Low Degree-of-freedom Collaborative Optimization And Its Application To Wing Design

Multidisciplinary design optimization (MDO) is one of the important development directions of aircraft design. Since MDO has been proposed, it is getting more attention and becomes prevailing. However there are still some problems. Multidisciplinary design optimization methods that appeared in recent years are too complicated. Polynomial response surface approximations are still the main surrogate models applied, but it is difficult to describe complicated relations with response surfaces. How to deal with outliers gets little attention when surrogate modes are constructed. It is difficult to make structure subsystem and aerodynamics subsystem concurrent when a wing is designed with MDO without accurate aerodynamic load distribution functions.Several research fields of MDO such as MDO methods, surrogate models, analysis and optimization models of structure and aerodynamics were investigated in this thesis.Low Degree-of-freedom Collaborative Optimization (LDFCO) was proposed through reducing the number of design variables and adjusting the objectives of subsystems based on Collaborative Optimization. Three test examples were used to verify the efficiency of LDFCO. The results show that LDFCO has high reliability and needs much less computation cost than CO. Based on outlier test and Sequential Kriging Optimization and according to the characteristics of surrogate models in MDO, a construction method of surrogate model for MDO–SKO based surrogate model was proposed. Several surrogate models of different levels of subsystems were researched and were applied to multidisciplinary design optimization of wings successfully.Two-step SKO was proposed and a structural layout optimization method was built based on two-step SKO, genetic algorithm, MSC. Patran and Nastran. A composite stiffened panel and a composite material wing were optimized with the structural layout optimization method. The results show that this optimization method has the ability to find out the approximate optimal solution, and can be used in engineering design conveniently.Based on Catia, Gambit and Fluent, an aerodynamics automatic analysis model was proposed. In order to transfer aerodynamics load among different subsystems, a quartic response surface with three coefficients was developed to fit lift distribution. Based on the aerodynamics automatic analysis model and the quartic response surface with three coefficients, a construction method of aerodynamics analysis surrogate models for high fidelity aerodynamics analysis models was proposed.Low Degree-of-freedom Collaborative Optimization was applied to solve Aerodynamic/structural multidisciplinary design optimization of a wing. The structure subsystem and the aerodynamics subsystem are parallel. Aerodynamics performance was calculated with VLM or Fluent. Structure analysis was performed using MSC. Patran and Nastran. The results show that Low Degree-of-freedom Collaborative Optimization can be applied to multidisciplinary design optimization of wings successfully.