) for realistic wings used in aircraft preliminary design. Comparisons of e utter predictions between the V-g method and the EVO method are presented for an intermediate complexity wing used in optimization studies. The results presented show that the EVO method can predict the onset of e utter for aircraft wings with reasonable accuracy and can be used in design optimization studies of aerospace vehicles/components. I. Introduction T HEdesign of modern e ight vehicles requires multidisciplinary designoptimization (MDO),theintegrationofstructures,aerodynamics,controlandpropulsiondisciplines,toachieveanoptimum design based on certain performance criteria and constraints. In the design of e ight vehicles, e utter is a critical parameter that must be considered in the early stage of the design cycle. Also, with aging aircraft,certainrestrictionsneedtobeimposedinordertoavoide utterinstabilityduring thee ightregimeoftheaircraft.Alargenumber of parameter changes must be investigated in the e utter design of military as well as commercial aircraft as a result of the complexity of modern composite/metallic structures. Accurate and efe cient methods of e utter prediction for aerospace vehicle components are needed for use in aeroelastic design optimization studies. There are several aeroelastic design optimization codes being used for aircraft and spacecraft structures, such as the Automated Structural Optimization System (ASTROS) 1 and MSCNASTRAN. 2 In aeroelastic design optimization the predominant dynamic e utter instability needs to be investigated for most e ight vehicles. Several methods are being used to predict the onset of e utter instability in aeroelastic design optimization. Most of these methods arebasedoncomplexeigenvalues (p-kmethod, K-method, orKE method). 2 Recently,Afolabietal. 3 developed amethodbased on eigenvector orientations (EVO) to predict the onset of e utter instability. In their work the method of EVO was used for limited examples of panel e utter. To gain a better understanding of the EVO method of e utter prediction, further investigations need to be carried out on realistic aircraft structures. This understanding will help to devise a prediction methodology that may be implemented in MDO codes for the preliminary design of e ight vehicles. The objectiveofthispaperisto further validate the EVOmethod 3 of e utter prediction for realistic examples used in aircraft preliminary design. Abriefreviewofthe EVOmethod for e utterprediction isdescribed inthe nextsection.Anexampleofanintermediatecomplexity wing used in design optimization studies is considered, and e utter prediction results are compared to the commonly used V-g method.

V. A. Tischler

Papers

Aeroelastic Tailoring of Composite Structures

Optimization of fiber reinforced composite structures

Multidisciplinary Design Optimization of a Built-Up Wing Structure with Tip Missile

Dynamics and control of space structures

Flutter Prediction Methods for Aeroelastic Design Optimization