Static magnetic field analysis of hollow-cup motor model and bow-shaped permanent magnet design

The hollow-cup Permanent Magnet (PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element (FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.     

Multi-scale simulation model of air system based on cross-dimensional data transmission method

The Secondary Air System (SAS) plays an important role in the safe operation and performance of aeroengines. The traditional 1D-3D coupling method loses information when used for secondary air systems, which affects the calculation accuracy. In this paper, a Cross-dimensional Data Transmission method (CDT) from 3D to 1D is proposed by introducing flow field uniformity into the data transmission. First, a uniformity index was established to quantify the flow field parameter distribution characteristics, and a uniformity index prediction model based on the locally weighted regression method (Lowess) was established to quickly obtain the flow field information. Then, an information selection criterion in 3D to 1D data transmission was established based on the Spearman rank correlation coefficient between the uniformity index and the accuracy of coupling calculation, and the calculation method was automatically determined according to the established criterion. Finally, a modified function was obtained by fitting the ratio of the 3D mass-average parameters to the analytical solution, which are then used to modify the selected parameters at the 1D-3D interface. Taking a typical disk cavity air system as an example, the results show that the calculation accuracy of the CDT method is greatly improved by a relative 53.88% compared with the traditional 1D-3D coupling method. Furthermore, the CDT method achieves a speedup of 2 to 3 orders of magnitude compared to the 3D calculation.     

Passive attitude stabilization of ionic-wind-powered micro air vehicles

The ionic-wind-powered Micro Air Vehicles (MAVs) can achieve a higher thrust-to-weight ratio than other MAVs. However, this kind of MAV has not yet achieved controlled flight because of the unstable thrust produced by the ionic wind and the dynamic instability related to the small size. In this paper, a passive attitude stabilization method of the ionic-wind-powered MAV using air dampers is introduced. The key factors that influence the performance of the air dampers, including the layout, position, and area of the air dampers, are theoretically studied. The appropriate optimal position of the air dampers is also obtained by Monte Carlo stochastic simulations. Then the proposed passive attitude stabilization method is applied to the ionic-wind-powered MAVs of different wingspan (2 cm and 6.3 cm). Finally, the experimental results show that using the proposed method, attitude stabilization is achieved for the first time for the ionic-wind-powered MAV. Moreover, the altitude control of an ionic-wind-powered MAV with a wingspan of 6.3 cm is also demonstrated.     

短碳纤维增强聚醚醚酮注塑成型进气道的性能北大核心CSCD

以含20%的短碳纤维增强聚醚醚酮树脂为主要原料,采用注塑成型的方法制备了进气道及试片。通过对材料力学性能、微观形貌、进气道CT无损检测、内型面三坐标进行分析,结果表明:按照给定的工艺参数注塑成型,复合材料的抗拉强度达208 MPa、拉伸模量16.7 GPa、冲压式剪切强度100 MPa,碳纤维在树脂基体中分布均匀,进气道本体材料内部缺陷较少,进气道内外型面光滑、尺寸精度较高。     

启动过程压缩空气储能向心涡轮三维流动特性研究

为研究压缩空气储能系统的向心涡轮启动过程内部流动损失特性，本文采用全三维计算流体动力学（CFD）模型对其启动过程过程进行了数值模拟，与实验结果对比表明，虽然该模型在启动初始阶段与转速稳定阶段存在一定误差，但仍能够整体上反映启动过程的效率变化特征。在此基础上，进一步分析了启动过程中动叶通道内损失区及流场变化特征，结果发现，动叶进口攻角是影响内部流场主要因素：在启动初始阶段，叶轮进口攻角较大，动叶载荷集中在叶片前缘，形成明显的通道分离涡与前缘涡；在快速启动段，攻角减小，动叶载荷沿弦长分布更为均匀，通道分离涡及前缘涡逐渐减小并向叶片吸力面迁移。在整个启动阶段，动叶通道内高损失区也随着通道分离涡逐渐迁移且变小，并向相邻叶片吸力面集中。     

状态/输入约束下飞-推一体化的保性能安全控制

基于飞行-推力一体化思想提出了一种针对搭载超燃冲压发动机的吸气式高超声速飞行器速度通道的状态/输入约束自适应鲁棒保性能安全控制方案。首先根据超燃冲压发动机的机理分析与计算流体动力模型数据，建立了安全子系统与性能子系统面向控制的仿射非线性模型。之后基于障碍Lyapunov理论与动态面设计方法设计了一套安全子系统状态约束控制器，从理论上保证了飞行器在跟踪指令的全过程中，发动机相关状态不会触碰安全边界，并结合自适应技术与辅助系统提高了该控制系统的鲁棒性。针对性能子系统设计了一套鲁棒自抗扰控制器，达到“保证安全的前提下不折损性能”的目的。仿真结果表明所设计的控制系统可以在保障安全的同时达到预想的性能，并显著放宽了超燃冲压发动机对飞行器飞行姿态的约束，保证了高超声速飞行器的机动灵活性。     

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.     

Design and analysis of a novel hybrid cooling method of high-speed high-power permanent magnet assisted synchronous reluctance starter/generator in aviation applications

To improve the heat dissipation performance, this paper proposes a novel hybrid cooling method for high-speed high-power Permanent Magnet assisted Synchronous Reluctance Starter/Generator (PMaSynR S/G) in aerospace applications. The hybrid cooling structure with oil circulation in the housing, oil spray at winding ends and rotor end surface is firstly proposed for the PMaSynR S/G. Then the accurate loss calculation of the PMaSynR S/G is proposed, which includes air gap friction loss under oil spray cooling, copper loss, stator and rotor core loss, permanent magnet eddy current loss and bearing loss. The parameter sensitivity analysis of the hybrid cooling structure is proposed, while the equivalent thermal network model of the PMaSynR S/G is established considering the uneven spraying at the winding ends. Finally, the effectiveness of the proposed hybrid cooling method is demonstrated on a 40 kW/24000 r/min PMaSynR S/G experimental platform.     

Vulnerability analysis of the Chinese coupled aviation and high-speed railway network

The integrated aviation and High-Speed Railway (HSR) transportation system plays a vital role for today’s inter-city transportation services. However, an increasing number of unexpected disruptions (such as operation failures, natural disasters, or intentional attacks) pose a considerable threat to the normal operation of the system, especially on ground transfer, leading to the extensive research on its vulnerability. Previous approaches mainly focus on interruptions within a single transportation mode, neglecting the role of ground transfer which serves as a coupled connection between aviation and High-Speed Railway. This paper proposes a network-based framework for evaluating the vulnerability of the Chinese Coupled Aviation and High-Speed Railway (CAHSR) network from the viewpoint of ground transfer interruption. Taking the end-to-end travel time and passenger flow information into consideration as an evaluation measure and analyzing from the perspective of urban agglomerations, an adaptive method is developed to identify the critical cities and further investigate their failure impacts on the geographic distribution of vulnerability. In addition, the proposed model explores variations of vulnerability under different failure time intervals. Based on the empirical study, some major conclusions are highlighted as follows: (A) Only a few cities show significant impacts on the network’s vulnerability when ground transfer interruptions occurred. (B) The distribution of vulnerability is not proportional to the distance between failure city and influenced city. (C) The vulnerability is more serious in the morning and evening when the ground transfer is disconnected. Our findings may provide new insights for maintenance and optimization of the CAHSR network and other real-world transportation networks.     

空中交通复杂性研究进展

空中交通复杂性是空中交通态势的本质属性，是空中交通管制工作负荷的主要驱动因素。空中交通复杂性的科学评价是实现空中交通精细化管理的关键，也是当前空管领域研究热点。本文介绍了国内外空中交通复杂性的研究团队，梳理了空中交通复杂性与工作负荷、安全水平等相互之间的区别和联系，并详细分析了现有研究的具体研究路线。在分析新一代空中交通管理系统特征的基础上，对空中交通复杂性的未来研究趋势和方向进行了展望。