UNBALANCE RESPONSE AND TOUCH-RUBBING THRESHOLD SPEED OF ROTOR SUBJECTED TO NONLINEAR MAGNETIC FORCES

Because of the effect of unbalance excitation and nonlinear magnetic force, the large vibration of the rotor supported by active magnetic bearing（AMB） will go beyond the radial gap of the bearing, even causing mechanical touch-rubbing when the system works at an operational speed closer to the critical speed. In order to investigate this problem, the linear model and nonlinear model of the single mass symmetric rigid rotor system supported by AMB are established respectively and the corresponding transfer functions of close-loop system are given. To pass through the numerical calculation by using MATLAB/Simulink, the effect of both the unbalance response and threshold speed of touch-rubbing of the system subjected to nonlinear magnetic forces and nonlinear output current of power amplifier are studied. Furthermore, threshold speed of touch-rubbing of the rotor-bearing system is defined and the results of numerical simulation are presented. Finally, based on above studies, two methods of increasing the touch-rubbing threshold speed are discussed.

Influence of High-Speed Milling Process on Mechanical and Microstructural Properties of Ultrafine Grained Profiles Produced by Linear Flow Splitting

The effects of milling parameters on the surface quality,microstructures and mechanical properties of machined parts with ultrafine grained(UFG)gradient microstructures are investigated.The effects of the cutting speed,feed per tooth,cutting tool geometry and cooling strategy are demonstrated.It has been found that the surface quality of machined grooves can be improved by increasing the cutting speed.However,cryogenic cooling with CO_2 exhibits no significant improvement of surface quality.Microstructure and hardness investigations revealed similar microstructure and hardness variations near the machined groove walls for both utilized tool geometries.Therefore,cryogenic cooling can decrease more far-ranging hardness reductions due to high process temperatures,especially in the UFG regions of the machined parts,whilst it cannot prevent the drop in hardness directly at the groove walls.

Virtual Speed Sensorless Desired Control Strategy of Maglev Single-sided Linear Induction Motors

单边短初级长次级直线感应电机己普遍应用于低速磁悬浮的驱动系统。由于在动态纵向边端效应影响下等效电路不对称，单边直线感应电机（single-sided linear inductionmotor，SLIM）的一些参数非线性变化。传统的应用于旋转电机的无速度传感器方法不再适用。首先分析了SLIM的M／T轴等效电路，选择次级磁链作为速度观测器状态变量。根据李雅普诺夫系统稳定性判据，推导出适用于SLIM的无速度传感器辨识；然后，采用反馈广义积分观测器控制稳态辨识速度的双幅脉振幅值；引入虚拟期望变量（virtualdesiredvariable，VDV）法，利用估算速度参与SLIM的恒滑差频率矢量控制。仿真与实验对所提控制算法的有效性和实用性进行了验证，所得结论可为磁悬浮的无速度传感器控制提供参考。

THE NEW SUPER-HIGH-SPEED DIGITAL CIRCUIT BASED ON LINEAR AND-OR GATES

The paper reveals the relation between the linear AND-OR gate and the emitter function logic. With theoretic calculation and PSPICE simulation, the paper proves that the linear AND-OR gates can work at super-high-speed and can be multi-cascaded. On the basis of analyzing the high-speed switch units which coordinate with linear AND-OR gates, two kinds of emitter coupled logic circuits are designed. The paper also discusses the design principles of super-high-speed digital circuits, and some examples of combinational and sequential circuits using linear AND-OR gate are given.

Evaluating Traffic Congestion Using the Traffic Occupancy and Speed Distribution Relationship: An Application of Bayesian Dirichlet Process Mixtures of Generalized Linear Model

Accurate classification and prediction of future traffic conditions are essential for developing effective strategies for congestion mitigation on the highway systems. Speed distribution is one of the traffic stream parameters, which has been used to quantify the traffic conditions. Previous studies have shown that multi-modal probability distribution of speeds gives excellent results when simultaneously evaluating congested and free-flow traffic conditions. However, most of these previous analytical studies do not incorporate the influencing factors in characterizing these conditions. This study evaluates the impact of traffic occupancy on the multi-state speed distribution using the Bayesian Dirichlet Process Mixtures of Generalized Linear Models (DPM-GLM). Further, the study estimates the speed cut-point values of traffic states, which separate them into homogeneous groups using Bayesian change-point detection (BCD) technique. The study used 2015 archived one-year traffic data collected on Florida’s Interstate 295 freeway corridor. Information criteria results revealed three traffic states, which were identified as free-flow, transitional flow condition (congestion onset/offset), and the congested condition. The findings of the DPM-GLM indicated that in all estimated states, the traffic speed decreases when traffic occupancy increases. Comparison of the influence of traffic occupancy between traffic states showed that traffic occupancy has more impact on the free-flow and the congested state than on the transitional flow condition. With respect to estimating the threshold speed value, the results of the BCD model revealed promising findings in characterizing levels of traffic congestion.

Influences of aerodynamic loads on hunting stability of high-speed railway vehicles and parameter studies

The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study.A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads：the aerodynamic loads can change the position of vehicle system（consequently the contact relations）,the wheel/rail normal contact forces,the gravitational restoring forces/moments and the creep forces/moments.A mathematical model for hunting stability incorporating such influences was developed.A computer program capable of incorporating the effects of aerodynamic loads based on the model was written,and the critical speeds were calculated using this program.The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method,the results were also compared with the situations without aerodynamic loads.It is shown that the most dominant factors a ff ecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not.The damping of yaw damper is the most dominant influencing factor for linear critical speeds,while the damping of lateral damper is most dominant for nonlinear ones.When the influences of aerodynamic loads are considered,the linear critical speeds decrease with the rise of cross wind velocity,whereas it is not the case for the nonlinear critical speeds.The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads.Combined actions of aerodynamic loads and suspension parameters also a ff ect the critical speeds.The effects of such joint action are more obvious for nonlinear critical speeds.

Investigation of Surface Roughness in High-Speed Milling of Aeronautical Aluminum Alloy

An approach is presented to optimize the surface roughness in high-speed finish milling of 7050- T7451 aeronautical aluminum alloy. In view of this, the multi-linear regression model for surface roughness has been developed in terms of slenderness ratio, cutting speed, radial depth-of-cut and feed per tooth by means of orthogonal experimental design. Variance analyses were applied to check the adequacy of the predictive model and the significances of the independent input parameters. Response contours of surface roughness were generated by using response surface methodology （RSM）. From these contours, it was possible to select an optimum combination of cutting parameters that improves machining efficiency without increasing the surface roughness.

A HIGH VELOCITY FEED UNIT DRIVEN BY LINEAR MOTOR

In order to realize high speed machining, the special requirements for feed transmission system of the CNC machine tool have to be satisfied. A high velocity feed unit driven by a induction linear motor is developed. The compositions of the high velocity CNC feed unit and main problems in the unit design are discussed.

A Study on the Dynamic Behavior of Wheel-Type Train Propelled by Superconducting Linear Synchronous Motor

This paper deals with a study on the dynamic behavior of 600 km/h wheel-type train propelled by superconducting linear synchronous motor (LSM). This train is of a traditional wheel-on-rail type with traction motors on wheel-bogies. However, for the 600 km/h speed, on the both sides of each vehicle, superconducting LSMs are attached and the ground coils are installed on the guideway. In this case, the guideway irregularities act as disturbance to the vehicle causing deterioration of ride comfort. And besides thrust force, the normal force could be created in superconducting LSM control, which influences vehicle dynamics during running. In this study, to examine the effect of guideway irregularity and normal force on dynamic behavior of proposed train, the vehicle dynamic model is driven and frequency analysis is performed through simulation. The simulation results show that the lateral directional acceleration is mainly influential to ride comfort;however this could be reduced effectively by electromagnetic damping force from linear generator. It is also shown that the normal force effect from superconducting LSM control is limited even though the attractive normal force acts favorably to ride comfort.

Travelling Wave Solution of the Fisher-Kolmogorov Equation with Non-Linear Diffusion

In this paper we study one-dimensional Fisher-Kolmogorov equation with density dependent non-linear diffusion. We choose the diffusion as a function of cell density such that it is high in highly cell populated areas and it is small in the regions of fewer cells. The Fisher equation with non-linear diffusion is known as modified Fisher equation. We study the travelling wave solution of modified Fisher equation and find the approximation of minimum wave speed analytically, by using the eigenvalues of the stationary states, and numerically by using COMSOL (a commercial finite element solver). The results reveal that the minimum wave speed depends on the parameter values involved in the model. We observe that when diffusion is moderately non-linear, the eigenvalue method correctly predicts the minimum wave speed in our numerical calculations, but when diffusion is strongly non-linear the eigenvalues method gives the wrong answer.

Prediction of Wind Speed Using a Hybrid Regression-Optimization Approach

Predicting wind speed is a complex task that involves analyzing various meteorological factors such as temperature, humidity, atmospheric pressure, and topography. There are different approaches that can be used to predict wind speed, and a hybrid optimization approach is one of them. In this paper, the hybrid optimization approach combines a multiple linear regression approach with an optimization technique to achieve better results. In the context of wind speed prediction, this hybrid optimization approach can be used to improve the accuracy of existing prediction models. Here, a Grey Wolf Optimizer based Wind Speed Prediction (GWO-WSP) method is proposed. This approach is tested on the 2016, 2017, 2018, and 2019 Raw Data files from the Great Lakes Environmental Research Laboratories and the National Oceanic and Atmospheric Administration’s (GLERL-NOAA) Chicago Metadata Archive. The test results show that the implementation is successful and the approach yields accurate and feasible results. The computation time for execution of the algorithm is also superior compared to the existing methods in literature.

Robust output feedback cruise control for high-speed train movement with uncertain parameters

In this paper, the robust output feedback cruise control for high-speed train movement with uncertain parameters is investigated. The dynamic of a high-speed train is modeled by a cascade of cars connected by flexible couplers, which is subject to rolling mechanical resistance, aerodynamic drag and wind gust. Based on Lyapunov＇s stability theory, the sufficient condition for the existence of the robust output feedback cruise control law is given in terms of linear matrix inequalities（LMIs）, under which the high-speed train tracks the desired speed, the relative spring displacement between the two neighboring cars is stable at the equilibrium state, and meanwhile a small prescribed H∞ disturbance attenuation level is guaranteed. One numerical example is given to illustrate the effectiveness of the proposed methods.

Reconstructing Sound Speed Profiles with Sea Surface Data

Ocean sound speed profile(SSP) is the key factor affecting acoustic propagation. The acquisition of SSPsin real time with high precision is meaningful for underwater activities. By means of the remote sensing method, thesea surface data could be obtained in near-real time. Typically, the subsurface fields are correlated with the sea surfaceparameters. Thus, the SSPs could be obtained by means of satellite remote sensing. In this paper, the history as wellas the current research over the reconstruction of subsurface fields by means of sea surface data is introduced. Thentwo methods to reconstruct the SSPs with sea surface data, including the linear regression method using the empiricalorthogonal function, and the self-organizing method based on the big data theory, are described in detail in the paper.

基于一阶线性自抗扰控制器的同步磁阻电机无速度传感器控制

同步磁阻电机在实现无速度传感器控制时出现交叉耦合效应,导致dq轴电感随着电流发生非线性变化,转速环使用传统PI控制器已无法满足系统较强的抗扰性能和较高的转子位置估计精度。为了改善此问题,该文提出一阶线性自抗扰控制器的同步磁阻电机无速度传感器控制策略,利用其机械运动状态方程,将同步磁阻电机的交叉耦合效应及负载扰动变化视为扰动。首先通过扩张状态观测器对负载扰动快速观测并进行前馈补偿,以此来提高系统抗扰性;其次利用静止实验法,得到dq轴磁链与电流的非线性函数模型,将该模型运用至磁链观测器中,以减小交叉耦合效应,提高转子位置估计精度;最后在1.5 kW的同步磁阻电机对拖加载实验平台上进行实验,验证了该控制方案的有效性。

基于扩展卡尔曼滤波的直线感应电机速度观测

为解决在直线感应电机(linear induction motor,LIM)高性能闭环控制系统取消速度传感器后,速度闭环中缺少速度反馈信息问题,在考虑LIM边端效应前提下,实现了一种基于扩展卡尔曼滤波算法的速度观测器。首先,基于考虑边端效应的三相LIM数学模型,推导出具有合适增益和协方差更新矩阵的扩展卡尔曼滤波观测器,并基于LIM的矢量控制系统,将观测器辨识的速度参数反馈到速度闭环系统中。然后,在Simulink中搭建带有速度观测器的LIM矢量控制系统模型,对观测器的辨识速度和电机实际速度进行对比。结果表明,利用辨识速度进行闭环控制可以保证系统稳定运行。在3种负载情况下,观测器的预测速度和实际速度之间的误差在0.51%~2.34%之间。对系统多种动态性能进行分析可知,基于扩展卡尔曼滤波观测器的LIM矢量控制系统,随着负载增大,预测速度的误差增大,推力误差减小,磁链幅值误差略微增大。因此,在考虑边端效应情况下,基于扩展卡尔曼滤波的观测器可以代替速度传感器实现空载和带载时的三相LIM控制。

基于短期观测记录的重现期风速预测

在偏僻地区或山区建设重要建筑物、构筑物或桥梁时,通常在附近安装风速观测仪器,获得至少1年的短期风速记录。提出了根据短期风速记录预测指定重现期风速极值及风压方法,为结构抗风设计提供了科学依据。提出独立风暴法提取短期风速记录的最大值,建立极值I型概率分布模型,采用最好线性无偏估计方法确定概率分布参数。依据短期风速最大值概率与年风速最大值概率的变换关系,建立年发生最大值的概率分布及重现期风速、风压的表达式。算例结果表明,重现期风速预测值的离散性与风速阈值有关,在预测值离散系数较小的情况下可确定重现期风速及其置信区间。

An Adaptive Howling Canceller Using 2-Tap Linear Predictor

This paper proposes an adaptive howling canceller using notch filter and 2-tap linear predictor, where howling consists of a single sinusoidal signal whose magnitude is much greater than other frequency’s magnitudes. The employed 2-tap linear predictor can quickly detect howling due to its high convergence speed. Although the output signal of the 2-tap linear predictor cannot be directly used as one of a howling canceller, we can obtain the frequency of howling from the filter coefficient. We utilize the filter coefficient of the 2-tap linear predictor to design a notch filter which achieves a very narrow elimination band. The designed notch filter removes only howling and retains other desired signals. Simulation results show that the proposed adaptive howling canceller can quickly detect and effectively remove howling.

计及风力发电机转速安全约束的DFIG一次调频模型预测控制策略

针对传统方法控制双馈感应发电机(DFIG)的调频效果过于依赖参数整定的问题,该文提出了一种基于模型预测控制(MPC),计及转速安全约束的风力发电机参与一次调频控制策略。该方法结合风力发电机动力学模型与频率响应模型建立预测模型,通过线性回归方法变参考值将风力发电机转速的稳定性纳入考虑。相较于虚拟惯性控制等方法将系统频率偏差与转子动能直接关联,该文方法通过建立全新的预测模型,实时统筹考虑整个系统的状态信息,无需反复调整参数,在考虑转速安全性的同时兼顾全局性能。最后,通过实际算例分析验证了该文调频策略的有效性以及相对现有方法的优越性。

多线切割保公差工艺对烧结钕铁硼永磁体表面质量的影响

采用多线切割保公差工艺切割烧结钕铁硼永磁体,利用SJ-410粗糙度仪、JMS-6010LA型扫描电子显微镜对微观形貌及表面粗糙度R_(a)进行表征。结果表明:随着进给速度增高和线速度的降低,金刚石磨粒压入深度减小,微观形貌由深犁沟、凹坑、破损变为浅犁沟、浅凹坑和破碎,材料去除机理由塑性去除变为塑性变形。粗糙度R_(a)随着进给速度和线速度的增高而减小;进给速度和线速度对法向载荷呈相反作用,在不同工艺参数下的材料去除方式中,塑性变形和塑性去除占据主导作用,进给速度10 mm/h和线速度1190 m/min的粗糙度最低,表面质量最优。切割时间只与进给速度有关,线弓随着进给速度增加,随线速度降低。

基于改进势场法的智能车超车动态路径规划

为了改进人工势场法(artificial potential field,APF)在智能车高速超车状态下规划出的轨迹规范性差、安全性得不到保障、以及路径不平滑的问题。设计用于指引智能车换道的换道引力势场,以保证换道轨迹的规范性;构建异向分布结构的障碍车斥力势场提高换道的安全性;并建立带有转向缺口的道路中心线斥力势场和设计平滑代价函数优化规划出的轨迹点,使规划出的路径更加平滑。基于线性二次型调节器(linear quadratic regulator,LQR)设计路径跟踪控制器跟踪规划出的路径。通过Simulink与Carsim联合仿真,结果表明:所改进的APF算法能规划出更加合理的路径,设计的LQR路径跟踪控制器跟踪误差趋近于零,能够较好地控制车辆完成超车换道。