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471.
在航空航天领域,作用在结构上动载荷的确定对结构健康监测是非常必要和重要的。为此,本文以类似机翼结构的变截面悬臂梁结构为研究对象,提出了一种基于光纤光栅传感器与卡尔曼滤波器的动载荷识别方法。首先,根据变截面梁单元形式,推导出变截面梁的质量矩阵与刚度矩阵,建立动力学运动方程。然后,以光纤光栅传感器测得的应变信息作为观测信号,通过卡尔曼滤波器生成的增益矩阵、新息序列矩阵以及协方差矩阵,得到灵敏度矩阵和估计力的增益矩阵。在此基础上,利用广义回归模型及其最小二乘算法,估算出动载荷大小、判断出动载荷激励位置。借助数值仿真与实验手段,分别验证了该方法对于单点正弦激励、方波激励、锯齿波激励以及多点同时激励等工况下的动载荷识别效果。结果表明,本文所提算法具有较好的动载荷识别效果和噪声抑制能力,能够为未来风洞试验和真实飞行试验环境中诸如大展弦比机翼表面气动压力等载荷实时辨识、气动外形自适应控制以及结构健康监测提供技术支撑。 相似文献
472.
Zheng Li Peng Chen Naiquan Zheng Hang Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(4):1317-1332
In recent years, with the continuous development of Global Navigation Satellite System (GNSS), it has been applied not only to navigation and positioning, but also to Earth surface environment monitoring. At present, when performing GNSS-IR (GNSS Interferometric Reflectometry) snow depth inversion, Lomb-Scargle Periodogram (LSP) spectrum analysis is mainly used to calculate the vertical height from the antenna phase center to the reflection surface. However, it has the problem of low identification of power spectrum analysis, which may lead to frequency leakage. Therefore, Fast Fourier Transform (FFT) spectrum analysis and Nonlinear Least Square Fitting (NLSF) are introduced to calculate the vertical height in this paper. The GNSS-IR snow depth inversion experiment is carried out by using the observation data of P351 station in PBO (Plate Boundary Observatory) network of the United States from 2013 to 2016. Three algorithms are used to invert the snow depth and compared with the actual snow depth provided by the station 490 in the SNOTEL network. The observations data of L1 and L2 bands are respectively used to find the optimal combination between different algorithms further to improve the accuracy of GNSS-IR snow depth inversion. For L1 band, different snow depths correspond to different optimal algorithms. When the snow depth is less than 0.8 m, the inversion accuracy of NLSF algorithm is the highest. When the snow depth is greater than 0.8 m, the inversion accuracy of FFT algorithm is higher. Therefore, according to the different snow depth, a combined algorithm of NLSF + FFT is proposed for GNSS-IR snow depth inversion. Compared with the traditional LSP algorithm, the inversion accuracy of the combined algorithm is improved by 10%. For L2 band data, the results show that the accuracy of snow depth inversion of various algorithms do not change with the variations of snow depth. Among the three single algorithms, the inversion accuracy of FFT algorithm is better than that of LSP and NLSF algorithms. 相似文献
473.
《中国航空学报》2020,33(3):1037-1056
The paper proposes a Virtual Target Guidance (VTG)-based distributed Model Predictive Control (MPC) scheme for formation control of multiple Unmanned Aerial Vehicles (UAVs). First, a framework of distributed MPC scheme is designed in which each UAV only shares the information with its neighbors, and the obtained local Finite-Horizon Optimal Control Problem (FHOCP) can be solved by swarm intelligent optimization algorithm. Then, a VTG approach is developed and integrated into the distributed MPC scheme to achieve trajectory tracking and obstacle avoidance. Further, an event-triggered mechanism is proposed to reduce the computational burden for UAV formation control, which takes into consideration the predictive state errors as well as the convergence of cost function. Numerical simulations show that the proposed VTG-based distributed MPC scheme is more computationally efficient to achieve formation control of multiple UAVs in comparison with the traditional distributed MPC method. 相似文献
474.
《中国航空学报》2020,33(2):609-620
During the launching of spacecraft, the on-board devices will undergo a series of pyroshock environments. In order to verify the reliability of these devices under these pyroshock environments, all of them are needed to take the shock test before launching. This paper has carried out an in-depth research on the simulation method of the pyroshock based on the true explosive excitation. In this study, a simulator containing multiple adjustment parameters is presented and the safety is considered by the design of the protective cover. And the working process of this setup is simulated with the explicit dynamic codes LS-DYNA. What’s more, the effects of the adjustment parameters on the three factors of shock Response Spectrum (SRS) of the resonant board are explored carefully. The rules achieved in this paper are verified by a typical example. The results indicate that the improved simulator can avoid the danger of explosive and make full use of the advantage of actual explosive excitation. And the test condition can be quickly realized at the simulator according to the effect rules of the three adjustable parameters. 相似文献
475.
Ankita Jain Dharmendra Singh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(2):813-825
Different types of classification techniques are available in the literature for the classification of Synthetic Aperture Radar (SAR) data into various land cover classes. Various SAR images are available for land cover classification such as ALOS PALSAR (PALSAR-1, PALSAR-2), RADARSAT and ENVISAT. In this paper, we have attempted to explore probability distribution function (pdf) based land cover classification using PALSAR-2 data. Over 20 different statistical distribution functions are analyzed for different classes based on statistical parameters. Probability distribution functions are selected based on Chi-squared goodness of fit test for each individual class. A decision tree based classifier is developed for classification based on the selected pdf functions and its statistical parameters. The proposed classification approach has an accuracy of 83.93%. 相似文献
476.
对Ni18%和0Cr15Ni5Cu2Ti超高强度马氏体沉淀硬化不锈钢异种钢材之间进行了电子束焊接工艺试验,就其工艺可焊性及接头性能、金相组织、焊缝质量、力学性能等开展研究,采用X-探伤、静载强度、金相观察、电镜扫描和能谱分析等检测手段对试件进行了分析并得出了相应结论。 相似文献
477.
常用的元件破损在线监测方法受外在因素影响较大,以γ能谱中关键裂变产物核素比活度进行在线定量分析是一种可靠的元件破损监测方法。针对新型LaBr3(Ce)元件破损监测仪,设计了元件破损模拟实验,对逸出的裂变产物采用HPGe和LaBr3(Ce)探测器进行了对比测量。通过不同冷却时间γ能谱的核素分析,确定了135Xe,88Kr,138Xe,88Rb,138Cs等可作为LaBr3(Ce)元件破损γ能谱监测的关键核素。同时,制备了覆盖能量范围(250~2 400)keV,含60Co,137Cs,133Ba;241Am,152Eu;109Cd,88Y,57Co及24Na的4组放射性标准溶液,在建立的效率校准系统上,校准了LaBr3(Ce)在线监测仪的效率。在反应堆一次异常情况分析中,已校准的LaBr3(Ce)元件破损监测仪对关键核素的现场分析结果与HPGe的取样分析结果一致,表明效率校准结果准确,校准方法可靠。 相似文献
478.
479.
Sylvain Chaty 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants. 相似文献
480.