Modeling, analysis, and experimentation of chaos in a switched reluctance drive system

In this brief, modeling, analysis, and experimentation of chaos in a switched reluctance (SR) drive system using voltage pulsewidth modulation are presented. Based on the proposed nonlinear flux linkage model of the SR drive system, the computation time to evaluate the Poincaré map and its Jacobian matrix can be significantly shortened. Moreover, the stability analysis of the fundamental operation is conducted, leading to determine the stable parameter ranges and hence to avoid the occurrence of chaos. Both computer simulation and experimental measurement are given to verify the theoretical modeling and analysis.published_or_final_versio

The wavelet-NARMAX representation : a hybrid model structure combining polynomial models with multiresolution wavelet decompositions

A new hybrid model structure combing polynomial models with multiresolution wavelet decompositions is introduced for nonlinear system identification. Polynomial models play an important role in approximation theory, and have been extensively used in linear and nonlinear system identification. Wavelet decompositions, in which the basis functions have the property of localization in both time and frequency, outperform many other approximation schemes and offer a flexible solution for approximating arbitrary functions. Although wavelet representations can approximate even severe nonlinearities in a given signal very well, the advantage of these representations can be lost when wavelets are used to capture linear or low-order nonlinear behaviour in a signal. In order to sufficiently utilise the global property of polynomials and the local property of wavelet representations simultaneously, in this study polynomial models and wavelet decompositions are combined together in a parallel structure to represent nonlinear input-output systems. As a special form of the NARMAX model, this hybrid model structure will be referred to as the WAvelet-NARMAX model, or simply WANARMAX. Generally, such a WANARMAX representation for an input-output system might involve a large number of basis functions and therefore a great number of model terms. Experience reveals that only a small number of these model terms are significant to the system output. A new fast orthogonal least squares algorithm, called the matching pursuit orthogonal least squares (MPOLS) algorithm, is also introduced in this study to determine which terms should be included in the final model

Intensified Arctic warming under greenhouse warming by vegetation–atmosphere–sea ice interaction

Observations and modeling studies indicate that enhanced vegetation activities over high latitudes under an elevated CO2 concentration accelerate surface warming by reducing the surface albedo. In this study, we suggest that vegetation-atmosphere-sea ice interactions over high latitudes can induce an additional amplification of Arctic warming. Our hypothesis is tested by a series of coupled vegetation-climate model simulations under 2xCO(2) environments. The increased vegetation activities over high latitudes under a 2xCO(2) condition induce additional surface warming and turbulent heat fluxes to the atmosphere, which are transported to the Arctic through the atmosphere. This causes additional sea-ice melting and upper-ocean warming during the warm season. As a consequence, the Arctic and high-latitude warming is greatly amplified in the following winter and spring, which further promotes vegetation activities the following year. We conclude that the vegetation-atmosphere-sea ice interaction gives rise to additional positive feedback of the Arctic amplification.open1188sciescopu

Analysis of chaos in current-mode-controlled dc drive systems

In this paper, chaotic behavior in current-mode-controlled dc drive systems has been analyzed. The key is to derive an iterative map that describes the nonlinear system dynamics. Analytical modeling of fundamental and subharmonic oscillations as well as their stability analysis are presented. The results show that the current-mode-controlled dc drive systems generally exhibit chaotic behavior. To avoid the occurrence of chaos, the stable ranges of various system parameters are determined. Both computer simulation and experimental measurement are given to verify the theoretical analysis.published_or_final_versio

Upper bound limit analysis of slope stability using rigid finite elements and nonlinear programming

In this paper, the development and application of a new upper bound limit method for two- and three-dimensional (2D and 3D) slope stability problems is presented. Rigid finite elements are used to construct a kinematically admissible velocity field. Kinematically admissible velocity discontinuities are permitted to occur at all inter-element boundaries. The proposed method formulates the slope stability problem as an optimization problem based on the upper bound theorem. The objective function for determination of the minimum value of the factor of safety has a number of unknowns that are subject to a set of linear and nonlinear equality constraints as well as linear inequality constraints. The objective function and constrain equations are derived from an energy-work balance equation, the Mohr-Coulomb failure (yield) criterion, an associated flow rule, and a number of boundary conditions. The objective function with constraints leads to a standard nonlinear programming problem, which can be solved by a sequential quadratic algorithm. A computer program has been developed for finding the factor of safety of a slope, which makes the present method simple to implement. Four typical 2D and 3D slope stability problems are selected from the literature and are analysed using the present method. The results of the present limit analysis are compared with those produced by other approaches reported in the literature.published_or_final_versio

Dynamic bifurcation in dc drives

Dynamic bifurcation as well as chaotic behavior in a fixed-frequency current-mode controlled dc chopper-fed dc motor drive system is presented. The key is to derive an iterative map that describes the nonlinear dynamics of the system operating in the continuous conduction mode. It illustrates that different bifurcation diagrams can be obtained by varying different system parameters. Analytical modeling of period-1 and hence period-p orbits as well as their stability analysis using the characteristic multipliers are also presented. Hence, those stable ranges of various system parameters can be determined. Moreover, chaotic behavior is quantified by evaluating the Lyapunov exponents. The proposed approach is so general that it can readily be applied to other current-mode dc drives.published_or_final_versio

求解弹性地基上四边自由板的功的互等定理法

2001-2002 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Acarbose: A New Option in the Treatment of Ulcerative Colitis by Increasing Hydrogen Production

Acarbose，which is clinically widely used to treat Type 2 Diabetes，is thought to act at the small intestine by competitively inhibiting enzymes that delay the release of glucose from complex carbohydrates, thereby specifically reducing post prandial glucose excursion. The major side-effect of treatment with acarbose, flatulence, occurs when undigested carbohydrates are fermented by colonic bacteria, resulting in considerable amount of hydrogen. We propose that enteric benefits of acarbose is partly attributable to be their ability to neutralise oxidative stress via increased production of H2 in the gastrointestinal tract. Therefore, symptoms of ulcerative colitis in human beings can be ameliorated by acarbose

Chaoization of switched reluctance motor drives

This paper presents a new technique for the chaoiztion of switched reluctance motor (SRM) drivers. Based on the chaotic modeling of SRM drives, effects of feedback controller gains on the stability of the rotor speed are investigated. In accordance, a control strategy combining piecewise proportional feedback and time-delayed feedback is proposed to produce bound-controllable oscillation around any specific rotor speed. To estimate the continuous influence of a certain control parameter, a Poincaré map sampling at every extreme points is constructed, then the bifurcation diagrams are drawn. Theoretical analysis and numerical simulation for a practical 12/8 motor driver are also given.published_or_final_versio

Subharmonics and chaos in switched reluctance motor drives

In this paper, the investigation of the nonlinear dynamics of an adjustable-speed switched reluctance motor (SRM) drive with voltage pulse width modulation (PWM) regulation is carried out. Nonlinear iterative mappings based on both nonlinear and approximately linear flux linkage models are derived, hence the corresponding subharmonic and chaotic behaviors are analyzed. Although both flux linkage models can produce similar results, the nonlinear one offers the merit of accuracy but with the sacrifice of computational time. Moreover, the bifurcation diagrams show that the system generally exhibits a period-doubling route to chaos.published_or_final_versio