基于显隐融合几何描述的薄壁串油结构优化设计方法研究

This project is based on the problems of fuel sloshing reduction under aircraft's large overload condition. The main purpose is to find out the design method for thin-walled structure with fuel balancing holes under extreme nonlinear constraints. Firstly, the fuel flow characteristics are studied kinematically and dynamically to make clear the boundary conditions of the structural optimization problem. Then, the structure's description method, which is able to flexibly control the geometrical and topological deformation, is analyzed. The criteria for activating the explicit- implicit conversion is established, which reveals the influence of mathematical description on the transformation of structural morphology. After that, the mixed explicit/ implicit structure optimization model is constructed. Thirdly, the SPH based modeling method for the thin-walled structure with fuel balancing holes is proposed. Further, the mechanics characteristic for large deformation aircraft wing ribs, and the impact by fuel sloshing are analyzed. Then a mechanic characteristic calculation model is created based on SPH. By bridging the SPH particles and the varying structural description, a mapping relationship is created between the structural description and SPH particle's properties. This converts the structure optimization problem into an adaptive optimization of the geometry and topology driven by the objective function. Based on this, a well-founded methodology is build for the optimization design of thin-walled structure with fuel balancing holes. Meanwhile, an efficient and parallel numerical implementation is carried out. Finally, a set of software is developed for aviation application, which provides both theoretical and practical support for the innovation design of aircraft's wing ribs.

本项目以飞机在大过载条件下的燃油晃动抑制问题为背景，研究在极端工况所引发的非线性约束影响下薄壁串油结构的优化设计方法。分析油箱内流体晃动规律的运动学、动力学特性，阐明薄壁串油结构优化问题的边界条件。研究能够高柔性控制几何形状与拓扑变换的结构描述方法，构筑触发显隐式描述方式相互转换的控制机制，揭示数学描述对结构形态变换的影响规律，构建基于显隐式结合的结构优化模型。研究薄壁串油结构的粒子法建模方式，分析大尺寸变形情况下的机翼肋板力学特性和剧烈燃油晃动引起的冲击载荷特性，构建基于粒子法的力学计算模型。研究粒子模型与动态结构描述间的耦合机制，建立动态结构描述与粒子属性之间的映射关系，将结构优化问题转化为一个由目标函数驱动的形状及拓扑变换自寻优问题。提出一套指导薄壁串油结构的优化设计方法与高效率并行化数值实现模型，开发相关软件，为飞机机翼肋板的创新设计提供基础理论与使能技术支撑。

本项目以飞机中的薄壁串油结构为对象，研究其在极端工况下由于燃油晃动引发的燃油串流、重心平衡与燃油测量问题，并在此问题下，探索显/隐式融合的几何描述与变换方法，并构建基于SPH的力学特性计算框架及薄壁串油结构优化设计数学模型构建与数值实现方法。.针对薄壁串油结构在极端工况下的边界条件，建立了基于SPH的自由液面描述方法，分析其光滑核函数、流体压缩特性、粒子几何及物理参数对自由液面晃动数值分析模型精度的影响；在此基础上，研究了不同充液比、姿态角、过载下的重心变化特性、油液晃动幅度及动、势能收敛准则，探索薄壁串油结构与流体运动学特性之间的内在联系；寻求流体晃动对薄壁串油结构的动力学影响机理，建立了粒子速度影响下的冲击载荷作用方程。.针对高柔性拓扑变换能力需求，提出将显式几何描述与隐式拓扑描述有机融合的图形学描述方法，研究几何形状显式变形控制方法，探索基于拉普拉斯算子的网格顶点位移能量描述方法；研究以变形控制点位移为驱动，由位移能量控制的网格变形机制；建立网格边界自适应划分算法，定义划分深度规则；提出网格边界处的面片分离策略，赋予网格分叉构型能力。.针对SPH在不同介质中的计算需求，研究了SPH在固体与液体介质中的建模方法，通过提出固体介质中的材料应力模型，构建了燃油（流体）和肋板（固体）SPH模型不同的控制方程、状态方程和核函数；建立了具有材料强度的连续介质力学控制方程，研究了力学特性计算框架与动态几何描述间耦合机制，最终构建了适用于大尺寸变形及流体冲击计算的力学特性计算框架。.针对飞机燃油晃动过程中燃油总机械能下降速度的加速需求，以优化飞机油箱肋板开孔布局为目标，研究了燃油总机械能及燃油重心等相关燃油质量特性数据与肋板的应变能和体积大小间的关系，建立了基于SPH的肋板开孔优化模型；在此基础上，利用建立的SPH流固耦合模型对真实飞机油箱肋板结构进行了优化。