Papers by Keyword: Multi-Scale Analysis

Abstract: Laser cladding of a Ni based powder on Cu-Ni-Al or cast iron was performed with a 4kW continuous Nd: YAG laser. The Cu-Ni-Al and cast-iron substrates are used for their thermal properties in glass mold industry. But the issue of these materials is their lack of resistance on corrosion and abrasion. The role of the Ni based alloy is to protect the mold without affecting its thermal properties (Heat Affected Zone (HAZ)). The purpose of this research is to produce a well bonded Ni based melted powder without pores or cracks on a non-planar surface (curvilinear section). An investigation of the impact of the processing parameters, power (1500-3200 W), scanning speed (2.5-10 mm/s) and powder feeding rate (24.5-32.5 g/min) on the bonding quality, the porosity propagation and HAZ appearance is performed. The used methods are neutronography, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Electron BackScatter Diffraction (EBSD). These multi-scale techniques are obviously complementary. Neutronography is a well-adapted non-destructive method to observe the porosity in the volume thanks to the contrast between materials. EBSD analysis allows us to analyze the microstructural evolution of the coating notably by observing the dendrites growth. This same method also permits to observe the HAZ nature according to the laser cladding parameters. Those methods allowed to optimize the processing parameters in a way to obtain perfect bonding, to avoid porosity propagation and to limit the HAZ emergence.

Abstract: Multi-axis ball end milling experiments of H13 die steel have been conducted with four different cutter postures, and the 3D topographies of machined surfaces are acquired by optical profiler. The multi-scale analysis is carried out on the machined surfaces based on 2D dual-tree complex wavelet transform (2D DT-CWT). The topographies are decomposed into different frequency bands, and the roughness in every frequency band is calculated. The results reveal that the roughnesses of the machined surfaces under different cutter postures are quite different, the roughness is the lowest when the lead angle is 12° and the tilt angle is-22°. The roughnesses under different cutter postures exhibit similar changing trend with the variation of frequency bands: the roughnesses in the high and low frequency bands are relatively lower, the roughnesses in the medium frequency bands are higher. The 2D DT-CWT provides an ideal comprehensive topography analysis method for performance evaluation of machined surfaces.

Abstract: Voltage sag is the major power quality problem and receives wide attention. Although wavelet analysis works well for detecting voltage sag features, the existence of noise can reduce the advantages of wavelet method or even make it ineffective. To solve the problem, the paper uses multi-scale wavelet information by multiplying the results of several scales, and then searches the local maxima from the product to find the transition moment of voltage sag. The proposed method can suppress the noise and improve the accuracy for detecting voltage sag features. Simulation result validates the effectiveness of the proposed method.

Abstract: Thin-walled members that have one dimension relatively large in comparison to the cross-sectional dimensions are usually modelled by using beam-column type finite element formulations. Beam-column elements however, are based on the assumption of rigid cross-section, thus they cannot consider the cross-sectional deformations such as local buckling and only allows considerations of the beam axis behaviour such as flexural or lateral-torsional buckling. Shell-type finite elements can be used to model the structure in order to consider these local deformation effects. Based on the Bridging multi-scale approach, this study proposes a numerical technique that is able to split the global analysis, which is performed by using simple beam-type elements, from the local analysis which is based on more sophisticated shell-type elements. As a result, the proposed multi-scale method allows the usage of shell elements in a local region to incorporate the local deformation effects on the overall behaviour of thin-walled members without necessitating a shell-type model for the whole member.

Abstract: Vibration-based energy harvester has been widely investigated during the past years. In .order to improve the power-generating ability and enlarge the frequency range of energy harvesters, this paper presents the design and analysis of a new magneto electric energy harvester that uses Terfenol-D/PZT/Terfenol-D laminate to harvest energy from nonlinear vibrations created by magnetic levitation. The mathematical model of the proposed harvester is derived and used in a parametric study. By multi-scale analysis, the frequency-response analysis of the system is obtained and discussed here. It is shown that the systems nonlinearity can broaden the harvesters working bandwidth, thus makes the harvester suitable to work in practical cases.

Abstract: The alignment of a strapdown inertial navagation system (SDINS) is the process whereby the orientation of body frame is determined with respect to the navigation frame [. In a broad sense, alignment of SDINS can be classified as initial alignment and in-flight alignment (IFA). The IFA is performed with IMU and external sensors during the vehicle flight [2,, in which the primary assistant sources are satellite system, radar, or other airborne equipment, offering reference signals like position, velocity, or attitude to assist the alignment process [4,. However, these sources have disadvantages in redundancy, independence, and stability, which will be incipient faults in emergency take-off or warfare. So it is necessary for us to analyse the subsidiary airborne equipments and design new in-flight alignment scheme.

Abstract: Multimedia technology development and the implementation of the Internet technology leading to a large number of image information appear, based on keywords retrieval methods of traditional text can not meet the requirement of image information retrieval, this makes the content-based image retrieval technology gradually become the focus of research. Based on the content retrieval technology of the key step is necessary in the extraction of image features, which can be used to extract the features such as color, texture and shape. However, because of the image characteristics can only hold each image similarity of a certain aspects, therefore how to better image will be based on content said image retrieval one of the important research direction. This article reviews some content-based image retrieval comparison, such as color features and the texture characteristics and the extraction of the kind of method, each have their own advantages is in.

Abstract: Anomalous traffic often has a significant impact on network activities and lead to the severe damage to our networks because they usually are involved with network faults and network attacks. How to detect effectively network traffic anomalies is a challenge for network operators and researchers. This paper proposes a novel method for detecting traffic anomalies in a network, based on continuous wavelet transform. Firstly, continuous wavelet transforms are performed for network traffic in several scales. We then use multi-scale analysis theory to extract traffic characteristics. And these characteristics in different scales are further analyzed and an appropriate detection threshold can be obtained. Consequently, we can make the exact anomaly detection. Simulation results show that our approach is effective and feasible.

Abstract: The mutation and form of logging curve can be represented by the variation of modulus maxima coefficients of wavelet transform within different scales exactly, then we can use wavelet multiscale edge detection theory to analyze characteristics of sequence stratigraphy boundaries in logging curves. Obtain the modulus maximum of approximation coefficient matrix and detail coefficient matrix after decompositing GR and SP curve in every scales.Compare and amend the modulus maximum of approximation coefficient matrix and detail coefficient matrix reciprocally, applicate the Mallat alternation foldover algorithm to reconstruction logging curve eventually ,we can get the fusion curves in different scales. The fusion curves can greatly enhance characteristics of sequence stratigraphy boundaries in logging curves.

Abstract: To consider the material properties of functional gradient beam structure change along the thickness. In this paper, the wavelet multi-scale method is used to solve beam differential equations with initial or boundary conditions. An operational matrix of integration based on the wavelet is established and the procedure for applying the matrix to solve the differential equations is formulated, and gets the stress of the beam when the material properties of gradient beam take arbitrary function. The results show that the proposed way is quite reasonable while comparing to the exact solution.