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301.
将小波包变换理论和伪魏格纳分布应用于齿轮箱故障诊断中,结合实例对轴承的振动信号进行分析,结果表明:小波包变换能有效地提取各频段的高频成分,通过对提取的信号做伪魏格纳分布,结果能形象、直观地反映出轴承故障的时-频信息,而且对故障信息具有较强的判别能力。 相似文献
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304.
Weibull分布环境因子工程计算方法 总被引:1,自引:0,他引:1
目前,常用的指数型环境因子计算公式缺乏广泛的适用性,不能适用小样本失效数据或零失效数据的情况,尽管工程中有相应的处理方法,但因有人为因素的影响使其结果不够客观。针对这一问题,提出Weibull分布环境因子小概率评估法,并给出工程具体实施方法,使结果更合理,更具实用价值。 相似文献
305.
采用分相控制的UDVR主电路结构,利用瞬时波形比较法,基于三角波比较的delta增量逆变技术,建立了UDVR的PSCAD/EMTDC仿真模型,解决了低压配电网线路遭受雷击、绝缘子闪络等引发的单相接地故障在线路重合闸期间引发的电压跌落问题,保证了敏感负荷在此期间的持续供电的电能质量.仿真结果表明:模型建立正确,控制方法可行. 相似文献
306.
针对磁记忆检测中缺陷信号持续时间短且频率范围小的特点,为提取磁记忆信号的有效特征,根据矩阵奇异值的特点,提出一种基于Wigner-Ville分布及局部奇异值分解的磁记忆信号特征提取方法.通过将时频分布矩阵从时间轴和频率轴分别划分为不同局部矩阵,提取出各矩阵的奇异值来构造特征向量.然后,将构造的特征向量作为支持向量机的输入向量对不同检测区域的金属磁记忆信号进行识别.实验结果表明:基于Wigner—Ville分布及局部奇异值分解算法构造的特征向量能有效提取磁记忆信号的特征信息,提高支持向量机的识别精度. 相似文献
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The Signal‐to‐Interference‐plus‐Noise Ratio (SINR) is an important metric of wireless communication link quality. SINR estimates have several important applications. These include optimizing the transmit power level for a target quality of service, assisting with handoff decisions and dynamically adapting the data rate for wireless Internet applications. Accurate SINR estimation provides for both a more efficient system and a higher user‐perceived quality of service. In this paper, we develop new SINR estimators and compare their mean squared error (MSE) performance. We show that our new estimators dominate estimators that have previously appeared in the literature with respect to MSE. The sequence of transmitted bits in wireless communication systems consists of both pilot bits (which are known both to the transmitter and receiver) and user bits (which are known only by the transmitter). The SINR estimators we consider alternatively depend exclusively on pilot bits, exclusively on user bits, or simultaneously use both pilot and user bits. In addition, we consider estimators that utilize smoothing and feedback mechanisms. Smoothed estimators are motivated by the fact that the interference component of the SINR changes relatively slowly with time, typically with the addition or departure of a user to the system. Feedback estimators are motivated by the fact that receivers typically decode bits correctly with a very high probability, and therefore user bits can be thought of as quasipilot bits. For each estimator discussed, we derive an exact or approximate formula for its MSE. Satterthwaite approximations, noncentral F distributions (singly and doubly) and distribution theory of quadratic forms are the key statistical tools used in developing the MSE formulas. In the case of approximate MSE formulas, we validate their accuracy using simulation techniques. The approximate MSE formulas, of interest in their own right for comparing the quality of the estimators, are also used for optimally combining estimators. In particular, we derive optimal weights for linearly combining an estimator based on pilot bits with an estimator based on user bits. The optimal weights depend on the MSE of the two estimators being combined, and thus the accurate approximate MSE formulas can conveniently be used. The optimal weights also depend on the unknown SINR, and therefore need to be estimated in order to construct a useable combined estimator. The impact on the MSE of the combined estimator due to estimating the weights is examined. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004 相似文献
309.
A. Gmez‐Corral 《海军后勤学研究》2004,51(8):1068-1089
The model considered in this paper involves a tandem queue consisting of a sequence of two waiting lines. The main feature of our model is blocking, i.e., as soon as the second waiting line reaches a certain upper limit, the first line is blocked. The input of units to the tandem queue is the MAP (Markovian arrival process), and service requirements are of phase type. Our objective is to study the sojourn time distribution under the first‐come‐first‐serve discipline by analyzing the sojourn time through times until absorption in appropriately defined quasi‐birth‐and‐death processes and continuous‐time Markov chains. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004 相似文献
310.
Nonparametric classes of life distributions are usually based on the pattern of aging in some sense. The common parametric families of life distributions also feature monotone aging. In this paper we consider the class of log‐concave distributions and the subclass of concave distributions. The work is motivated by the fact that most of the common parametric models of life distributions (including Weibull, Gamma, log‐normal, Pareto, and Gompertz distributions) are log‐concave, while the remaining life of maintained and old units tend to have a concave distribution. The classes of concave and log‐concave distributions do not feature monotone aging. Nevertheless, these two classes are shown to have several interesting and useful properties. We examine the closure of these classes under a number of reliability operations, and provide sharp reliability bounds for nonmaintained and maintained units having life distribution belonging to these classes. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 419–433, 1999 相似文献