全文获取类型
收费全文 | 53篇 |
免费 | 26篇 |
国内免费 | 10篇 |
专业分类
航空 | 53篇 |
航天技术 | 16篇 |
综合类 | 6篇 |
航天 | 14篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2009年 | 4篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1989年 | 1篇 |
排序方式: 共有89条查询结果,搜索用时 15 毫秒
31.
32.
M. Mutyalarao Ram Krishan Sharma 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The evolution of objects in geostationary transfer orbit (GTO) is determined by a complex interplay of atmospheric drag and luni-solar gravity. These orbits are highly eccentric (eccentricity >0.7) and have large variations in velocity and perturbations during a revolution. The periodic changes in the perigee altitudes of these orbits are mainly due to the gravitational perturbations of the Sun and the Moon. The re-entry time of the objects in such orbits is sensitive to the initial conditions. The aim of this paper is to study the re-entry time of the cryogenic stage of the Indian geo-synchronous launch vehicle, GSLV-F04/CS, which has been decaying since 2 September 2007 from initial orbit with eccentricity equal to 0.706. Two parameters, initial eccentricity and ballistic coefficient, are chosen for optimal estimation. It is known that the errors are more in eccentricity for the observations based on two line elements (TLEs). These two parameters are computed with response surface method using a genetic algorithm for the selected eight different zones, based on rough linear variation of the mean apogee altitude during 200 days orbit evolution. The study shows that the GSLV-F04/CS will re-enter between 5 December 2010 and 7 January 2011. The methodology is also applied to study the re-entry of six decayed objects (cryogenic stages of GSLV and Molniya satellites). Good agreement is noticed between the actual and the predicted re-entry times. The absolute percentage error in re-entry prediction time for all the six objects is found to be less than 7%. The present methodology is being adopted at Vikram Sarabhai Space Centre (VSSC) to predict the re-entry time of GSLV-F04/CS. 相似文献
33.
翼盒结构复杂,航行中承载条件恶劣,利用有限测点信息重构其它位置响应对于实时健康监测具有很强的现实意义。通过误差反向传播神经网络训练得到响应之间的非线性关系,建立基于神经网络的响应重构方法,开展有限元分析对其进行数值仿真验证,并将该方法应用于实测随机激励环境下翼盒典型承力结构的响应重构及损伤定位与判断分析。结果表明:采用该方法重构出的预测响应功率谱密度的均方根相对误差不超过1.90 dB,主要频点误差小于10%;判断出翼盒关键测点e 的损伤或故障发生在所截取片段数据3 s 后,其故障特征频率为240 Hz 左右,该方法应用于响应重构预示及健康监测分析具有可行性。 相似文献
34.
Stochastic structural optimization using particle swarm optimization, surrogate models and Bayesian statistics 总被引:4,自引:4,他引:0
This paper focuses on a method to solve structural optimization problems using particle swarm optimization (PSO), surrogate models and Bayesian statistics. PSO is a random/stochastic search algorithm designed to find the global optimum. However, PSO needs many evaluations compared to gradient-based optimization. This means PSO increases the analysis costs of structural optimization. One of the methods to reduce computing costs in stochastic optimization is to use approximation techniques. In this work, surrogate models are used, including the response surface method (RSM) and Kriging. When surrogate models are used, there are some errors between exact values and approximated values. These errors decrease the reliability of the optimum values and discard the realistic approximation of using surrogate models. In this paper, Bayesian statistics is used to obtain more reliable results. To verify and confirm the efficiency of the proposed method using surrogate models and Bayesian statistics for stochastic structural optimization, two numerical examples are optimized, and the optimization of a hub sleeve is demonstrated as a practical problem. 相似文献
35.
《中国航空学报》2020,33(10):2620-2632
The gears in aero-engines perform energy and motion transfer between the High-Pressure Rotor (HPR) and accessories. Firstly, an occurred fault with radial cracks in the driven gear disk was diagnosed as High Cycle Fatigue (HCF) failure through necessary examinations. Analysis of fault tree and test signals indicated that the fracture was relevant to the swing vibration of the driven gear excited by the unbalance excitation on HPR. Secondly, a corresponding mechanism model was established, in which the gear meshing effect was considered, with lateral and swing vibration mode. The Governing Equations (GEs) and the Finite Element Model (FEM) were established and verified. Then, the modal shapes, harmonic response, and transient response were analyzed, indicating that the swing vibration of the driven gear could be significantly excited by the unbalance on HPR, which induced the cracks in the driven gear disk to extend radially. Furthermore, influences of factors on the unbalance response were obtained, in which the unbalance response appeared local minimum points and maximum points. Meanwhile, 1# and 2# bearing stiffness had rather significant influences on the response. Thus it is efficient to modify them to achieve vibration control. 相似文献
36.
柔性喷管力矩特性的识别 总被引:3,自引:0,他引:3
本文在试验、测量、计算获得柔性喷管的总力矩—摆角响应曲线的基础上,对其物理特性作了分析,建立了辨识其力矩特性的数学模型。利用三次样条函数的特点,较准确地再现了该数学模型所代表的矛盾方程组,然后又利用多元线性回归分析,最终求得了组成总力矩的弹性力矩,粘滞摩擦力矩、库伦摩擦力矩、惯性力矩和偏位力矩等以及它们的力矩系数。并在计算机上进行了仿真试验,对建立的数学模型和分析方法作了验证。 相似文献
37.
38.
39.
40.
以某型着陆器为研究对象,建立其软着陆过程的动力学仿真模型,并结合Monte Carlo法研究不确定着陆姿态下的某型软着陆性能。然后,分析着陆器的软着陆性能与其缓冲机构构型参数之间的相关关系,并基于实验设计方法与动力学仿真模型得到样本点,建立以着陆器缓冲机构构型参数和着陆姿态参数为输入、软着陆性能指标值为输出的响应面模型。最后,基于响应面模型,考虑着陆器姿态的不确定性,运用结合第二代非劣排序遗传算法(NSGA-II)和多岛遗传算法(MIGA)的分级优化方法实现了着陆器缓冲机构的优化计算,得到了最佳缓冲机构构型参数。通过仿真模型校验,优化后着陆器的抗翻倒能力与底面抗损坏能力分别提升了3.546%和 5.140% 。 相似文献