Cloud attenuation statistics from radiometric measurements over a tropical location Kolkata,India

The objective of this study is to investigate cloud attenuation at 30 GHz frequency using ground-based microwave radiometric observations at a tropical location, Kolkata. At higher frequencies and lower elevation angles, cloud attenuation is of major concern at a tropical location. The location experiences high value of liquid water path (LWP), which is responsible for cloud attenuation, during the Indian summer monsoon (ISM) and pre-monsoon season. Significant amount of cloud attenuation has been observed during monsoon season at 30 GHz. Two years observations of exceedance probability of cloud attenuation and worst month statistics are presented. The variation of cloud attenuation with frequencies for different elevation angles has also been investigated. The seasonal and diurnal patterns of cloud attenuation are examined. Cloud attenuation, inferred from radiometric measurements before rain commencement, has been compared to rain attenuation at Ku-band. Exceedance probabilities of cloud and rain attenuation have been compared.     

武装直升机红外成像仿真

虚拟仿真以其低成本、短周期、高质量的特点,逐渐成为复杂环境下红外成像制导武器设计分析、验证和评估的主要手段之一。以某武装直升机目标为对象,首先利用基于航空发动机物理模型的方法,通过全尺寸几何建模、计算蒙皮、尾喷和羽烟等主要红外辐射源的流场和温度场,利用灰度等级描述红外辐射信息,生成不同视向角下的近场红外辐射亮度显示,并存储形成数据库。然后根据具体使用时的条件从数据库中调用,按照距离进行大气衰减,最终形成视点处的红外辐射亮度显示。实验结果证明,算法生成的武装直升机红外图像真实感强,实时性好,可用于红外成像制导导弹仿真和夜航模拟训练系统的红外视景显示,具有一定的军事参考价值。     

近地轨道卫星太阳电池阵功率衰减估计

针对LEO(Low Earth Orbit,近地轨道)卫星的太阳电池阵输出功率衰减问题,在分析卫星轨道半长轴、太阳入射角、日地距离等参数变化与影响的基础上,提出按照轨道衰减快慢来区分太阳活动高年与低年,进而通过区分高年与低年,再根据不同季节分别进行太阳电池阵输出功率的衰减估计,而无须做功率归一化。同时,重点关注了夏至前后的最低输出功率的衰减情况,以此作为在轨卫星长期管理中的能源参考,建立平均电流和功率衰减因子估计模型,并结合实际工程数据进行了衰减估计。结果表明,太阳电池阵输出功率的年衰减因子约为-0.012,年衰减率约为1.2%。该结果可应用于在轨卫星长期管理的遥测诊断辅助。     

Intrinsic physical relationships between rotor modal shapes and instantaneous vibrational energy flow transmission characteristics: Theoretical and numerical analysis and application

The modal vibration of the rotor is the main cause of excessive vibration of the aero-engine overall structure. To attenuate the vibration of the rotor under different modal shapes from the perspective of energy control, the intrinsic physical relationships between rotor modal shapes and instantaneous vibrational energy flow transmission characteristics is derived from the general equation of motion base on the structural intensity method. A dual-rotor-support-casing coupling model subjected to the rotor unbalanced forces is established by the finite element method in this paper. The transmission, conversion and balance relationships of the vibrational energy flow for the rotors in the first-order bending modal shape, the conical whirling modal shape and the translational modal shape are analyzed, respectively. The results show that the vibrational energy flow transmitted to the structure can be converted into the strain energy, the kinetic energy and the energy dissipated by the damping of the structure. The vibrational energy flow transmission characteristics of rotors with different modal shapes are quite different. Especially for the first-order bending modal shape, the vibrational energy flow and the strain energy are transmitted and converted to each other in the middle part of the rotor shaft, resulting in large deformation at this part. To attenuate this harmful vibration, the influences of grooving on the shaft on the first-order bending vibration are studied from the perspective of transmission control of vibrational energy flow. This study can provide theoretical references and guidance for the vibration attenuation of the rotors in different modal shapes from a more essential perspective.     

带时变通信时间延迟的卫星编队姿态协同自适应L2增益控制

针对卫星编队姿态协同分布式控制问题,提出一种基于Lyapunov方法的编队飞行协同控制策略.首先,考虑到实际编队飞行中星问通信存在时变时间延迟及模型不确定问题,结合变结构控制的思想设计一种针对时滞系统稳定性分析的Lyapunov函数,从而由直接Lyapunov方法得到可对模型参数进行估计的自适应分布式姿态协同控制器,并...     

富燃料推进剂燃烧产物粒度参数的激光衰减法测量

介绍了激光衰减法测量粒子参数的基本原理.搭建了激光衰减法测量高铝含量富燃料推进剂实验系统,解决了燃烧环境下粒度测试的光学介入问题,对高铝含量富燃料推进剂中粒子参数进行测量,对所得的凝相燃烧产物进行电镜分析,并对电镜照片进行分析处理,计算出燃烧后凝相产物平均粒径,验证了激光衰减法测量粒子参数的可行性和合理性.     

光纤衰减测试系统的研究

在光纤通信中，光纤衰减是光纤捏的一项重要指标，通常需要测试光纤在某一较宽频段内各个波长的光纤衰减值，以选择合适的光源工作波长，笔者设计了一种新颖的双频检测光电系统，并采用单片机进行数据采集和处理。     

A new landing impact attenuation seat in manned spacecraft biologically-inspired by felids

When manned spacecraft comes back to the earth, it relies on the impact attenuation seat to protect astronauts from injuries during landing phase. Hence, the seat needs to transfer impact load, as small as possible, to the crew. However, there is little room left for traditional seat to improve further. Herein, a new seat system biologically-inspired by felids’ landing is proposed.Firstly, a series of experiments was carried out on cats and tigers, in which they were trained to jump down voluntarily from different heights. Based on the ground reaction forces combined with kinematics, the experiment indicated that felids’ landing after self-initial jump was a multi-step impact attenuation process and the new seat was inspired by this. Then the construction and work process of new seat were redesigned to realize the multi-step impact attenuation. The dynamic response of traditional and new seat is analyzed under the identical conditions and the results show that the new concept seat can significantly weaken the occupant overload in two directions compared with that of traditional seat. As a consequence, the risk of injury evaluated for spinal and head is also lowered, meaning a higher level of protection which is especially beneficial to the debilitated astronaut.     

对卫星网络轨道／频率协调中若干问题的探讨

以国际电联的相关建议为基础，就卫星网络轨道及频率协调中所碰到的若干问题，诸如天线增益，极化隔离，雨衰及ＳＣＰＣ保护比，给出了合理及可实现的估算方法，同时强调了功率密度在不同的应用场合，常有不同的定义方式。     

A noise attenuation method for medium-energy electron measurements in the radiation belt

From the viewpoint of plasma particle measurements in the radiation belt, background noise is a serious problem. High-energy particles penetrating the sensor shielding generate spurious signals, and their count rate often can be comparable to the true signals. In order to attenuate such background noise during medium-energy (5–83 keV) electron measurements, we propose the double energy analyses (DEA) method. DEA is conducted by a combination of an electrostatic analyser (ESA) and avalanche photo-diodes (APDs); ESA and APD independently determine the energy of each incoming particle. By using the DEA method, therefore, the penetrating particles can be rejected when the two energy determinations are inconsistent; spurious noise are caused only when the deposited energy at an APD is by chance consistent with the measured energy by ESA. We formulate the noise count rate and show the advantage of DEA method quantitatively.