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排序方式: 共有486条查询结果,搜索用时 125 毫秒
291.
介绍了某型民用飞机电子设备舱排气系统主要组成,排气系统推力回收喷管的工作原理和设计要求,并分别通过理论计算和CFD三维仿真模拟,验证了该推力回收喷管的性能和关键设计尺寸。 相似文献
292.
基于粗糙核Fisher鉴别分析的特征提取及其在发动机故障诊断中的应用 总被引:2,自引:0,他引:2
将粗糙集理论的属性约简与核Fisher鉴别分析方法结合起来,提出一种基于粗糙核Fisher鉴别分析的故障特征提取方法.首先采用粗糙集理论的属性约简删除与分类无关或关系不大的特征,降低输入特征维数,排除干扰特征的影响,减小了特征提取计算量;再采用核Fisher鉴别分析方法进一步提取非线性特征;最后将该方法应用于航空发动机滑油系统故障特征提取及故障识别中.结果表明:该方法获取的特征在提高分类正确率的同时,还有效地降低了输入特征维数,提高了分类效率,并且对分类器具有较强的适应性和鲁棒性. 相似文献
293.
分形理论和小波在脉象识别中的应用 总被引:1,自引:0,他引:1
首先介绍了运用现代科学对脉象分类的意义和传统的脉象分类方法,尔后提出利用分形理论提取脉搏信号的分数维和基于小波变换的多尺度空间能量分布特征作为波形的重要特征,用于脉象分类识别.利用这些特征矢量用BP神经网络对实测的脉象数据进行了分类,取得了令人满意的分类正确率.通过两种提取方法相比较,盒维数方法更简单易行. 相似文献
294.
Mehrdad Ranaie Alireza Soffianian Saeid Pourmanafi Noorollah Mirghaffari Mostafa Tarkesh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(6):1558-1572
In recent decade, analyzing the remotely sensed imagery is considered as one of the most common and widely used procedures in the environmental studies. In this case, supervised image classification techniques play a central role. Hence, taking a high resolution Worldview-3 over a mixed urbanized landscape in Iran, three less applied image classification methods including Bagged CART, Stochastic gradient boosting model and Neural network with feature extraction were tested and compared with two prevalent methods: random forest and support vector machine with linear kernel. To do so, each method was run ten time and three validation techniques was used to estimate the accuracy statistics consist of cross validation, independent validation and validation with total of train data. Moreover, using ANOVA and Tukey test, statistical difference significance between the classification methods was significantly surveyed. In general, the results showed that random forest with marginal difference compared to Bagged CART and stochastic gradient boosting model is the best performing method whilst based on independent validation there was no significant difference between the performances of classification methods. It should be finally noted that neural network with feature extraction and linear support vector machine had better processing speed than other. 相似文献
295.
296.
Qiaoyun Fan Xuyang Zhong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(4):1132-1142
A novel autonomous star identification algorithm is presented in this study. In the proposed algorithm, each sensor star constructs multi-triangle with its bright neighbor stars and obtains its candidates by triangle voting process, in which the triangle is considered as the basic voting element. In order to accelerate the speed of this algorithm and reduce the required memory for star database, feature extraction is carried out to reduce the dimension of triangles and each triangle is described by its base and height. During the identification period, the voting scheme based on double feature constraints is proposed to implement triangle voting. This scheme guarantees that only the catalog star satisfying two features can vote for the sensor star, which improves the robustness towards false stars. The simulation and real star image test demonstrate that compared with the other two algorithms, the proposed algorithm is more robust towards position noise, magnitude noise and false stars. 相似文献
297.
Mazlan Hashim Samsudin Ahmad Mohd Amin Md Johari Amin Beiranvand Pour 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Lineament extraction from satellite remotely sensed data has been one of the widely used applications of remote sensing in geology. In fact, recent advances in digital image processing allow such lineament extraction to be accomplished in semi-automatic to fully automatic approaches. However, satellite remotely sensed data acquired in heavily vegetated regions such as tropical rainforest, are vulnerable to higher inherent noise levels attributed to the resultant effects of scattering by clouds and adjacency effects of highly inhomogeneous vegetation cover within the pixel dimension. In this study, we examined the effects of noise levels to lineament extraction using a fully automatic approach, consisting of a combination of edge-line detection algorithms. Ancillary information from a digitized topographic map and image classification was used to discriminate between cultural and natural lineaments from the extracted lineaments. Adapting the combination of edge detection and a line-linking algorithm, we have found the optimal parameters for automatic lineament extraction of such complex areas using Enhanced Thematic Mapper (ETM+) data. A noise level of 30% is the maximum threshold before artifacts are generated. It is therefore concluded that the combination of edge-based and line-linking digital image processing operations with the priori local optimal parameters is crucial in lineament feature extraction in heavily vegetated regions. 相似文献
298.
摘要: 高精度星相机光学系统是实现高性能星相机的关键技术.从工程实际出发,梳理星相机光学系统像质评价的指标,重点论述星点质心位置指标分解、光学系统评价指标分解过程.分析认为星相机光学系统设计过程中需关注质心位置偏差和质心位置与理想像高的偏差、温度分析需兼顾均匀温升及梯度温度变化.给出一个继承于双高斯结构形式的设计实例,结合像差理论进行消热设计和畸变控制,分析不同温度条件下不同类别恒星的质心位置一致性.设计结果表明该光学系统可满足高精度星相机指标要求. 相似文献
299.
星敏感器是一种高精度姿态传感器,具有断续拍摄空间目标的能力,可作为空间目标监视平台。将星敏感器断续观测的短弧准确关联是实现空间目标精确定轨的前提。通过对空间目标的大量观测数据统计发现,空间目标的赤纬随赤经的变化始终满足一条周期为360°的正弦曲线且峰值与轨道倾角有关。对新旧航迹的赤经赤纬变化规律进行研究,提出一种基于正弦拟合的空间目标短弧关联算法,避免了空间目标初定轨的步骤,节约了算法运行时间。仿真中观测时长最短为50s,通过对目标密集的GEO带增加额外约束,可区分倾角相差0.01°的轨道。当航迹段间隔3h时,3组噪声水平目标关联的准确率均达90%以上。 相似文献
300.