Widespread compact fluorescent lamp evaluations in 50 Hz electrical network

Rapid development in electrical technology has imposed strong challenges to modern power system. Power quality has become a great concern due to proliferation of power electronic technology in modern electrical loads. Specifically for lighting load such as compact fluorescent lamps (CFLs), one of the concerning issues is harmonics. CFL is a cost-competitive and energy efficient compared to incandescent lamp. Inevitably, CFL produces harmonics current due to nonlinearity behaviour of the electronic ballast circuit. This paper presents a study on the widespread installation of CFL lamps in electrical power network. Initially, the harmonic current characteristics of local-branded CFL was identified from laboratory measurement. Then, a simulated CFL model was developed in MATLAB/Simulink to replicate the identified characteristics. The same step was repeated for other two different brands where eventually all models were embedded into a distribution network. The results show that at low voltage level, with installation more than 50 units for each type of CFL, the harmonic voltage distortion exceeded the 8% total harmonic distortion (THD) limit as stipulated in EN50160 standard. However, at higher voltage, the amount of THD decreased to average 0.94% and further down to average 0.28% at small transmission voltage level

Characterizing the Effective Bandwidth of Nonlinear Vibratory Energy Harvesters Possessing Multiple Stable Equilibria

In the last few years, advances in micro-fabrication technologies have lead to the development of low-power electronic devices spanning critical fields related to sensing, data transmission, and medical implants. Unfortunately, effective utilization of these devices is currently hindered by their reliance on batteries. In many of these applications, batteries may not be a viable choice as they have a fixed storage capacity and need to be constantly replaced or recharged. In light of such challenges, several novel concepts for micro-power generation have been recently introduced to harness, otherwise, wasted ambient energy from the environment and maintain these low-power devices. Vibratory energy harvesting is one such concept which has received significant attention in recent years. While linear vibratory energy harvesters have been well studied in the literature and their performance metrics have been established, recent research has focused on deliberate introduction of stiffness nonlinearities into the design of these devices. It has been shown that, nonlinear energy harvesters have a wider steady-state frequency bandwidth as compared to their linear counterparts, leading to the premise that they can used to improve performance, and decrease sensitivity to variations in the design and excitation parameters. This dissertation aims to investigate this premise by developing an analytical framework to study the influence of stiffness nonlinearities on the performance and effective bandwidth of nonlinear vibratory energy harvesters. To achieve this goal, the dissertation is divided into three parts. The first part investigates the performance of bi-stable energy harvesters possessing a symmetric quartic potential energy function under harmonic excitations and carries out a detailed analysis to define their effective frequency bandwidth. The second part investigates the relative performance of mono- and bi-stable energy harvesters under optimal electric loading conditions. The third part investigates the response and performance of tri-stable energy harvesters possessing a symmetric hexic potential function under harmonic excitations and provides a detailed analysis to approximate their effective frequency bandwidth. As a platform to achieve these objectives, a piezoelectric nonlinear energy harvester consisting of a uni-morph cantilever beam is considered. Stiffness nonlinearities are introduced into the harvester’s design by applying a static magnetic field near the tip of the beam. Experimental studies performed on the proposed harvester are presented to validate some of the theoretical findings. Since nonlinear energy harvesters exhibit complex and non-unique responses, it is demonstrated that a careful choice of the design parameters namely, the shape of the potential function and the electromechanical coupling is necessary to widen their effective frequency bandwidth. Specifically, it is shown that, decreasing the electromechanical coupling and/or designing the potential energy function to have shallow wells, widens the effective frequency bandwidth for a given excitation level. However, this comes at the expense of the output power which decreases under these design conditions. It is also shown that the ratio between the mechanical period and time constant of the harvesting circuit has negligible influence on the effective frequency bandwidth but has considerable effect on the associated magnitude of the output power

Benchmarking in a rotating annulus: a comparative experimental and numerical study of baroclinic wave dynamics

The differentially heated rotating annulus is a widely studied tabletop-size laboratory model of the general mid-latitude atmospheric circulation. The two most relevant factors of cyclogenesis, namely rotation and meridional temperature gradient are quite well captured in this simple arrangement. The radial temperature difference in the cylindrical tank and its rotation rate can be set so that the isothermal surfaces in the bulk tilt, leading to the formation of baroclinic waves. The signatures of these waves at the free water surface have been analyzed via infrared thermography in a wide range of rotation rates (keeping the radial temperature difference constant) and under different initial conditions. In parallel to the laboratory experiments, five groups of the MetStr\"om collaboration have conducted numerical simulations in the same parameter regime using different approaches and solvers, and applying different initial conditions and perturbations. The experimentally and numerically obtained baroclinic wave patterns have been evaluated and compared in terms of their dominant wave modes, spatio-temporal variance properties and drift rates. Thus certain ``benchmarks'' have been created that can later be used as test cases for atmospheric numerical model validation

Optimal Roof Coverage and Identification of Potential Roof Problems in Underground Coal Mines Using LED Lighting

The popularity and implementation of light emitting diode (LED) lighting have increased drastically over recent years into both residential and industrial applications. However, due to MSHA permissibility requirements, LED lighting is not currently being fully utilized in underground coal mining. While previous research has focused on examining the benefits that LED lighting possesses over other common light sources, very few have been done to find the optimum configuration to illuminate underground excavations better for the safety of the miners. In this research, multiple experiments were conducted to evaluate the potential impacts LED lighting can have on underground mine safety. The optimal light setup that provided the most roof coverage was found to be between 5 and 7 feet of separation, which is similar to what is usually used on roof bolting machines. It was also determined that LED lighting performs well in terms of discontinuity identification compared to what is commonly used in underground coal mining. The results of this research will serve as a design parameter for lighting manufacturers to use. These tests were done to simulate possible lighting locations on a roof bolting machine, but the results can be employed for other underground equipment as well

A Time-linearized Navier-Stokes Solver for Annular Gas Seal Rotordynamic Analysis

A time-linearized CFD solver for analyzing rotordynamics of gas seals is presented offering an improvement over existing linearized CFD solvers. Previous linearized solvers required structured grids and axisymmetric domains, limiting the complexity of the geometries of the seals that could be analyzed. A preexisting, full-order, in-house CFD solver was available which operated on fully 3D and unstructured grids and was well suited for complex seal geometries. A linearized version of the in-house code is developed as a companion to the full-order solver, retaining its unstructured and fully 3D features. Furthermore, boundary conditions are developed for the linearized solver allowing it to take advantage of the geometric symmetries that were required by earlier linearized solvers without necessarily being limited to them. Additionally, a linearization procedure is presented which is general enough to be used for the many various features of the full-order solver. As the in-house code continues to be developed and new features are included, the same linearization procedure can be used to keep the companion code up to date. The full-order, in-house solver and the time-linearized companion code combine to become a powerful CFD-perturbation solver accessible to all complexities of seal geometries. This dissertation also presents an analytical formula that describes features of cavity flow as it pertains to annular gas seals in order to progress the fundamental understanding of the flow physics of roughened seals. An existing semi-empirical analytical formula, developed to describe the cavity flow of aircraft bomb bays, is modified using the full-order, in-house CFD solver. The numeric model is validated against experimental measurements and used to adjust empirical parameters of the formula to match cavity flow conditions unique to annular seals. The modified analytical formula is able to predict features of cavity flows found in annular gas seals better than existing formulae. Finally, the companion, time-linearized CFD solver is verified using two simple cases and the combined full-order and time-linearized CFD-perturbation solver is used to predict rotordynamic properties for two gas seal geometries. The first case used to verify the linearized solver is a channel flow with an oscillating back-pressure and the second is a stationary flow with an oscillating wall. The first gas seal case the combined CFD-perturbation solver is used for is a straight seal based on the High Pressure Oxidizer Turbopump (HPOTP) of the Space Shuttle Main Engine (SSME). The second is a stepped labyrinth seal. The rotordynamic predictions are compared with established bulk-flow models of the two cases and conclusions are presented

Wave modelling - the state of the art

This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered. The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, nonlinear interactions in deep water; 4, white-capping dissipation; 5, nonlinear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments

An immersed boundary method for particles and bubbles in magnetohydrodynamic flows

This thesis presents a numerical method for the phase-resolving simulation of rigid particles and deformable bubbles in viscous, magnetohydrodynamic flows. The presented approach features solid robustness and high numerical efficiency. The implementation is three-dimensional and fully parallel suiting the needs of modern high-performance computing. In addition to the steps towards magnetohydrodynamics, the thesis covers method development with respect to the immersed boundary method which can be summarized in simple words by From rigid spherical particles to deformable bubbles. The development comprises the extension of an existing immersed boundary method to non-spherical particles and very low particle-to-fluid density ratios. A detailed study is dedicated to the complex interaction of particle shape, wake and particle dynamics. Furthermore, the representation of deformable bubble shapes, i.e. the coupling of the bubble shape to the fluid loads, is accounted for. The topic of bubble interaction is surveyed including bubble collision and coalescence and a new coalescence model is introduced. The thesis contains applications of the method to simulations of the rise of a single bubble and a bubble chain in liquid metal with and without magnetic field highlighting the major effects of the field on the bubble dynamics and the flow field. The effect of bubble coalescence is quantified for two closely adjacent bubble chains. A framework for large-scale simulations with many bubbles is provided to study complex multiphase phenomena like bubble-turbulence interaction in an efficient manner

GAMER: a GPU-Accelerated Adaptive Mesh Refinement Code for Astrophysics

We present the newly developed code, GAMER (GPU-accelerated Adaptive MEsh Refinement code), which has adopted a novel approach to improve the performance of adaptive mesh refinement (AMR) astrophysical simulations by a large factor with the use of the graphic processing unit (GPU). The AMR implementation is based on a hierarchy of grid patches with an oct-tree data structure. We adopt a three-dimensional relaxing TVD scheme for the hydrodynamic solver, and a multi-level relaxation scheme for the Poisson solver. Both solvers have been implemented in GPU, by which hundreds of patches can be advanced in parallel. The computational overhead associated with the data transfer between CPU and GPU is carefully reduced by utilizing the capability of asynchronous memory copies in GPU, and the computing time of the ghost-zone values for each patch is made to diminish by overlapping it with the GPU computations. We demonstrate the accuracy of the code by performing several standard test problems in astrophysics. GAMER is a parallel code that can be run in a multi-GPU cluster system. We measure the performance of the code by performing purely-baryonic cosmological simulations in different hardware implementations, in which detailed timing analyses provide comparison between the computations with and without GPU(s) acceleration. Maximum speed-up factors of 12.19 and 10.47 are demonstrated using 1 GPU with 4096^3 effective resolution and 16 GPUs with 8192^3 effective resolution, respectively.Comment: 60 pages, 22 figures, 3 tables. More accuracy tests are included. Accepted for publication in ApJ

Development of a two dimensional stochastic methodology and a computer model to assess response to the nonlinear seismic wave propagation

Seismic wave propagation in spatially variable soil continuum can be described by partial differential equations (PDE) with stochastic coefficients. Typical method of analysis in this area is a spectral analysis approach, where time series is presented by a Fourier expansion or a Fourier integral transform. This approach has a limited capability being applicable to the linear problems only. The novelty of presented method is that it can handle any nonlinear elastic - plastic stochastic constitutive model. The output of the project is the 2D seismic random wave propagation model accounting for the spatial variability of soil properties, described by the linear and nonlinear constitutive models. This model allows accessing the seismic hazard of a region of interest with account of its specific geological and topographic features. Time dependent ground velocities, accelerations, stress components and pressure applied to the walls of an engineering structure (power plant) have been predicted to estimate the seismic lifeline hazard of engineering facilities. Nonlinear seismic wave propagations are simulated based on a dynamic two dimensional theory of mechanics of continuum with account of nonlinear Hencky-Nadai constitutive models. Boundary conditions relate to the acceleration profile given by accelerometer or seismometer, zero stress components at the ground surface, free surface conditions at the top and non-reflected (absorbed) boundary conditions at distal boundaries. This model describes heterogeneous spatially distributed ground soil properties, based on a set of nonlinear constitutive equations. Mathematical frame is presented by a coupled set of a nonlinear hyperbolic system of equations, with respect to three components of stress tensor and two components of a velocity vector. Analytical expressions for relating eigenvalues and eigen functions are found using MATLAB symbolic toolbox. The finite volume, characteristically based Total Variation Diminishing (TVD) method used to predict ground motion wave propagations parameters of interest in a time – space domain as a function of a seismic profile, distance, soil properties. Monte-Carlo simulations are used to model the probability of different outcomes in a process of seismic wave propagation

An appropriate index to assess the global cancellation level of the harmonic currents consumed by a set of single-phase uncontrolled rectifiers and a set of fluorescent lamps

An in-depth study of harmonic current reduction in European commercial buildings due to the harmonic cancellation effect when a set of single-phase uncontrolled rectifiers and a set of fluorescent lamps are connected at the same voltage level is essential, since both types of non-linear loads are very present in commercial and residential sectors. This paper provides an appropriate index to assess the global cancellation level of the harmonic currents for this study. The equivalent circuit per phase of the typical three-phase power system of European commercial installations is presented and simplified for the cancellation analysis of the harmonic currents consumed by a set of multiple identical single-phase uncontrolled rectifiers and a set of multiple identical fluorescent lamps connected at the same voltage level. The suitability and usefulness of the proposed index are shown by applying it to that analysis, which leads to some results of practical interest. This index can be generalized to any number of sets of multiple identical non-linear loads and can be applied in graphical and optimization studies that will allow a greater benefit from the harmonic cancellation effect to be obtained given the global nature of the index.Peer ReviewedPostprint (published version