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421.
YAG单晶基片的精密抛光及SPM检测 总被引:1,自引:0,他引:1
利用扫描探针显微镜(SPM)对YAG单晶基片精密加工表面进行了检测,获得了YAG单晶基片表面及表面层的基本特征,表明了SPM作为表面物理量检测是一种重要显微工具. 相似文献
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一种基于混沌神经网络的拟人智能控制方法 总被引:4,自引:2,他引:2
提出一种基于混沌神经网络(CNN)的拟人智能控制方法.首先利用拟人智能控制理论得到定性控制律(线性或非线性),然后利用CNN实现控制律的定量化.Hopfield神经网络具有快速的优化能力,但容易陷入局部极小,将遍历性的渐变混沌噪声引入其中,形成具有快速全局优化能力的CNN.对二级倒立摆控制的仿真和实验结果均表明该方法有效. 相似文献
424.
航天工程中的有害振动可通过高阻尼橡胶减振器进行控制,但核心耗能单元和其他部件之间的连接容易失效。为了改进高阻尼橡胶减振器中阻尼材料和钢板的连接模式,使两者在较大变形下具有较高的机械连接性能,并且避免采用高温高压整体硫化的生产工艺,提出了一种带限位台阶的装配式高阻尼橡胶减振器。该减振器的阻尼材料和钢板之间采用常温胶黏连接模式,且在阻尼材料和钢板的连接边界面上设置了若干个具有一定高度的阶梯状限位台阶。对限位阶梯总高度分别为3 mm、4 mm、5 mm的3种不同装配式高阻尼橡胶减振器进行了不同加载频率和幅值的性能试验。试验结果表明:新型装配式高阻尼橡胶减振器在大变形下具有较强的耗能能力。带限位台阶的减振器和没有限位台阶的减振器相比,最大储能模量提高了22.3%,损耗因子提高了24.9%,且在较大位移幅值工况下,滞回曲线由原本的椭圆形变成类8字型,在保证较高阻尼力的同时使得滞回曲线所包络的面积增大,最大增幅可达588%。该新型减振器无需高温高压整体硫化,可以显著降低生产成本并提高生产效率,具有显著的性能优势和广泛的应用前景。 相似文献
425.
对等网中基于漏洞传播的P2P蠕虫是严重的安全威胁.根据P2P蠕虫的传播特点,提出了一种P2P蠕虫检测方法PWD (P2P Worm Detection).PWD主要由基于应用识别技术的预处理和基于未知蠕虫检测技术的P2P蠕虫检测2部分组成,改进了干扰流量的识别和过滤规则,提出了P2P蠕虫检测规则,并引进博弈论的研究方法讨论了检测周期的选取问题.仿真结果和局域网环境下的实验结果都表明,PWD是检测P2P蠕虫和遏制其传播的有效方法. 相似文献
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427.
Recently, flutter active control using linear parameter varying (LPV) framework has attracted a lot of attention. LPV control synthesis usually generates controllers that are at least of the same order as the aeroelastic models. Therefore, the reduced-order model is required by syn-thesis for avoidance of large computation cost and high-order controller. This paper proposes a new procedure for generation of accurate reduced-order linear time-invariant (LTI) models by using sys-tem identification from flutter testing data. The proposed approach is in two steps. The well-known poly-reference least squares complex frequency (p-LSCF) algorithm is firstly employed for modal parameter identification from frequency response measurement. After parameter identification, the dominant physical modes are determined by clear stabilization diagrams and clustering tech-nique. In the second step, with prior knowledge of physical poles, the improved frequency-domain maximum likelihood (ML) estimator is presented for building accurate reduced-order model. Before ML estimation, an improved subspace identification considering the poles constraint is also proposed for initializing the iterative procedure. Finally, the performance of the proposed procedure is validated by real flight flutter test data. 相似文献
428.
Liang Chen Qile Zhao Zhigang Hu Xinyuan Jiang Changjiang Geng Maorong Ge Chuang Shi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):367-384
Lots of ambiguities in un-differenced (UD) model lead to lower calculation efficiency, which isn’t appropriate for the high-frequency real-time GNSS clock estimation, like 1 Hz. Mixed differenced model fusing UD pseudo-range and epoch-differenced (ED) phase observations has been introduced into real-time clock estimation. In this contribution, we extend the mixed differenced model for realizing multi-GNSS real-time clock high-frequency updating and a rigorous comparison and analysis on same conditions are performed to achieve the best real-time clock estimation performance taking the efficiency, accuracy, consistency and reliability into consideration. Based on the multi-GNSS real-time data streams provided by multi-GNSS Experiment (MGEX) and Wuhan University, GPS + BeiDou + Galileo global real-time augmentation positioning prototype system is designed and constructed, including real-time precise orbit determination, real-time precise clock estimation, real-time Precise Point Positioning (RT-PPP) and real-time Standard Point Positioning (RT-SPP). The statistical analysis of the 6 h-predicted real-time orbits shows that the root mean square (RMS) in radial direction is about 1–5 cm for GPS, Beidou MEO and Galileo satellites and about 10 cm for Beidou GEO and IGSO satellites. Using the mixed differenced estimation model, the prototype system can realize high-efficient real-time satellite absolute clock estimation with no constant clock-bias and can be used for high-frequency augmentation message updating (such as 1 Hz). The real-time augmentation message signal-in-space ranging error (SISRE), a comprehensive accuracy of orbit and clock and effecting the users’ actual positioning performance, is introduced to evaluate and analyze the performance of GPS + BeiDou + Galileo global real-time augmentation positioning system. The statistical analysis of real-time augmentation message SISRE is about 4–7 cm for GPS, whlile 10 cm for Beidou IGSO/MEO, Galileo and about 30 cm for BeiDou GEO satellites. The real-time positioning results prove that the GPS + BeiDou + Galileo RT-PPP comparing to GPS-only can effectively accelerate convergence time by about 60%, improve the positioning accuracy by about 30% and obtain averaged RMS 4 cm in horizontal and 6 cm in vertical; additionally RT-SPP accuracy in the prototype system can realize positioning accuracy with about averaged RMS 1 m in horizontal and 1.5–2 m in vertical, which are improved by 60% and 70% to SPP based on broadcast ephemeris, respectively. 相似文献
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430.