驱动模式和转速对某星载天线扰动特性的影响

空间天线姿态调整过程中产生的微振动，对航天器指向精度和稳定性影响较大，因此其微振动分析与设计已成为高精度航天器设计的重要内容。基于Ansys软件和Admas软件，建立天线结构的多柔体系统动力学分析模型，分析典型驱动条件下天线结构的扰动力和扰动力矩，通过地面微振动物理试验，验证动力学分析方法的可靠性。基于天线多柔体系统动力学分析模型，探讨驱动模式、驱动转速对天线扰动力和扰动力矩的影响。结果表明:扰动力和力矩主要幅值集中在频率f=0~50 Hz的低频段;驱动模式和驱动转速对天线结构的扰动频率无明显影响，主要影响扰动力和扰动力矩的幅值;单轴驱动模式下，驱动转速n=0.2 °/s时，天线的扰动最剧烈;XY双轴同时驱动时，X轴和Y轴转动单元引起的天线扰动产生一定程度的叠加，天线结构的扰动更为剧烈，扰动力和扰动力矩变化较为复杂。研究工作可为空间天线的微振动抑振策略制定提供技术支持。     

Research on the evaluation method of lunar soil disturbance based on the fitting of Gaussian surface

It is crucial to maintain the layer sequence information on in situ lunar soil during the lunar soil sampling. In this paper, a discrete element model for direct push sampling of the lunar weathering layer is established, and the relationship between the perturbation rate of the lunar soil layer sequence information and the sampling depth is obtained. A quantitative evaluation method of the perturbation rate of the structural information on the lunar soil layer sequence based on the Gaussian curvature is proposed by reconstructing the center-of-mass point cloud model of the marked layer lunar soil particles in MATLAB. The proposed method can accurately describe the perturbation rate of lunar soil layer sequence information and can analyze the degree of lunar soil disturbance according to the displacement of the sampling tube and mechanical parameters in real-time inversion during the sampling process. When the sampling depth is 40 mm, the minimum and maximum perturbation rates of sampling along the penetration direction of the machine are 5.261 % and 27.649 %, respectively. The perturbation rate shows a trend of first decreasing and then increasing. The method proposed in this study could effectively solve the problem that the disturbance of lunar soil bedding information was difficult to evaluate in the sampling process of lunar regolith.     

Non-synchronous blade vibration analysis of a transonic fan

This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case. Single-passage unsteady calculations at a near stall operating point of 82% design speed show that the dominant frequencies of mass flow were not the harmonics of the rotor rotational frequency. A full-annulus fluid–structure interaction analysis was subsequently carried out to examine the unsteady flows and their interactions with blade vibrations. The results show that the modal displacement of the backward traveling seventh nodal diameter of the second torsion mode grew exponentially, which reveals that the blade vibration was non-synchronous. The vibration pattern indicates that the aerodynamic mode was resonant with the structural vibration mode. Around the rotor tip, the circumferential vortical propagation induced by interactions among the main flow, tip leakage flow, and tip clearance vortex was the source of aerodynamic excitation. To clarify the mechanism of the non-synchronous vibration, the coupling between aerodynamic disturbance and structural response, i.e., aliasing, was summarized. The frequency spectra of the fluctuating pressure show that an aerodynamic Backward Traveling Wave (BTW) was co-aliased to a structural BTW due to the propagation of the circumferential vortex. The correlation between the frequency and free convective speed of the aerodynamic disturbance determined the directions of aliasing.     

随机扰动下的航天器姿轨保持自抗扰控制

空间飞行器在轨运行过程中除受空间摄动外，还因飞行器任务需要产生随机扰动力和扰动力矩。针对空间飞行器受随机扰动产生的耦合运动控制问题，提出了利用自抗扰方法进行轨道保持和姿态稳定的控制方法。通过引入二阶线性扩展状态观测器，对系统总扰动和状态进行观测。结合PD控制方法结合总扰动前馈补偿，克服空间主要摄动及飞行器本身产生的随机扰动，实现轨道保持和姿态稳定。仿真试验结果表明:该方法可以有效克服总扰动的影响，实现姿轨协同控制。     

天基星空背景观测覆盖范围计算方法研究

针对日趋复杂的空间环境，天基观测由于其分布灵活和全天候观测的特性受到越来越多的关注，该类问题为典型的星空背景观测（above-the-horizon，ATH）问题。基于分段积分思想，提出了一种ATH观测三维空间覆盖范围的计算方法，涵盖了该问题所有可能的10种积分形式，适用于因观测约束参数不同取值而形成的任意几何构型场景。不仅在二维平面覆盖问题上与现有方法进行了比较并验证，还首次解决了ATH在三维空间中覆盖体积的定量解析计算难题。仿真结果表明，平面和空间覆盖最大化所对应的最优观测轨道高度存在明显差异，空间覆盖计算模型能更为准确有效地表示卫星覆盖性能，同时能为星座优化设计提供参考。     

Frequency steering of spaceborne clocks based on XPNAV-1 observations

Due to high stable rotations, timing of pulsars provides a natural tool to correct the frequency deviation of spaceborne atomic clocks. Based on processing the observational data about a year of Crab pulsar given by XPNAV-1 satellite, we study the possibility of correcting the frequency deviation of spaceborne atomic clocks using pulsar timing. According to the observational data in X-ray band and the timing model parameters from radio observations, the pre-fit timing residuals with a level of 6...     

Optimized design of high-efficiency lunar soil sampling tube structure based on stress–strain law

Understanding the influence of the sampling apparatus on in-situ lunar soil lamination information during the sampling process of the direct push-through lunar weathering layer is of great importance. This paper develops a discrete element model for direct push-through lunar weathering layer sampling using the CUG-1A simulated lunar soil developed by the China University of Geosciences as a simulation object and determines the stress–strain law of the inner wall of a sampling tube. A method for optimizing the inner wall structure of a sampling tube based on the stress–strain law is proposed. The structural disturbance of the marker layer and the lunar soil disturbance rate evaluation function are used to assess the degree of disturbance of the laminar information during the sampling process. The results show that the proposed method can effectively reduce the structural disturbance of the lunar soil in-situ laminar information. In addition, it can also optimize the structural information disturbance of the marker layer. The proposed method can decrease the simulated lunar soil disturbance rate from 0.31 to 0.251 and effectively reduce the penetration force load by 15–20% in the direct push-through sampling process.     

Robust extension of the simple sea-surface irradiance model to handle cloudy conditions for the global ocean using satellite remote sensing data

Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em^?2day^?1; and a mean net bias of 2.917 Em^?2day^?1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions.     

车载惯导系统抗扰动自对准方法对比研究

自对准技术是陆基机动平台及装备用惯导系统的一项关键技术,其核心在于惯导系统如何在风扰、发动机振动、人员走动等各种干扰下实现快速、高精度对准.针对目前常用的惯性系解析自对准、Kalman滤波估计自对准和惯性系奇异值分解(SVD)自对准等三种方法进行了研究和对比分析,根据三种对准方法各自的实现原理,提出了一种有针对性的抗扰动优化方法,并通过了数学仿真分析和车载试验验证.结果 表明,在车载使用环境下,后两种方法都能获得较为准确的姿态信息,惯性系SVD方法可以达到与Kalman滤波方法相当的对准精度和收敛速度,且无需先验信息即可获得最优解,表现出了较好的工程应用优势.