蜂窝壁缺失所致应力集中分析

蜂窝或胞壁缺失是蜂窝夹层结构缺陷形式的一种,由于蜂窝（壁）的缺失,导致蜂窝芯子的连续性被破坏,并产生应力集中。本文从蜂窝细观尺度出发,通过数值解析与有限元模拟相结合的方式对缺陷周围胞壁正应力进行分析,首先,通过有限元模拟得到胞壁的拉应力结果,结果表明,应力集中带状区上的胞壁标准化拉应力沿横向符合近似卡方概率密度函数的分布形式;存在一个临界位置使蜂窝壁拉应力分布曲线出现反转。其次,对蜂窝缺陷最大拉应力处的壁内弯矩值与胞壁缺失个数的关系进行了推导。最后,给出了预估弯曲应力的公式,并分析了缺陷形状对预估公式参数的影响。      

蜂窝芯体材料面外等效弹性模量预测与分析

基于最小势能原理和最小余能原理,选择比Kelsey模型所用表征单元更简化的单元为研究对象,推导出与之完全相同的蜂窝芯体面外等效弹性模量的解析表达式。采用有限元法预测一组典型商用正六边形蜂窝芯体的面外等效弹性模量,并将解析解模型预测值、有限元模型预测值与厂家公布的材料试验数据进行对比。提出一组基于解析解模型的修正公式用于预测与分析典型正六边形蜂窝芯体的面外等效弹性模量。     

铝蜂窝复合材料X,Y方向低温有效热导率的测试与研究

本文概述了铝蜂窝复合材料在x、y方向低温有效热导率的测试方法,给出部分测试结果。对试样的低温有效热导率给出了计算模型,并讨论、分析了测试计算结果。     

Transition prediction and sensitivity analysis for a natural laminar flow wing glove flight experiment

Natural laminar flow technology can significantly reduce aircraft aerodynamic drag and has excellent technical appeal for transport aircraft development with high aerodynamic efficiency. Accurately and efficiently predicting the laminar-to-turbulent transition and revealing the maintenance mechanism of laminar flow in a transport aircraft’s flight environment are significant for developing natural laminar flow wings. In this research, we carry out natural laminar flow flight experiments with different Reynolds numbers and angles of attack. The critical N-factor is calibrated as 9.0 using flight experimental data and linear stability theory from a statistical perspective, which makes sure that the relative error of transition location is within 5%. We then implement a simplified e^N transition prediction method with a similar accuracy compared with linear stability theory. We compute the sensitivity information for the simplified e^N method with an adjoint-based method, using the automatic differentiation technique (ADjoint). The impact of Reynolds numbers and pressure distributions on TS waves is analyzed using the sensitivity information. Through the sensitivity analysis, we find that: favorable pressure gradients not only suppress the development of TS waves but also decrease their sensitivity to Reynolds numbers; there exist three special regions which are very sensitive to the pressure distribution, and the sensitivity decreases as the local favorable pressure gradient increases. The proposed sensitivity analysis method enables robust natural laminar flow wings design.     

适用于长时间烧蚀防热的蜂窝增强低密度材料

针对长时间烧蚀防热对防热材料的需求,研制了两种蜂窝增强低密度烧蚀防热材料,采用电弧风
洞加热设备对其防热性能进行了考核,并对其力学及热物理性能进行了研究。结果表明,在两种长时间(1 000
s 左右)热环境的考核下,蜂窝增强低密度材料烧蚀后背面温度均低于200℃,表面碳层均匀、完整,无明显烧蚀
量,显示了优异的隔热性能和良好的抗气流冲刷能力。     

基于多级铝蜂窝缓冲器的新型着陆器性能分析

在未来可行走探月着陆器的总体设计中,如何降低着陆过程中的冲击载荷,实现柔顺落震以保护本体结构和有效载荷的安全,是一项重要内容。本文基于所设计的可行走着陆器整机构型对缓冲驱动一体化缓冲器优化分析。首先,对3种不同规格的铝蜂窝材料分别进行静压力试验,利用试验数据和蜂窝有效吸能模型对多级铝蜂窝的搭配方式进行优化;然后,采用Ansys/Ls-dyna对优化后的三级铝蜂窝进行仿真和试验验证,与传统的两种铝蜂窝材料的缓冲器相比具有一定的柔顺性和安全性;最后,利用Adams软件进行整机仿真验证。验证结果显示:着陆器本体质心过载曲线平滑柔顺,可为我们后续开展的载人登月、月表基地建设等工程实施提供技术支撑。     

Numerical optimization of transonic natural laminar flow nacelles

Natural laminar flow nacelle is a promising technology for drag reduction. In this paper,an optimization platform is established for the design of transonic axisymmetric and threedimensional natural laminar flow nacelles for large civil aircraft. The platform adopts the class/shape transformation method for geometric parameterization, a four-equation transition model for transition prediction, and the differential evolution algorithm combined with the radial basis function surrogate model as the...     

双层梯度蜂窝吸波结构优化设计

设计了一种带蒙皮和金属底板的双层梯度蜂窝吸波结构，并利用Hashin-Shtrikman（HS）模型获得其等效电磁参数。在此基础上，以反射率低于-10dB带宽最大为优化目标，利用保收敛粒子群优化算法（Guarantee Convergence Particle Swarm Optimization，GCPSO）对四种不同排序方案的双层梯度蜂窝吸波结构进行优化设计。结果表明，入射电磁波的角度和极化方式以及吸波材料的选择、排序和厚度对双层梯度蜂窝结构的吸波性能有很大的影响；不同入射角度下TM极化时的吸波特性明显优于TE极化，在入射角为60^°时最为明显；对比四种方案优化结果显示，case 1方案由于选用损耗角较小的吸波材料充当透波层，分布于蒙皮下面，而选用损耗角较大的吸波材料作吸收层，并置于吸波结构底层，因而具有最大的优化目标函数，吸波效果最佳，且蜂窝高度仅为具有相同吸波效果的case 3方案的49.44%。因此，选择case 1方案作为本文最终优化结果。     

Higher-order vibration of thick composite and sandwich plates based on an alternative higher-order model

The transverse stretching vibration of thick sandwich plates, which is attributed to largely different stiffness at the adjacent layers, is a challenging issue, and efficient approach for such issue is less reported in the published literature. Thus, natural frequencies corresponding to stretching vibration modes are generally neglected in engineering design, which might impact structural safety as frequencies of the exciting force are close to transverse stretching vibration frequencies. This paper proposes an alternative higher-order model for dynamic analysis corresponding to the higher-order vibration modes. The proposed model is classified in the displacement-based equivalent single-layer theory, as the number of displacement parameters in the proposed model is independent of the layer number. The continuity of displacements and transverse shear stresses can be fulfilled at the interfaces between the adjacent layers of structures. To demonstrate the capability of the proposed model, typical examples are analyzed by utilizing the proposed model, the three-dimensional finite element method and the chosen higher-order models. By comparing with the exact three-dimensional elasticity solutions, it is found that the proposed model can yield more accurate natural frequencies corresponding to the higher-order displacement modes than the selected models. Moreover, the factors influencing reasonable prediction of the higher-order frequencies are investigated in detail, which can provide a reference for the accurate prediction of the higher-order frequencies.