| Constraint functions are formulated and their analytical sensitivities derived for multi-axial states of stress arising in actively controlled airplane structures from combined maneuver loads and random gust responses. A complete formulation of the reduced-order gust response problem for aeroservoelastic design synthesis, tailored toward integration with control system design techniques based on modern control, is presented. A method for obtaining accurate stress and stress sensitivity information from reduced order Linear Time Invariant (LTI) state space models of integrated aeroservoelastic systems, using Lyapunov's Equation, is formulated. It includes an adaptation of the Mode Acceleration method and reduced-order analytic sensitivities of stress covariances. Efficient approximations to reduce computational effort in a Nonlinear Programming/Approximation Concepts (NLP/AC) approach are derived. The constraints, analytic sensitivities, and approximations are integrated into a Multidisciplinary Aeroservoelastic Optimization capability. A realistic aeroservoelastic model of a typical passenger airplane is used as a test case. Results include convergence studies for the assessment of order reduction effects on the accuracy of the integrated structure/aerodynamic/control models as well as validations of the derived constraint, sensitivity and approximation formulations. |
