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31.
在分析目标运动对频率步进信号一维距离像影响的基础上,提出了一种改进的频率步进信号,即参差脉冲重复间隔频率步进信号,研究了这种信号的数学模型和处理方法。理论分析和仿真结果表明,与频率步进信号相比,参差脉冲重复间隔频率步进信号的多普勒性能有了很明显的改善,一维距离像不会随目标的运动而产生失真。另外,根据参差脉冲重复间隔频率步进信号的特点,提出了利用距离微分法实现速度粗补偿和利用脉组误差函数法实现速度精补偿的方法和步骤,仿真结果证明,这两种方法是有效、稳健、可靠的。 相似文献
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提出了一种基于空时DFT投影的宽带信号二维角估计算法. 该方法采用3个共面的均匀线阵,每一均匀线阵对宽带信号空间采样,然后进行空时二维DFT变换,在空时频率域对宽带信号进行投影变换,用MUSIC算法实现宽带来波信号方向余弦的估计. 利用3个方向余弦估值进行配对,然后求得来波的方位角和仰角估计. 该方法既保留了投影算法的优点,即不需要源的先验知识;不需变换矩阵和在低信噪比有好的性能,又避免二维谱峰搜索.仿真实验表明了算法是有效的. 相似文献
34.
Vasiliev I.A. Ivashov S.I. Makarenkov V.I. Sablin V.N. Sheyko A.P. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(5):25-29
A subsurface radar using a multi-frequency signal has been developed. It is designated for surveying building structures and works. The characteristic feature of this device is the possibility of obtaining sounding plane radio images featuring a high resolution attaining 1…2 cm. The main applications of this device includes the survey of building structures to reveal their heterogeneities and defects and the investigation of premises to detect bugging devices 相似文献
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对于异步联网系统中网架结构比较薄弱的省网系统或者系统解列后形成的孤岛,发生故障时会引起比较大的频率波动,在此情况下对感应电动机进行建模时考虑其频率特性尤为重要。基于感应电动机一阶机械暂态模型,利用解析法分别推导出不同负载特性下稳态及动态转差率关于系统频率的表达式,并在此基础上计算吸收的有功功率和无功功率,进而分析感应电动机的功率频率特性。在MATLAB中建立感应电动机五阶电磁暂态仿真模型,仿真分析不同负载特性感应电动机的功率频率特性。仿真结果与理论推导结果吻合,验证了在简化模型下推导得到的感应电动机频率特性解析式的正确性和有效性。 相似文献
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China manned space station is designed to operate for over ten years. Long-term and sustainable research on space science and technology will be conducted during its operation. The application payloads must meet the ‘‘long life and high reliability" mission requirement. Gearbox machinery is one of the essential devices in an aerospace utilization system, failure of which may lead to downtime loss even during some disastrous catastrophes. A fault diagnosis of gearbox has attracted attentions for its significance in preventing catastrophic accidents and guaranteeing sufficient maintenance. A novel fault diagnosis method based on the Ensemble Multi-Fault Features Indexing(EMFFI) approach is proposed for the condition monitoring of gearboxes. Different from traditional methods of signal analysis in the one-dimensional space, this study employs a supervised learning method to determine the faults of a gearbox in a two-dimensional space using the classification model established by training the features extracted automatically from diagnostic vibration signals captured. The proposed method mainly includes the following steps. First, the vibration signals are transformed into a bi-spectrum contour map utilizing bi-spectrum technology,which provides a basis for the following image-based feature extraction. Then, Speeded-Up Robustness Feature(SURF) is applied to automatically extract the image feature points of the bi-spectrum contour map using a multi-fault features indexing theory, and the feature dimension is reduced by Linear Discriminant Analysis(LDA). Finally, Random Forest(RF) is introduced to identify the fault types of the gearbox. The test results verify that the proposed method based on the multi-fault features indexing approach achieves the target of high diagnostic accuracy and can serve as a highly effective technique to discover faults in a gearbox machinery such as a two-stage one. 相似文献
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Predicting the cutting forces required for five-axis flank milling is a challenging task due to the difficulties involved in determining the Undeformed Chip Thickness(UCT) and CutterWorkpiece Engagement(CWE). To solve these problems, this paper presents a new mechanistic cutting force model based on the geometrical analysis of a flank milling process. In the model,the part feature and corresponding cutting location data are taken as input information. The UCT considering cutter runout is calculated according to the instantaneous feed rate of the element cutting edges. A solid-discrete-based method is used to precisely and efficiently identify the CWE between the end mill and the surface being machined. Then, after calibrating the specific force coef-ficients, the mechanistic milling force can be obtained. During the validation process, two practical operations, three-axis flank milling of a vertical surface and five-axis flank milling of a nondevelopable ruled surface, are conducted. Comparisons between predicted and measured cutting forces demonstrate the reliability of the proposed cutting force model. 相似文献
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针对一个基于四位数字移相器的相控阵天线试验子阵,对其进行波束指向性能分析,得到扫描波束的波束宽度、指向误差和增益跌落等参数,计算数据与试验结果基本吻合,该分析方法将可应用于更大规模相控阵天线的性能分析。 相似文献