A combined finite element-state space modeling environment forinduction motors in the ABC frame of reference: the no-load condition

A combined finite element state-space modeling environment capable of predicting no-load induction motor performance is introduced. The authors focus on the model derivation and the no-load simulation. The model is based on the natural ABC frame of reference and includes full effects of discrete winding layouts, magnetic saturation, and space harmonics. The model does not require the existence of actual motor hardware. The method is totally flexible and allows the design engineer to answer what-if questions before any resources are committed to prototyping. The method was shown to produce motor parameter results which correlate very well with corresponding test data of an example 1.2 hp 200 V three-phase induction motor     

Effects of broken bars/end-ring connectors and airgapeccentricities on ohmic and core losses of induction motors in ASDsusing a coupled finite element-state space method

In this paper, effects of rotor abnormalities such as broken squirrel-cage bars, broken cage connectors and airgap eccentricity on ohmic and core losses of induction motors are presented. In this investigation, a comprehensive time-stepping coupled finite element-state space (TSCFE-SS) model was fully utilized to compute the time-domain elemental flux density waveforms and various time-domain waveforms of motor winding currents useful for core loss and ohmic loss computations. Such investigation is feasible by use of the TSCFE-SS model due to its intrinsic nature and characteristics. The results obtained from the simulations of an example 1.2-hp induction motor clearly indicate that faults due to broken squirrel-cage bars/end-connectors can increase motor core losses in comparison to the healthy case. The results also give the effect of saturation on the core loss distributions within the cross-section of the motor, and indicate the potential for possible excessive loss concentrations and consequent hot spots near zones of bar and connector breakages in the rotor     

城市能源消耗、环境负荷现状及其对策分析

能源是社会经济发展的基础 ,城市能源消耗对环境空气质量影响很大 ,也是改善整个大气环境质量的关键。本文综合分析了我国 18个城市能源消耗状况及其对环境空气质量的影响 ,针对以煤为主的能源结构 ,提出了运用高温气化和高温贫氧燃烧等煤的清洁利用技术 ,以减轻大气污染。     

On-line current monitoring and application of a finite elementmethod to predict the level of static airgap eccentricity in three-phaseinduction motors

The introduction reviews the real practical problems of airgap eccentricity in large 3-phase induction motors. On-line monitoring methods for diagnosing airgap eccentricity are also discussed and a state of the art review on the application of current monitoring to detect airgap eccentricity is presented. The limitations of the classical MMF and permeance wave approach for predicting the severity of airgap eccentricity are discussed. The time stepping finite element (FE) method and FFT analysis technique are used as `analyses tools' to predict the frequency components in the current (Hz and dB) as a function of static airgap eccentricity. Excellent agreement is obtained between the measured and predicted frequency components (Hz) in the current spectra which are a function of static eccentricity. The FE method is also used to predict the magnitude (dB) of these frequency components in the current spectrum with different levels of static airgap eccentricity. These predictions are much closer to the measured values in comparison to previous attempts using the classical MMF and permeance wave approach. The contents of this paper will be of particular interest to the manufacturers and industrial users of three-phase induction motors     

A combined approach for determining the thermal performance of radiant barriers under field conditions

This paper deals with a combined approach for assessing the thermal performance of radiant barriers under field conditions, based both on dynamic simulations and field measurements. The methodology involves the combination of model predictions and experimental results of a complex roof including a radiant barrier installed on a dedicated test cell. During the empirical validation of the building thermal model and more particularly thanks to the results of sensitivity analysis, simplifications of the model were made. These considerations lead to successive simplified versions of the model and finally a very simplified one, which is used to determine the thermal resistance of the complex roof. We first present the detailed thermal model, elaborated with a prototype of building simulation code. We then describe the experimental test cell and put the emphasis on the details of the roof. The simplification of the detailed model is then explained and the results presented. A value of the thermal resistance is finally obtained and confirms the potential of radiant barriers for a tropical climate.     

Analysis of a three-phase induction machine including time andspace harmonic effects: the a, b, c reference frame

This paper presents a mathematical modeling that uses the concept of harmonic inductances to derive voltage and torque equations of a three-phase induction machine using a, b, c and A, B, C formulation. Phase currents and electromagnetic torque are obtained by numerical integration of equations considering any supply voltage waveform. Two cases were studied-operation of induction motor supplied with sinusoidal waveform, and operation of an induction motor supplied by a three-phase inverter     

风力发电系统中组合风速的建模及仿真

在实验室进行风力发电系统模拟,风速模拟是其中重要的一个环节,正确的风速模型不仅可以反应风速实际变化情况,而且能给风力发电系统的模拟研究提供准确的参数。文章采用4分量组合风速模型,用Matlab/Simulink对组合风速进行建模仿真。仿真结果表明,该数学模型能够较精确地反映风速的实际突变性、渐变性及随机性等特点,适用于风力发电系统的模拟研究工作。     

A finite element analysis modeling tool for solid oxide fuel cell development: coupled electrochemistry, thermal and flow analysis in MARC

A 3D simulation tool for modeling solid oxide fuel cells is described. The tool combines the versatility and efficiency of a commercial finite element analysis code, MARC^®, with an in-house developed robust and flexible electrochemical (EC) module. Based upon characteristic parameters obtained experimentally and assigned by the user, the EC module calculates the current density distribution, heat generation, and fuel and oxidant species concentration, taking the temperature profile provided by MARC^® and operating conditions such as the fuel and oxidant flow rate and the total stack output voltage or current as the input. MARC^® performs flow and thermal analyses based on the initial and boundary thermal and flow conditions and the heat generation calculated by the EC module. The main coupling between MARC^® and EC is for MARC^® to supply the temperature field to EC and for EC to give the heat generation profile to MARC^®. The loosely coupled, iterative scheme is advantageous in terms of memory requirement, numerical stability and computational efficiency. The coupling is iterated to self-consistency for a steady-state solution. Sample results for steady states as well as the startup process for stacks with different flow designs are presented to illustrate the modeling capability and numerical performance characteristic of the simulation tool.     

Numerical simulation of the pressure drop and heat transfer of two phase slug flows in microtubes using moving frame of reference technique

Enhancement in heat transfer using two phase slug flow in microtubes and microchannels has encouraged researchers to focus on this topic as one of the potential methods for miniaturizing heat sinks and exchangers. Numerical simulation of two phase slug flow is time consuming, so some researchers conduct their numerical studies using the moving frame of reference technique for a unit cell consisting of only one slug, i.e. a single phase study, in order to accelerate the simulation process. Both single phase and two phase simulation methods have been performed in the present study and results have been compared. This shows to what extent the moving frame of reference assumption is valid in the case of two phase flow in hydrophilic microtubes when a thin liquid film exists around moving gas bubbles. The present comparison has been conducted for pressure drop and heat transfer for two thermal boundary conditions i.e. constant wall temperature and constant wall heat flux. It has been shown that the moving frame of reference method overpredicts pressure drop and heat transfer and possible reasons have been discussed. This also shows that in a slug flow with no film around bubbles more heat transfer could be achieved.     

Renewable energy and the environment in South Africa: A way forward

The need to mitigate the adverse environmental impacts of fossil fuel usage, the volatility of fuel prices and enhancement of national energy security, have largely driven a phenomenal growth, around the world, in renewable energy (RE) generation (particularly grid-connected), over the past two decades. The necessity to apply policy support instruments to promote the dissemination of these technologies is now a universally accepted norm. Different countries and societies depending on the prevailing socio-economic environment draft and apply their policy frameworks differently and debates abound as to which mechanisms should have been most suitable under which circumstance. Most of these debates, however, assume the existence of an intrinsic political environment in favour of the process. In South Africa the current political environment is not very conducive to the development of a sustainable RE industry. This paper explores some of the anomalies and barriers and suggests possible options for a way forward to a viable RE industry in the country.     

Heat transfer in HCCI multi-zone modeling: Validation of a new wall heat flux correlation under motoring conditions

The present study focuses on the development and a preliminary validation of a heat transfer model for the estimation of wall heat flux in HCCI engines via multi-zone modeling. The multi-zone model describes heat flow between zones and to the combustion chamber wall. Mass, species and enthalpy transfer, which affect the temperature field within the combustion chamber, are also considered between zones, accounting for the convective heat transfer terms. The multi-zone heat transfer model presented herein has been developed for HCCI combustion simulation and although it has been used in the past, its validation was based on cylinder pressure data under firing conditions. In the present study a more accurate validation of the model is conducted. This is achieved by comparing the multi-zone model heat loss rate predictions to the corresponding predictions of a validated CFD code. The cases examined correspond to actual motoring cases, against which the CFD code has been validated in a previous work. Moreover, a sensitivity analysis is presented, to assess the effect of the zone configuration, i.e. zone thickness and number, on the predicted heat loss rate and temperature profiles. In addition, a comparison is made between the results obtained from the proposed heat flux correlation and one in which the temperature gradient at the wall is approximated via finite differences.     

Assessment and recalibration of the Heliosat-2 method in global horizontal irradiance modeling over the desert environment of the UAE

Remote estimation of global horizontal irradiance (GHI) by Heliosat-2 model has been benchmarked against ground-based measurements in different locations. The obtained results have shown that the level of agreement between ground-based and model-based GHI values are location dependent. To our knowledge no similar studies have been carried out over the Arabian Peninsula. The unique climatic condition in the Peninsula, characterized by high concentrations of airborne dust particles and high humidity makes the region a particularly interesting case.In this study Heliosat-2 method was used to derive the ground surface GHI in the United Arab Emirates. Inputs to the model were monthly Linke turbidity factor normalized to an air mass of 2 and a cloud index derived from SEVIRI sensor onboard the European satellite Meteosat. The Linke turbidity factor was obtained from a ground network of seven stations distributed across the UAE. A SEVIRI-based technique was developed and used to derive cloud index from high-resolution visible channels. Ground surface GHI measurements were collected from four inland stations for a period ranging from mid-2007 to mid-2010. The obtained results show that the Heliosat-2 model underestimates the GHI. The obtained root mean square error (RMSE) and mean bias error (MBE) values ranged from 16.3% to 18.5% and ?13.6% to ?15.8%, respectively. A constant bias was observed between modeled and measured GHI throughout the four stations. To correct this bias, the empirical equation used in Heliosat-2 to estimate the clear sky diffuse horizontal irradiance (DHI_clear) was recalibrated. With the new DHI_clear empirical equation, the modified Heliosat-2 model becomes more adapted to desert and dusty environments such as that of the UAE. By applying the modified DHI_clear equation, the RMSE and MBE values dropped to 9.5–10.3% and ?1.2 to +0.8%, respectively.     

Modeling of end-use energy consumption in the residential sector: A review of modeling techniques

There is a growing interest in reducing energy consumption and the associated greenhouse gas emissions in every sector of the economy. The residential sector is a substantial consumer of energy in every country, and therefore a focus for energy consumption efforts. Since the energy consumption characteristics of the residential sector are complex and inter-related, comprehensive models are needed to assess the technoeconomic impacts of adopting energy efficiency and renewable energy technologies suitable for residential applications.The aim of this paper is to provide an up-to-date review of the various modeling techniques used for modeling residential sector energy consumption. Two distinct approaches are identified: top-down and bottom-up. The top-down approach treats the residential sector as an energy sink and is not concerned with individual end-uses. It utilizes historic aggregate energy values and regresses the energy consumption of the housing stock as a function of top-level variables such as macroeconomic indicators (e.g. gross domestic product, unemployment, and inflation), energy price, and general climate. The bottom-up approach extrapolates the estimated energy consumption of a representative set of individual houses to regional and national levels, and consists of two distinct methodologies: the statistical method and the engineering method.Each technique relies on different levels of input information, different calculation or simulation techniques, and provides results with different applicability. A critical review of each technique, focusing on the strengths, shortcomings and purposes, is provided along with a review of models reported in the literature.     

Thermal power generation and environment: A review of the Indian case

Thermal power has emerged as the major source of electric power in lndia over the years and is expected to rise further. The environmental effects of thermal power generation are becoming a major concern. A review of the status at present, in terms of regulations and their application in the power industry, is presented here.     

基于瑞利概率分布的风力发电系统中组合风速的改进及建模仿真

风速作为风力发电机组的输入信号,其模拟的正确性直接影响着整个风力发电系统的性能分析与研究。通常计算机仿真所得风速是通过对不同风速的简单组合而实现的某个地区及时间段的平均风速,仿真风速无法体现自然风的多样性。针对此问题,文章提出一种实现自然风的方法。依据某风电场风资源评估报告所给出的风频分布曲线,以瑞利分布规律随机配置各种风速信号,在Matlab/Simulink的运行环境下,仿真出改进的风速,使不同风速随机分配,并且在某个时间段内各种风速出现的概率符合瑞利概率分布。据此方法所得风速更加接近实际自然风,且涵盖从切入风速到切出风速范围内所有风速类型,对风力发电系统的性能分析与研究具有一定的实际意义。     

A low-carbon future: Spatial planning's role in enhancing technological innovation in the built environment

The scope of spatial planning activity includes issues of governance, corporate organisation, policy integration, statutory and regulatory frameworks, and technical analysis and design. The nature of its potential contribution to achieving low-carbon built environments will vary according to the resolution of tensions between pressures for leadership, consistent decision making and speed of change and the value placed on diversity, flexibility and innovation.     

考虑感应电动机稳定约束的城市综合能源系统暂态过程优化控制模型

针对由可再生能源或清洁能源供能的城市综合能源系统中的感应电动机,在多能源形式的供能和负荷波动及不确定性条件下的运行稳定性问题,提出了一种考虑综合能源系统中多种类可再生电源及多能源负荷协调的感应电动机临界转矩优化。首先建立含综合能源的电网广义负荷模型;其次基于戴维南等值电路对感应电动机负荷的外部网络进行等效;最后推导感应电动机转矩方程,进而提出城市电网感应电动机暂态过程优化方法。以某城市综合能源网为例,采用BPA软件建立城市综合能源系统等值模型,仿真结果验证了文章所提方法的有效性。     

The impact of growth, energy and financial development on the environment in China: A cointegration analysis

This article aims to investigate the impact of financial development, economic growth and energy consumption on environmental pollution in China from 1953 to 2006 using the Autoregressive Distributed Lag (ARDL) bounds testing procedure. The main objective is to examine the long run equilibrium relationship between financial development and environmental pollution. The results of the analysis reveal a negative sign for the coefficient of financial development, suggesting that financial development in China has not taken place at the expense of environmental pollution. On the contrary, it is found that financial development has led to a decrease in environmental pollution. It is concluded that carbon emissions are mainly determined by income, energy consumption and trade openness in the long run. Moreover, the findings confirm the existence of an Environmental Kuznets Curve in the case of China.     

Oxidation and combustion of the n-hexene isomers: A wide range kinetic modeling study

A detailed chemical kinetic mechanism has been developed to study the oxidation of the straight-chain isomers of hexene over a wide range of operating conditions. The main features of this detailed kinetic mechanism, which includes both high and low temperature reaction pathways, are presented and discussed with special emphasis on the main classes of reactions involved in alkene oxidation. Simulation results have been compared with experimental data over a wide range of operating conditions including shock tube, jet stirred reactor and rapid compression machine. The different reactivities of the three isomers have been successfully predicted by the model. Isomerization reactions of the hexenyl radicals were found to play a significant role in the chemistry and interactions of the three n-hexene isomers. A comparative reaction flux analysis is used to verify and discuss the fundamental role of the double bond position in the isomerization reactions of alkenyl radicals, as well as the impact of the allylic site in the low and high temperature mechanism of fuel oxidation.     

Corrosion resistance of stainless steel bipolar plates in a PEFC environment: A comprehensive study

Bipolar plate is a key component of Polymer Electrolyte Fuel Cell (PEFC) with several essential functions, and has to resist to harsh cell operating conditions. Usually made of graphite or carbon composite, this component is studied worldwide in order to develop a commercially viable alternative: different ways have been being investigated, and to date, stainless steel (SS) appears as a good candidate material, but corrosion issues hinder its general use. This paper offers a comprehensive study of parameters impacting SS plate material corrosion through ex situ electrochemical investigations. Impact of ageing under various conditions is reported and studied in terms of film structure, semiconductivity behaviour, and cation release, on as received 316L and 904L alloys, and also surface-treated by low-cost surface modifications.