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381.
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针对第一部分提出的六类典型飞行器控制问题的共性伪线性系统模型,介绍了二阶伪线性系统的直接参数化设计方法:通过设计伪线性状态反馈控制律,可使闭环系统化为一个具有指定特征结构的二阶线性定常系统,并提供了控制系统设计中的所有自由度。另外,还以希望的闭环向量结构要求、闭环系统的干扰抑制要求和最小闭环特征值灵敏度要求为例,展示了通过综合优化设计自由度来实现控制系统的多目标设计思想。最后展望了伪线性系统理论的发展前景。 相似文献
383.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(6):1568-1579
Global Navigation Satellite Systems Reflectometry (GNSS-R) utilizes GNSS signals reflected off the Earth surface for remote sensing applications. Due to weak power of reflected signals, GNSS-R receiver needs to track reflected signals by open loop. The first step is to calculate the position of specular point. The specular point position error of the existing algorithm—Quasi-Spherical Earth (QSE) Approach—is about 3 km which may cause troubles in data post-processing. In this paper, gradient descent algorithm is applied to calculate position of specular point and the calculation is based on World Geodetic System 1984 (WGS 84) ellipsoid in geodetic coordinate. The benefit of this coordinate is that it is easy to investigate the effect of real surface’s altitude. Learning rate—the key parameter of the algorithm—is adaptively adjusted according to initial error, latitude and gradient descent rate. With self-adaptive learning rate strategy, the algorithm converges fast. Through simulation and test on Global Navigation Satellite System Occultation Sounder II (GNOS II), the performances of the algorithm are validated. The specular point position error of the proposed algorithm is about 10 m. The speed of the proposed algorithm is competitive compared with the existing algorithm. The test on GNOS II shows that the proposed algorithm has good real-time performance. 相似文献
384.
《中国航空学报》2020,33(8):2230-2241
With several attractive properties, rotary lip seals are widely used in aircraft utility system, and their reliability estimation has drawn more and more attention. This work proposes a reliability estimation approach based on time-varying dependence analysis. The dependence between the two performance indicators of rotary lip seals, namely leakage rate and friction torque, is modeled by time-varying copula function with polynomial to denote the time-varying parameters, and an efficient copula selection approach is utilized to select the optimal copula function. Parameter estimation is carried out based on a Bayesian method and the reliability during the whole lifetime is calculated based on a Monte Carlo method. Degradation test for rotary lip seal is conducted and the proposed model is validated by test data. The optimal copula function and optimal order of polynomial are determined based on test data. Results show that this model is effective in estimating the reliability of rotary lip seals and can achieve a better goodness of fit. 相似文献
385.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2662-2673
The Newton-Kantorovich/Radau pseudospectral method is implemented in a homotopy scheme to solve the rigid spacecraft time-optimal three-axis reorientation problem. First, the reorientation differential equations associated with the current homotopic variable are linearized about the nominal (previous homotopic variable) solution. Then, the Radau pseudospectral method is used to solve the resulting linearized differential equations. By successively updating the nominal solution with the Newton-Kantorovich approach, the linearized solving procedure is iterated to achieve high-order precision. Because no numerical integration is needed and only linear algebraic equations are solved, the proposed method is computationally efficient. Finally, performance of the proposed method is illustrated through numerical examples. 相似文献
386.
基于航空连续供氧系统和呼吸过程,建立了吸入气、气管气各组分计算模型,并依据此模型计算分析了不同乘员供氧标准不同座舱高度所需氧流量。结果表明:所建模型适用于不同乘员类型的连续供氧流量计算,为连续供氧流量标准提供了理论依据。针对大型运输机乘员多的特点,介绍了多乘员连续供氧试验方法、试验原理,并对试验数据进行了分析。试验结果表明:在通气量为15和20 L/min的情况下,12 km及其以下高度各测试点的氧分压均达到100~83.8 mmHg,满足供氧防护生理要求。 相似文献
387.
388.
目前无线传感器网络对时间空间连续分布的物理量进行监测时存在着节点分布不合理,覆盖效率低,网络计算量大等问题。采用流体力学中数值分析的动态嵌套网格技术,设计了一种新的基于动态嵌套网格技术的无线传感器网络覆盖算法。最后对该算法进行仿真实验,结果表明该算法在相同监测精度时所得到的覆盖效率、覆盖均匀性、能效指标等比传统的覆盖算法有所优化。 相似文献
389.
L. Alfonsi L. Spogli J.R. Tong G. De Franceschi V. Romano A. Bourdillon M. Le Huy C.N. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We use observations of ionospheric scintillation at equatorial latitudes from two GPS receivers specially modified for recording, at a sampling rate of 50 Hz, the phase and the amplitude of the L1 signal and the Total Electron Content (TEC) from L1 and L2. The receivers, called GISTM (GPS Ionospheric Scintillation and TEC Monitor), are located in Vietnam (Hue, 16.4°N, 107.6°E; Hoc Mon, 10.9°N, 106.6°E). These experimental observations are analysed together with the tomographic reconstruction of the ionosphere produced by the Multi-Instrument Data Analysis System (MIDAS) for investigating the moderate geomagnetic storm which occurred on early April 2006, under low solar activity. The synergic adoption of the ionospheric imaging and of the GISTM measurements supports the identification of the scale-sizes of the ionospheric irregularities causing scintillations and helps the interpretation of the physical mechanisms generating or inhibiting the appearance of the equatorial F layer irregularities. In particular, our study attributes to the turning of the IMF (Interplanetary Magnetic Field) between northward and southward direction an important role in the inhibition of the generation of spread F irregularities resulting in a lack of scintillation enhancement in the post-sunset hours. 相似文献
390.