航天器运输包装箱仿真验证平台技术研究

针对数量有限的物理跑车试验无法满足减振与保温性能测试需求的问题，提出一套航天器运输包装箱动力学与热学仿真验证方法，包括：建立适用于包装箱系统的刚柔耦合多体动力学系统，通过结合线路条件测试生成的动力学系统外部激励，实现减振性能虚拟跑车测试；建立基于计算流体力学的包装箱热学模型，通过模拟自然对流和空调控制，实现包装箱保温性能虚拟跑车测试；基于C/S架构和导航式流程设计思想，建立航天器运输包装箱仿真验证平台，通过实际案例证明该平台仿真结果与实际跑车测试数据具有较高的一致性。     

散射对高温气体-碳黑颗粒混合物辐射传输的影响

基于全光谱k分布(Full spectrum k distribution,FSK)模型、MIE理论和有限体积法(Finite volume method,FVM),构建了均温、均质辐射参与性气体-碳黑颗粒混合物介质热辐射传输模型,并分析了碳黑不同尺寸、不同体积浓度以及介质不同路径长度和不同温度条件下,因忽略碳黑颗粒散射所导致的介质热辐射传输特性(如辐射热流、辐射源项)的计算误差。研究结果表明:体积分数不变,增大粒径,计算误差呈现出先增大后减小的趋势;数密度不变,增大粒径,或者粒径不变,增大体积分数,均将使得计算误差相应增大;粒径、体积分数不变,增大路径长度,或者升高介质温度,均将增大计算误差。通常对于含有大颗粒、高碳黑浓度的辐射参与性气体-碳黑颗粒混合物介质,碳黑颗粒散射不能忽略。     

Development and performance evaluation of tropospheric scintillation model on Ku-band satellite link over Akure,Nigeria

Existing amplitude scintillation prediction models often perform less satisfactorily when deployed outside the regions where they were formulated. This necessitates the need to evaluate the performance of scintillation models developed in one region using data data from other regions while documenting their relative errors. Due to its variation with elevation angle, frequency, other link parameters and meteorological factors, we employed three years (January 2016 to December 2018) of concurrently measured satellite radio beacons and tropospheric weather parameters to develop a location-based amplitude scintillation prediction model over the Earth-space path of Akure (7.17^oN, 5.18^oE), South-western Nigeria. The satellite beacon measurement used Tektronix Y400 NetTek Analyzer at 1 s integration time while meteorological parameters, namely; temperature, pressure and relative humidity were measured using Davis Vantage Vue weather station at 1 min integration time. Comparative study of the model’s performance with nine (9) existing scintillation prediction models indicates that the best and worst performing models, in terms of root mean square error (RMSE), are the Statistical Temperature and Refractivity (STN) and direct physical and statistical prediction (DPSP) models with values 11.48 and 51.03 respectively. Also, worst month analysis indicates that April, with respective enhancement and fade values of 0.88 and 0.90 dB for 0.01% exceedance, is the overall worst calendar month for amplitude scintillation.     

机载托架自动校准系统的设计与实现

为了解决机载托架传统校准方法精度低、耗时、费力等问题,设计了一种高精度、高效率并且操作简单的成品托架自动校准系统。该系统运用调平精度较高的"循环多次"最高点不动调平方法,建立高精度机载托架校准的静力学数学模型,运用VC与Matlab的COM接口编程技术开发机载托架自动校准系统,并建立良好的人机交互界面。试验结果表明,利用该方法对机载托架进行校准,无论是校准精度还是校准效率都较传统方法有很大提高。     

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.     

R141b在圆形微通道内的沸腾换热实验研究

为提高换热强度、解决设备内部高热流密度散热问题,采用实验方法研究R141b在不同直径(D=0.5mm和1.0mm)水平圆形微通道内的沸腾换热特性,分析了热流密度(q=2.0kW/m~2～47.6kW/m~2)、质量干度(x=0～0.6)、质量流速(G=111.11kg/(m~2·s)～333.33kg/(m~2·s))的变化对平均传热系数h的影响,探究不同情况下影响沸腾换热的主导因素。实验研究表明:平均传热系数h随热流密度q的增加而减小,在不同范围内减小速率有明显差异;热流密度q=2kW/m~2～5kW/m~2时质量流速G对平均传热系数h影响较明显,热流密度较高时质量流速G对换热影响很小;在质量流速G=111.11kg/(m~2·s)～333.33kg/(m~2·s),质量干度x0.3时,平均传热系数h随质量干度x增加而明显下降,在设计微通道换热器时应尽量使R141b处于初始沸腾阶段以获得更好换热效果,并采取一定措施预防干度过高引起的换热恶化。     

Mapping mean lake surface from satellite altimetry and GPS kinematic surveys

Lake water height is a key variable in water cycle and climate change studies, which is achievable using satellite altimetry constellation. A method based on data processing of altimetry from several satellites has been developed to interpolate mean lake surface (MLS) over a set of 22 big lakes distributed on the Earth. It has been applied on nadir radar altimeters in Low Resolution Mode (LRM: Jason-3, Saral/AltiKa, CryoSat-2) in Synthetic Aperture Radar (SAR) mode (Sentinel-3A), and in SAR interferometric (SARin) mode (CryoSat-2), and on laser altimetry (ICESat). Validation of the method has been performed using a set of kinematic GPS height profiles from 18 field campaigns over the lake Issykkul, by comparison of altimetry’s height at crossover points for the other lakes and using the laser altimetry on ICESat-2 mission. The precision reached ranges from 3 to 7 cm RMS (Root Mean Square) depending on the lakes. Currently, lake water level inferred from satellite altimetry is provided with respect to an ellipsoid. Ellipsoidal heights are converted into orthométric heights using geoid models interpolated along the satellite tracks. These global geoid models were inferred from geodetic satellite missions coupled with absolute and regional anomaly gravity data sets spread over the Earth. However, the spatial resolution of the current geoid models does not allow capturing short wavelength undulations that may reach decimeters in mountaineering regions or for rift lakes (Baikal, Issykkul, Malawi, Tanganika). We interpolate in this work the geoid height anomalies with three recent geoid models, the EGM2008, XGM2016 and EIGEN-6C4d, and compare them with the Mean Surface of 22 lakes calculated using satellite altimetry. Assuming that MLS mimics the local undulations of the geoid, our study shows that over a large set of lakes (in East Africa, Andean mountain and Central Asia), short wavelength undulations of the geoid in poorly sampled areas can be derived using satellite altimetry. The models used in this study present very similar geographical patterns when compared to MLS. The precision of the models largely depends on the location of the lakes and is about 18 cm, in average over the Earth. MLS can serve as a validation dataset for any future geoid model. It will also be useful for validation of the future mission SWOT (Surface Water and Ocean Topography) which will measure and map water heights over the lakes with a high horizontal resolution of 250 by 250 m.