基于经验模分解的PPP时间比对数据消噪方法

精密单点定位(PPP)时间比对数据会受到观测噪声的影响,因此对时间比对数据进行消噪是一项重要工作。提出一种基于经验模分解(EMD)的PPP时间比对数据消噪方法,并将该方法与Vondrak滤波方法的消噪效果进行对比。结果表明,两种方法的消噪效果相当,均能有效滤除PPP时间比对数据中的随机噪声,明显改善时间比对的稳定度。     

固有模态函数(IMF)积检测器——以低信噪比情况下超宽带雷达信号检测为例

首次提出了一种固有模态函数积检测器.首先通过经验模式分解(EMD)把带噪信号分解成有限个固有模态函数(IMF).检测的基本思路是,对各个IMF分量的绝对值作逐点乘积,用于抑制噪声并凸现信号,最后进行滤波和判决.本文以UWB信号为例,数据源于UWB雷达实验系统.在低信噪比(SNR),UWB脉冲与噪声波形相似,且噪声概率密度函数(PDF)未知情况下,进行实验.结果表明,当峰峰信噪比低于5 dB时,该检测器性能优于Teager能量算子(TEO).     

改性双基推进剂代用料的研制

以典型改性双基推进剂配方为基础,对高能液体炸药组分A(GY)、固体炸药组分B(GG)的惰性替代物进行了选择分析,确定了其代用料的主要组分为硝化棉(NC)、惰性增塑剂(DZ-1)及惰性固体填料(YT-1).分别从增塑剂的溶解能力、固体填料含量及溶棉比三方面研究了其对改性双基推进剂代用料流动性的影响.研究表明,上述三方面因...     

固有模态函数（IMF）积检测器——以低信噪比情况下超宽带雷达信号检测为例

首次提出了一种固有模态函数积检测器。首先通过经验模式分解（EMD）把带噪信号分解成有限个固有模态函数（IMF）。检测的基本思路是，对各个IMF分量的绝对值作逐点乘积，用于抑制噪声并凸现信号，最后进行滤波和判决。本文以UWB信号为例，数据源于UWB雷达实验系统。在低信噪比（SNR），UWB脉冲与噪声波形相似，且噪声概率密度函数（PDF）未知情况下，进行实验。结果表明，当峰峰信噪比低于5dB时，该检测器性能优于Teager能量算子（TEO）。     

小波去除噪音算法研究

介绍了小波变换滤除噪音的机理和与傅立叶变换相比的优越性,其中包括确定性噪音和随机噪音。讨论了增强去噪效果的几种改进方案并提出一种试验估计去噪方法,对工程应用有一定的实用价值。     

A theoretical model of semi-elliptic surface crack growth

A theoretical model of semi-elliptic surface crack growth based on the low cycle strain damage accumulation near the crack tip along the cracking direction and the Newman–Raju formula is developed. The crack is regarded as a sharp notch with a small curvature radius and the process zone is assumed to be the size of cyclic plastic zone. The modified Hutchinson, Rice and Rosengren(HRR) formulations are used in the presented study. Assuming that the shape of surface crack front is controlled by two critical points: the deepest point and the surface point.The theoretical model is applied to semi-elliptic surface cracked Al 7075-T6 alloy plate under cyclic loading, and five different initial crack shapes are discussed in present study. Good agreement between experimental and theoretical results is obtained.     

关于对喷水室热工计算公式的分析及修正

通过分析喷水室内水和空气之间的热质交换过程，指出目前采用的热工计算公式的不足，并在此基础上推导出喷水室热平衡方程新公式，对理论教学起到一定的指导作用。     

An empirical solar radiation pressure model for satellites moving in the orbit-normal mode

We present a family of empirical solar radiation pressure (SRP) models suited for satellites orbiting the Earth in the orbit normal (ON) mode. The proposed ECOM-TB model describes the SRP accelerations in the so-called terminator coordinate system. The choice of the coordinate system and the SRP parametrization is based on theoretical assumptions and on simulation results with a QZS-1-like box-wing model, where the SRP accelerations acting on the solar panels and on the box are assessed separately. The new SRP model takes into account that in ON-mode the incident angle of the solar radiation on the solar panels is not constant like in the yaw-steering (YS) attitude mode. It depends on the elevation angle of the Sun above the satellite’s orbital plane. The resulting SRP vector acts, therefore, not only in the Sun-satellite direction, but has also a component normal to it. Both components are changing as a function of the incident angle. ECOM-TB has been used for precise orbit determination (POD) for QZS-1 and BeiDou2 (BDS2) satellites in medium (MEO) and inclined geosynchronous Earth orbits (IGSO) based on IGS MGEX data from 2014 and 2015. The resulting orbits have been validated with SLR, long-arc orbit fits, orbit misclosures, and by the satellite clock corrections based on the orbits. The validation results confirm that—compared to ECOM2—ECOM-TB significantly (factor 3–4) improves the POD of QZS-1 in ON-mode for orbits with different arc lengths (one, three, and five days). Moderate orbit improvements are achieved for BDS2 MEO satellites—especially if ECOM-TB is supported by pseudo-stochastic pulses (the model is then called ECOM-TBP). For BDS2 IGSOs, ECOM-TB with its 9 SRP parameters appears to be over-parameterized. For use with BDS2 IGSO spacecraft we therefore developed a minimized model version called ECOM-TBMP, which is based on the same axis decomposition as ECOM-TB, but has only 2 SRP parameters and is supported by pseudo-stochastic parameters, as well. This model shows a similar performance as ECOM-TB with short arcs, but an improved performance with (3-day) long-arcs. The new SRP models have been activated in CODE’s IGS MGEX solution in Summer 2018. Like the other ECOM models the ECOM-TB derivatives might be used together with an a priori model.     

某飞行器推力矢量试验测力装置研制

为满足某飞行器推力矢量试验的测试要求,采用两台六分量应变天平和一个空气桥组成测力装置来实现飞机全机气动力和喷管推进特性同时分别测量。基于有限元软件,对天平的应变及空气桥对天平的干扰进行了分析。结果表明:空气桥对天平力分量的干扰值优于5%,对力矩(滚转力矩除外)分量的干扰值优于15%,达到了设计指标。通过校准获得了单独天平、天平带空气桥(充压、不充压)状态下的校准公式,校准结果表明:两台天平各分量的综合加载误差均优于0.3%,天平带空气桥(充压、不充压)状态下各分量的综合加载误差优于0.5%,空气桥对天平的干扰量值与有限元分析结果一致。理论分析与实测结果证明:研制的天平及空气桥达到了预定目标,它的测量精准度高,满足推力矢量风洞试验需求。     

TA17钛合金板状连接件的疲劳裂纹扩展行为研究

TA17钛合金是航空航天等工程中重要的结构材料,其疲劳裂纹扩展性能直接影响整体结构的安全性和完整性。本文基于Cr2Ni2MoV钢材紧凑拉伸试样斜裂纹疲劳裂纹扩展的试验结果,验证了ABAQUS软件XFEM模块用于分析平面应力状态下疲劳裂纹扩展的有效性,然后采用XFEM模块分析了TA17钛合金及其连接件的疲劳裂纹扩展性能。结果表明降低最大荷载、减小加载比和采用长圆孔型均可有效提高TA17钛合金连接件的疲劳寿命。采用XFEM模块可以预测连接件疲劳寿命的S-N曲线,预测TA17钛合金结构载荷增大33.3%,疲劳寿命减小为原来的1/4,可为工程疲劳设计提供参考依据。