Abstract
Constraint functions are formulated and their analytical sensitivities derived for multi-axial 2D states of stress arising in actively controlled airplane structures from combined maneuver loads and random gust responses. Failure criteria based on maximum normal and shear stresses (or strains) are considered. These criteria are non-linear in nature and involve interactions between stress and strain tensor components. The gust response is based upon random gust analysis using state space mathematical models and statistical properties of gusts in the atmosphere. The covariance matrix of the stress (or strain) tensor components at a point is used to define a quadratic surface representing combinations of equal probability. It is shown how a single critical combination can be determined analytically for all combinations on the equal probability surface. Analytic sensitivities of the resulting constraint with respect to design variables are derived. A constraint function approximation is also derived to reduce the computational effort in an Approximation-Concepts based optimization strategy. The constraint, the analytic sensitivities and approximations are then integrated into a Multidisciplinary Aeroservoelastic Optimization capability, and results for a large flexible commercial transport airplane are presented.
Published Version
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