Efficiency is one of the key issues in numerical simulation of large-scale problems with complex 3-D geometry. Traditional domain based methods, such as finite element methods, may not be suitable for these problems due to, for example, the complexity of mesh generation. The Boundary Element Method (BEM), based on boundary integral formulations (BIE), offers one possible solution to this issue by discretizing only the surface of the domain. However, to date, successful applications of the BEM are mostly limited to linear and continuum problems. The challenges in the extension of the BEM to nonlinear problems or problems with non-continuum boundary conditions (BC) include, but are not limited to, the lack of appropriate BIE and the difficulties in the treatment of the volume integrals that result from the nonlinear terms. In this thesis work, new approaches and techniques based on the BEM have been developed for 3-D nonlinear problems and Stokes problems with slip BC. For nonlinear problems, a major difficulty in applying the BEM is the treatment of the volume integrals in the BIE. An efficient approach, based on the precorrected-FFT technique, is developed to evaluate the volume integrals. In this approach, the 3-D uniform grid constructed initially to accelerate surface integration is used as the baseline mesh to evaluate volume integrals. The cubes enclosing part of the boundary are partitioned using surface panels. No volume discretization of the interior cubes is necessary. This grid is also used to accelerate volume integration. Based on this approach, accelerated BEM solvers for non-homogeneous and nonlinear problems are developed and tested. Good agreement is achieved between simulation results and analytical results. Qualitative comparison is made with current approaches. Stokes problems with slip BC are of particular importance in micro gas flows such as those encountered in MEMS devices. An efficient approach based on the BEM combined with the precorrected-FFT technique has been proposed and various techniques have been developed to solve these problems. As the applications of the developed method, drag forces on oscillating objects immersed in an unbounded slip flow are calculated and validated with either analytic solutions or experimental results.

The rapid growth of communication technology with the success of internet, has brought huge profits and great convenience to our daily life. Computer networks can be built using either wired or wireless technologies. It will be an important issue that how to select a medium for the transmission. Wired Ethernet has been the traditional choice in most of the networks. However, it has to deploy the Ethernet wires. For the wired internet networks, the power line communication (PLC) technology will be an alternative choice. In this wire-line communication system, the power line network is used as the transmission medium. Therefore, computer networks can work on the existing power line system. No extra new transmission infrastructure is needed. So far, several PLC standards are available, shch as X-10, CEBus(Consumer Electronic Bus), Echonet and Homeplug. This thesis studies the Homeplug AV specification developed by the Homeplug powerline Alliance. By employing MATLAB/Simulink, we build up a PLC baseband transmission model and simulation platform. We carry out the Homeplug AV baseband transmission performance in system level on this platform. The Homeplug AV adopts 3072-point FFT which is not the power of two. It will be a challenge to design the 3072-point FFT processor. Here, we use Xilinx System Generator to design and implement the 3072-point FFT processor. The function verification of the implemented 3072-point FFT processor for Homeplug AV system is carried out by simulation.

The topic of this thesis presents a digital front end (DFE) of the digital video broadcasting over terrestrial (DVB-T). The DVB-T system is similar to most of the prior digital communication system. It is roughly divided into two major parts, one for channel coding/decoding, and the other for modulation/demodulation. The thesis is mainly focused on the DVB-T digital video broadcasting demodulation part of the receiver and the integration of a complete digital front demodulation system. The major operational processor of the DFE is a 2K/8K dual-mode FFT processor, which has been implemented by the TSMC ( Taiwan Semiconductor Manu-facturing Company ) 0.35um 2P4M CMOS process technology to justify the simulation results as well as the correctness of the proposed architecture.

The various versions of CreditRisk+ have widely been used in the financial industry. We compute the loss distribution under CreditRisk+ model by fast fourier transform technique in order to have faster and more stable results. Moreover, we link the parameters of the model to the exogenously observed variables which could be obtained from the financial markets by the use of Poisson INAR process. It is shown that the estimation of the parameters become available under this setup. This enables us to build a system that allows users to monitor and predict the banks loss characteristics without having specific and current information on banks.

Calculation of electromagnetic wave propagation over irregular terrain is an important problem in many applications such as coverage calculations for radars or communication links. Many different approaches to this problem may be found in the literature. One of the most commonly used methods to solve electromagnetic boundary value problems is the Method of Moments (MoM). However, especially at high frequencies, the very large number of unknows required in the MoM formulation, limits the applicability of this method, since the memory requirement and the operation count increases by O(N2) and O(N3), respectively, where N is the number of the unknowns. Several approaches have been proposed in the literature to reduce the memory requirement and the operation count of the MoM. These approaches rely on the special structure of the impedance matrix generated by the MoM. The Conjugate Gradient (CG) method is a non stationary iterative technique that can be used to solve general asymmetric/non-Hermitian systems with an operational cost of O(N2) per iteration. Furthermore, the computational time can be improved by the Fast Fourier Transform (FFT) algorithm to perform the matrix vector multiplication that appear in any iterative technique. This approach has been successfully used in the literature to solve scattering from electrically large objects and it has been shown that the computational cost and memory requirement can be reduced to O(KNlogN) with K being the number of iterations. In this thesis, CG method accelerated with Fast Fourier Transform (CG FFT) method is applied to the problem of electromagnetic propagation over irregular terrain. Applications for electrically large rough terrain profiles are presented. The accuracy of the method is compared to the direct solution of the MoM, CG method and Free Space model with recoveries by Hata model or multiple knife-edge diffraction and reflection. The solution works on quasi-planar surfaces and profiles with small deviation like little breezy sea surface properly.

The photoreflectance(PR) and Electroreflectance(ER) of surface-intrinsic-n+ type doped GaAs exhibit many Franz-Keldysh oscillations (FKOs), which enable the electric field (F) to be determined from the technique of the fast Fourier transform (FFT). It is known that F's determined from PR are subjected to photovoltaic effect, but it is difficult to estimate the strength of modulating field (dF) of the pump beam in the PR measurements . Alperovich et. al. have used imaginary part of FFT to determine the strengths of dF's in the ER measurements [V. L. Alperovich, et. al. Appl. Phys . Lett. 71, 2788 (1997)]. Here, we will apply this method to the PR measurements. The dF's thus obtained will be compared with those deduced from photo-voltage measurements. The result shows that the method of Alperovich's can be used to determine the strength of dF in the PR measurements.

<p>The majority of all power cuts that affects individuals and communities are caused by earth faults on the power transmission lines at 10kV and 20kV level [1]. If these power cuts could be eliminated, less disturbances and interrupts would lead to large amounts of money savings.</p><p>Swedish Neutral has developed such a protection system. When an earth fault occurs power is injected into the neutral point of the transformer. The RCC (Residual Current Compensation) protection calculates a compensation current exactly 180 degrees out of phase to the fault current. Doing this, the voltage at the fault location becomes very close to zero, without affecting the power transmission.</p><p>The protection system can only compensate automatically for the fundamental frequency (50Hz), and manually for the 3^rd, 5^th, 7^th and 9^th harmonics. In most cases, when the harmonics are very small it is not necessary to compensate for them. There are though cases when compensation for the harmonics is necessary.</p><p>This thesis focuses on finding the best method to extract the content of a sampled signal regarding both simplicity and speed. Both amplitude and phase of each harmonic must be calculated. Is the proposed method suitable for the current computer system and how can it easily be implemented.</p><p>Because the fundamental frequency is known and the harmonics are all multiples of the fundamental frequency it makes the task less complex. It is not necessary to use the FFT algorithm. The DFT can be calculated using correlation. Both phase and amplitude can be calculated very precisely with few samples and not so many computer operations.</p>

<p>Kraven på dagens trådlösa förbindelser kommer hela tiden att öka och med detta följer även högre krav på nya produkter som kan tillgodose de ökade kraven. För att göra processen från idé till produkt snabbare krävs enkla verktyg för att snabbt kunna gå från den formulerade standarden till en hårdvaruprototyp. Detta arbete har använt sig av ett av dessa verktyg som idag finns tillgängliga, Xilinx System Generator for DSP 1.1, för att ta fram sändare och mottagare för en del av den trådlösa standarden IEEE 802.11a. Arbetet ger en beskrivning av hur sändare och mottagare är uppbyggda samt även synpunkter på System Generator och beskrivningar av problem som uppstod under arbetet. </p> / <p>The demands on todays wireless communications will continue to increase and with this follows a demand for shorter and shorter development times for the products that are going to satisfy this demand. To accomplish this shorter development time simple tools for going from the formulated standard to a hardware prototype is needed. This work uses one of these tools today available, Xilinx System Generator for DSP 1.1, to develop a transmitter and a reciever for a part of the wireless standard IEEE 802.11a. The work gives a description of the building blocks of the transmitter and the reciever but also some views on System Generator and descriptions of problems that were encountered during the work.</p>

Fused floating-point arithmetic units such as a floating-point fused Dot-Product (fused DP) and a floating-point fused Add-Subtract (fused AS) are employed for the implementation of the butterfly unit of the FFT due to their characteristics of low power and less area. In addition, the fused DP has less delay and lower error. Among the elements of the fused DP, two internal mantissa multipliers occupy the largest area and consume the largest power. A Multiple-Constant Multiplier (MCM) architecture has high speed, low power consumption, and small area compared to a conventional multiplier. The MCM is used for the internal mantissa multiplier, providing a solution for low power and high performance. Despite the benefits of the MCM, it lacks precision compared to a conventional multiplier. Due to this, the butterfly unit using the MCM has higher error. In this report, a new architecture of the butterfly unit has been designed by merging conventional MCMs. The new architecture provides two options. It either reduces the error or it lowers the power compared to a conventional MCM butterfly unit. / text

Une technique de corrélation d'images numériques (DIC) a été adaptée à l'étuded'échantillons de glace polycristalline colonnaire, afin de caractériser le développementdes hétérogénéités de déformation à une échelle intragranulaire au cours du fluage transitoireen compression. Ces hétérogénéités sont dues à la grande anisotropie viscoplastiquedu cristal de glace (avec un seul plan de glissement facile pour les dislocations), qui estresponsable d'interactions fortes entre les grains voisins lorsque l'échantillon se déforme,et de la mise en place de fortes contraintes internes. L'orientation particulière des plans deglissement et la structure colonnaire des échantillons, sans gradient de microstructure dansl'épaisseur, permet de considérer la déformation plastique essentiellement dans le plan.Les champs de déformation mesurés en surface peuvent donc être considérés en premièreapproximation comme représentatifs de tout le volume de l'échantillon. Les orientationscristallographiques, et désorientations locales à l'échelle intragranulaire, ont également étémesurées avec un analyseur optique de texture, avant et après déformation.De très fortes localisations de la déformation sont mises en évidence par la DIC;les déformations équivalentes locales peuvent atteindre plus de dix fois la valeur macroscopique.La structure des motifs de localisation évolue peu durant le régime de fluagetransitoire et elle est caractérisée par des bandes de localisation qui traversent l'échantillonobliquement, sur des distances allant jusqu'à dix fois la taille des grains. La corrélationentre le facteur de Schmid du plan de glissement d'un grain et sa déformation locale esttrès faible : l'agencement local des grains et les interactions intergranulaires jouent doncun rôle primordial dans la distribution spatiale des déformations. A l'échelle du grain, lesfortes désorientations de réseau ont été associées aux composantes locales du déplacement.On a montré en particulier que les distorsions sous forme de "bandes en genou" (ou kinkbands) étaient corrélées à un déplacement le long de l'axe c du grain, mesuré par DIC.Les microstructures expérimentales ont été implémentées dans un modèle plein champFFT qui simule le comportement élasto-viscoplastique des polycristaux (code CraFT).Les champs de déformation simulés présentent globalement les mêmes caractéristiquesque les champs expérimentaux. En particulier, la majorité des zones de localisation dela déformation sont bien reproduites, spatialement et en intensité. Cependant, il n'a pasété possible de reproduire le comportement macroscopique des échantillons à la décharge.La déformation retardée effective est d'un ordre de grandeur inférieure à celle mesuréeexpérimentalement. Il est probable que cette limitation soit liée à l'e↵et du champ descontraintes internes, généré par la structure des champs de dislocations, et qui n'a pas étépris en compte dans la loi de comportement.