In this dissertation, we discuss an adaptive angular discretization scheme for the neutral-particle transport equation in three dimensions. We mesh the direction domain by dividing the faces of a regular octahedron into equilateral triangles and projecting these onto “spherical triangles” on the surface of the sphere. We choose four quadrature points per triangle, and we define interpolating basis functions that are linear in the direction cosines. The quadrature point’s weight is the integral of the point’s linear discontinuous finite element (LDFE) basis function over its local triangle. Variations in the locations of the four points produce variations in the quadrature set. The new quadrature sets are amenable to local refinement and coarsening, and hence can be used with an adaptive algorithm. If local refinement is requested, we use the LDFE basis functions to build an approximate angular flux, interpolated, by interpolation through the existing four points on a given triangle. We use a transport sweep to find the actual values, calc, at certain test directions in the triangle and compare against interpolated at those directions. If the results are not within a userdefined tolerance, the test directions are added to the quadrature set. The performance of our uniform sets (no local refinement) is dramatically better than that of commonly used sets (level-symmetric (LS), Gauss-Chebyshev (GC) and variants) and comparable to that of the Abu-Shumays Quadruple Range (QR) sets. On simple problems, the QR sets and the new sets exhibit 4th-order convergence in the scalar flux as the directional mesh is refined, whereas the LS and GC sets exhibit 1.5-order and 2nd-order convergence, respectively. On difficult problems (near discontinuities in the direction domain along directions that are not perpendicular to coordinate axes), these convergence orders diminish and the new sets outperform the others. We remark that the new LDFE sets have strictly positive weights and that arbitrarily refined sets can be generated without the numerical difficulties that plague the generation of high-order QR sets. Adapted LDFE sets are more efficient than uniform LDFE sets only in difficult problems. This is due partly to the high accuracy of the uniform sets, partly to basing refinement decisions on purely local information, and partly to the difficulty of mapping among differently refined sets. These results are promising and suggest interesting future work that could lead to more accurate solutions, lower memory requirements, and faster solutions for many transport problems.

Abstract The dynamic models for different linear or nonlinear beam structures are proposed in this dissertation. The proposed mathematical model for a turbo-disk, which is valid for whatever isotropic or orthotropic turbo-blades with or without shrouds, accounts for the geometric pretwist and taper angles, and considers coupling effect among bending and torsion effect as well. The Kelvin-Voigt internal and external damping effects have been included in the formulation. The effect of fiber orientation on the natural frequencies of a fiber-reinforced orthotropic turbo-blade has also been investigated. The eigenvalue problems of a single pre-twisted taper-blade or a shrouded turbo-blade group are formulated by employing the differential quadrature method (DQM). The DQM is used to convert the partial differential equations of a tapered pre-twisted beam system into a discrete eigenvalue problem. The Chebyshev-Gauss- Lobatto sample point equation is used to select the sample points in these analyses. The effect of the number of sample points on the accuracy of the calculated natural frequencies has also been studied. The integrity and computational efficiency of the DQM in this problem will be demonstrated through a number of case studies. The effects of design parameters, i.e. Kelvin-Voigt internal and linear external damping coefficients, the fiber orientation, and the rotation speed on the dynamic behavior for a pretwisted turbo-blade are investigated. The dynamic response of a nonlinear electrode actuator used in the MEMS has also been formulated and analyzed by employing the proposed DQM algorithm. The transitional responses of the derived nonlinear systems are calculated by using the Wilson¡V method. Results indicated the curve shape of the electrode and the cantilever actuator may affect the pull-in behavior and the residual vibration of the electrostatic actuators significantly. Numerical results demonstrated the validity and the efficiency of the DQM in solving different type beam problems.

Reproduction de : Thèse de doctorat : Mathématiques : Faculté des sciences de Paris : 1868. / Titre provenant de la page de titre du document numérisé.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Wenbo Li, Dept. of Mathematical Sciences. Includes bibliographical references.

With the emergence of multi-standard and cognitive radios, the need for reconfigurable RF circuits increased. Such circuits require wide-band quadrature voltage controlled oscillators (QVCOs) to provide the local oscillator (LO) signal for up and down conversion. Wide-band QVCOs performance has lagged behind their narrowband VCO counterparts and numerous circuit techniques have been introduced to bridge the gap. This dissertation presents techniques that have been used to implement wide-band reconfigurable QVCOs with focus on dual-resonance based circuits. System and circuit analysis are performed to understand the tuning-range, phase noise, and power tradeoffs and to consider quadrature phase errors. An 8.8-15.0 GHz actively coupled QVCO and a 13.8-20GHz passively coupled QVCO are presented. Both oscillators employ dual-resonance to achieve extended tuning ranges. Impulse sensitivity functions were used to study the impact of different passive and active device noises on the overall phase noise performance of the dual-resonance oscillator and the actively and passively coupled quadrature oscillators. The quadrature phase error due to the different architecture parameters were investigated for the actively and passively coupled quadrature oscillators. The advantages of using switched capacitor tuning as a major part of passive tuning are identified, and the advantage of employing switches with large bandwidths, such as those associated with phase change materials, is mathematically quantified. Furthermore, a novel method for accurate off chip phase error measurement using discrete components and phase shifters that does not require calibration is introduced.

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In modern telecommunications, there is a need for quadrature oscillator exhibiting an accurate and stable phase relation. For example, identical two mutually coupled relaxation oscillator can generate identical quadrature signals, and have extremely accurate and stable phase relation. In this thesis, we propose a current cross-coupled relaxation oscillator with quadrature outputs. The oscillator consists of two identical current relaxation oscillators and a current comparator. The circuit takes the high frequency advantage of current mode circuit. Because of cross-coupled feedback, this oscillator have highly accurate ( <1¢X) and stable quadrature outputs. It is implemented by using TSMC 0.35£gm 2P4M CMOS technology.

Quadrature digital modulation techniques are widely used in modern communication systems because of their high performance and flexibility. However, these advantages come at the cost of high power consumption. As a result, power consumption has to be taken into account as a main design factor of the modulator.<p>In this thesis, a low-power quadrature digital modulator in 0.18um CMOS is presented with the target system clock speed of 150 MHz. The quadrature digital modulator consists of several key blocks: quadrature direct digital synthesizer (QDDS), pulse shaping filter, interpolation filter and inverse sinc filter. The design strategy is to investigate different implementations for each block and compare the power consumption of these implementations. Based on the comparison results, the implementation that consumes the lowest power will be chosen for each block. First of all, a novel low-power QDDS is proposed in the thesis. Power consumption estimation shows that it can save up to 60% of the power consumption at 150 MHz system clock frequency compared with one conventional design. Power consumption estimation results also show that using two pulse shaping blocks to process I/Q data, cascaded integrator comb (CIC) interpolation structure, and inverse sinc filter with modified canonic signed digit (MCSD) multiplication consume less power than alternative design choices. These low-power blocks are integrated together to achieve a low-power modulator. The power consumption estimation after layout shows that it only consumes about 95 mW at 150 MHz system clock rate, which is much lower than similar commercial products. <p>The designed modulator can provide a low-power solution for various quadrature modulators. It also has an output bandwidth from 0 to 75 MHz, configurable pulse shaping filters and interpolation filters, and an internal sin(x)/x correction filter.

Quadrature digital modulation techniques are widely used in modern communication systems because of their high performance and flexibility. However, these advantages come at the cost of high power consumption. As a result, power consumption has to be taken into account as a main design factor of the modulator.<p>In this thesis, a low-power quadrature digital modulator in 0.18um CMOS is presented with the target system clock speed of 150 MHz. The quadrature digital modulator consists of several key blocks: quadrature direct digital synthesizer (QDDS), pulse shaping filter, interpolation filter and inverse sinc filter. The design strategy is to investigate different implementations for each block and compare the power consumption of these implementations. Based on the comparison results, the implementation that consumes the lowest power will be chosen for each block. First of all, a novel low-power QDDS is proposed in the thesis. Power consumption estimation shows that it can save up to 60% of the power consumption at 150 MHz system clock frequency compared with one conventional design. Power consumption estimation results also show that using two pulse shaping blocks to process I/Q data, cascaded integrator comb (CIC) interpolation structure, and inverse sinc filter with modified canonic signed digit (MCSD) multiplication consume less power than alternative design choices. These low-power blocks are integrated together to achieve a low-power modulator. The power consumption estimation after layout shows that it only consumes about 95 mW at 150 MHz system clock rate, which is much lower than similar commercial products. <p>The designed modulator can provide a low-power solution for various quadrature modulators. It also has an output bandwidth from 0 to 75 MHz, configurable pulse shaping filters and interpolation filters, and an internal sin(x)/x correction filter.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 152-156). Also available via the Internet.