Research On The Layout Optimization Design Method Of Composite Wing Structures

The application proportion of composites has become an important advanced standard for modern airliners. Passenger jets usually employ semirigid shell wing structures, in which stiffened wing panels are the main load-bearing components. To apply composite materials in these structures could reduce weight significantly, and improve filght performances. Structural layout defined in preliminary design phase might bring the desicive influences in the overall properties of the structure. Therefore the research on layout design method of the composite wing structures is valuable in engineering.A two-level optimization strategy is proposed in this thesis for the layout design of large scale composite wing structures, which optimizes the positional relationships between different components to increase the structural efficiency as an objective. System level adjusts stiffness standard according to structural deformation, while subsystems optimize the layout to satisfy the designated constraints. The approaching degrees of various failure critical loads are employed to gauge the structure's carrying efficiency. By optimizing the efficiency as an objective, the continuity of the problem could be guaranteed, which facilitates numerical optimization. Stiffened wing panels are simulated by the equivalent stiffness models, and their global buckling loads are predicted based on energy method. The nonlinear effect of stringers'support elasticity on the local buckle resistance of the anisotropic skin is investigated, and a general approximation model is proposed using matching relationships between structural siffnesses as input parameters. The calculation efficiency is improved by evaluating the structure mechanical features using various approximation models. Finally, the optimization framework is integrated into the interface of PATRAN software by PCL secondary development codes, and the accuracy and fesibility are verified by the example of layout optimization for a large scale composite wing structure.The research results in this thesis demonstrate that: Equivalent stiffness model could provide satisfied accuracy in the global buckling analysis of composite stiffened panels; there is a nonlinear relationship between the local buckling resistance of the skin in composite stiffened structure and the stiffeners'support stiffnesses, as well as the anisotropy of the skin itself, and the relationship could be approximated by surrogate models; based on various simplifying methods, the objective improved the structural efficiency; the wing structure two-level layout optimization framework could convert the discrete layout parameters into continuous stiffness coefficients, and the layout optimization of wing panels considering buckling cases could be achieved, which improves the reliability of optimization process and converges rapidly, as well as it provides satisfied global optimization capability.