某大型飞机后缘襟翼气动/机构综合优化设计

大型飞机增升装置的研制不仅需要其提供足够的气动性能,也需要对噪声、舒适性等进行综合考量设计,而增升装置是提高大型飞机综合性能的重要系统,也是目前技术发展亟待研究和解决的重要问题。对于增升装置机构设计,通过设计较为简单的铰链襟翼机构来引导襟翼达到较优位置,然后选择气动性能较好的位置作为新的优化位置,求得较优机构位置。机构位置改变结合气动性能验证需要进行大量的迭代计算以及结果优化,因此以机构设计为基础,探究多目标优化计算的新方法,最终实现气动结构一体化设计目标。选用铰链式后缘襟翼为研究对象,综合考量后缘襟翼旋转与扰流板下偏联合运动对于气动性能影响,利用所研究方法,对其进行气动机构一体化设计并得出设计结果。     

Assessing the performance of BDS-3 for multi-GNSS static and kinematic PPP-AR

As of 2021, a total of four different GNSS constellations – namely, GPS, GLONASS, Galileo, and BDS-3 – can be used with Full Operational Capability (FOC). In this work, the contribution of BDS-3 FOC to GPS + GLONASS + Galileo (GRE) PPP-AR is investigated, considering the three different cut-off angles (7°, 30°, and 45°) and different lengths of static observation sessions (24-, 12-, 6-, 3-, 1-, 0.5-, 0.25-hour). The data of 31 IGS-MGEX stations is processed with GRE PPP-AR and GREC3 (GPS + GLONASS (using float mode) + Galileo + BDS-3) PPP-AR modes. The results showed that BDS-3 degraded the horizontal (except for 24-h sessions) and vertical accuracy of static GRE PPP-AR solutions regardless of the elevation cutoff angle and observation time. The kinematic results showed that BDS-3 significantly contributed to the accuracy of GRE kinematic PPP-AR for 30° and 45° cutoff angles. The convergence time analysis showed that BDS-3 only contributes to GRE kinematic PPP-AR for the vertical component.     

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.     

固溶时间对激光选区熔化AlSi10Mg显微组织及显微硬度的影响

采用SEM、EDS、显微硬度等分析方法研究了535℃固溶温度下不同固溶时间对激光选区熔化(Selective laser melting) AlSi10Mg铝合金显微组织及显微硬度的影响。结果表明,在535℃固溶温度下,由纳米尺寸网状Al-Si共晶和过饱和α-Al固溶体组成的激光选区熔化AlSi10Mg显微组织对固溶时间非常敏感,固溶2 min后熔池边界及网状共晶组织消失,固溶5 min后共晶Si便发生明显球化,共晶Si尺寸随着固溶时间的延长而增大。伴随着显微组织的变化,AlSi10Mg的显微硬度从固溶前的HV(119±3.2)迅速降低,并随着固溶时间的延长最终稳定在HV57左右。     

一种改进的模糊度子集选取方法及其性能评估

模糊度固定（ambiguity resolution, AR）能在一定程度上加快精密单点定位收敛并提高定位精度。但是模糊度固定率和计算效率会随模糊度数量的增加而降低，因此部分模糊度固定（partial ambiguity resolution, PAR）备受关注。PAR技术的关键在于模糊度子集选取，提出了一种改进的模糊度子集选取法，将高度角、信噪比以及模糊度方差联合作为模糊度子集选取的指标。实验结果表明：静态模式下，相比于全模糊度固定（full ambiguity resolution, FAR）和基于高度角的PAR方法，该方法的固定率分别提升9.65%和2.56%，首次固定时间分别缩短6.86%和3.43%，收敛时间分别缩短15.57%和5.13%，当三种方法固定率大致相同时，定位精度分别提升4.74%和5.39%；动态模式下，该方法的固定率分别提升22.75%和0.92%，首次固定时间分别缩短12.44%和0.44%，当三种方法固定率大致相同时，定位精度分别提升3.50%和4.89%。总体而言，无论是在静态还是动态模式下，该方法相比于FAR和基于高度角的PAR方法，性能均有所提升。