【作者】 张颖颖；

【导师】 郭东明；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2008， 硕士

【摘要】 风洞试验是飞机研制过程中的必经环节,因此研制能够准确模拟气动载荷对飞机结构作用机理的风洞模型至关重要。研究表明,只有弹性比例模型才能准确地模拟高速风洞中飞机的振颤特性。弹性比例模型要求在弹性、结构和模态方面与原结构相似,其设计可看成材料与拓扑几何特征并发设计问题,而拓扑优化是解决该问题的有效方法。目前,连续体拓扑优化形成的孔洞多为不规则形状,而飞机机身龙骨结构多为规则栅格状。因此,限制孔洞形状,开展带规则几何约束的连续体频率拓扑优化研究具有重要的工程应用价值。本文首先对不考虑几何约束的一般连续体拓扑优化进行了研究。结合双向渐进结构法,发展了基于单元特性更改的双向渐进结构法(即双向EPCM);以结构的多阶固有频率为优化目标,建立了优化模型;基于单元敏度分析,以弹性模量和密度很小且相互匹配的空洞单元替代实体单元实现单元的删除;比较了空洞单元的弹性模量与密度的匹配关系对模态的影响;改进了敏度再分配方法,对棋盘格式进行抑制;以壳体平板为优化对象验证了方法的可行性。其次,在一般连续体拓扑优化的基础上,对孔洞的形状施加几何约束,开展了带规则几何约束的连续体频率拓扑优化研究。利用ANSYS进行建模和模态分析,求出结构的固有频率和振型;给出了规则方孔的几何描述;以结构的多阶固有频率为优化目标,以体积、孔洞形状、最小尺寸和对称性为约束,以孔洞的位置尺寸和单元的存在状态为设计变量,建立了带规则几何约束的连续体结构拓扑优化模型;采用带规则几何约束的双向EPCM方法进行求解;基于目标函数敏度分析进行插孔,并对已插孔的位置尺寸进行步长加速寻优;调整已插孔的位置尺寸,保证单元存在状态为整型变量;利用Matlab编制了通用的优化程序;以双层平板结构为优化对象验证了方法的可行性。最后,将带规则几何约束的双向EPCM方法应用到圆形机身弹性比例模型的研制中。将机身简化为双层圆柱壳结构,采用局部建模分析再将其扩展成完整结构的专门方案,以圆柱壳一节径下的前三阶频率为优化目标,实现了圆柱壳“变拓扑”的频率优化设计。更多还原

【Abstract】 Wind tunnel test is an inevitable part in the development process of aircraft, so it’s of vital importance to develop models which could simulate the mechanism how aerodynamic loads act on aircraft precisely. Researches indicate that only the elastic scale model could simulate aircraft’s vibration in high speed tunnel accurately. Elastic scale model should be similar to original design in both geometry and corresponding modes. It can be seen as a concurrent design problem which concerns material and topology geometric characteristics. And topology optimization is an effective solution. At present, holes generating in topology optimization is mostly irregular geometric. However fuselage keel structure is generally regular grid. Therefore, in order to realize optimization design similar to real aircraft in both structure and modes, restricting hole’s shape and making a study on frequency topology optimization of continuum with regular geometrical constraints plays a great value for engineering application.In this paper, firstly common topology optimization of continuum without geometrical constraints is studied. On the basis of BESO method, Bi-directional Element’s Property Changing Method (BEPCM) is developed; optimization model of continuum is constructed with multiple frequencies as objects; based on element sensitivity analysis, element deletion is realized by changing a solid element into a void element with small and mutually matched elastic module and density; how matching relationship of void element’s module and density influences modes is given; Sensitivity Redistribution Method is modified to restrain checkerboard; above method is applied to shell plate and verified feasible.Secondly, based on the common topology optimization of continuum, by restricting hole’s shape, frequency topology optimization with regular geometrical constraints is studied. Modeling and modal analyzing is conducted by ANSYS and frequencies and modal shapes of structure are outputted; geometry description of regular square hole is presented; optimization model of continuum is constructed, with multiple frequencies as objects, volume, hole shape, minimum size and symmetry as constraints, position, size of holes and element existing state as design variables; BEPCM with regular geometrical constraints is adopted; holes insertion strategy based on objective analysis is given; accelerative search and adjustment of position and size of inserted holes is adopted; optimization program is compiled using Matlab; above method is applied to double layer flat and proved feasible.Finally, BEPCM with regular geometrical constraints is applied to topology optimization of circular fuselage elastic scale model. The model is simplified to double cylindrical shell and special strategy that the whole structure could be expanded by local modeling is adopted. With the first three frequencies at the first diameter as objects, frequency topology optimization of cylindrical shell is realized.更多还原