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.     

燃料电池接触电阻与温度相关性研究

研究双极板与气体扩散层接触电阻的形成机理，分析影响该接触电阻的因素，包括温度、载荷以及粗糙度等参数。通过建立数学模型以及利用仿真工具来预测接触电阻数值与变化规律，并进行金属双极板和碳纸气体扩散层的界面接触电阻测试用于模型验证，模型计算结果与实验结果吻合较好。     

高马赫数V字形钝化前缘平板表面压力特性

针对三维内转式进气道V字形唇口下游面临的严酷压力载荷问题，将唇口简化为V字形钝化前缘平板，在来流马赫数为6的条件下，采用数值模拟结合激波风洞压敏涂料测量方法，研究了半径比R/r = 0 ~ 20（V字形根部倒圆半径R与前缘钝化半径r之比）的平板表面压力演化特性。结果表明，随着R/r增大，V字形钝化前缘产生的三维波系结构发生变化，引起下游平板表面压力演变出4种类型。R/r较小时，V字形钝化前缘激波干扰产生的大范围流动分离，诱导形成了偏离中心线较远的分叉状高压区（Type Ⅰ，分叉型）；随着R/r增大，流动分离减弱，分叉状高压区逐渐消失，由透射激波扫掠壁面所形成的条带状高压和超声速射流对撞所形成的中心线高压区逐渐显露，依次出现过渡型（Type Ⅱ）、严酷型（Type Ⅲ）和渐匀型（Type Ⅳ）压力分布。平板上分叉型和过渡型的压力最大值仅为4.3 ~ 7.2p∞（p∞为来流静压），但V字形钝化前缘处的流场品质恶劣；严酷型的压力最大值，随着射流对撞强度的增强而增大，最高可达19p∞；渐匀型的压力最大值，随着射流对撞强度的减弱，逐渐趋近于二维钝前缘平板产生的压力最大值4p∞。     

高倍频程火山烟雾超宽带平板天线

在3m×1.5m×0.2m的尺寸限制下，基于电阻加载技术设计了一种新颖的高倍频程火山烟雾超宽带平板天线。该天线采用同轴馈电，通过扫参仿真优化低频匹配电路，实现了从标准的传输线阻抗（50Ω）到自由空间波阻抗（377Ω）的完美渐变，获得了最佳的低频拓展辐射性能。仿真结果表明天线在300kHz~300MHz的频带范围内驻波比（VSWR）小于2.5（S11<-7.2dB），首次实现了1000倍频程超宽带辐射，远场辐射方向图表明天线在前向实现了近似均匀场辐射。研制了实物天线，并开展了实验测量，实验结果表明天线在前向实现了近似均匀场辐射，天线的波形保真特性良好，天线背向辐射小于5%。