基于距离代价函数和信息熵的发动机性能参数估计研究

研究发动机部件性能参数变化规律,对于减少维修次数和推动视情维修具有重要意义。针对测量参数个数少于待估性能参数的情况,给出了一种通过构建代价函数和优化算法的参数估计方法。原代价函数只考虑当前点参数,缺少与前面点参数的联系,因此结合自组织神经网络,构造了包含以前与当前点参数的距离代价函数。并提出了一种快速的参数估计方法。由于准确的部件性能参数很难获取,并且参数趋势估计不同于单纯的点估计问题,以对应的测量参数为基础,利用信息熵方法评定部件性能参数估计效果。进一步得到距离代价函数对应的参数信息熵为0.6805,优于原代价函数的估计结果。最后通过实例验证了参数估计方法的有效性。      

机载220 GHz云雷达衰减订正模拟试验

针对220 GHz云雷达回波信号的衰减问题，结合典型云滴谱和云参数，对水云和冰云模拟取样2 100次，应用离散偶极子近似法计算了220 GHz云雷达探测云滴粒子的衰减系数kc和雷达反射率因子Z的关系。在考虑大气和云对220 GHz云雷达信号衰减的基础上，对水云和冰云的机载220 GHz雷达回波强度进行了数值模拟，根据得到的kc-Z关系，进行衰减订正的模拟试验。结果表明:水滴云比冰晶云的衰减系数大2~3个数量级;相对于小粒子的水云和冰云，大气吸收是造成机载220 GHz云雷达衰减的主要原因。高频段的雷达信号在传播路径上的衰减非常明显，本研究中给出的kc-Z关系适用于220 GHz频率雷达的云衰减订正计算。     

Ionospheric correction using GPS Klobuchar coefficients with an empirical night-time delay model

We proposed an ionospheric correction approach called NKlob to mitigate the ionospheric delay errors. NKlob is a modification of the original GPS Ionospheric Correction Algorithm (ICA), which uses an empirical night-time model depending on the time, geomagnetic location and periodicities of the ionospheric behavior to replace the night-time constant delay in GPS ICA. Performance of NKlob was evaluated by the independent total electron contents (TECs) derived from Global Ionospheric Maps (GIMs) of the International GNSS Services (IGS) and Jason-2 altimetry satellite during 2013–2017. Compared to GIM TECs, NKlob corrects 51.5% of the ionospheric delay errors, which outperforms GPS ICA by 6.3%. Compared to Jason-2 TECs, NKlob mitigates the ionospheric errors by 58.1%, which is approximately 3.7% better than that of GPS ICA. NKlob shows significant improvement in low-latitude and equatorial regions with respect to GPS ICA, meanwhile exhibiting comparable performance at middle and high latitudes. Since NKlob only requires slight technical changes at the processing level of GPS receivers, we suppose that it can be easily implemented for better ionospheric delay corrections of real-time GPS single-frequency applications.     

Adaptive level of autonomy for human-UAVs collaborative surveillance using situated fuzzy cognitive maps

Collaborating with a squad of Unmanned Aerial Vehicles (UAVs) is challenging for a human operator in a cooperative surveillance task. In this paper, we propose a cognitive model that can dynamically adjust the Levels of Autonomy (LOA) of the human-UAVs team according to the changes in task complexity and human cognitive states. Specifically, we use the Situated Fuzzy Cognitive Map (SiFCM) to model the relations among tasks, situations, human states and LOA. A recurrent structure has been used to learn the strategy of adjusting the LOA, while the collaboration task is separated into a perception routine and a control routine. Experiment results have shown that the workload of the human operator is well balanced with the task efficiency.     

Beidou wide-area augmentation system clock error correction and performance verification

On December 27, 2018, the Beidou-3 System (BDS-3) has completed the deployment of 18 Medium Earth Orbit (MEO) satellites combined as a space constellation. In addition to the augmentation information for the new system signals B1C and B2a, the BDS-3 is compatible with the three augmentation information broadcast by the BDS-2 system for B1I and B3I signals: equivalent clock error correction, User Differential Ranging Error (UDRE) and Grid Ionosphere Vertical Error (GIVE). In this paper, the observation data of Beidou monitoring network are used to analyze the pseudo-range observation quality of the smooth transition signals B1I and B3I of BDS-2 and BDS-3. At the same time, the relationship between the equivalent clock error correction and the prediction error of the satellite clock is analyzed by using the Two-Way Satellite Time and Frequency Transfer (TWSTFT) data. The results show that the correlation between the equivalent clock error correction and the monitored clock error by using the TWSTFT data is greater than 60%. We calculate the UDRE by using the equivalent clock error correction. The results show that the satellite equivalent clock error correction can improve the accuracy of User Equivalent Range Error (UERE) by about 50%. This paper also compares the positioning accuracy of the BDS-2 satellites with the BDS-2 satellites combined BDS-3 satellites. The results show that the three-dimensional positioning accuracy is improved by about 30% after the BDS-3 satellites are added.     

飞向晕轨道的探测器轨道优化

晕轨道的稳定流形为从地球到晕轨道的转移轨道设计提供了便利．以往都采用在晕轨道上的目标点施加脉冲,这样,稳定流形只是为转移轨道的设计提供一个初始猜想,探测器并没有运行在稳定流形上,因而并未真正利用稳定流形节省燃料的优势．利用基于序优化理论的微分修正法,研究从晕轨道近地点稳定流形上不同点进入稳定流形所需要的燃料消耗,寻找燃耗最少的转移轨道．仿真表明,对于晕轨道近地点入轨,找到的稳定流形射入点机动比以往的晕轨道入轨点机动节省约33％的燃料消耗．此外,还对晕轨道上不同入轨点的入轨代价进行了研究,得到了晕轨道近地点入轨的最小燃耗解．     

火星探测转移轨道中途修正分析

中途修正分析是深空探测任务设计的关键步骤。首先讨论火星探测中途修正速度增量的求解方法,并由此对多次修正问题进行了Monte Carlo仿真分析。为满足不同的计算需求,针对速度增量的求解问题,给出了精确算法和快速算法两种思路,并对二者的解算精度进行了对比。以2018年某火星探测轨道为例,根据设定误差,计算得出了各次修正速度增量和残余误差随修正时间变化的数据曲线,进而对修正时机的选择问题进行了讨论,并对5次修正策略进行了仿真分析。实验表明,Monte Carlo仿真数据能够直观地反映多次修正的基本规律,讨论结果可以为修正策略的制定提供一种思路和数据参考。
     

Theories and methods for designing hypersonic high-enthalpy flow nozzles

Hypersonic high-enthalpy wind tunnels have been a challenge to ground tests in aerospace research area for decades and its test flow uniformity is one of the most important parameters for evaluating wind tunnel performances. Regarding to the performance requirement, theories and methods for designing hypersonic flow nozzles at high enthalpy conditions are quite difficult, but very interesting topics, especially when air molecule dissociations take place in wind tunnel test gas reservoirs. In thi...     

三轴磁强计测量误差修正方法

三轴磁强计测量误差修正对卫星姿态确定和控制具有重要意义。文章针对三轴磁强计测量误差的来源进行理论分析,引入磁场输入引起的常值漂移,建立了三轴磁强计测量误差修正模型,并基于该模型在磁环境模拟器中对Honeywell公司的三轴磁强计（HMR2300R）进行标定。实验结果表明改进模型可以将测量误差控制在50 nT以内,满足低成本敏感器在微小卫星姿态确定中的应用要求。     

不依赖GPS的磁图测绘与校正新方法

针对水下磁场测绘中因载体难以经常上浮修正导航误差而导致的测绘结果坐标误差较大的问题,结合磁场测量的特殊性,并采用边导航边校正的思想,提出了一种不依赖GPS的全新磁图测绘方法。首先以惯性导航系统为标准进行第一次测绘并获得具有一定坐标误差的初始磁图,然后对初始磁图进行图形处理与信息提取,在此基础上进行第二次测绘。在第二次测绘中用从初始磁图获得的特征信息结合磁场传感器与惯性器件的输出构建卡尔曼滤波器,从而达到同时修正自身运动状态与初始磁图的目的。理论分析与仿真结果都证实了本方法可以通过两次误差较大的低精度测绘获得精度高得多的测绘结果。