Estimating inter-system biases for tightly combined Galileo/BDS/GPS RTK

The overlapping carrier frequencies L1/E1, L5/E5a and B2/E5b from GPS/Galileo/BDS allow inter-system double-differencing of observations, which shows a clear advantage over differencing of the observations of each constellation independently. However, the inter-system biases destroy the integer nature of the inter-system double-differencing ambiguities. Two methods of direct rounding and parameter estimation are used to determine the ISB value. By analyzing data collected from Curtin University from 2015 to 2018, the phase and code inter-system bias (ISB) are related to the receiver type, firmware version and the selected overlapping frequency. Upgrade of receiver firmware version results in changes of ISB values. For example, the upgrade of Javad firmware in Dec, 15, 2017 causes the difference of 0.5 cycles ISB between BDS GEO and non-GEO satellites. By comparing the three dynamic models which include white noise process, random walk process, and random constant in the parameter estimation method, the ISB determined by the random constant model is consistent with the value obtained by the direct rounding method. After the calibration of ISBs, the performances of tightly combined positioning are assessed. The success rate of ambiguity resolution and accuracy of positioning for the tight combination (TC) are significantly improved in comparison with that for the loose combination (LC) over short baselines. For L5/E5a, on which only few satellites can be observed, the maximum increase in success rates of ambiguity resolution can reach 31.7%, i.e., from 54.9% of LC to larger than 86.6% of TC, and the positioning accuracies can even be increased by 0.13 m, i.e., from 0.208 of LC to 0.074 m of TC in East direction for the mix-receiver TRIMBLE NETR9-SEPT POLARX4 in 2018.     

Lock-in phenomenon of tip clearance flow and its influence on aerodynamic damping under specified vibration on an axial transonic compressor rotor

In this study, the lock-in phenomenon of Tip Clearance Flow(TCF) instabilities and their relationship to blade vibration are investigated numerically on an axial transonic rotor with a large tip clearance. The capabilities of simulating instability flow and lock-in phenomenon are verified on a transonic rotor and a NACA0012 airfoil by comparing with the test data, respectively.The lock-in phenomenon is first numerically confirmed that may occur to TCF instabilities when its frequency is close to...     

无轴向通流对转轴间的流动与传热特性

为研究航空发动机对转轴间的流动与换热,建立了无轴向通流的对转环腔湍流边界层的修正卡门三层结构速度分布模型。基于该速度分布模型并依据动量传递与热量传递的比拟理论,推导了外轴内壁面换热努塞尔数的表达式及准则关系式。与CFD数值计算的速度分布、外轴内壁面换热努塞尔数进行对比验证,结果表明,对转环腔湍流边界层的修正卡门三层结构模型给出了一致的速度分布和换热规律。理论与CFD计算得到的外轴内壁面换热努赛尔数在低旋转雷诺数下符合较好,高旋转雷诺数下偏离不超过20%。     

星间红外探测与测量系统

文章主要介绍了具有凝视成像功能的红外探测系统的研究和设计。首先简要描述了红外测 角系统的组成和工作原理;然后重点论述了红外探测系统的性能指标和光学设计;最后对红外探测系统设 计研究作了总结和展望。     

Analysis of the code and phase between-receiver inter-system biases of the overlapping frequencies for GPS/Galileo/BDS

The overlapping-frequency signals from different GNSS constellations are interoperable and can be integrated as one constellation in multi-GNSS positioning when inter-system bias (ISB) is properly disposed. The look-up table method for ISB calibration can enhance the model strength, maximize the number of integer-estimable ambiguities, and thus is preferred. However, the characteristics and magnitudes of the receiver code ISB and phase fractional ISB (F-ISB) are not well known and the wrong values of the biases can seriously degrade the positioning results. In this contribution, we first estimate the between-receiver code ISB and phase F-ISB of hundreds of the baselines up to around 25km in the European Permanent GNSS Network (EPN) and the Multi-GNSS Experiment (MGEX) for the overlapping frequencies L1-E1 (L1), L5-E5a (L5) and E5b-B2b (L7). The data collected from 1st January 2016 to 1st January 2019. Second, the receiver-type and firmware-version combinations for the receivers of Trimble, Leica, Javad, Septentrio and NovAtel are carefully classified. Results show that the Septentrio receivers have consistent code and phase ISB values for the three overlapping frequencies i.e. only one value for each frequency and no receivers are different. The Leica, Trimble and Javad receivers have two or more ISB values for at least one of the three frequencies. A few receivers with biases to the groups are also found and listed. Third, the code ISB and phase F-ISB of the groups are adjusted by the least-squares method. The root mean square errors (RMSE) of the least square adjustment are 0.240 m, 0.250 m and 0.200 m for code of L1, L5 and L7 frequencies, respectively, and are 0.0009 m, 0.0015 m and 0.0031 m for phase of L1, L5 and L7 frequencies, respectively. Finally, the effects of code ISB errors on code positing are investigated with the zero-baseline MAT1_MATZ. The distance root mean square error (DRMS) of L1-E1 code positioning can be reduced by 48.2% with 5 GPS and Galileo satellites and the DRMS degrades quickly when the code ISB error is larger.     

导航星座星间链路信号捕获搜索策略研究

针对导航星座星间链路信号动态范围大、捕获性能要求高之间的矛盾,利用星历信息辅助信号捕获。在此基础上,分析了信号捕获串行搜索、码并行搜索和频率并行搜索的计算代价,给出了不同信号体制和星历误差下各搜索策略对应的运算量表达式,并结合典型的应用场景进行了算例分析。分析结果表明星间信号捕获在星历误差较小时采用串行搜索策略具有最少的计算量,在星历误差较大时采用码并行搜索策略计算量最少。     

北斗系统地固系自主定轨算法

为避免传统惯性系自主定轨算法中的多次坐标转换,针对地固系分布式自主定轨算法原理及其中的关键技术开展研究。给出在地固系中进行自主星历生成的总体框图,推导了地固系自主定轨算法的基本方程,提出一种新的以地固系位置速度为状态量的状态转移矩阵解析计算方法并分析其计算量,证明了地固系自主定轨算法可以进一步降低定轨算法复杂度,且无需上注地球定向参数进行坐标转换。使用仿真数据和真实在轨测量数据的测试结果表明,提出的地固系分布式自主定轨算法与传统算法定轨精度相当,说明了所提算法的可行性,验证了星载自主定轨原型软件的有效性。     

浅析彩电I2C总线的故障调整与检修方法

大屏幕彩色电视机中均采用了I^2C总线控制，使复杂的输入/输出接口电路变得简单化，提高了单元电路的使用寿命，降低了故障率和维修成本，但有时因元件老化等原因会导致总线参数变化，引起电视机某些功能失常。为此，本篇介绍了大屏幕彩色电视机中I^2C总线的常见调整及故障检修方法。     

三维梯度功能材料层间力学模型与应力分析

本文对非均质耐热梯度功能材料（FGM）层间的结构与性能进行了研究，通过对陶瓷－金属FGM的宏、细观结构分析，建立了基层间三维力学模型，导出了应力分析方程，本方法的确定不仅可以指导FGM的成分，组织和结构设计，而且还可以加速FGM实用比的进程通过典型的算例数值分析，表明其具有重要的理论意义和实用价值。     

CCSDS Proximity-1及其在编队飞行小卫星群中的应用

讨论近距离空间链路协议 Proximity- 1的层次结构和传输帧 Version- 3构成 ,分析包括 CCSDS标准包和用户自定义数据的数据业务及定时业务。针对编队飞行小卫星群的星间数据交换和自主测控 ,对 Proximity- 1应用于小卫星群星间通信和星间测距作了探讨