Study Of Aero-structure Coupled Optimization For High Aspect Ratio Wings Using Multi-model Fusion Method

Due to the inherent advantages including high lift-to-drag ratio and large inner volume,high-aspect ratio wings have been widely used in modern aircraft systems,such as large intercontinental airplanes,long-range strategic bombers,high-altitude long-endurance UAVs,etc.Because of the large flexibility of high-aspect ratio wings,the aero-structure coupled problem should be considered in the design process,which makes the modeling and optimization procedure quite complex and time-consuming.To reduce the computational cost of the aero-structure coupled analysis and improve the design quality,the multi-model fusion idea is used for the aero-structure coupled optimization design of high-aspect ratio wings.This thesis mainly focuses on studies of aero-structure coupled modeling with various levels of fidelity and multi-model fusion based optimization methods.The main contents are summarized as follows:(1)The development history of aero-structure coupled analysis and optimization method,the-state-of-the-art of the key technologies of multi-disciplinary design optimization and multi-model fusion methods are summarized in detail.Furthermore,the existing problems in this field are pointed out and the study contents of this thesis are determined.(2)The modeling methods of multi-fidelity aero-structure coupled analysis for high-aspect ratio wings are studied.Based on the API functions provided by UG,the parametric model of three-dimensional wings is constructed.Aerodyanmic computational fluid dynamic(CFD)and structural finite element analysis(FEA)are adopted in aerodynamic modeling and structural modeling respectively.Then,the aero-structure coupled analysis is achieved by customizing the data exchange interface to transfer information between the two disciplines.The high fidelity and low fidelity aero-structure coupled analysis models are established by adjusting the grid density.The simulation results show that the overall trend of the analysis results from low fidelity model with coarse grids is almost the same as that of high fidelity model with fine grids,but the computational cost of low fidelity model is only 16.7% of the high fidelity model.Thus,it is reasonable to employ multiple fidelity models for optimizing aero-structure coupled high-aspect ratio wings using multi-model fusion method.(3)Based on the idea of the multi-model fusion method(MMF),a static enhanced multi-model fusion(SEMMF)method is proposed.The core idea of the SEMMF method is to construct a Kriging metamodel to replace the scaled low fidelity model,which overcomes the defect that the traditional MMF method needs to call a large amount of low fidelity models during the optimization process.Testing results on standard numerical benchmarks show that approximate models constructed by the SEMMF method have higher fidelity than the models constructed by Kriging method under the same computational cost.Then,the SEMMF method is employed to perform the optimization design of a high-aspect ratio wing.The comparison results show that SEMMF method can further improve the overall performance compared with the Kriging method under the same computational cost.After optimization,the overall performance is improved by 12.61%(i.e.,the structural mass is reduced by 24.49%,and lift-to-drag ratio is slightly improved.).Thus,effectiveness of the SEMMF method is validated in solving the aero-structure coupled problem.(4)To further improve the optimization efficiency,a dynamic enhanced multi-model fusion(DEMMF)method is proposed based on the aforementioned SEMMF method.A hybrid double-point sequence sampling strategy is developed.A combination of the minimum of the predicted objective function(MP)criterion and maximum of the Root Mean Square Error(RMSE)criterion is used for generating sequential samples.The SEMMF method is used to construct the fusion approximate model and the genetic algorithm is employed for optimization under the current approximate model.New samples are adaptively allocated through the hybrid double-point sequence sampling strategy to gradually improve the accuracy of the approximate model until the convergence conditions are satisfied(i.e.,accuracy evaluation criterion and optimal evaluation criterion).The test results show that the DEMMF method with hybrid double-point sequence sampling strategy outperforms the Kriging method with MP criterion/double-point criterion and the DEMMF method with MP criterion in terms of global convergence and optimization efficiency(5)Based on the studies of aero-structure coupled modeling with various levels of fidelity and multi-model fusion methods,the aero-structure coupled optimization framework is developed for design and optimization of a high-aspect ratio wing.Compared with the baseline design,the structural mass is reduced 49.48% and the lift-to-drag ratio increases 1.59%,so the synthetic performance of the wing is improved.Moreover,the DEMMF method with hybrid double-point sequence sampling strategy obtains the optimal result with the lowest computational cost compared with the direct optimization method(sequence quadratic programming,genetic algorithm),the static surrogate-based optimization method(SEMMF method)and other dynamic surrogate-based optimization methods(Kriging method with single-point criterion,Kriging method with double-point criterion and DEMMF method with single-point criterion).Thus,it is illustrated that the proposed multi-model fusion based aero-structure coupled optimization strategy for high-aspect ratio wing is efficient and practical for engineering practices.