BP神经网络预测复合材料热压罐成型均匀性

复合材料热压罐成型过程中的固化度差值是复合材料固化度均匀性的主要表征参数之一。基于3层BP神经网络，以复合材料双平台固化工艺曲线的加热速率、保温时间和保温温度为输入参数，建立了成型过程任一时刻最大固化度差值的快速估算模型。仿真复合材料热压罐成型过程，得到最大固化度差值作为试验样本数据，对BP神经网络进行训练，训练结束后对该模型的准确性进行验证。结果表明:该BP神经网络估算模型准确性和效率较高，为复合材料热压罐成型最大固化度差值的估算提供了一种快速有效的新方法。      

地球同步轨道星地量子信道特性研究

为了研究地球同步轨道量子密钥分发过程中星地量子信道特性，项目团队研制了搭载于实践二十卫星的极弱光偏振态分发设备，开展了地球同步轨道卫星与地面间光子偏振态的传输实验。实验时，星载偏振光分发设备根据遥控指令以50MHz频率驱动四个激光器出光，分发|0〉、|π/2〉、|π/4〉和|3π/4〉四种偏振态光子，经过长距离的空间传输后由地面站望远镜接收，最后由超导探测器探测。研究结果表明，地球同步轨道卫星到地面站的光学链路衰减约为100~110 dB，通道误码率约为2%~8%，满足量子密钥分发误码率的安全性要求。     

SABRE预冷器计算模型及其在整机模型中的应用

预冷器的性能对SABRE等预冷组合循环发动机具有重要影响,为实现发动机方案设计阶段预冷器的快速设计与评估,建立了预冷器准二维快速评估模型。将SABRE预冷器的几何结构简化为一个扇环形区域,沿径向和周向将该区域划分为二维节点。应用守恒方程及传热关联式完成单个节点计算,再求解节点矩阵的平衡方程组,计算内外流体特定节点上参数的二维分布,得到预冷器出口参数。将模型嵌入发动机总体性能程序中,实现了发动机设计及非设计点的预冷器性能计算的功能。与文献数据对比结果表明,预冷器模型传热计算误差小于5%,摩擦阻力误差小于10%。整机计算结果显示,Ma0~5范围内,预冷器空气侧温降范围为143K至932K,温降随飞行马赫数升高单调上升。预冷器传热有效度范围为0.896-0.945,空气侧总压恢复系数范围为0.852-0.904。     

星载天线展开过程立体视觉动态测量技术

介绍了基于立体视觉原理的星载天线动态展开过程测量方法，通过基于标准长度的标定方法、双目立体视觉交会坐标解算和动态多目标点识别跟踪等关键技术的研究，实现了对可展开天线各关节点在展开过程中的三维运动轨迹的测量，并实现了试验验证。试验结果表明，该方法可获得各关节点在不同时刻的三维点坐标，解算出展开运动的运动速度、加速度和展开后的面型等参数，为大型可展开天线柔性机构设计、动力学分析和展开可靠性分析等提供必要的参考。     

Ground experiments of Chang’e-5 lunar regolith penetrating radar

The Lunar Regolith Penetrating Radar (LRPR) is an Ultra-Wideband (UWB) array-based Ground penetrating radar (GPR) onboard the lander of Chang’e-5 (CE-5) mission. The primary scientific objectives of the LRPR are to probe the thickness and structure of lunar regolith of the landing site, and support the drilling and sampling process. In order to evaluate the performance of the LRPR, a series of ground experiments are performed using the LRPR prototype mounted on a CE-5 lander model. The performance of the LRPR is evaluated by comparing the experimental data with the simulated data. Data processing and imaging method are verified, and the interferences from the lander and other aspects are analyzed. The results of the ground experiments and simulation demonstrate that the LRPR is able to meet the design requirement of 2-m detection depth. They also indicate that the upper and lower interfaces of the stratified structure in the lunar regolith can be well distinguished by the LRPR when the dielectric constant difference is greater than 0.3, and the imaging effect of the location under the dense antennas is better than that of other positions. However, the identification capability of the LRPR to the independent blocky objects is relatively poor mainly due to the clutters caused by the lander, the sparsity of the antenna elements compared to the size of the basalt block, the limited aperture of the antenna array, and the tail of the transmitted waveform.     

导流锥结构参数对燃气弹射筒内压力冲击平滑效果影响研究

针对导流锥结构参数对内弹道流场耦合影响问题，基于动态分层动网格技术，构建了含导弹运动和二次燃烧的内弹道数值模型，并验证了模型可靠性。解耦分析了导流锥半径、高度及冲击高度对内弹道流场特性和载荷的影响。结果表明：导流锥的结构直接决定燃气飞溅现象的产生和流场结构的紊乱程度，导流锥的半径、高度和冲击高度的改变会对燃气反射点的位置、二次燃烧的区域以及剧烈程度产生影响;结构优化后的导流锥，较大程度地缓解了冲击现象，获得了较好的平滑效果，筒底压力较实验装置降低了24.5%。     

Impact of rain on wave retrieval from Sentinel-1 synthetic aperture radar images in tropical cyclones

The main objective of our work was to investigate the impact of rain on wave observations from C-band (~5.3 GHz) synthetic aperture radar (SAR) in tropical cyclones. In this study, 10 Sentinel-1 SAR images were available from the Satellite Hurricane Observation Campaign, which were taken under cyclonic conditions during the 2016 hurricane season. The third-generation wave model, known as Simulating WAves Nearshore (SWAN) (version 41.31), was used to simulate the wave fields corresponding to these Sentinel-1 SAR images. In addition, rainfall data from the Tropical Rainfall Measuring Mission satellite passing over the spatial coverage of the Sentinel-1 SAR images were collected. The simulated results were validated against significant wave heights (SWHs) from the Jason-2 altimeter and European Centre for Medium-Range Weather Forecasts data, revealing a root mean square error (RMSE) of ~0.5 m with a 0.25 scatter index. Winds retrieved from the VH-polarized Sentinel-1 SAR images using the Sentinel-1 Extra Wide-swath Mode Wind Speed Retrieval Model after Noise Removal were taken as prior information for wave retrieval. It was discovered that rain did indeed affect the SAR wave retrieval, as evidenced by the 3.21-m RMSE of SWHs between the SAR images and the SWAN model, which was obtained for the ~1000 match-ups with raindrops. The raindrops dampened the wave retrieval when the rain rate was < ~5 mm/hr; however, they enhanced wave retrieval for higher rain rates. It was also found that the portion of the rain-induced ring wave with a wave number > 0.05 rad/m (~125 m wavelength) was clearly observed in the SAR-derived wave spectra.     

Evaluation of a regional real-time precise positioning system based on GPS/BeiDou observations in Australia

The performance of real-time (RT) precise positioning can be improved by utilizing observations from multiple Global Navigation Satellite Systems (GNSS) instead of one particular system. Since the end of 2012, BeiDou, independently established by China, began to provide operational services for users in the Asia-Pacific regions. In this study, a regional RT precise positioning system is developed to evaluate the performance of GPS/BeiDou observations in Australia in providing high precision positioning services for users. Fixing three hourly updated satellite orbits, RT correction messages are generated and broadcasted by processing RT observation/navigation data streams from the national network of GNSS Continuously Operating Reference Stations in Australia (AUSCORS) at the server side. At the user side, RT PPP is realized by processing RT data streams and the RT correction messages received. RT clock offsets, for which the accuracy reached 0.07 and 0.28?ns for GPS and BeiDou, respectively, can be determined. Based on these corrections, an accuracy of 12.2, 30.0 and 45.6?cm in the North, East and Up directions was achieved for the BeiDou-only solution after 30 min while the GPS-only solution reached 5.1, 15.3 and 15.5?cm for the same components at the same time. A further improvement of 43.7, 36.9 and 45.0 percent in the three directions, respectively, was achieved for the combined GPS/BeiDou solution. After the initialization process, the North, East and Up positioning accuracies were 5.2, 8.1 and 17.8?cm, respectively, for the BeiDou-only solution, while 1.5, 3.0, and 4.7?cm for the GPS-only solution. However, we only noticed a 20.9% improvement in the East direction was obtained for the GPS/BeiDou solution, while no improvements in the other directions were detected. It is expected that such improvements may become bigger with the increasing accuracy of the BeiDou-only solution.     

A holistic approach to SIM platform and its application to early-warning satellite system

This study proposes a new simulation platform named Simulation Integrated Management (SIM) for the analysis of parallel and distributed systems. The platform eases the process of designing and testing both applications and architectures. The main characteristics of SIM are flexibility, scalability, and expandability. To improve the efficiency of project development, new models of early-warning satellite system were designed based on the SIM platform. Finally, through a series of experiments, the correctness of SIM platform and the aforementioned early-warning satellite models was validated, and the systematical analyses for the orbital determination precision of the ballistic missile during its entire flight process were presented, as well as the deviation of the launch/landing point. Furthermore, the causes of deviation and prevention methods will be fully explained. The simulation platform and the models will lay the foundations for further validations of autonomy technology in space attack-defense architecture research.     

Aerodynamic Performance and Aeroacoustic Characteristics of Model Rotor with Anhedral Blade Tip in Hover

Experimental investigation on the aerodynamic performance and aeroacoustic characteristics of model rotors with different tip anhedral angles in hover are conducted in the paper.Three sets of model rotors with blade-tip anhedral angle 0°(reference rotor),20°and 45°respectively are designed to analyze the influence of the anhedral angle on the hovering performance and aeroacoustics of rotor.In the environment of anechoic chamber,the hover experiments under the different collective pitch and blade numbers,are carried out to measure the figure of merit(FM),time history of sound pressure and sound pressure level(SPL)of the three rotor models.Based on test results,the comparison and analysis of hovering performance and aeroacoustic characteristics among the three rotor models have been done.Meanwhile,for the sake of analysis,the rotor wake and blade pressure distribution are simulated by means of computational fluid method(CFD).At last,some conclusions about the effects of blade-tip anhedral angle on the aerodynamic performance and aeroacoustic characteristics in hover are obtained.An anhedral blade tip can enhance the FM of the rotor,and decrease the rotor loads noise to some extent.