Papers by Keyword: Frequency Spectrum

Abstract: The spectrum of the load component is retained and the spectrum of other components are eliminated by the identifying spectrum is processed with addition or subtraction in the frequency domain. The method avoids an error that Gibbs’ vibration is generated as the signals multiply each other in frequency domain is equivalent to the signals are convolution in time domain in the filtering. On the basis of Fourier transformation, the method only using addition or subtraction obtains useful frequency components. Compare with other processing methods, the processing result can satisfy the identifying requests. In practice, the method is simple and convenient and the operational error is less. It is a try for digital signal process.

Abstract: —when the noise cancellation system ( NC ) is used in the down link of the power line carrier terminal, it can cancel the background noise and narrowband interference, but the downlink signal tone distorts at the same time. This is because the VAD algorithm of the NC system is sensitive to dramatic changes in the power of signal tone. Through detailed researches on time frequency characteristics of signal tone and error factors of network transmission, a new signal tone detection algorithm that applicable to downlink NC system was put forward, The algorithm detects signal tones through changes of frequency-domain power and time-domain signal period of every frame. After theoretical evaluation and practice tests, it is observed that the above-mentioned algorithm can correctly detect signal tones without influence on functions of the NC system, so as to avoid the occurrence of distortion.

Abstract: Numerical study of flow over sphere at supercritical Reynolds numbers by SST equations model and DES method based on SST model has been done. The simulation on Re = 9.4×10⁵,1.88×10⁶,2.82×10⁶ were given. Compared with the Results of experiments, the calculations of drag coefficients at Re=1.88×10⁶、2.82×10⁶ agreed well with Achenbach’s results. The trailing vortex structure was shown through the identification method of three dimensional flow field. It had a good agreement with Taneda’s results. The time histories and spectrum characteristics of the drag and the lateral force were investigated by the transient mothod.

Abstract: This paper mainly researches the deterministic methods that discriminating threshold by signal noise ration of different kinds of genes, approaches the relation between frequency spectrum and signal noise ration under Voss mapping and Z-curve mapping, and concludes the deterministic methods and threshold results of different kinds of gene thresholds.

Abstract: The static signal is collected through the experiment, and the probability density function model is established. The static random signal noise is analyzed by frequency spectrum, power spectrum and high order spectrum analysis. It is found that the third order spectrum of the laser static signal is zero by the high order spectrum analysis. Noise signal is only to analyze on the frequency spectrum and power spectrum. The results show that the static laser signal has the characteristics of stationary Gauss random signal.

Abstract: The activity of partial discharge (PD) is one of the major causes of failure of high voltage transformers. Partial discharge detection is usually used as a preventive technique to avoid large-scale losses in the power system. Suitable and reliable methods to detect and localize PD in equipment winding insulation, such as in a transformer, are still widely researched. Among the methods used are based on the acoustic wave, on the electrical determination of the dominant capacitive region in frequency domain, and on the travelling wave method. After a brief review on current methods, a technique based on the frequency spectra of the measured signals showing the characteristic of the transfer functions is proposed. A Matlab simulation of the proposed technique is then presented. PD signals are injected at various points in a transformer winding to represent PD sources at different location within the winding. The main difficulties encountered in current methods, which is the noise and the limit in the detection frequency range, is overcome. In the frequency spectra of the proposed method, the crests and troughs could be used for locating the source of the discharge activity in a power transformer winding.

Abstract: In this paper we introduce the computer software fault analysis system to the power fault detection system, and design power fault elimination system of electrical engineering automatic control, and do simulation and experimental study on the performance. When using the turbine blade of electric machinery to detect fault, we can get the automated troubleshooting displacement curve, and using computer simulation to get the electric mechanical stress distribution nephogram. To further verify the effectiveness of the algorithm, we test the frequencies for eight different units, and obtain eight different sets of five order fault diagnosis frequency, and draw the frequency spectrum distribution of frequency response. It provides the theory reference for the automation of power system fault exclusion.

Abstract: The vibration is severe for a hydraulic turbine runner chamber of a large bulb hydraulic generator set. A measurement and analysis system is composed of an acceleration transducer, a charge amplifier, and a dynamic data collecting & analyzing system. It is used to test the frequency spectrum, which provide a basis for the optimization design based on the modal analysis, so that its natural frequencies can stagger these frequencies of vibration sources, the resonance does not occur and the vibration is reduced.

Abstract: Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality. We report the terahertz spectrum of Non-uniform graphene films based femtosecond probing with more than 6 THz spectral coverage and the 1 GHz resolution using high-speed asynchronous optical sampling, and it operates at 2 kHz scan rate without a mechanical delay stage. The overall waveform creates shock and the oscillation amplitude reached 0.37E-4 mV, main-peaks time delay is 151.83fs between graphene and substrate, frequency spectrum oscillatory fades at 2.8 THz and appeared obvious absorption peak.

Abstract: The article describes the experimental analysis method of worm gear boxes for specific products. The measuring station for the dynamic load worm reducers testing can simulate various extreme transition modes of operation. There are assessed low and high frequency vibration.