差动变压器式位移传感器的仿真建模研究

差动变压器式位移传感器（LVDT）具有工作可靠性高、输出电压准确度高、线性度好等优点,在伺服系统中得以广泛应用。但传统的设计周期长、成本高,短时间内难以设计出线性度好的传感器。提出使用Maxwell建立传感器模型的方法,利用Maxwell快速改变模型尺寸的优势,对影响传感器性能的补偿线圈绕法进行了仿真。经试验验证,该模型可有效地模拟真实产品,显著地提高实际工程中传感器的设计效率及产品的线性度。     

基于dSPACE的频率特性测试与模型辨识研究

为了满足伺服控制系统设计需要,提出了一种利用dSPACE系统对被测对象进行频率特性测试与模型辨识的方法,对该方法所使用的激励信号与响应数据处理进行了研究。利用dSPACE硬件平台产生离散正弦扫频信号,利用软件合成的方法实现相关分析运算,使用Matlab进行数据处理,完成被测对象频率特性曲线绘制,采用Levy方法进行了模型辨识。应用结果表明,该方法使用方便,对传递函数具有较高的辨识精度,可以为控制算法设计提供理论依据。     

基于频响函数模型修正影响因素的仿真

首先推导了基于频响函数模型修正的理论公式,在此基础上通过平面桁架模型修正的仿真算例,比较研究了基于频响函数模型修正方法具体实现过程中数据测量噪声、频率点选择以及频段选择等因素对修正结果的影响。研究表明,频率点的选择是基于频响函数模型修正的关键因素,合理的频率点选择既能够减小计算量,降低修正方程的条件数,同时还能够抑制测量噪声的影响;此外,提高实测数据的精度,增加修正频段的宽度也是改善模型修正效果的有效手段。     

Impact of loading effects on determination of the International Terrestrial Reference Frame

The International Terrestrial Reference Frame (ITRF), as a realization of the International Terrestrial Reference System (ITRS), is represented by a set of station positions and linear velocities. They are intended to be used as regularized coordinates to which some corrections should be added to access instantaneous coordinates. The latest ITRS realization is the ITRF2005, which has integrated time series of station positions to form long-term solutions for the four space geodetic techniques. Currently, a purely linear model is used to parameterize station displacements in the estimation process, plus occasional discontinuities in case of earthquakes or equipment changes. However the input data have been derived without applying surface loading models and so surface loading effects are supposed to be embedded in the coordinates as measured quantities. We evaluate the effect of applying a posteriori loading corrections, which include the effect of atmospheric, non-tidal ocean, and continental water loading, to time series of positions estimated from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS) data. We notice that they reduce about 50% or more of the annual signals in the translation and scale parameter time series of the SLR and VLBI techniques, except in SLR Z translation. In general, the estimated secular frame definition is negligibly affected and estimated positions and velocities are not significantly modified for stations that have accumulated a large number of observations. A multi-technique combination of such derived frames allows concluding that, for some cases, loading model corrections might degrade co-located station coordinates almost as much as they benefit them. However, most significant improvement of the estimated secular coordinates is observed for stations with less than 100 estimated positions as demonstrated with a multi-technique combination.     

基于多模型滚动时域估计的卫星故障诊断

研究了卫星姿态控制系统故障诊断问题, 将滚动时域估计与交互式多模型(IMM)方法相结合, 利用滚动时域估计方法对系统状态进行估计, 系统转换概率也相应地利用了一个时间段的估计误差作为依据, 而不是只考虑一个时刻的估计误差, 因此有效减少了大噪声以及个别错误测量对诊断结果的影响. 最后的仿真结果证明了该算法的有效性.      

飞机结构数字孪生关键建模仿真技术

飞机结构安全性设计思想经历了从静强度设计、安全寿命设计、损伤容限与耐久性设计到单机追踪的演变,未来有进一步向结构数字孪生的方向发展的趋势。飞机结构数字孪生是数字线程驱动的,多学科、多物理、多尺度、多保真度、多概率的模拟仿真系统,采用在线传感器监测、离线地面检查、飞机运行历史等多源数据,反映并预测对应飞机结构实体在全寿命周期内的行为和性能,有望革新现有的飞机结构使用和维护模式。面向疲劳寿命管理,提出飞机结构数字孪生的5项关键建模仿真技术,分别是载荷和损伤的数据获取技术、多尺度建模和力学分析技术、含裂纹复杂结构的精确高效仿真技术、基于降阶的数字孪生高效建模技术和考虑不确定性与多源异构数据的剩余寿命评估技术,并详细探讨这五项关键技术的研究现状与发展方向,为飞机结构数字孪生的系统研究与工程应用提供参考。     

Advanced high-order nonlinear chirp scaling algorithm for high-resolution wide-swath spaceborne SAR

Spaceborne Synthetic Aperture Radar (SAR) is a well-established and powerful imaging technology that can provide high-resolution images of the Earth’s surface on a global scale. For future SAR systems, one of the key capabilities is to acquire images with both high-resolution and wide-swath. In parallel to the evolution of SAR sensors, more precise range models, and effective imaging algorithms are required. Due to the significant azimuth-variance of the echo signal in High-Resolution Wide-Swath (HRWS) SAR, two challenges have been faced in conventional imaging algorithms. The first challenge is constructing a precise range model of the whole scene and the second one is to develop an effective imaging algorithm since existing ones fail to process high-resolution and wide azimuth swath SAR data effectively. In this paper, an Advanced High-order Nonlinear Chirp Scaling (A-HNLCS) algorithm for HRWS SAR is proposed. First, a novel Second-Order Equivalent Squint Range Model (SOESRM) is developed to describe the range history of the whole scene, by introducing a quadratic curve to fit the deviation of the azimuth FM rate. Second, a corresponding algorithm is derived, where the azimuth-variance of the echo signal is solved by azimuth equalizing processing and accurate focusing is achieved through a high-order nonlinear chirp scaling algorithm. As a result, the whole scene can be accurately focused through one single imaging processing. Simulations are provided to validate the proposed range model and imaging algorithm.     

扩压段对高超声速推进风洞起动的影响

高超声速推进风洞是进行超燃冲压发动机模型地面模拟的重要试验设备。其中,扩压段的设计非常重要,它不是孤立的,而与主流系统和引射系统密切相关。通过对不同几何形状的扩压段在不同安装位置进行调试,研究在风洞起动过程中整个系统流动状态的演变规律,探索扩压段的优化设计。实验表明,扩压段应安装在距主喷管较近的位置,并具有与主喷管相匹配的入口面积和形状。扩压段的形状应设计成能使主气流通过一系列斜激波串减速的通道。扩压段应具有一定的长度以保证主气流减速到一定程度。     

基于协议分析的入侵检测技术的研究

协议分析技术是在特征模式匹配技术基础之上发展起来的一种新的入侵检测技术。它从网络通信协议特有的规则性出发,不必进行字节的逐个比较,而是直接找到待分析字节的位置,将待分析字节取出,进行分析。基于协议分析的入侵检测系统具有一些显著的特点。文中提出了一种结合协议分析技术的入侵框架模型。研究表明,该模型提高了检测效率,减少了漏报和误报。     

两种模型用于卫星钟差预报的性能分析

利用二次多项式和GM（1,1）灰色系统两种模型对GPS卫星钟差进行了预报分析。计算结果表明：在短期（1d）预报中,两者的预报误差在1ns量级以内;在长期（210d）预报中,灰色模型预报精度明显高于二次多项式模型预报精度,并且灰色模型长期（210d）预报Cs钟的精度高于Rb钟。