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     

Numerical and experimental study of a looped travelling‐wave thermoacoustic electric generator for low‐grade heat recovery

Thermoacoustic technology has drawn increasing attention due to its advantages such as reliability and environmental benignity. Aiming at low‐grade heat recovery, we developed a travelling‐wave thermoacoustic electric generator consisting of a looped travelling‐wave thermoacoustic engine and a linear alternator. In order to explore the operating characteristics of the electric generator, we numerically analyzed the acoustic field characteristics with a modified model. The analysis shows that high acoustic impedance appears in all three stages, and the travelling‐wave component dominates the acoustic field of the loop, which is significant for both thermoacoustic conversion and acoustic power propagation. Furthermore, we also investigated the effects of external electric compliance, resistance, and hot end temperature on the output electric power, thermal‐electric efficiency, and other related parameters. In the experiments, a thermal‐electric efficiency of 3.7% with an output electric power of 24 W has been achieved, when the hot end temperature is 120°C. The relative Carnot efficiency can exceed 14% when the hot end temperature is between 120°C and 190°C. The promising results demonstrate the significant potential of thermoacoustic electric generation in low‐grade heat recovery.     

基于神经网络的输电线路行波故障测距方法

针对单端行波测距法难以区分故障点反射波和对端母线反射波的问题,提出一种利用神经网络非线性拟合能力实现故障定位的测距方法。首先利用相模变换获取故障反向行波,对反向行波进行小波模极大值变换;然后提取模极大值突变时刻和对应极性,从中选取3个有效时刻构成满足时差、波速与线路长度关系的一组"有效时差对";最终配合极性信息构造神经网络的输入样本,对网络进行训练和测试后,可利用该网络输出故障距离,从而实现故障定位。仿真结果表明,该方法适用性强,有较高的可靠性和精确度。     

Green–Naghdi type III viscous fluids

We investigate constitutive theory for a new type of thermoviscous fluid. Equations are derived which reduce to the classical heat conduction equation under Fourier’s law when the new parameters tend to zero. Basic solutions for parallel flows are found and a travelling wave analysis is presented.     

线性扩散波洪水演算方法的应用研究

求解了线性扩散波方程在自由下边界条件下的解析解,着重探讨了如何将扩散波解析解用于天然河道的洪水演算之中。利用运动差分解的数值扩散在一定条件下可以模拟扩散波物理扩散的概念,导出了一类推求扩散方程数值解的方法,据此建立了具有预见期的洪水演算方法,并将这 两种方法应用于两条天然河道,均得到了较高的计算精度。     

考虑行波效应的混凝土高坝系统地震分析与损伤评价

为研究地震动行波效应的影响,基于时程分析的数值方法,对国内某高坝系统在强震作用下的动力响应进行模拟,即引入等效三维一致粘弹性人工边界,推导了计入水流向行波效应的地震动输入公式,将等效荷载作用于人工边界对行波输入进行验证;考虑坝体和基岩材料非线性,结合与规范相统一的混凝土本构和能量等效性假设,推导出归一化混凝土本构与损伤因子的对应关系;模拟库水可压缩性和坝体伸缩横缝的开合非线性,以不耦合损伤变量的简化地震损伤评估方法进行安全评价。结果表明,上部坝肩和左、右侧边表孔顶部是抗震的薄弱部位,不考虑水流向行波效应对高坝抗震设计偏保守。     

Analytical derivation of a coupled-circuit model of a claw-polealternator with concentrated stator windings

A lumped-parameter coupled-circuit model of a claw-pole alternator is derived. To derive the model, analytical techniques are used to define a three-dimensional (3-D) Fourier-series representation of the airgap flux density. Included in the series expansion are the harmonics introduced by rotor saliency, concentrated stator windings, and stator slots. From the airgap flux density waveform, relatively simple closed-form expressions for the stator and rotor self- and mutual-inductances are obtained. The coupled-circuit model is implemented in the simulation of an alternator/rectifier system using a commercial state-model-based circuit analysis program. Comparisons with experimental results demonstrate the accuracy of the model in predicting both the steady-state and transient behavior of the machine     

End effect in linear induction and rotating electrical machines

The finite length of the iron core (stator) has a significant impact on the performance of linear induction machines (LIMs). The performance of a cylindrical symmetric linear induction machine (CSLIM) has been studied considering the impact of the finite stator length. The analytical procedure, originally developed for calculation of plane linear induction machines, has been modified to facilitate the analysis of CSLIM. The procedure is based on Fourier series expansions of the electromagnetic quantities and the air-gap length. This study further provides information on the effect of finite length of tooth in the direction of rotation in rotating electrical machines. As examples, the overheating of the stator core in a 500 MVA synchronous hydrogenerator and the detrimental impact of the end effect on a 506.5 MVA synchronous turbogenerator in a nuclear power station is described.     

The large scale electric power system as a distributed continuum

By modeling an electric power system of generators and transmissions lines as a continuum, a nonlinear partial differential equation is written which exhibits the travelling wave behavior that has been observed in experiments with synchronized phasor measurements. The fact that disturbances spread through the interconnected power system with a certain velocity of propagation is reasonable but not quantitatively well understood. The model relates the velocity of propagation to parameters in the distributed model. Numerical simulations of the continuum model are presented     

The performance improvement of a cascade thermoacoustic engine by adjusting the acoustic impedance in the regenerator

A novel cascade configuration consisting of one standing wave unit and one travelling wave unit arranged in series is studied in this paper. Theoretically, a straight‐line cascade engine provides an efficient energy conversion, reduces the difficulties of fabrication and allows no Gedeon streaming. In order to achieve such a powerful cascade thermoacoustic engine, the regenerator of the travelling wave unit must be operated in high impedance and travelling wave phasing region. Various techniques of phase adjustment by modifying the configurations and geometrical dimensions of the system are investigated both numerically and experimentally in order to adjust the position of the sweet spot as well as to promote the acoustic impedance in the regenerator. It is found that the effective tuning methods with less modification here are accomplished by changing the volume of down‐cavity and reducing the flow area of down‐resonator by inserting the pencil. The exploration also shows that the acoustic field in the system is quite sensitive to the effect of down‐resonator length. The performance of the proposed system is clearly improved after the phase‐adjustment schemes are completely implemented, in which the regenerator works within the sweep spot zone with high acoustic impedance. Copyright © 2016 John Wiley & Sons, Ltd.     

Incorporating the Effects of Magnetic Saturation in a Coupled-Circuit Model of a Claw–Pole Alternator

A method of representing the effects of magnetic saturation in a coupled-circuit model of a claw-pole alternator is presented. In the approach considered, the airgap flux density produced by each winding is expressed as a function of magnetic operating point. A challenge in the implementation is that the airgap flux densities consist of several significant harmonics, each of which changes at a distinct rate as iron saturates. Despite this complication, it is shown that relatively simple measurements can be used to determine model parameters. The model is implemented in the analysis of several alternator/rectifier systems using a commercial state-model-based circuit analysis program. Comparisons with experimental results over a wide range of speeds and operating conditions demonstrate its accuracy in predicting both the steady state and transient behavior of the systems.     

Existence of travelling waves in a diffusive vector disease model with distributed delay

This paper is concerned with a diffusive vector disease model with distributed delay. The existence of travelling wave front solutions connecting the zero equilibrium and the positive equilibrium is established by using an iterative technique and a nonstandard ordering for the set of profiles of the corresponding wave system recently developed by Wang, Li and Ruan (Travelling wave fronts in reactiondiffusion systems with spatio-temporal delays. J. Differential Equations 222 (2006), 185–232). The existence of travelling front solutions shows that there is a moving zone of transition from the disease free state to the infective state.     

Induction machine field orientation along airgap and stator flux

Airgap and stator flux field orientation control (FOC) methods are discussed as an alternative to the familiar rotor flux orientation approach. The principal motivation is the relative accessibility of the two alternative fluxes. Motor flux models are developed in a unified manner, and it is shown that inherent coupling between flux and torque exists in the stator and airgap models. Two decoupling methods are presented. Simulation results are given for an airgap oriented control; the performance approaches that of a rotor flux oriented drive     

Peristaltic transport in an asymmetric channel with heat transfer — A note

The problem of heat transfer for the motion of a viscous incompressible fluid induced by travelling sinusoidal waves has been analytically investigated for a two-dimensional asymmetrical channel. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The flow is investigated in a wave frame of reference moving with the velocity of the wave. The momentum and energy equations have been linearized under long-wavelength and low-Reynolds number assumptions and closed form expressions for temperature and coefficient of heat transfer have been derived. The effect of Hartmann number, Eckert number, width of the channel and phase angle on temperature and coefficient of heat transfer are discussed numerically and explained graphically.     

Minimum airgap flux linkage requirement for self-excitation instand-alone induction generators

A minimum airgap flux linkage is required for the self-excitation and stable operation of an isolated induction generator feeding an impedance load. With the aid of bifurcation theory, it is shown that the minimum airgap flux linkage requirement is the value at which the derivative of the magnetizing inductance with respect to the airgap flux linkage is zero. This minimum airgap flux linkage determines the minimum or maximum load impedance and minimum excitation capacitance requirements. This result is demonstrated using single-phase and three-phase induction generators     

Turbulent open channel flow with heat transfer subjected to the control of a spanwise travelling wave

Turbulent open channel flows with heat transfer subjected to the control of a spanwise travelling wave have been investigated by means of direct numerical simulation (DNS). The three-dimensional Navier–Stokes and energy equations are numerically solved using a fractional-step method. The spanwise travelling wave is induced by a body force that is confined within the viscous layer with its maximum at the bottom wall and decaying exponentially away from it. The objective of this study is to reveal the near-wall turbulence behaviours, the turbulent heat transfer, and thermal structures under the control of the spanwise travelling wave. Three typical frequencies of the spanwise travelling wave, i.e., high-, middle- and low-frequency, corresponding to the exciting periods at T⁺ = 25, 50 and 100, are investigated to reveal the dynamics of turbulent motions and heat transfer. The Prandtl number (Pr) varies from 1 up to 100. To elucidate the behaviours of turbulence statistics and heat transfer, some typical quantities, including the mean velocity, velocity and vorticity fluctuations, temperature and its fluctuation, turbulent heat fluxes, and the structures of the temperature fluctuation, are exhibited and analyzed.     

Discharge of a shock wave from an open end of a tube

IntroductionWhen a Pressure wave such as the shock waveprOPagates along a constant area straight tube andreaches at the open end, an impulsive wave is emittedOutward from the tube exit toward the surrounding areaand causes an impulsive noise laal a sonic boomproduced by a supersonic aircraft. Therefore, someauthors have investigated the discharge of a weakcompression wave from an open end in order to reducethe impulsive noise in relation to'the high speed railWaytUImel in the previous paped'…     

Existence of Travelling Wave Fronts for a Diffusive Vector Disease Model with Delay

In this paper, the existence of monotone travelling front solutions is established for a diffusive vector disease model with a discrete delay. We show that if the delay is sufficiently small, then there exists a travelling wave fronts for the delayed diffusive model connecting the zero equilibrium with the positive equilibrium. The approach used in this paper is the upper-lower solution technique and monotone iteration method for delayed reaction-diffusion systems. 2000 Mathematics Subject Classification. Primary 35K57; secondary 35R10, 92D30. This research was partially supported by the National Natural Science Foundation of China (10131050).     

Comparison between characterization and diagnosis of brokenbars/end-ring connectors and airgap eccentricities of induction motorsin ASDs using a coupled finite element-state space method

This paper describes how a rigorous and comprehensive time-stepping coupled finite element-state space (TSCPE-SS) modeling technique can be utilized in diagnostics and differentiation between induction motor rotor (cage) abnormalities of broken bars/connectors and airgap eccentricities. The model is used for the computation of time-domain performance characteristics, such as the stator phase current waveforms and developed torque profiles including these abnormalities. This is followed by analysis of the current waveforms and torque profiles using fast Fourier transform to obtain their corresponding frequency spectra. Comparison between the TSCFE-SS model's simulation results, which correlate very well with theoretical results, clearly illustrate that rotor bar and/or end-ring connector breakages can be distinguished from static and dynamic airgap eccentricities. This paper also gives an interesting comparison between the effects and implications of these various rotor abnormalities on machine parameters and performance characteristics. Furthermore, the results indicate that frequency components reported earlier to be produced only by the combined effects of static and dynamic airgap eccentricity could be observed in case of either static or dynamic eccentricity. Finally, this paper demonstrates the possible opportunities that can be made use of in noninvasive detection of airgap eccentricities via TSCFE-SS and current signature techniques