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This paper introduces a novel approach in image processing based on a vector image model. A major advantage of the model is that it allows vector operations to be performed on an image. An example of a vector operation is the comp...
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This paper introduces a novel approach in image processing based on a vector image model. A major advantage of the model is that it allows vector operations to be performed on an image. An example of a vector operation is the computation of mechanical moments for detecting inhomogeneities in an object or equivalently edges in an image. A new edge operator derived from a vector image model yields an edge vector field analogous to the Hamiltonian gradient field of the image. The distinct feature of the edge vector field is that edge vectors form current loops encompassing the objects. This feature is exploited to develop a new boundary extraction algorithm based on particle motion in a force field. The edge vector field forces a particle to move along the edges while an orthogonal normalized Laplacian gradient vector field guarantees that the particle will not drift away from the edges. The object boundary can be obtained from the convergent path of the particle trajectory. Using a fine stepping factor, the extracted boundary can achieve subpixel accuracy. The proposed algorithm has major advantages over the conventional edge-detection, edge-thinning, and edge-linking techniques in that it effectively utilizes both direction and magnitude of edges. The algorithm is simple, robust and performs very well even on high curvature objects.
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Automated signal classification systems are finding increasing use in many applications for the analysis and interpretation of large volumes of signals. Such systems show consistency of response and help reduce the effect of varia...
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Automated signal classification systems are finding increasing use in many applications for the analysis and interpretation of large volumes of signals. Such systems show consistency of response and help reduce the effect of variabilities associated with human interpretation. This paper deals with the analysis of ultrasonic NDE signals obtained during weld inspection of piping in boiling water reactors. The overall approach consists of three major steps, namely, frequency invariance, multiresolution analysis, and neural network classification. The data are first preprocessed whereby signals obtained using different transducer center frequencies are transformed to an equivalent reference frequency signal. Discriminatory features are then extracted using a multiresolution analysis technique, namely, the discrete wavelet transform (DWT). The compact feature vector obtained using wavelet analysis is classified using a multilayer perceptron neural network. Two different databases containing weld inspection signals have been used to test the performance of the neural network. Initial results obtained using this approach demonstrate the effectiveness of the frequency invariance processing technique and the DWT analysis method employed for feature extraction.
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Inverse problems are encountered in many fields of science and engineering. In electromagnetics, for example, inverse problems may involve the reconstruction of the source or scatterer on the basis of information contained in elec...
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Inverse problems are encountered in many fields of science and engineering. In electromagnetics, for example, inverse problems may involve the reconstruction of the source or scatterer on the basis of information contained in electromagnetic measurements. In general, the measurements can be related to the scatterer via integral equations. This paper presents a neural network approach for solving the inverse problem associated with such equations. Results of implementing the method on an application problem are presented.
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The use of reduced magnetic vector potential (RMVP) in the three-dimensional finite element analysis of eddy current nondestructive testing (ECT) has demonstrated great flexibility, accuracy, and efficiency in case of coil excita...
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The use of reduced magnetic vector potential (RMVP) in the three-dimensional finite element analysis of eddy current nondestructive testing (ECT) has demonstrated great flexibility, accuracy, and efficiency in case of coil excitation. This paper investigates the application of the RMVP in another class of eddy-current testing applications where the test sample of finite size is immersed in a uniform excitation field. The paper also shows that RMVP cannot be used in eddy-current testing problems having infinite current foil and infinite conducting plates.
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This paper presents a signal inversion technique in nondestructive evaluation (NDE) application for defect profile reconstruction using the element-free galerkin (EFG) method and state space search. The advantage of EFG method is...
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This paper presents a signal inversion technique in nondestructive evaluation (NDE) application for defect profile reconstruction using the element-free galerkin (EFG) method and state space search. The advantage of EFG method is that it relies only on a set of nodes, instead of a complex mesh to discretize the solution domain. In the inversion procedure, remeshing is avoided to increase the efficiency and accuracy of the solution, which is a major advantage over the traditional finite-element method (FEM). The iterative state space search method using the tree structure is developed for implementing the defect updating scheme. Preliminary results are presented for validation. The robustness of the technique has been shown on noisy signals.
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Numerical models capable of modeling magnetic flux leakage (MFL) methods of nondestructive testing are of significant interest to industry. The nonlinear nature of the MFL problem necessitates the use of an iterative model, thereb...
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Numerical models capable of modeling magnetic flux leakage (MFL) methods of nondestructive testing are of significant interest to industry. The nonlinear nature of the MFL problem necessitates the use of an iterative model, thereby resulting in excessive computational effort. This paper describes an approach for developing an equivalent linear model (ELM) where the ferromagnetic region is appropriately partitioned into different domains with each domain being assigned a constant permeability value depending on the magnetization level and the flaw size. The nonlinear behavior of the multi-layered object is then modeled using a linear MFL model. The strategy results in significant computational savings without a substantial loss in accuracy. Results supporting the validity of the approach have been obtained using a 3D magnetostatic finite element (FE) model.
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Magnetostatic methods that are used for the nondestructive evaluation (NDE) of ferromagnetic materials can be modeled by partial differential equations. Conventional numerical methods such as finite difference, finite elements or ...
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Magnetostatic methods that are used for the nondestructive evaluation (NDE) of ferromagnetic materials can be modeled by partial differential equations. Conventional numerical methods such as finite difference, finite elements or boundary integral methods for large problems typically require an iterative matrix inversion scheme to solve the system of equations. Parallel implementation of such schemes is extremely difficult due to the data dependencies in the matrices. Monte Carlo methods offer an alternative approach by reducing the differential equation to simple, independent, random processes that are inherently amenable to parallel implementation. This paper investigates the use of Monte Carlo methods for modeling magnetostatic flux leakage NDE phenomena. The model is validated by comparing the results with those obtained with finite element models. The approach offers significant reduction in computational burden especially for 3-D problems.
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Magnetic flux leakage (MFL) methods are used extensively for inspecting ferromagnetic materials. The analysis of the MFL signal is however fraught with problems associated with the sensitivity of the signal to a number of factors ...
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Magnetic flux leakage (MFL) methods are used extensively for inspecting ferromagnetic materials. The analysis of the MFL signal is however fraught with problems associated with the sensitivity of the signal to a number of factors such as the MFL sensor velocity and variations in the permeability of the test specimen. The interpretation can be simplified if the signals can be processed to attain invariance to these conditions. This paper presents novel methods for obtaining permeability invariant and velocity invariant MFL signals.
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The paper presents a hybrid numerical model for simulating electromagnetic scattering from a two dimensional object embedded in multilayered media. The domain is first divided into interior and exterior regions using a cylindrical...
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The paper presents a hybrid numerical model for simulating electromagnetic scattering from a two dimensional object embedded in multilayered media. The domain is first divided into interior and exterior regions using a cylindrical surface. Finite element formulation is used to solve for the field in the internal region, and the solution of the field is used to find the induced current in the elements that discretize the 2D object. The scatterer is represented as a summation of line sources embedded in multilayered media, and the scattered field is found by summing the contributions from these sources. Simulation results are presented.
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This paper presents a finite element model for simulating electrodynamic and magnetostrictive vibration absorber systems. The model employs a decoupled formulation to compute motion induced voltages in a magnetomechanical coupled ...
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This paper presents a finite element model for simulating electrodynamic and magnetostrictive vibration absorber systems. The model employs a decoupled formulation to compute motion induced voltages in a magnetomechanical coupled system. The model is first validated by comparison with experimental measurements. An application of the model for optimization of the system damping performance using model predictions, is presented. The model is also used to calculate the frequency response of a magnetostrictive actuator.
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