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351.
为了那摇不断的虔诚,为了那搅不散的梦境,为了那捂不热的冰峰,为了那撇不下的绿茵,每年冬季,各地藏胞如涓流汇为江河般源源涌入云南德钦县,因为那里有他们魂牵梦萦的梅里雪山,“梅里”藏语即“神奇”,该山与果洛的阿尼玛卿,那曲的念青唐古拉及阿里的万山之王冈仁波钦合称藏区四大神山,在藏族人心目中,梅里是座永远让人敬畏的灵性之山。 相似文献
353.
Tang lin Li Xiao Zhang Shi-chai 《桂林航天工业高等专科学校学报》2006,11(2):83-86
In order to solve the current problems in the college English teaching and meet the demands of the "College English Curriculum Requirements", the Open Model in College English teaching is proposed in the thesis. The thesis describes the model from the five components, 相似文献
354.
研究弹性飞行器的动态耦合问题,首先导出了非定常气动力作用下的弹性飞行器的纵向运动方程。就简化的非定常气动力数学模型提出了分析气动弹性飞行器稳定性的影响方法,而后对弹性飞行器的动态耦合特性提出了定性的分析方法。并从有效抑制飞行器的弹性振动角度,研究了主动反馈控制、操纵面及陀螺位置的合适选择的协同设计问题。 相似文献
355.
关于高维数据拟合提出两种计算方法,用各种实例在计算机上计算,给出了等值面图形绘制方法,直观地表示高维空间曲面。应用实例表明,有杉本方法进行四维数据插春效果令人满意,铁于微机实现,等值面绘制快速精确。 相似文献
356.
Reliability design optimization of composite structures based on PSO together with FEA 总被引:1,自引:1,他引:0
The present work aims to develop a method for reliability-based optimum design of composite structures. A procedure combining particle swarm optimization (PSO) and finite element analysis (FEA) has been proposed. Numerical examples for the reliability design optimization (RDO) of a laminate and a composite cylindrical shell are worked out to demonstrate the effectiveness of the method. Then a design for composite pressure vessels is studied. The advantages and necessity of RDO over the conventional equi-strength design are addressed. Examples show that the proposed method has good stability and is efficient in dealing with the probabilistic optimal design of composite structures. It may serve as an effective tool to optimize other complicated structures with uncertainties. 相似文献
357.
In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation (CPPM) and linear frequency modulation (LFM), which can be widely used in electronic countermeasures, is addressed. An approach is proposed to estimate the initial frequency and chirp rate of the combined signal by exploiting the second-order cyclostationarity of the intra-pulse signal. In addition, under the condition of the equal pulse width, the pulse repetition interval (PRI) of the combined signal is predicted using the low-order Volterra adaptive filter. Simulations demonstrate that the proposed cyclic autocorrelation Hough transform (CHT) algorithm is theoretically tolerant to additive white Gaussian noise. When the value of signal noise to ratio (SNR) is less than 4 dB, it can still estimate the intra-pulse parameters well. When SNR = 3 dB, a good prediction of the PRI sequence can be achieved by the Volterra adaptive filter algorithm, even only 100 training samples. 相似文献
358.
Operations in assembling and joining large size aircraft components are changed to novel digital and flexible ways by digital measurement assisted alignment.Positions and orientations(P&O)of aligned components are critical characters which assure geometrical positions and relationships of those components.Therefore,evaluating the P&O of a component is considered necessary and critical for ensuring accuracy in aircraft assembly.Uncertainty of position and orientation(U-P&O),as a part of the evaluating result of P&O,needs to be given for ensuring the integrity and credibility of the result;furthermore,U-P&O is necessary for error tracing and quality evaluating of measurement assisted aircraft assembly.However,current research mainly focuses on the process integration of measurement with assembly,and usually ignores the uncertainty of measured result and its influence on quality evaluation.This paper focuses on the expression,analysis,and application of U-P&O in measurement assisted alignment.The geometrical and algebraical connotations of U-P&O are presented.Then,an analytical algorithm for evaluating the multi-dimensional U-P&O is given,and the effect factors and characteristics of U-P&O are discussed.Finally,U-P&O is used to evaluate alignment in aircraft assembly for quality evaluating and improving.Cases are introduced with the methodology. 相似文献
359.
Evaluation of COMPASS ionospheric model in GNSS positioning 总被引:1,自引:0,他引:1
Xiaoli Wu Xiaogong Hu Gang Wang Huijuan Zhong Chengpan Tang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
As important products of GNSS navigation message, ionospheric delay model parameters are broadcasted for single-frequency users to improve their positioning accuracy. GPS provides daily Klobuchar ionospheric model parameters based on geomagnetic reference frame, while the regional satellite navigation system of China’s COMPASS broadcasts an eight-parameter ionospheric model, COMPASS Ionospheric Model(CIM), which was generated by processing data from continuous monitoring stations, with updating the parameters every 2 h. To evaluate its performance, CIM predictions are compared to ionospheric delay measurements, along with GPS positioning accuracy comparisons. Real observed data analysis indicates that CIM provides higher correction precision in middle-latitude regions, but relatively lower correction precision for low-latitude regions where the ionosphere has much higher variability. CIM errors for some users show a common bias for in-coming COMPASS signals from different satellites, and hence ionospheric model errors are somehow translated into the receivers’ clock error estimation. In addition, the CIM from the China regional monitoring network are further evaluated for global ionospheric corrections. Results show that in the Northern Hemisphere areas including Asia, Europe and North America, the three-dimensional positioning accuracy using the CIM for ionospheric delay corrections is improved by 7.8%–35.3% when compared to GPS single-frequency positioning ionospheric delay corrections using the Klobuchar model. However, the positioning accuracy in the Southern Hemisphere is degraded due apparently to the lack of monitoring stations there. 相似文献
360.
Explicit expression of collision probability in terms of RSW and NTW components of relative position
Xian-Zong Bai Lei Chen Guo-Jin Tang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The existing analytical and numerical computing methods for collision probability (Pc) provide sufficiently accurate results, but do not reveal the direct connection between Pc and conjunction geometry or error covariance. This paper derived an explicit expression of Pc under the circular orbit assumption, based on analysis of closest approach distance and Chan’s analytical formulae for Pc. The Pc was expressed as an explicit function of the radial, in-track, cross-track components of relative position and error covariance. The explicit expression is simple and compact, relates Pc with components of relative position, which are two kinds of important conjunction risk criteria. By introducing non-zero flight-path angle and ratio of velocity’s magnitude, a modified expression of Pc was presented for objects in eccentric orbits. For objects with eccentricity less than 0.01 (which account for 62% of all LEO objects), the relative error of the explicit expression is less than 0.107, or 0.252 for typical conjunction cases. What really matters in conjunction risk assessment is the order of magnitude rather than the specific value of Pc, the precision of the explicit expression is sufficient for conjunction risk assessment and decision-making for most LEO objects. 相似文献