L'objectif de la thèse est d'explorer les comportements mécaniques effectifs des matériaux poreux impliqués dans les problèmes de pores ou d'inclusion, avec pour objectif principal d'homogénéiser un matériau aussi hétérogène que possible, plus d'informations de géométrie physique à une échelle donnée. Nous examinons séparément ici quatre microstructures typiques de matériaux ressemblant à des roches couvrant différents constituants: nous avons cherché à déterminer comment la présence de pores et une inclusion de morphologies différentes influent sur les comportements macroscopiques élastiques, débit plastique et dépendant du temps. Un modèle d'homogénéisation par étapes pour les comportements élastoplastiques et viscoplastiques est proposé, basé sur une méthode d'homogénéisation par transformée de Fourier rapide, afin d'améliorer le comportement local depuis la transition à la micro-échelle vers la méso-échelle, puis vers la macroscopie. Une série de simulations est calculée et comparée. Nous portons une attention particulière au comportement anisotrope des matériaux à la fois pore et inclusion configurée à la même échelle et à différentes échelles Nous fournissons une solution de référence pour ce type de matériaux couvrant l’effet des géométries de pores et d’inclusion en raison de la limitation à l’obtention d’un critère analytique. En plus nous proposons un modèle d’endommagement plastique multi-échelle. les comparaisons entre les résultats numériques et les données expérimentales montrent que ce modèle peut bien caractériser son comportement en défaillance avec des micro-structures complexes. / The objective of this thesis aims to explore the effective mechanical behaviors of porous materials involved with pore or inclusion problem. The key point to this problem is to homogenize such a highly heterogeneous material incorporating more physical geometry information at a given scale. In this work, four typical microstructure of rock-like materials are respectively considered here covering different constituents. We sought to determine how the presence of pores and inclusion with different morphologies influence the macroscopic elastic, plastic flow and time-dependent behaviors. For this propose, a two-step homogenization model for elastoplastic and viscoplastic behaviors is proposed based on a Fast Fourier Transform homogenization method to upscale the local behavior from the micro-scale transition to meso-scale and then to macroscale. A series of simulations are computed and compared. Particular attentions are focused on the anisotropic behavior for the materials with both pore and inclusion configured at same and different scales. We provide a reference solution for this kinds of materials covering the effect of pore and inclusion geometries due to a limitation to obtain an analytical criterion. Moreover, we proposed a damage plastic model with multi-scale characters. Comparisons between numerical results and experimental data show that this model can well characterize its failure behavior with complex micro-structures.

A Discrete Fourier Transform (DFT) changes the basis of a group algebra from the standard basis to a Fourier basis. An efficient application of a DFT is called a Fast Fourier Transform (FFT). This research pertains to a particular type of FFT called Decimation in Frequency (DIF). An efficient DIF has been established for commutative algebra; however, a successful analogue for non-commutative algebra has not been derived. However, we currently have a promising DIF algorithm for CSn called Orrison-DIF (ODIF). In this paper, I will formally introduce the ODIF and establish a bound on the operation count of the algorithm.

On-line induction machine condition monitoring techniques have been used widely in the detection of motor broken rotor bars for decades. Research has found that when broken bars occur in the machine rotor, the anomaly of electromagnetic field in the air gap will cause two sideband frequency components presenting in the stator current spectrum. Therefore, identification of these sideband frequencies can be used as a convenient and reliable approach to broken rotor bar fault diagnosis. Discrete Fourier Transform (DFT) is a conventional spectral analysis method used in this application. However, the use of DFT has several limitations. The most important one among them is the restriction of frequency resolution by window length. Due to this limitation, the accuracy of broken rotor bar detection can be highly affected in cases such as light machine load and limited data records. However, Prony's method for spectral analysis has the ability of overcoming the restriction of data window length on the frequency resolution, from which the DFT suffers. Such feature makes Prony's method a promising choice for broken rotor bar diagnosis when the machine is operating under light or varying load, or when only restricted data is available. In this thesis, I have demonstrated the implementation of this technique in the induction motor broken rotor bar detection, revealed its better performance than DFT in terms of maintaining high resolution in frequency domain whilst using a much shorter window, and analyzed the influential factors to the method of Prony Analysis (PA). In this thesis, an induction machine model that includes broken rotor bars is developed using Matlab/Simulink and verified by comparing the experimental and the simulated results. The Prony Analysis method for broken bar diagnosis is implemented and tested using both simulated and measured stator current data. Comparisons between PA and DFT results are presented, clearly indicating improvements of broken bar diagnostics using PA. / Thesis (M.Eng.Sc.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2008

Thesis (Ph. D.)--Texas Christian University, 2007. / Title from dissertation title page (viewed Dec. 10, 2007). Includes abstract. Includes bibliographical references.

In this thesis, an FFT (Fast Fourier Transform) hardware circuit is designed for OFDM systems. A new memory table permutation deletion method, which can reduce the size of memory storing twiddle factors table, is proposed. The architecture of the FFT circuit is based on the faster split-radix algorithm with SDF (Single-path Delay Feedback) pipeline structure. The bits number of the signal is carefully selected by system simulation to meet the system requirements. Based on the simulation results, a small area FFT circuit is carried out for OFDM systems.

Fast Fourier transformation (FFT) is a powerful analytical tool with wide-ranging applications in many fields. The standard FFT algorithms inherently assume that the length of the input and output sequence are equal. In practice, it is not always an accurate assumption. In certain case only some of the inputs to the transformation function are non-zero but lot of other are zero. In this thesis, a novel architecture of a 1024-point FFT, which adopts the transform decomposition (TD) algorithm, is presented to further reduce the complexity when the non-zero input data are consecutive. To implement this FFT processor, fixed point simulation is a conducted by using MATLB. The hardware implementation is realized by using the Verilog Hardware Description Language (HDL) which is taped out in TSMC0.18 Cell-Based Library for system verification.

Thesis (doctoral)--Georg-August-Universität zu Göttingen, 1919. / Cover title. Vita. Includes bibliographical references (p. [47]).

Thesis (M.S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2004. / Dr. Feodor Vainstein, Committee Member; Dr. Doug Blough, Committee Chair; Dr. David Schimmel, Committee Member. Includes bibliographical references (leaves 71-75).

Thesis (M.S.)--Brigham Young University. Dept. of Computer Science, 2003. / Includes bibliographical references (p. 120-130).

The Cartesian Cubic lattice is known to be sub optimal when consideringband-limited signals but is still used as standard in three-dimensional medical magneticresonance imaging. The optimal sampling lattices are the body-centered cubic latticeand the face-centered cubic lattice. This report discusses the possible use of thesesampling lattices in MRI and presents verification of the non standard Fouriertransform method that is required for MR image creation for these sampling lattices.The results show that the Fourier transform is consistent with analytical models.