Papers by Keyword: Wavelet Transform (WT)

Abstract: Understanding the characteristics of stochastic loading is the premise and foundation for structure analysis. Traditional amplitude spectrum and power spectral density (PSD) method based on Fourier transform (FT) has limitation, that is, it loses any information with time and can not reflect the non-stationary characteristics of stochastic loading. Wavelet transform possesses assembling ability in both time and frequency domain,and it possess stronger ability of analyzing non-stationary signal. In this paper, the method of estimating PSD and time-dependent PSD of stochastic loading using wavelet transform is researched. The calculating process is programmed and the method is validated by a numerical example. The analysis result of example indicates that the method presented in this paper is feasible.

Abstract: Ground-roll is an interferential wave existing widely in seismic data, and it is an important step in seismic data processing to suppress ground-roll. Wavelet Transform lacks of detecting the singularities of the signal with straight line or curve, and the method can separate the different waves at the same time because of Curvelet transform simultaneously has the characteristics of frequency and direction. The experiment results show that the Curvelet transform has better effects in ground-roll suppression.

Abstract: The practical wrist pulse of the healthy person and the coronary heart disease patient were analyzed by wavelet transform (WT) and hilbert huang transform ( HHT), and the characteristic information (percentage of energy density) of the pulse signal was discussed. The simulation results show that both WT and HHT are efficient ways in analyzing and processing pulse signal, and can draw main characteristic information from pulse signal. However the basis function is preselected in WT, it doesnt need to be preselected in HHT. In HHT the intrinsic mode function (IMF) is obtained by empirical mode decomposition (EMD), it can reflect the instantaneous frequency of pulse signal, and has the actual physical meaning. The resolving power of time and frequency in WT is restricted by Heisenberg uncertainty principle, and is restricted by each other. While the resolving power of time and frequency in HHT is adaptively changed according to signal intrinsic characteristics. The HHT is more adaptive than WT in analyzing pulse signal. The HHT can offer a new idea to diagnose cardiovascular disease by wrist pulse signal.

Abstract: There are large number of transient signals will be produced when the operation mode is changed. And the frequency of the transient signals distributed in wide range. The most of them are damped and oscillated. The impedance is a popular feature in power system, and it has been widely used in relay protection and fault location. So the impedance calculation based on the damped sinusoidal signal have been the important way to diagnosis the fault, locate the fault and so on. But the methods used now are based on the fundamental impedance calculation theory, lacking theoretical basis. In fact, the traditional methods for fundamental signal calculation are not appropriate for the quantitative analysis of damped sinusoidal signal. The paper analyzed the impedance calculation based on damped sinusoidal signal, combined the features of damped sinusoidal signals and the traditional impedance calculation method. The two typical signal analysis methods for damped sinusoidal signal extraction are used to calculate the accurate impedance based on the different extraction results. And the analysis laid a foundation for the impedance calculation using damped sinusoidal signals.

Abstract: With the popularization of the rural electricity utilization, the rural electric safety was still an immediate problem to be solved. It was difficult to exactly detect and judge electric shock signals in the summation leakage current on the low-voltage electric power grid. A detection method of electrical contact signals based on sliding window and wavelet multi-resolution method was proposed. Under the different signal-to-noise ratio level, the summation leakage current was reconstructed by wavelet decomposition reconstruction algorithm. According to the characteristic of the slow change of the normal leakage current and the rapid change of the electric shock current within a short time, the electric shock current were extracted from the restructured summation leakage current signal by sliding window method. The mean square error and correlation analysis between the extracted signal and the actual testing results were studied. The analysis results show that the proposed method could identify electric shock current in the summation leakage current among noise, and its detection precision was superior to single sliding window method.

Abstract: Image fusion is process which combine relevant information from two or more images into a single image. The aim of fusion is to extract relevant information for research. According to different application and characteristic of algorithm, image fusion algorithm could be used to improve quality of image. This paper complete compare analyze of image fusion algorithm based on wavelet transform and Laplacian pyramid. In this paper, principle, operation, steps and characteristic of fusion algorithm are summarized, advantage and disadvantage of different algorithm are compared. The fusion effects of different fusion algorithm are given by MATLAB. Experimental results shows that quality of fused image would be improve obviously.

Abstract: Aiming at the large calculation workload of adaptive algorithm in adaptive filter based on wavelet transform, affecting the filtering speed, a wavelet-based neural network adaptive filter is constructed in this paper. Since the neural network has the ability of distributed storage and fast self-evolution, use Hopfield neural network to implement adaptive filter LMS algorithm in this filter so as to improve the speed of operation. The simulation results prove that, the new filter can achieve rapid real-time denoising.

Abstract: The improved method for image edge detection based on wavelet transform modulus maxima included following steps: wavelet transform was adopted to compute local modulus maximum of edge and noise. Based on the differences between wavelet transforms of edge and noise, the separation of noise and edge was achieved by detecting local modulus maximum with quadratic discriminate method. Simulation results indicate that the inconsistency between high precision localization and high denoising ability existing in traditional edge detection algorithm could be resolved by means of the algorithm.

Abstract: In this study, displacement and strain energy mode shapes obtained from the structure, are processed using continuous spatial wavelet transforms for damage identification. A cantilever and simply supported beam are analysed in ANSYS to obtain mode shapes by performing modal analysis both for damaged and undamaged conditions. Different wavelets are processed to choose the best mother wavelet for detecting crack, a representation of damage. The dimensions of crack like depth are varied from 0.5 mm. Spatial distribution of wavelet coefficients obtained is used for identifying the damage. The quantification of the damage is done by using Lipchitz constant. It is observed that by using strain energy mode shapes the percentage of damage (crack) identification level can be improved than by using displacement mode shapes. The minimum damage level that the strain mode shape can identify is approximately 3% of the element thickness, whereas with displacement mode shapes, it is about 7% of the element thickness. Different types of crack configurations like single surface crack, double surface cracks and internal cracks are simulated and studied using both the modal methods. It is observed that the strain energy mode method could identify internal cracks also.

Abstract: Multi-resolution optical flow is the main trends of the current optical flow calculation. Wavelet transform and Gaussian filter are widely used to build multi-resolution structure of the image. In this paper, LK optical flow method mixed with pyramid was used to study the optical flow field. The different effects of wavelet transform and Gaussian filter in the flow distribution was also discussed. Experimental results show that the selected image decomposition method has a significant role in optical flow field calculation.