Strcutural Mass Prediction In Conceptual Design Of Blended Wing Body Aircraft

The blended wing body(BWB),due to its higher efficiency of aerodynamics and lower level of noise,has been considered as one of the most potential aircraft configurations oriented towards "Green Aviation".The BWB aircraft is a kind of unconventional configuration aircraft and its structural mass prediction is quite challenging due to lack of relevant experience and historical data.However,the mass prediction plays a crucial role in aircraft conceptual design,and the accuracy of mass prediction has a large impact on fesibilty of aircraft conceptual design.Therefore,a reliable structural mass prediction method for the BWB aircraft conceptual design is a key technology to be solved.To this end,a structural mass prediction method for BWB aircraft conceptual design is studied,which combines physics-based finite element method(FEM)and statistical-based empirical method.And,a structural mass estimation tool is developed,which provides an effective way for mass predication in the conceptual design of BWB aircraft.The main contents and contributions of this dissertation are summarized as follows:1)Determining the cabin layout for BWB aircraft is an important decision in the conceptual design stage,which has a great influence on the shape and structural mass of the aircraft.A method for rapid design of cabin layout is developed based on Knowledge-Based Engineering(KBE)method by integrating the knowledge and specifications of cabin layout into the process of geometric model generation of the cabin layout.And the method can be used to investigate the influences of cabin layouts on the configuration and structural mass for the BWB aircraft.2)A parameterization method for the geometry of BWB aircraft is studied,including parameterization of fuselage,wing and vertical tail.Based on the parameterization method,a geometry model can be automatically generated by using CATIA secondary development method,which can be used as a unified model for aerodynamic analysis and structural optimization.3)The main load-carrying structural mass estimation method for the BWB aircraft based on the finite element method is studied.By uses of parameterization method and equivalent method with finite element(FE)model,the modeling process can be simplified and the FE model can be generated automatically by using Patran Command Language(PCL).A global–local optimization strategy is proposed,in which the procedure of optimization is divided into two levels.One is Global optimization which uses to optimize the dimensions of spars,ribs,frames and floors to minimize the structural mass while the other is Local optimization which optimizes the cross section shape of local panels.The optimization is an iterative process and will be repeated until the convergence criterion is satisfied.The example shows that the optimization strategy has advantage of high efficiency that is quite useful in the structural optimization of conceptual design stage.4)The structural mass estimation method for the BWB aircraft is studied.The main load-carrying mass calculation using FEM,and non-ideal and secondary structures mass calculation based on empirical equation are integrated,which can predict the whole structural mass of the BWB aircraft.Compared to the structural mass of a typical BWB aircraft,the results show that the method proposed in this paper has higher accuracy.5)A structural mass estimation toolset for the BWB aircraft is developed,which includes rapid design tool for cabin layout,mass predication tool for main load-carrying structures and structural mass estimation tool of BWB aircraft.By use of this toolset the structural mass estimations and comparisons for different cabin layouts,different configurations and different structural layouts are performed.The results indicate that the cabin layout design,configuration design,main load-carrying structure analysis and optimization,and structural mass prediction can be accomplished rapidly by using the method and toolset proposed in this paper.The method with its toolset provides a rational method and effective tools for the structural mass prediction in conceptual design of the BWB aircraft.