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Optimality criteria methods for structural optimization with flutter constraints
Published June 26, 1995 by Royal Aeronautical Society in United Kingdom
Besides the more common Mathematical Programming (MP) techniques, Optimality Criteria (OC) methods provide another way to obtain a quick near optimum design, specially when the initial design lies in the infeasible domain.
The first part of the paper is devoted to a brief historical review of Optimality Criteria Methods with aeroelastic constraints. It is followed by a description of a redesign formula which in turn is applied to a series of increasingly complex design tasks available at C.A.S.A. for systematic assessment of optimization algorithms with flutter constraints.
The first task is an academic example with two design variables that shows the behavior of the resizing algorithm in a two design variables space while starting from a wide variety of initial points.
In the second task, a dynamic model of a typical turbopropeller with metallic wing is used. First, the magnitudes of six balance masses that are attached to an aileron are sought that will provide a required flutter speed with a minimal addition in weight. It is shown that the automated design procedure is robust in that it converges to nearly the same final design while starting from different starting designs. Next, 215 structural wing sizes (spars, ribs, skins) are allowed to vary in addition to the six balance masses. It is shown that the design procedure can overcome the initial flutter deficiency and decreases the weight objective. In addition, a comparison with an alternative Mathematical Programming technique is presented showing good correlation. Sensitivity analyses to some parameters of the redesign formula are made at this stage.
In the third task, a dynamic model of the Airbus 340 horizontal tailplane build in composites is used. Several design models with a different number of design variables (52, 122 and 808) are used to show an increase of flutter speed in 15% with minimum number of layers added. A ""Hybrid"" method that uses the OC redesign formula while the design lies in the infeasible domain to switch to the MP technique once the feasible domain has been reached is shown to provide better convergence characteristics than when only MP is used.