Speed Control of Travelling Wave Type Ultrasonic Motors Using Artificial Neural Network

Ultrasonic motor (USM) is a newly developed motor, and it has some excellent performances and useful features, therefore, it has been expected to be of practical use. However, the driving principle of USM is different from that of other electromagnetic type motors, and the mathematical model is complex to apply to motor control. Furthermore, the speed characteristics of the motor have heavy nonlinearity and vary with driving conditions. Hence, the precise speed control of USM is generally difficult. This paper proposes a new speed control scheme for USM using an artificial neural network. An accurate tracking response can be obtained by random initialization of the weights of the network owing to the powerful on line learning capability. Two prototype ultrasonic motors of travelling wave type were fabricated, both having 100 mm outer diameters of stator and piezoelectric ceramic. The usefulness and validity of the proposed control scheme are examined in experiments.

THE NONLINEAR STABILITY OF TRAVELLING WAVE SOLUTIONS FOR A REACTING FLOW MODEL WITH SOURCE TERM

In this paper, author considers a 3 x 3 system for a reacting flow model propesed by [9]. Since this model has source term, it can be considered as a relaxation approximation to 2 x 2 systems of conservation laws, which include the well-known p-system. From this viewpoint, the author establishes the global existence and the nonlinear stability of travelling wave solutions by L-2 energy method.

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.

Influence of the Domain Boundary on the Speeds of Traveling Waves

Let H > 0 be a constant, g ≥ 0 be a periodic function and Ω ={(x, y) ||x| H + g (y), y ∈R}. We consider a curvature flow equation V = κ + A in Ω, where for a simple curve γt Ω, V denotes its normal velocity, κ denotes its curvature and A > 0 is a constant. [1] proved that this equation has a periodic traveling wave U, and that the average speed c of U is increasing in A and H, decreasing in max g' when the scale of g is sufficiently small. In this paper we study the dependence of c on A, H, max g' and on the period of g when the scale of g is large. We show that similar results as [1] hold in certain weak sense.

REMARK ON CRITICAL SPEED OF TRAVELING WAVEFRONTS FOR NICHOLSON'S BLOWFLIES EQUATION WITH DIFFUSION

This note is devoted to the son＇s blowflies equation with diffusion, a critical speed of traveling waves, we give behavior with respect to the mature age study on the traveling wavefronts to the Nicholtime-delayed reaction-diffusion equation. For the a detailed analysis on its location and asymptotic

ASYMPTOTIC STABILITY OF TRAVELING WAVES FOR A DISSIPATIVE NONLINEAR EVOLUTION SYSTEM

This paper is concerned with the existence and the nonlinear asymptotic stabil- ity of traveling wave solutions to the Cauchy problem for a system of dissipative evolution equations {θt=vζx＋（ζθ）x＋aθxx,ζt=-θx＋βζxx;with initial data and end states （ζθ）（x,0）=（ζ0,θ0）（x）→（ζ±,θ±）as x→∞.We obtain the existence of traveling wave solutions by phase plane analysis and show the asymptotic nonlinear stability of traveling wave solutions without restrictions on the coeffi- cients a and v by the method of energy estimates.

The dynamics of traveling wavefronts for a model describing host tissue degradation by bacteria

In this paper,we mainly investigate the dynamics of traveling wavefronts for a model describing host tissue degradation by bacteria.We first establish the existence of spreading speed,and show that the spreading speed coincides with the minimal wave speed of traveling wavefronts.Moreover,a lower bound estimate of the spreading speed is given.Then,we prove that the traveling wavefronts with large speeds are globally exponentially stable,when the initial perturbation around the traveling wavefronts decays exponentially asχ→-∞,but the initial perturbation can be arbitrarily large in other locations.The adopted methods are the weighted energy and the squeezing technique.

Shape analysis and damped oscillatory solutions for a class of nonlinear wave equation with quintic term

This paper aims at analyzing the shapes of the bounded traveling wave solu- tions for a class of nonlinear wave equation with a quintic term and obtaining its damped oscillatory solutions. The theory and method of planar dynamical systems are used to make a qualitative analysis to the planar dynamical system which the bounded traveling wave solutions of this equation correspond to. The shapes, existent number, and condi- tions are presented for all bounded traveling wave solutions. The bounded traveling wave solutions are obtained by the undetermined coefficients method according to their shapes, including exact expressions of bell and kink profile solitary wave solutions and approxi- mate expressions of damped oscillatory solutions. For the approximate damped oscillatory solution, using the homogenization principle, its error estimate is given by establishing the integral equation, which reflects the relation between the exact and approximate so- lutions. It can be seen that the error is infinitesimal decreasing in the exponential form.

BOUNDED TRAVELING WAVE SOLUTIONS OF VARIANT BOUSSINESQ EQUATION WITH A DISSIPATION TERM AND DISSIPATION EFFECT

This article studies bounded traveling wave solutions of variant Boussinesq equation with a dissipation term and dissipation effect on them. Firstly, we make qualitative analysis to the bounded traveling wave solutions for the above equation by the theory and method of planar dynamical systems, and obtain their existent conditions, number, and general shape. Secondly, we investigate the dissipation effect on the shape evolution of bounded traveling wave solutions. We find out a critical value r^＊ which can characterize the scale of dissipation effect, and prove that the bounded traveling wave solutions appear as kink profile waves if ｜r｜≥ r^＊; while they appear as damped oscillatory waves if ｜r｜ 〈 r^＊. We also obtain kink profile solitary wave solutions with and without dissipation effect. On the basis of the above discussion, we sensibly design the structure of the approximate damped oscillatory solutions according to the orbits evolution relation corresponding to the component u（ξ） in the global phase portraits, and then obtain the approximate solutions （u（ξ）, H（ξ））. Furthermore, by using homogenization principle, we give their error estimates by establishing the integral equation which reflects the relation between exact and approximate solutions. Finally, we discuss the dissipation effect on the amplitude, frequency, and energy decay of the bounded traveling wave solutions.

Speed Estimation Using Commercial Wi-Fi Device in Smart Home

With the development of Internet of Things(IoT),the speed estimation technology has attracted significant attention in the field of indoor security,intelligent home and personalized service.Due to the indoor multipath propagation,the speed information is implicit in the motion-induced reflected signal.Thus,the wireless signal can be leveraged to measure the speed of moving target.Among existing speed estimation approaches,users need to either carry a specialized device or walk in a predefined route.Wi-Fi based approaches provide an alternative solution in a device-free way.In this paper,we propose a direction independent indoor speed estimation system in terms of Electromagnetic(EM)wave statistical theory.Based on the statistical characteristics of EM waves,we establish the deterministic relationship between the Autocorrelation Function(ACF)of Channel State Information(CSI)and the speed of a moving target.Extensive experiments show that the system achieves a median error of 0.18 m/s for device-free single target walking speed estimation.

The minimal speed of traveling wave fronts for a three-cornponent competition system with nonlocal dispersal

In this paper,we study the linear determinacy of the minimal speed of traveling wave-fronts for a three-component competition system with nonlocal dispersal.We first trans-form this system into a cooperative system.Then,by constructing suitable upper solu-tions,we give some general conditions to ensure the linear determinacy of the minimalspeed.Finally,we provide some more precise conditions that only rely on the parametersof the system such that the linear determinacy of the minimal speed is assured.

100 kHz弹光调制器多功能调制仿真

针对弹光调制器(photoelastic modulator,PEM)在超高速全偏振领域的测量问题,研究一种目标频率在100 kHz附近的圆型PEM,由弹光晶体和2个方位角相差45°的压电驱动器组成。通过理论计算弹光晶体谐振频率和压电驱动器振动频率,当二者频率达到一致时,PEM工作在谐振状态,此时PEM的调制效率达到最高。当PEM达到谐振状态并趋于稳定后,调节两压电驱动器驱动电压的幅值与相位,实现纯驻波模式和纯行波模式两种特殊调制,纯驻波模式可实现纯电控制下调制快轴的延迟量和方位角;纯行波模式可实现纯电控制下调制快轴以PEM谐振频率的半频速度高速旋转。最后,利用COMSOL有限元仿真模拟两种调制模式下PEM,验证两种调制状态下的PEM振型及其快轴方向,表明PEM可实现多功能弹光调制,为后续偏振测量提供理论支撑。

基于双端行波频率变化特性的中低速磁浮交通供电轨故障定位方法

中低速磁浮供电轨供电过程中容易发生直流接地故障,由于其供电距离较短、接地网结构复杂,发生直流接地故障后不易准确定位故障点。为此针对以上问题,根据列车运行过程中车体与轨道无接触的特点,建立中低速磁浮牵引供电系统,分析双端故障测距与单端故障测距的优缺点,研究供电轨发生接地故障后故障行波时域分布与频域分布的关系;并通过计算式计算分析行波频谱的产生机理,得出故障行波的频率分布不受车站内阻抗、过渡电阻的影响,只与故障点位置和故障行波到达线路两端的时间相关;基于此,提出基于双端频率变化特性的中低速磁浮交通供电轨故障定位方法,根据故障行波频率特性与行波速度计算故障点位置。并且通过仿真验证,该方法不受故障点位置、过渡电阻大小影响,且适用于单处接地故障、多处接地故障类型,故障误差始终保持在1%以内,相比传统的直流牵引供电系统故障定位方法,测量精度更高,适用于中低速磁浮交通供电轨接地故障。

Asymptotic Speed of Wave Propagation for A Discrete Reaction-Diffusion Equation

We deal with asymptotic speed of wave propagation for a discrete reactlon-diffusion equation. We find the minimal wave speed c★ from the characteristic equation and show that c★ is just the asymptotic speed of wave propagation. The isotropic property and the existence of solution of the initial value problem for the given equation are also discussed.

超高速快轴旋转圆形弹光调制技术研究

针对目前广义椭偏测量速度受限问题,提出利用对称性更优的圆形弹光调制器代替机械旋转补偿器实现超高速测量。对弹光调制器内部受力进行理论研究,得到纯行波模式调制条件并利用COMSOL仿真验证。仿真结果表明,当弹光调制器处于纯行波调制模式时可视为一种快轴方向高速旋转的相位调制器。通过建立阻尼弦振动模型分析不同快轴方向下弹光晶体表面振动位移分布,提出一种弹光调制器在纯行波调制模式下的中心支撑方式用于实验。实验结果表明弹光调制器的快轴以f/2的角速率做圆周运动。同时验证了中心支撑方式可确保弹光调制器谐振后所受阻力均匀且最小,达到最佳支撑效果。研究结果可用于后续广义椭偏测量及各类高速偏振调制领域。

基于ZYNQ处理器的高速行波采集装置研究与实现

通过研究基于电子式互感器的分布式行波测距系统,提出一种基于ZYNQ的行波测距高速采集系统的实现方案,研究了其实现的关键技术。首先,介绍了高速采集单元的实现原理和系统架构,通过ZYNQ内部的AXI总线实现了一种高速AD数据在CPU和FPGA之间DMA交互的方法;其次,设计了一种余数均摊算法,解决了AD采样间隔不均匀影响行波测距精度的问题;最后,提出了一种FPGA硬件实现的相位调节算法,可以有效消除行波相位误差的同时,大大降低CPU运算负荷。产品经过挂网运行及测试,精度和可靠性都达到了国内领先水平。

埋地管道泄漏三维坐标-波速联合估计方法

为实现埋地输气管道泄漏精确定位,使用加速度传感器在土表检测泄漏振动声波,并提出基于非均匀L形阵列的泄漏源三维坐标和波速联合估计方法。大孔径非均匀L形阵列内嵌小孔径L子阵,由小孔径子阵结合Root-MUSIC算法求解远场信源DOA与波速的约束关系,再利用大孔径L阵进行波速和近场信源距离的二维空间谱估计,最后根据估计结果计算三维坐标从而降低计算量。定位实验结果验证了L形阵列性能的优越性,基于L形阵列的联合估计法能够估计不同土壤条件下的泄漏振动声波传播速度,并得出泄漏源的三维坐标。相较于使用理论波速的定位方法,联合估计法定位误差降低了90.9%,避免了理论波速误差对定位的不利影响。联合估计法的计算耗时比直接三维空间谱估计降低了88%,且定位精度保持不变。根据远/近场判据计算出信源范围rmin~rmax,实验验证该范围内可实现精确定位。

基于行波的高压输电线路故障定位方法

针对行波故障定位方法中波速不确定性带来测距误差问题,提出一种新的避开波速和输电线路弧度的故障测距方法。首先,阐述利用多尺度小波变换对故障信号进行去噪的方法;然后,测量初始行波到达不同母线时的时间参数,进一步利用时间参数从故障距离表达式中消除输电线路波速和弧度的影响;最后,对比有/无变压器的故障定位结果。仿真结果表明,虽然有变压器时误差会偏大,但整体分析,该方法具有较高的精度和可靠性。

The existence and non-existence of travelling front in high order auto-catalysis chemical reaction

This article studies propagating wave fronts in an isothermal chemical reaction A + nB →(n + 1)B involving two chemical species,a reactant A and an auto-catalyst B whose diffusion coefficients,DA and DB,are unequal due to different molecular weights and/or sizes.More accurate bounds v* and v* that depend on DB/DA,when the ratio is less than 1,are derived such that there is a unique travelling wave of every speed v v* and there does not exist any travelling wave of speed v < v*.The refined bounds for DB/DA < 1 case is compatible to what has been shown in earlier work for DB/DA > 1 when n 3.

海洋内波对海底精密定位的影响

全球导航卫星系统-声呐组合观测技术通常基于具有固定结构的声速剖面实施;由于海洋密度分层导致的内波会导致海洋声速场时空变化。本文探讨了海洋声速误差对水下定位的影响,仿真不同内波影响条件下的四维时空声速场变化,在此基础上,分别研究了具有固定声速结构的静态声速剖面时,海洋内波对水下定位的影响和采用估计海洋声速梯度的水下定位模型时,海洋内波引起的海洋声速时空变化参数估计问题,验证了该模型可以提取海洋内波影响。研究表明:海底定位精度与内波的振幅、频率、波长等紧密有关,且定位误差主要来源于大尺度低频内波,而小尺度、高频内波更多表现为随机误差从而影响观测精度;而水平梯度刻画极为复杂,单船载观测难以实现,需要进行多载体联合观测。