共查询到20条相似文献,搜索用时 79 毫秒
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本文用模式识别技术,对航道上航行的船舶进行分类判决.根据船舶辐射噪声的二阶统计特性——自相关函数,我们提取了四个特征量,用统计判庆理论对三类船舶的辐射噪声进行了分类判决.文中给出了海上实验数据的分类结果. 相似文献
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本文把子波变换多分辨的特点应用于舰船噪声的分析中。这种新的分析方法克服了短时间谱在时频平面上均匀分割带来低频域频率分辨率低,而高频域时间分辨低的缺点。船辐射噪声的尺度谱保留了传统倍频程方法在频率域分割的优点,且还有高频域时间分辨高的特点。从大庆31号油船辐射噪声的尺度谱上可清楚看到在低频域上有二根横线,其尺度值换算为频率后为27.8 Hz和44.1 Hz,反映在此频率附近,信号能量较高;同时还可清楚看到在高频域上有9.5 Hz叶片频的调幅现象。在它的短时谱图中是无法同时看到这二个特征的。本文在描述和显示船辐射噪声的谱特征时充分利用它们符合局部平稳过程的特点,把平稳谱和非平稳谱拆开描述和显示,获得很好的结果 相似文献
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Imitation of the act of diagnosing engine faults by an expert auto-mechanic just by hearing the noise from a defective vehicle has been attempted with a robust instrumentation technique. In the present experimental work, the prime objective is to establish a process to identify the piston-bore defect by analyzing the engine noise. The aim is to develop a robust filtering algorithm in order to be able to use the technique in the natural environment of an auto workshop. The algorithm uses engine noise data from healthy and defective vehicles acquired in the natural workshop environment. Effectiveness of conventional parameters that are used (six of the most preferred) in statistical learning systems to tackle similar problems has been assessed. Additionally, six more statistical parameters have been derived and proposed to achieve a more effective statistical-learning based decision making system. These additional parameters have been derived from the continuous wavelet transform (CWT) coefficients. The appropriate coefficient level has been decided by using the frequency marginal integration of the CWT coefficients. A deeper level of CWT scalogram analysis has been carried out to establish the appropriateness of complex Morlet wavelet function, for the class of problem under investigation. Then the proposed technique uses a third degree polynomial kernel function and sequential optimization based support vector machine (SVM) based on all the twelve parameters in order to identify the piston-bore defect from engine noise signature. It has also been shown that Feed-forward Back-propagation Neural Network (FBNN) is equally effective with higher number of training samples. 相似文献
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鉴于时延信息严重威胁着混沌通信的保密性,提出了一种利用频谱仪直接确定激光器时延信息的新方法。通过记录和观察信号的频谱,发现其频谱受到了时延信息的调制;进一步对频谱作逆傅里叶变换,即可直接获取光反馈混沌激光器的时延信息。实验中对腔长L=11.02 m的单反馈和腔长近似相等(L1=11.02 m, L2=11.25 m)或腔长成整数比(L1=11.02 m, L2=22.03 m) 的双反馈情形进行了研究。分析结果表明:在两外腔长度近似相等的情况下,2个外腔长度信息不能被隐藏;当反馈外腔长度成整数比时可以从频谱中提取出半导体激光器的反馈延迟时间。 相似文献
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Simon Toft Sørensen Ole Bang Benjamin Wetzel John M. Dudley 《Optics Communications》2012,285(9):2451-2455
We show that the noise properties of fiber supercontinuum generation and the appearance of long-tailed “rogue wave” statistics can be accurately quantified using statistical higher-order central moments. Statistical measures of skew and kurtosis, as well as the coefficient of variation provide improved insight into the nature of spectral fluctuations across the supercontinuum and allow regions of long-tailed statistics to be clearly identified. These moments – that depend only on analyzing intensity fluctuations – provide a complementary tool to phase-dependent coherence measures to interpret supercontinuum noise. 相似文献
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This paper compares two traffic representations for the assessment of urban noise frequency spectrum: (i) a static one, based on mean vehicle speeds and flow rates, (ii) a dynamic one, which considers vehicle interactions along the network. The two representations are compared on their suitability to match real on-field noise levels, recorded on a three lane quite busy street. Representation (i) fails in reproducing spectra envelopes that correspond to this site. In particular, it underestimates low frequencies, what can conceal the real impact of traffic flow on urban sound quality. Representation (ii) greatly improves estimation. It guarantees accurate environmental noise assessment, since it reproduces all traffic situations that are encountered in the site. Moreover, its 1s-based structure allows for the evaluation of spectra variations, with a good accuracy. 相似文献
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References: 《声学学报:英文版》2007,26(4):313-324
The structure law of the ship noise demodulation spectrum harmonic clan feature and corresponding applications to the recognition problem are studied by theoretical derivation and sample analysis.In order to recognize the propeller blade-number,the ship propeller cavitation noise model is established on the basis of five hypotheses.Further,the mathematical expressions of the structure law are deduced by the model.And the class space of the propeller blade-number is analysed mathematically.The results can be applied to target recognition as expert knowledge.Finally,the demodulation spectrum harmonic clans of experiment samples are obtained by using the wavelet packet.The structure law is validated by the statistic analysis of experiment samples.It is shown that the statistical average results of experiment samples are consistent very well with the theory structure law,and 78.6% of the samples basically accord with the theory structure law. 相似文献
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A calculation of the energy release rate resulting from the combustion of propane-air mixtures is presented and the result is used to calculate the far field noise spectrum for an open flame by using appropriate Fourier transform techniques. The results illustrate the broad band nature of combustion noise and show that, for the range of parameters indicated, the peak frequency in the octave band is in the range 400–1000 Hz. The results also indicate that the shape of spectrum is influenced by the time history of the heat release rate and the turbulence intensity and length scales; on the other hand, the peak frequency is a function of the heat release per unit mass of fuel which is essentially the same for hydrocarbon fuels. 相似文献
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The identification of acoustic source accurately is a fundamental problem in noise control. In the practical project, if the contribution of multi-source-noise to the whole was identified, and then the noise level can be reduced accordingly. This paper presents a new approach to acoustic noise identification by introducing modern spectrum estimation and grey relational analysis (GRA). Modern spectrum was used to recognize the main noise source and GRA was used to recognize the similarity among different curves of power spectrum. The ranking of the noise sources was obtained on the basis of their individual contribution to the overall noise. The results of simulation signals confirmed the feasibility and validity of the method proposed in this dissertation and it will play an important role in noise control, signal source identification and other fields. 相似文献