运动基航天飞行模拟器信号缩比策略

对于大幅值的输入信号,三阶多项式缩比法易产生信号畸变且参数配置复杂;而Hermite缩比函数法的触发速度较慢.提出两种改进的缩比方法:基于三阶多项式缩比法的最优参数配置法和加入线性缩比的非线性缩比法.前一种方法通过参数的优化配置最大化稳定区,以防止信号的畸变;后一种方法则利用线性缩比的特性将缩比度限制在稳定区内.仿真结果表明:线性缩比的加入可以防止三阶多项式缩比法信号的畸变;最优配置参数法应用方便且整体效果较好.为航天飞行模拟提供了更有效的缩比策略.     

机械连接件中螺栓孔角裂纹应力强度因子数值计算(英文)

The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors （SIFs） along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.     

考虑轨道摄动的外热流计算分析

为改进传统外热流算法未考虑外热流经多次反射后的吸收和国外商业软件未考虑轨道摄动及太阳矢量变化对外热流的影响等不足,重新定义了外热流角系数和外热流辐射传递因子,综合SGP4轨道模型和Gebhart方法,给出了考虑摄动等因素的辐射传递因子和轨道外热流计算模型,以及相应的计算流程。通过仿真分析论证了考虑多次反射及摄动等因素的重要性。     

对数正态分布场合环境因子基于截尾样本的统计分析

本文导出了寿命分布为对数正态分布时基于截尾样本环境因子的点估计和近拟置信限，对所给近似置信区间作了模拟研究。     

Self-similar stochastic processes in solar wind turbulence

Solar wind data is used to estimate the autocorrelation function for the stochastic process x(τ) = y(t + τ) − y(t), considered as a function of τ, where y(t) is any one of the quantities B²(t), n_p(t)V²(t), or n_p(t). This process has stationary increments and a variance that increases like a power law τ^2γ where γ is the scaling exponent. For the kinetic energy density and the proton density the scaling exponent is close to the Kolmogorov value γ = 1/3, for the magnetic energy density it is slightly larger. In all three cases, it is shown that the autocorrelation function estimated from the data agrees with the theoretical autocorrelation function for a self-similar stochastic process with stationary increments and finite variance. This is far from proof, but it suggests that these stochastic processes may be self-similar for time scales in the small scale inertial range of the turbulence, that is, from approximately 10 to 10³ s.     

船载遥测设备海上跟踪同步星标校的方法

结合船载遥测设备和测量船的特点,提出船载遥测设备海上跟踪同步星标校的方法,并通过试验数据进行验证。该方法克服了传统近场标校方法中存在的不足,实现了船载遥测设备海上精确标校。     

Walker星座碰撞检测及碰撞概率分析

针对Walker星座的碰撞问题,在狭义碰撞的基础上,设计一种Walker星座碰撞检测模型。该模型考虑星座实际在轨构型发散与维持偏差,给出了Walker星座构型维持条件下的广义碰撞检测与碰撞概率计算方法,并提出了表征Walker星座构型防碰撞性能的安全度系数。利用该检测模型,在进行Walker星座设计时不仅可以避免狭义碰撞,还可以实现星座在构型维持阈值内的广义碰撞安全性分析,实现星座构型择优。通过案例仿真分析,证明了该系统模型的可行性及可靠性。     

基于现代教育技术的专业建设

概述了现代教育技术对教学各环节的作用、专业建设中主要要素 ,论述基于现代教育技术的专业建设中应考虑的要素 ,提出专业建设必须立足于现代教育技术的运用。     

基于贝叶斯因子和二阶概率方法的圣地亚热传导模型确认挑战问题

针对美国圣地亚国家实验室为促进模型确认方法的发展所提出的热传导挑战问题,根据现代模型确认思想总结了该挑战问题解答中应包含的核心内容。在确认度量环节采用贝叶斯因子考察了实验数据是否支持所给模型,在此基础上通过二阶概率方法得到了模型预测的分布,以此计算出模型预测结论的置信度。该过程中考虑了模型参数的随机不确定性和认知不确定性,最后通过灵敏度分析辨识了模型参数的不确定性对模型预测的影响。研究表明该挑战问题中的实验数据支持所给模型,模型预测受导热系数的不确定性影响最大,模型预测材料在调控条件下的失效概率不满足调控要求,该结论的置信度为99.97%。     

An extended chirp scaling algorithm for spaceborne sliding spotlight synthetic aperture radar imaging

A system impulse response with low sidelobes is critical in synthetic aperture radar（SAR） images because sidelobes contribute to noise and interfere with nearby scatterers. However,the conventional tricks of sidelobe suppression are unable to be exactly applied to the case of spaceborne sliding spotlight SAR due to great azimuth shifts in both time and frequency domains. In this paper, an extended chirp scaling algorithm is presented for spaceborne sliding spotlight SAR data imaging. The proposed algorithm firstly uses the spectral analysis（SPECAN） technique to avoid the azimuth spectrum folding effect and then employs the chirp scaling（CS） algorithm to achieve data focusing, i.e., the so-called two-step approach. To suppress the sidelobe level, an efficient strategy for the azimuth spectral weighting which only involves matrix multiplications and short fast Fourier transformations（FFTs） is proposed, which is a post-process executed on the focused SAR image and particularly simple to be implemented. The SAR image processed by the proposed extended CS algorithm is very precise and perfectly phase-preserving. In the end, computer simulation results verify the analysis and confirm the validity of the proposed algorithm.