| Blended wing body(BWB)aircraft is a new type of aircraft with the wing and fuselage blended together.Because of the advantages in aerodynamics,structure,capacity and environmental protection,the BWB aircraft is considered to be a possible solution for the long range airliner of next generation.A key technology of BWB aircraft design is the integrated analysis and optimization method in conceptual design.To this end,a methodology including multidisciplinary analysis,comprehensive evaluation,efficient optimization algorithm and visualization techniques is established,which provides an effective method and tool for BWB conceptual aircraft design.The main contents of the dissertation are as follows:1)The geometric,aerodynamic,mass,stability and control models for the BWB aircraft are studied and built.The multidisciplinary analysis model for the BWB aircraft is established by combination of the above models with the propulsion,performance,direct operating costs,and emission models.In the geometry model,a parameterization method is used to quickly generate the cabin layout and 3D geometry of the BWB aircraft.For mass,stability and control models,both engineering estimation and numerical analysis are adopted for conceptual analysis.2)To evaluate the competitiveness of a commercial aircraft,a comprehensive evaluation model with four layer architecture is established by AHP(Analytic Hierarchy Process).The model contains four evaluation criteria including economic,comfort,environmental protection and adaptability.By generating judgment matrixes,the evaluation criteria are transformed to 22 specific indexes of commercial aircrafts.A mechanism for a group of experts to evaluate one target is introduced to improve the reasonability of weight distributions.3)In order to improve the efficiency and usability of the optimization method application,a new optimization algorithm and an efficient visualization method are proposed.The subset simulation method,originally developed for structural reliability problems,is used to solve optimization problems.In this thesis,subset simulation is extended to solve multi-objective optimization problems by taking advantages of the non-dominated sorting algorithm and duplication-removal sorting algorithm.A parallel mechanism is proposed to further reduce the computational cost.With the combination of a variety of visualization techniques,a visualization method is proposed to make it more intuitive on optimization formulation,process monitoring and result processing in conceptual design.The method is demonstrated to be useful for optimization formulation,parameters correlation study and decision making.4)The integration of multidisciplinary analysis model,comprehensive evaluation model,subset simulation optimization algorithm and visualization method is completed with a MATLAB programming.Through implementation of the integration,a tool for comprehensive analysis,evaluation and optimization for BWB aircraft conceptual design is developed.5)The developed tool is tested by a typical aircraft design with BWB configuration.Three optimization problems are conducted,including a single objective optimization problem with the objective of minimum maximum takeoff weight,a multi objective optimization problem with the objectives of minimum approach speed and minimum direct operating cost,and an unconstrained optimization problem based on the comprehensive evaluation model.The test example demonstrates that the proposed models can be used for comprehensive analysis,evaluation and optimization of the BWB aircraft.And,the developed tool can be used to support the decision making in conceptual design.To evaluate the technical benefits of the BWB aircraft,the optimal results are compared with a conventional aircraft.The result shows that the BWB aircraft has an advantage in reducing operating costs when compared to conventional aircrafts.However,due to the lack of effective high-lifting devices and conventional tails,the BWB aircraft has a disadvantage on taking off performance,landing performance,stability and controllability performance. |
