For a wave system of three dimension, produced by the interactions betw een two progressive gravity wave trains on the free water surface in uniform water depth, a perturbation expansion method with chain rule has been applied to obtain the third order solution, including the resonant and non-resonant cases In the resonant case, the growth of the induced resonant wave motion with time and its propagating time distance is displayed in the form of mathematics and figure clearly, by applying the transmission of the energy flux. As for verifying the accuracy of this paper, the third order solution is valid when the wave system is degenerated into a progressive gravity wave train on the free water surface and the standing waves respectively. Furthermore, the experimental results of Longuet-Higgins & Smith (1966) and McGoldrick et al.(1966) are cited to compare, presenting the analytical results in this paper are great agreements.

The field of high power density power supplies has received much attention in recent years. The area of the most concern is to increase the switching frequency so as to achieve a reduction in the power supply size. Such concern in high frequency power conversion units has led to many resonant structures (quasi, multi, and pseudo). In all resonant types, the power transfer from the source to the load is controlled by varying the ratio of operating to resonant frequencies. Every effort has been made to reduce the switching losses using zero voltage and/or zero current techniques. In contrast, little attention has been given to the area of the design of the magnetic components at high frequency operation. It is usually accepted that the weak point in further high frequency power supply design is in the magnetic devices ( transformer and inductor ). No accurate model of the transformer taking into account the high frequency range has been performed yet. It is well known that as the frequency increasess o the transformerm odel becomesm ore complicated,d ue to the complexity of the transformer element distribution, and the nature of frequency dependence of some of these elements. Indeed, work of this kind can take many directions, and the attempt here is to introduce a number of mathematics, analytical, numerical, and practical directions to model the transformer. The main factors affecting the high frequency performance are the eddy current losses, leakage flux and the effects due to the transformer elements, where the transformer is part of the resonant converter. Two dimensional transformer finite element modelling is used to examine different cases, including open and short circuit conditions. The frequency dependency of the winding resistance and leakage inductance is fully explained. The practical design of the transformer and testing is used to valididate the simulation results. These results are supported by the results obtained from the mathematical formulation. Special attention is given to reducing both copper losses and leakage in the windings. Three dimensional modelling of the high frequency transformer and the solution using a program solving the full set of Maxwell's equations is the original part of the present work. Frequency response characteristics are found and compared to that obtained from the test. Curves of these characteristics are used to predict a simplified transformer equivalent circuit. This circuit is used with the simulation of a full bridge series resonant converter, where all units ( switches, control, isolation, feedback, and transformer ) are represented by an equivalent circuit. The power supply operation and its behaviour in respect to the change with frequency of each of the transformer elements are examined. Two cases are considered through the simulation, when the operating frequency is above and when it is below the resonant tank frequency. The simulated results are validated by building a practical power supply. In addition, the numerical solution of modelling the transformer by an equivalent network is also introduced. The highest possible number of elements (R, L, and Q) are used, where all the elements are found using 2D FEM solution of both magnetostatic and electrostatic fields. This network is solved using the trapezoidal rule of integration and electric network theory. The examination of the influences of the distribution capacitances on the internal winding frequency response characteristic is carefully examined. The last work in the present research is focussed on finding a general model of an exact transformer equivalent circuit to cover the wide frequency range. The thesis is completed with a conclusion.

With rapid progress in microelectronics technology, high-performance Integrated Circuits (ICs) bring huge challenge to design the power supplies. Fast loop response is required to handle the high transient current of devices. Power solution size is demanded to reduce due to the size reduction of integrated circuits. The best way to meet these harsh requirements is to increase switching frequency of power supplies. Along with the benefits of increasing switching frequency, the power supplies will suffer from high switching loss and high gate charge loss as these losses are frequency dependant losses. This thesis investigates the best topology to minimize the switching loss. The Series-Parallel Resonant Converter (SPRC) with current-doubler is mainly analyzed for high frequency low voltage high current application. The advantages and disadvantages of SPRC with current-doubler are presented. A new adaptive synchronous rectifiers timing control scheme is also proposed. The proposed timing control scheme demonstrates it can minimize body diode conduction loss of synchronous rectifiers and therefore improve the efficiency of the converter. This thesis also proposes two families of new resonant gate drive circuits. The circuits recover a portion of gate drive energy that is total lost in conventional gate drive circuit. In addition to reducing gate charge loss, it also reduces the switching losses of the power switches. Detail operation principle, loss analysis and design guideline of the proposed drive circuits are provided. Simulation and experimental results are also presented. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-01-29 22:37:09.812

No description available.

Thesis (M.S. in Mechanical Engineering)--Washington State University. / Includes bibliographical references.

Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Masters) -- California Institute of Technology, 1939. / Title from home page (viewed 04/29/2010). Includes bibliographic references.

Note:

The study of acoustic resonance in fluid-filled piping systems with and without mean flow is important for the nuclear industry. For this industry, it is vital to understand the acoustic resonance in their systems; however, no comprehensive experimental benchmark data or accurate modeling tool exists for predicting such a phenomenon. The main goals of the current research are to create a new experimental data bank for the conditions not tested earlier using the configurations of straight lines and branches, and to evaluate the applicability of the linear wave solution using different damping methods and a computational fluid dynamic (CFD) code to simulate the acoustic resonance in fluid-filled piping systems. In this experimental study, data on resonant frequencies and resonant amplitudes are collected and analyzed for a frequency range of 20–500 Hz for straight and branched tubes by varying their wall thicknesses, materials, and branch configurations at different flow rates and outlet boundary conditions. To be closer to the nuclear industry medium, water is employed in our experiments, contrasting to the fact that most of the available experiments reported were with air at a much lower sonic velocity. I consider here, in particular, measurements at the end of closed branches, upstream, downstream, and at different locations of the main line, as well as the interactions of different sonic velocities along the main pipes. A small diameter is chosen for the branched experiments since the decrease in the width of the main line and the branches has a pronounced effect on the resonant amplitudes due to an increased interaction among the unsteady shear layers forming across the side branches. The experimental results show that there is a strong effect of turbulent flow, wall material, and wall thickness on resonant amplitudes at frequencies above ∼250 Hz. Numerical investigations are performed solving the one-dimensional (1D) linear wave equation with constant and frequency-dependent damping terms and a CFD code. Employing frequency-dependent damping methodologies shows improvement in terms of resonant amplitude prediction over constant volumetric drag method. Comparing the 1D and CFD results shows that the CFD solution yields better predictions. / February 2017

Improved transient performance and converter miniaturization are the major driving factors behind high frequency operation of switching power supplies. However, high speed operation is limited by topology, control, semiconductor, and packaging technologies. The inherent mitigation of switching loss in resonant converters makes them prime candidates for use when the limits of switching frequency are pushed. The goal of this thesis is to address two areas that practically limit the achievable switching frequency of resonant topologies. Traditional control methods based on single cycle response are impractical at high frequency; forcing the use of pulse density modulation (PDM) techniques. However, existing pulse density modulation strategies for resonant converters in dc/dc applications suffer from: • High semiconductor current stress. • Slow response and large filter size determined by the low modulating frequency. • Possibly operating at fractions of resonant cycles leading to switching loss; thereby limiting the modulating frequency. A series resonant converter with variable frequency PDM (VF-PDM) with integral resonant cycle control is presented to overcome the limitations of existing PDM techniques to enable efficient operation with high switching frequency and modulating frequency. The operation of the circuit is presented and analyzed, with a design procedure given to achieve fast transient performance, small filter size, and high efficiency across the load range with current stress comparable to conventional control techniques. It is shown that digital implementation of the controller can achieve favourable results with a clock frequency four times greater than the switching frequency. Driving the synchronous rectifiers is a considerable challenge in high current applications operating at high switching frequency. Resonant gate drivers with continuous inductor current experience excessive conduction loss, while discontinuous current drivers are subject to slow transitions and high peak current. Current source drivers suffer from high component count and increased conduction loss when applied to complementary switches. A dual-channel current source driver is presented as a means of driving two complementary switches. A single coupled inductor with discontinuous current facilitates low conduction loss by transferring charge between the MOSFET gates to reduce the number of semiconductors in the current path, and reducing the number of conduction intervals. The operation of the circuit is analyzed, and a design procedure based on minimization of the total synchronous rectifier loss is presented. Implementation of the digital logic to control the driver is discussed. Experimental results at megahertz operating frequencies are presented for both areas addressed to verify the theoretical results. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2012-09-09 20:43:56.997