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821.
Lu Cao Xiaolong Li Xiaoqian Chen Yong Zhao 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
This paper proposes a new control strategy (which we call “minimum sliding mode error feedback control, MSMEFC”) for small satellite attitude control. As we know, the attitude control algorithm plays a significant role in the whole performance of the satellite, especially under the existence of uncertain disturbances from the space. Without loss of generality, the MSMEFC is presented based on the sliding mode theory. It is assumed that the equivalent control error is defined to offset the uncertain disturbances to improve the control performance. Hence, in order to estimate the optimal equivalent control error, a cost function is derived on the basis of the principle of minimum sliding mode error. Then, the equivalent control error wills feedback to the conventional sliding mode control to obtain the final MSMEFC. According to the theoretical analyzes, the sliding mode after the MSMEFC will approximate to the ideal sliding mode, resulting in enhancing the control performance. Moreover, an adaptive non-singular terminal sliding mode is employed to compare with the performance of MSMEFC. Several simulations are performed to verify the effectiveness of proposed MSMEFC in the presence of serious perturbations, even in some fault-tolerant scenarios. 相似文献
822.
Jun Chen Shoujing Yin Rulin Xiao Qianxiang Xu Changsong Lin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The objectives of this study are to validate the applicability of a shortwave infrared atmospheric correction model (SWIR-based model) in deriving remote sensing reflectance in turbid Case II waters, and to improve that model using a proposed green-shortwave infrared model (GSWIR-based model). In a GSWIR-based model, the aerosol type is determined by a SWIR-based model and the reflectance due to aerosol scattering is calculated using spectral slope technology. In this study, field measurements collected from three independent cruises from two different Case II waters were used to compare models. The results indicate that both SWIR- and GSWIR-based models can be used to derive the remote sensing reflectance at visible wavelengths in turbid Case II waters, but GSWIR-based models are superior to SWIR-based models. Using the GSWIR-based model decreases uncertainty in remote sensing reflectance retrievals in turbid Case II waters by 2.6–12.1%. In addition, GSWIR-based model’s sensitivity to user-supplied parameters was determined using the numerical method, which indicated that the GSWIR-based model is more sensitive to the uncertainty of spectral slope technology than to that of aerosol type retrieval methodology. Due to much lower noise tolerance of GSWIR-based model in the blue and near-infrared regions, the GSWIR-based model performs poorly in determining remote sensing reflectance at these wavelengths, which is consistent with the GSWIR-based model’s accuracy evaluation results. 相似文献
823.
825.
Lin Cheng Zhenbo Wang Fanghua Jiang Junfeng Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(3):1114-1123
In this study, an adaptive neural network control approach is proposed to achieve accurate and robust control of nonlinear systems with unknown dynamics, wherein the neural network is innovatively used to learn the inverse problem of system dynamics with guaranteed convergence. This study focuses on the following three contributions. First, the considered system is transformed into a multi-integrator system using an input–output linearization technique, and an extended state observation technique is used to identify the transformed states. Second, an iterative control learning algorithm is proposed to achieve the neural network training, and stability analysis is given to prove that the network’s predictions converge to ideal control inputs with guaranteed convergence. Third, an adaptive neural network controller is developed by combining the trained network and a proportional-integral controller, and the long-standing challenge of model-based methods for control determination of unknown dynamics is resolved. Simulation results of a virtual control mission and an aerospace altitude tracking mission are provided to substantiate the effectiveness of the proposed techniques and illustrate the adaptability and robustness of the proposed controller. 相似文献
826.
827.
C-HGB (Common Hypersonic Glide Body)作为美国现今试验成功率最高的高超声速滑翔飞行器已被美国防部列入重点发展项目,并预计发展为三军通用武器。本文针对此类"球+双锥+弹翼"的气动外形和隐身性能进行了研究。采用考虑交互作用的正交设计进行了多约束下参数敏感性分析,并采用改进的基于DE差分变异算子的具有自适应学习机制的优化算法进行气动优化,对优化后的外形采用简单高效的锐边化设计,在提高升阻比的同时可降低雷达散射截面积,极大提高突防能力。锐边设计改变了弹体部分表面温度分布,降低制造成本的同时对热防护系统的设计和红外隐身具有一定积极意义。结果表明:锐边化设计可以得到较好的气动隐身性能,是未来高超声速滑翔飞行器的潜在设计方案。 相似文献
828.
针对民航院校的交通运输专业飞行运行管理方向的飞行计划实践课程,基于CDIO工程教育教学模式理念和方法,提出了以案例为导引,"多目标-多层次-多效果"的教学模式,重点阐述了基于CDIO模式的飞行计划实践课程的教学模式改革与实践应用。教学实践证明:该项研究对深化民航院校的教学改革,更新实践课程的教学模式,培养应用型和创新型人才具有一定的意义。 相似文献
829.
830.
Zhujun Gu Weimin Ju Lin Li Dengqiu Li Yibo Liu Weiliang Fan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Vegetation fractional coverage (VFC) is an important vegetation parameter affecting exchanges of carbon, water, energy between the atmosphere and surface. In this study, the applicability of tonal and texture measures calculated using an IKONOS_2 image in retrieving VFC of forests was investigated in the urban area of Nanjing city, China. Four spectral vegetation indices (VI) and six texture measures (TEX) were related to VFCs acquired from in situ measurements. Models for estimating VFC based on VIs or/and TEXs were established and validated for planted low broad-leaf forest plots (PLB), planted mature forest plots (PMF), natural broad-leaf forest plots (NBF), and all forest plots (ALLv), respectively. The results show that high spatial resolution remote sensing data is applicable to estimate VFC in urban areas, and TEXs may act as effective supplements of vegetation indices (VIs) for the retrieval of VFC. VIs are suitable for VFC estimation of mature forests (such as NBF and PMF) with high vegetation density, and TEXs can yield a more accurate estimate for planted forests (such as PLB and PMF) with regular spatial distribution if they are calculated with proper parameters, such as window size. The combination of VIs and TEXs improve the estimation of VFC if forest types are not previously differentiated. The results can be used as a reference for determining effective spectral or texture parameters in VFC estimation under similar environmental conditions according to vegetation maturity and regularity. 相似文献