Design, Analysis And Optimization For The Low Detectable Structures Of Aircraft Wing

Low detectability is one of most important requirements for military air vehicle. There are many effective ways that can lower the detectability. One of them is use of low detectable structure to reduce the radar cross section (RCS) of the military aircraft. The low detectable (LD) structure is a kind of the multifunctional structure which is able to meet the demand of aircraft external shape, to carry the loads and to reduce electromagnetic scattering. Usualy, it is consist of radar-transparent skins, radar absorbent materials and carrying-structures. To obtain the effective LD structure of wing, this dissertation investigates the design, analyse and optimization for the LD structure of wings. The major contributions include that:1) Based on the mechanism of the electromagnetic scattering and features of wing structure, four low detectable wing structures, which aim at low cost and use for unmanned combat air vehicles, are proposed. The models for these four LD structures are fabricated. The RCS of the four models are measured in the anechoic chamber. The results of the RCS experiments and the comparisons with conventional wing structure indicate that the low detectable wing structure is an effevtive and promising means to reduce the RCS of wing.2) In order to conduct the quantitative analysis for the electromagnetic scattering features of low detectable wing structures, the numerical analyzed models for electromagnetic scattering of low detectable wing structures must be established. Based on analyses and comparsions among several RCS prediction methods, it is concluded that the finite-difference time-domain (FD-TD) method is most suitable method for the numerical simulations of low detectable wing structures. This FD-TD numerical models and simulations provide an efficient way of the quantitative analysis for the electromagnetic scattering of low detectable wing structures, and further pave the way for optimization.3) To investigate the effectiveness of the low detectable wing structures used in air vehicles, applications of the LD structures to a cruise missile model with conventional configuration and the unmanned combat air vehicle model with flywing configuration are carried out. The finite difference-time domain (FD-TD) method is used for the numerical simulations of radar cross section for the cruise missile and the UCAV models. The simulation results of electromagnetic scattering indicate that the RCS of cruise missile and UCAV models are reduced substantially after using of low detectable wing structures.4) In order to improve the LD wing structures'capacity in reducing RCS, the optimization methods are applied to LD wing structures. The RCS in terms of the azimuths or the frequency is minimized by using an efficient deterministic optimization method based on the surrogate models. To consider the uncertainties, which exits in fabrication of the LD structures, the robust design optimization is proposed for the design of the LD structures. The results obtained from the robust design optimization show that that the RCS of the low detectable wing structures is reduced radically, and its sensitivity to design variables'uncertainties is minimized.5) To improve aerodynamic performance, to minimize structure's weight and to reduce the radar cross section (RCS) of the LD wing, the multidisciplinary optimization method is applied to the design of low detectable wing structures and a wing design problem of the unmanned aerial vehicle is used for an application example. An approach, which is based on a two-level optimization strategy and the surrogate models, is proposed for this multidisciplinary optimization problem. The results indicate that the approach is able to solve the wing multidisciplinary optimization problem which involves with aerodynamics, structure and low detectability. A set of Pareto optimal solutions is obtained by this approach. Based on a set of Pareto optimal solutions, desiger can make the trade-offs between different objectives and select an appropriate compromise design.