Strict doubly ergodic infinite transformations

We give examples of rank-one transformations that are (weak) doubly ergodic and rigid (so all their Cartesian products are conservative), but with non-ergodic two-fold Cartesian product. We give conditions for rank-one infinite measure-preserving transformations to be (weak) doubly ergodic and for their k-fold Cartesian product to be conservative. We also show that a (weak) doubly ergodic nonsingular group action is ergodic with isometric coefficients, and that the latter strictly implies W-measurable sensitivity.     

Ergodicity of avalanche transformations

In this paper, we study dynamical systems of product type and some particular inducing scheme motivated by neural dynamics (called avalanche transformation). We derive the distribution of avalanche sizes and give sufficient conditions such that the avalanche transformation is ergodic. Moreover, we deduce a multivariate central limit theorem as a corollary.

In memoriam: Wenbo V. Li (1963–2013)     

A numerical model for induction heating processes coupling electromagnetism and thermomechanics

This paper presents a mathematical and numerical model developed for coupling the various physical phenomena (electromagnetic, thermal and mechanical) taking place in axisymmetrical induction heating processes. All three electromagnetic, thermal and mechanical models are time dependent and take full account of the electromagnetic and thermal non‐linear effect especially with magnetic materials. The electromagnetic problem is discretized and solved in the workpiece, air and inductors. The heat transfer equation and the mechanical equilibrium equations are solved in the workpiece only, both using a finite element method. The mechanical model can take into account thermoelastic–plastic behaviour for the part. The model has been successfully applied to several cases of induction heating. Comparisons between numerical and experimental results show an excellent agreement. Copyright © 2003 John Wiley & Sons, Ltd.     

High velocity linear induction launchers

Electromagnetic launchers (EMLs) have received great attention in the last decades because of their potential application to a variety of energy, transportation, space, and defense systems. Particularly, they can serve as kinetic weapons, such as ground-based and naval artillery, space-based anti-missile guns, Earth-to-Orbit launcher, and mass transportation. The main advantage is that EMLs can accelerate projectiles to hyper velocities, i.e. velocities greater than those achievable with conventional cannons. The Linear Induction Launcher (LIL) is an air-cored electromagnetic coil launcher operating on the principle of the induction motor. Polyphase excitation of the coils constituting the barrel is designed to create an electromagnetic wave packet, which travels with increasing velocity from the breech to the muzzle. The projectile is a hollow conducting cylinder (sleeve) carrying the payload within it. Relative motion (slip) of the wave packet with respect to the projectile induces azimuthal currents in the sleeve that interacts with the exciting magnetic field to produce both propulsive and centering forces. This paper deals with the design of a high velocity linear induction launcher with muzzle velocity up to 6000 m/s. It addresses the design specifications of the launcher and utilizing a projectile weighing 1 kg. In the paper, the design specifications with simulation results for the phase voltages, the currents, the velocity, and the temperature rise of the sleeve are presented.     

A rule induction approach to improve Monte Carlo system reliability assessment

A Decision Tree (DT) approach to build empirical models for use in Monte Carlo reliability evaluation is presented. The main idea is to develop an estimation algorithm, by training a model on a restricted data set, and replacing the Evaluation Function (EF) by a simpler calculation, which provides reasonably accurate model outputs. The proposed approach is illustrated with two systems of different size, represented by their equivalent networks. The robustness of the DT approach as an approximated method to replace the EF is also analysed. Excellent system reliability results are obtained by training a DT with a small amount of information.     

A FEM/BEM for axisymmetric electromagnetic and thermal modelling of induction furnaces

In this paper, we propose a numerical method to solve a mathematical model for axisymmetric induction furnaces used for melting materials like metals or silicon. A finite/boundary element method (FEM/BEM) is introduced to solve the eddy current problem giving the electromagnetic field. In order to solve the non‐linear heat transfer problem involving change of state, we use an enthalpy formulation and propose an iterative algorithm to solve the corresponding finite element approximation. Numerical results for an industrial induction heating system are presented. Copyright © 2006 John Wiley & Sons, Ltd.     

异步电机定子的振动与模态分析

准确计算异步电机定子的振动模态和固有频率是降低电机噪声和振动的基础。该文基于异步电机简化的物理模型,利用三维有限元软件,全面研究了异步电机定子的固有频率和振动模态。根据等效替换原理,利用多个离散的耦合单元体等效替换铁芯的有限元模型,有效的提高了定子的计算结果的准确度。在综合考虑散热筋、加强筋、底脚和铁芯叠片结构对定子固有频率计算结果准确度的影响后,使得该有限元模型的计算结果达到了很高的准确度。计算结果与实验结果进行了比较验证。     

On a famous problem of induction

Summary A Bayesian solution is provided to the problem of testing whether an entire finite population shows a certain characteristic, given that all the elements of a random sample are observed to have it. This is obtained as a direct application of existing theory and, it is argued, improves upon Jeffreys’s solution.      

吸气剂真空感应熔炼系统的改进

介绍降低吸气剂真空感应熔炼系统极限压力的措施和效果.     

Space and time harmonics related problems and their mitigation for position and speed sensorless slip-ring induction motor drives applications

There have been renewed interests in slip-ring induction machines due to their increasing use in both grid connected and stand-alone wind power generation schemes. Despite the squirrel cage induction generators’ advantages of being brushless, low-cost, needing less maintenance and having inherent overload protection, the biggest advantage of variable-speed wound rotor induction machines is in its doubled energy capture. Also in high power induction motor drives such as static Kramer drives or static Scherbius drives use of wound rotor induction motors is a must. Thus it becomes necessary to measure the speed of the machine for closed loop control for such high performance drives. Recently, a sensorless position and speed estimation scheme was proposed for wound rotor wind power generator. In this paper, the limitation of the scheme caused by space and time harmonics have been investigated. Simulation results have been presented to explain the mechanism of the space and time harmonics caused distortion of current. Experimental results showing the deterioration of speed detection scheme at light load for a slip-ring induction motor have been presented. Finally, improvements have been applied experimentally to obtain better speed estimation.     

Optimal design of flux observer in induction machines

Abstract

Flux estimation is essential in most advanced control schemes of induction machines like indirect field‐orientation control and feedback linearizing approach. In this paper, optimal control theory and Lyapunov stability analysis are applied to design the full‐order flux observer of induction machines. The observer refers only to measurable quantities which are composed of terminal voltages, currents and rotor speed. The time‐invariant and time‐varying portions of the error dynamics of the observer are minimized separately. The degree of relative stability of the observer can be prescribed at the beginning of the design and is independent of speed variations. In the presence of uncertainty in rotor resistance, a sufficient condition for the design with bounded estimation errors is derived and the resultant residual can be formulated explicitly. Results from computer simulations show that the method exhibits excellent convergent characteristics and robustness to rotor resistance uncertainty.     

Metallurgical evaluation of a five inch cylindrical induction melter

The metallurgical condition of a cylindrical induction melter (CIM) vessel was evaluated after approximately 375 h of operation over a two-year span at temperatures between 1400 to 1500 °C. Wall thinning and significant grain growth was observed in the lower portion of the conical section and the drain tube. No through-wall penetrations were found in the cylindrical and conical sections of the CIM vessel and only one leak site was identified in the drain tube. Failure of the drain tube was associated with localized over heating and creep. The observed degradation resulted from cumulative service at elevated temperature.^[1] A recommendation was made to implement a support for the conical section of the CIM and to increase the wall thickness of the drain tube. Thus, the possibility of drain tube misalignment in the induction coils and localized over heating will be minimized. In addition, the use of grain stabilized Pt/Rh alloy should be evaluated as a method to prevent grain growth.     

A simple approach to electronic charge induction in atomistic simulations

Summary A scheme is presented for periodically updating atom-centered partial charges due to changing local electric fields that arise during the course of a molecular simulation. The effects of electrostatic induction, due to polarization of the local electron density of bonded atom pairs, are realized through the approximation of the bond polarizability tensor as being cylindrically symmetric and directed along the bond axis, with negligible lateral polarizability. This simplification allows the reduction of polarization effects to a scalar bond polarization parameter, and subsequent partitioning of the local electron density into charge modifiers located at atom centers. The induced charges assigned to each atom are determined self-consistently. This simplification permits a reasonable approximation of both the magnitude and direction of molecular dipole moments and of molecular polarizabilities in the case of small-molecule fluorocarbons. The model is extended to the calculation of atom-centered partial atomic charges for two conformations of poly(vinylidenefluoride). The proposed method fits well into the framework of established atomistic simulation techniques based on Coulombic nonbonded atomic interactions.     

家用电磁灶线圈盘对热效率测试影响的研究

在电磁灶工作状态下,对标准锅以及水溶液的若干温度点分别监测,研究电磁灶线圈盘产生的电磁感应对标准锅以及容器中水的整个加热过程的影响,并运用GB 21456-2008《家用电磁灶能效限定值及能源效率等级》的测试方法计算家用电磁灶热效率值。试验结果表明:线圈盘的分布不均会导致电磁感应强度不均,从而会在标准锅锅体产生不同的温度场。感应磁场越强,局部温度就越高,感应磁场越弱,局部温度就越低。     

The differential induction machine: Theory and performance

This paper presents the theory and performance of a differential induction machine, which is a special type of induction machine having two shafts projected from the two ends of a single stator. Application of a differential load on the two shafts cause them to run at different speed as a motor, which permits true differential movement and thus can meet the requirements of a differential drive in an electric vehicle. The machine is also capable of regeneration in the differential mode. This paper presents the construction of the above machine and performance of the same based on experimental results from a laboratory prototype. The equivalent circuit of the motor has been presented and verified experimentally.     

基于多传感器融合的电喷汽油机过渡工况进气流速预测模型

为了解决车用汽油发动机工作在过渡工况时,进气状态变化大,空气流量传感器的滞后响应严重影响空燃比控制精度的问题,提出了一种基于多传感器融合的过渡工况进气流速的预测模型,建立了过渡工况进气流速预测的径向基神经网络的拓朴结构,以HL495Q电喷汽油机加减速工况实验数据进行离线训练,仿真结果表明该预测模型能准确地预测过渡工况的空气进气流速,为精确及时地测试汽油机空气进气流量提供了一种新的方法.     

A comparative analysis of outcome of carbide-tool holder quenching in various liquids upon induction brazing

The paper provides some results of prediction of hardness and hardened layer thickness of a 35KhGSA steel holder of carbide tool upon quenching in aqueous solution of salts and bases, in water, and in oils at various quenchant temperatures. Thermokinetic cooling paths of the holder surface points are shown to differ quantitatively and qualitatively between the first two quenchants and oils at room temperature. Numerical investigation of quenching in water at 100°C has revealed an abrupt increase, by a factor of 2–3, in the holder surface cooling rate as soon as the cooling curve enters the austenite-to-bainite phase transformation region. For the case of quenching in an aqueous solution of salts and bases a functional relation has been found between the thickness of the holder surface layer quenched to maximum hardness and the quenchant temperature.     

薄板焊接变形中频感应矫正技术

目前针对船舶上层建筑中的薄板焊接变形矫正主要采用火焰矫正法,但此种方法效率低、操作安全性差,且难以实现自动化.为了更好地实现薄钢板焊接变形感应热矫正的自动化控制,提高矫正过程的精度,本文采用COMSOL Multiphysics仿真软件对尺寸参数为1 000 mm×600 mm×6 mm的薄钢板进行多物理场非线性耦合模拟,采用数值仿真分析方法分析了感应热矫正中温度场分布及应力变形规律,探究电参数对温度场及矫正效果的影响,同时进行了船用薄钢板中频感应矫正试验.结果表明:线圈电流频率及电流强度的增加可以有效提高薄板温升速率,改善热矫正效果.综合考虑操作安全性、感应电源负载等因素,制定了薄板焊接变形感应热矫正的电参数选择方案:当电流强度为110~120 A,电流频率为7 kHz时,可以得到较好的加热与矫正效果。     

Optimal control of an induction heating process using automatic differentiation

We consider an optimal control problem arising in an induction heating process. The main difficulty is to obtain accurate and efficient derivatives of the discrete form of the cost function. In this work we use automatic differentiation. Unlike numerical differentiation based on finite differences, derivatives generated by automatic differentiation are free of truncation error. Numerical results show the performance of the method in terms of accuracy and computational efficiency. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis of the features of the measurement of the magnetization of hollow cylinders using an induction transducer

A formula for calculating the effect of the dimensions of a hollow cylinder of material with a high magnetic permeability on the fraction of the magnetic flux, closing through its inner cavity, is obtained. The influence of this effect on the results of a measurement of the magnetization of hollow cylinders of different length and wall thickness is analyzed. It is shown that it is necessary to take this into account in magnetic measurements. Translated from Izmeritel’naya Tekhnika, No. 4, pp. 47–50, April, 2009.