维修扩孔对碳纤维复合材料层合板与金属板双钉连接强度的影响分析

复合材料双钉连接结构的复材孔周由于载荷分布不均、应力状态复杂而易于损伤破坏，开孔区域通常是连接结构的薄弱环节，飞机结构维修时一般将连接孔圆整为标准尺寸来恢复其结构强度，对此研究双钉扩孔维修后的载荷分布规律及影响因素，对结构部件保证适航性和提高连接效率具有重要意义。本文以复合材料/铝合金连接结构为研究对象，通过ABAQUS软件建立了嵌入Hashin失效判据和改进Camanho刚度折减系数的双钉单剪连接三维渐进损伤分析模型，并进行了试验验证，着重分析了不同维修孔径组合对双钉单剪连接的拉伸静强度及损伤的影响。结果表明，有限元分析得到的载荷-位移曲线和失效模式与试验结果基本吻合，最大误差为8.9%；靠近加载端的螺栓D₂的载荷高于靠近金属板固定端的螺栓D₁；按标准连接参数增大D₂直径（W/D₂减小）可以改善双钉连接孔边应力集中，提高初始强度和极限强度，过大的D₂直径会减小复材板的净横截面积，导致连接强度下降；摩擦系数增大会延缓复材板初始损伤的发生，导致整体刚度衰减显著延缓。     

Distortion minimization for multimedia transmission in NOMA HAP-UAV integrated aerial access networks

Aerial access networks have been envisioned as a promising 6G solution to enhance the ground communication systems in both coverage and capacity. To better utilize the spectrum and fully explore different channel characteristics, this paper constructs an integrated network comprising the High Altitude Platform (HAP) and Unmanned Air Vehicles (UAVs) with the Non-Orthogonal Multiple Access (NOMA) technology. In order to improve the transmission quality of images and videos, a power management scheme is proposed to minimize the distortion of the transmissions from the HAP and UAVs to the terminals. The power control is formulated as a non-convex problem constrained by the maximal transmit power and the minimal terminal rate requirements. The variable substitution and the first-order Tailor’s expansion is used to transform it into a sequence of convex problems, which are subsequently solved through the gradient projection method. Simulation demonstrates the signal distortion and error rate improvement achieved by the proposed algorithm.