Papers by Keyword: Wavelet Analysis

Abstract: In order to further understand the Agave americana var. marginata electrical signals in High Voltage Pulse Stimulation conditions, a new method is provided in this paper by using wavelet soft threshold noise reduction and the power spectrum analysis. The results show that the level `of its electrical distribution in uV. The plant electrical signal amplitude arithmetic mean increases with the increase of pulse stimulation signal but for a little effect on the natural frequency of the plant, its frequency is mainly distributed in the 0.07813 Hz ~0.1953 Hz.

Abstract: A novel four-stage data mining method for clock bias prediction based on wavelet analysis and chaotic neural networks is proposed. The basic ideas, prediction models and steps of clock bias prediction based on wavelet analysis and chaotic neural network are discussed respectively. And then, to validate the feasibility and validity of the proposed method, make a careful precision analysis for satellite clock bias prediction with the performance parameters of GPS satellite clock, and make comparison and analysis with Grey system model and neural network model. The results of simulation shows that the prediction precision of the novel four-stage model based on wavelet analysis and chaotic neural networks is more better, can afford high precise satellite clock bias prediction for real-time GPS precise point positioning.

Abstract: This paper evaluates the feasibility and effectiveness, within controlled conditions of an active pitch catch sensing PZT sensors on two panels and an aircraft structure made from carbon fiber reinforced plastic (CFRP) pre-impregnated materials. Once cured, the exhibits were subjected to partial and full penetration damages. Two PZT sensors each acting as an actuator and receiver were placed across the investigated region at 100mm apart. Three conditions were set on each panel for each undamaged, damaged and repaired area. Fifty readings were carried out on each panel for each condition. Feature extraction of the wavelet propagations were applied for the post processing from the captured Lamb wave data. The aircraft structure was also used to acquire data with the same above condition. A promising result shows that the interrogation of the actuating PZT sensors can differentiate the studied condition for both panels and structure. In addition, distinguished wavelet patterns were contributed by the surface irregularities due to damage and additional repair plies for both panels and aircraft structure.

Abstract: Using wavelet analysis for non-stationary signal de-noising of electro-mechanical system is considered to be the best approach, and wavelet threshold de-noising method is the most simple method that needs the minimum amount of calculation. But this method in selecting threshold functions needs to be improved. Based on different domestic and foreign methods of improving threshold function, propose an improved bivariate threshold function. According to the simulation of non-stationary signal de-noising, the results show that the optimal de-noising results of different signals exist by taking different parameters. Compared with all the de-noising effects, application of the bivariate threshold function considering signal-to-noise ratio and mean square error is superior to the traditional soft and hard threshold functions. At the same time, it can significantly improve the filtering precision, and reserve the main signal details while effectively removing the noise well.

Abstract: Multi-terminal HVDC transmission system based on voltage source converter is a promising topology for the integration of the renewable energy sources. The fault characteristics of VSC-MTDC system under DC side faults was analyzed in this paper, as well as the particular requirements for the protection strategy. On the basis of the work metioned above, a four-terminal DC connected transmission system model was built in PSCAD/EMTDC. The boundary protection algorithm was proposed and the wavelet analysis was introduced. The protection scheme for VSC-MTDC transmission lines is based on the attenuation characteristics of line boundary for high frequency transient signals, which constitutes the operation criteria of the boundary protection. The protection scheme puts forward an effective method for the protection selectivity of the VSC-MTDC transmission system.

Abstract: The self-excited vibration of machinery is a common vibration in mechanical vibrations. Mechanical self-excited vibration destroys the normal working of the mechanical device and leads to mechanical fatigue damage. If the self-excited vibration reaches to the vibration frequency of machinery, it can produce the resonance and result in the scrapping of mechanical devices. The study of mechanical self-excited vibration has great significance. According to mathematical finite element methods, this paper establishes the mathematical model of the mechanical natural frequency through the finite volume method and gives the mathematical derivation formula of mechanical devices self-vibrated frequency. The second part of the paper simulates self-vibrated process of machinery using the professional software ANSYS software. First, it establishes a three-dimensional model of the mechanical device through the pre-processing module and analyzes mechanical self-excited vibration through calculation module and gets the frequency modal map of self-excited vibration process. It studies the mechanism of the mechanical self-excited vibration combining with modern signal analysis techniques--wavelet analysis. It gets the vibration source location which provides a reliable theoretical basis for the study of mechanical self-excited vibration.

Abstract: This paper first of all gives an introduction to the structure of rolling bearing, development stage of fault and the main fault types; then, it makes an analysis of the common detection methods and the technologies involved in rolling bearing fault; at last, based on the emphasis on the rolling bearing on-line detection and fault diagnosis system of acoustic emission technology, it elaborates the basic principles of acoustic emission, rolling bearing fault detection and diagnosis system experiment setting. Meanwhile, it introduces modern signal processing technology into acoustic emission information feature extraction and state recognition, such as wavelet analysis and wavelet packet analysis.

Abstract: Wavelet transform can carry on multi-scale and multi-resolution analysis of the signal through arithmetic function such as stretching and translation and so on .In this paper, applying Morlet complex wavelet performed wavelet transform of the month precipitation time sequence of Quzhou Jiuhua station, and analyzed period on different time scales. The future precipitation was analyzed based on main periods. The result showed that month precipitation has multi-scale characteristic and the main periods of month precipitation are 5-month, 11-month and 26-month. The periodic changes on large-scale nest the periodic changes on small-scale. The wavelet analysis can process signal in time frequency domain, which provide references for development and management of water resources.

Abstract: For Fiber-Grating Perimeter-Intrusion alarm system, a Fiber-Grating intelligent adaptive alarm algorithm based on wavelet analysis and difference algorithm was proposed. The algorithm precedes the real-time waveform by wavelets decomposition, and acquired the assertion values of each subband by difference calculation. Through the method of comparing the assertion value of some subband, intelligent adaptive alarm system was realized. The experiments indicate that the proposed algorithm can give an alarm for illegal intrusion with good performance and false alarm below 1.5%, and it provides a promising application prospect for intelligent adaptive alarm.

Abstract: High-accuracy modeling is the key problem of ship deformation measurement based on inertial measuring method. This paper is to find a high-accuracy modeling method based on the ship deformation data measured by optical devices. According to different modeling methods, mathematical models are designed by the analysis of the initial measurement data. Wavelet analysis method is introduced in the process of modeling. Attitude matching method is selected as the simulation algorithm and Kalman filter equations are set up based on the algorithm. Simulation results show that the ship deformation can be represented accurately by mathematical models. The Precision Estimation result is better than 0.4''.