Research On Structure Topology Optimization Method For Fuselage Flutter Model

To develop aircraft in design process,wind tunnel model test is needed to validate the correctness of the theoretical analysis.Wind tunnel test must be completed to ensure the flutter security of airplane,in modern aircraft design,it is necessary to use scale model with both elastic and structural similarity in flutter wind tunnel experiments,the advantage is that it can improve experimental accuracy and design efficiency and reduce the cost.Since the structure of airplane is complicated, and there are restriction of wind tunnel conditions and machining technique,how to design scale model with both elastic and structural similarity is a problem worth studying.Airplane flutter scale model should maintain the load transfer characteristics of the original structure, and acquired by simplifying the original airplane structure to make it small in size.It is a structural inverse problem for proper natural frequencies as well as structural similarity.In optimization design perspective,the evolutionary structural optimization (ESO) method is an effective and feasible topology optimization algorithm for structure design. Therefore,based on bi-direction evolutionary structural optimization method (BESO),facing porous and irregular shape often appears in topology optimization, a fuselage flutter model design method to the achieve structure similarity is presented.Work is as follows:First, research on BESO method using natural frequencies as target is done,combined with finite element method, topology optimization model is built, which takes the exits state of elements as design variables.Based on element sensitivity, topological optimization program is made in APDL and Matlab software, the program conducts to modify the structure in bi-direction. Aiming at the common issues of topological optimization, the element sensitivity calculating process is improved and the post-processing of result is done in the corresponding program.The optimization design example of stiffened plate is presented to validate the above method.Second, a regular shaped grid frame structure is discussed, including its internal and boundary conditions.Then the mapping relationship among finite elements, sub-geometrical feature and integral bar is established.The ratio criterion for structural modification is raised, and applied to structural design of stiffened plate with grid shape, and avoids producing a large number of irregular branch shape and holes in optimization process.The purpose of taking the entire bars as design variables is attained as well as structure similarity.Finally, this topology optimization method is applied to cylindrical fuselage flutter model design,a fraction of the middle part of the fuselage is chosen as design object. The scale flutter model is simplified into a stiffened cylindrical shell sustained by space grid-like framework. Additional size optimization is carried out to construct a scale model which the load transfer and distribution characters are build similarly with the original airplane. Example result shown that the proposed approach is feasible to achieve given natural frequencies, maintains the character of inner frame structure completely, and the similarity between optimized structure and original structure is fully achieved. So that this method is feasible and referable for aircraft flutter model design.