Possibilities for Increasing the Efficiency of Contactless Emitters of Acoustic Waves

An electromagnetic-acoustic emitter has been designed that is capable of exciting widespectrum acoustic waves on a narrow section of the surface of metalware with a low voltage across the inductor. An engineering solution has been proposed that allows one to place emitter’s inductor directly on the surface of an article.     

谐振管内非线性驻波的间断Galerkin方法*

基于伪一维瞬态可压缩Navier-Stokes方程和理想气体状态方程,并结合保持强稳定性的三阶Runge-Kutta格式和斜率限制器技术,构建一种整体轴向谐振激励下求解变截面谐振管内非线性驻波的间断Galerkin方法。分别对直圆柱形、指数形以及圆锥形谐振管内的非线性驻波进行数值仿真计算,通过与现有数值仿真结果对比,验证了本方法的正确性,并重现了已有试验中非线性驻波压力波形中的第二峰值。在直圆柱形和指数形谐振管内研究间断Galerkin方法的两种网格加密方式对于不同形状下谐振管内非线性驻波仿真计算的数值精度、消除数值振荡和准确捕捉激波的不同作用,以及不同CFL数对于数值精度的影响。在指数形谐振管内,通过与有限体积法不同网格数目下的数值仿真结果和计算时间对比,验证了本方法具有耗时短、效率高以及计算精度高的优点。在圆锥形谐振管内,研究不同流速下谐振管内压力和速度波形的变化,并发现随着流速的增加,谐振管小端处的压力幅值增加,大端处速度幅值也随之增加且速度波形中会产生激波。通过间断Galerkin方法分析研究几种谐振管内非线性驻波的各种物理属性,为谐振管形状优化提供了重要参考,也为实现谐振管内非线性驻波的工程应用奠定了良好的基础。     

A Potentiometric Method of Detecting Moving Boundaries in the Determination of Transference Numbers

SUMMARY

A new method is described by which transference numbers for both leading and following ions can be determined in a moving boundary experiment. The boundary is detected by the change in potential accompanying its passage into the volume between two microprobes sealed into the moving boundary tube. With the aid of a volume calibration, the transference number of the leading ion can thereby be determined. A method of measuring ionic mobilities directly is described in which the same microprobes are used to measure both the potential gradient and the boundary velocity. Transference numbers for the following ion can also be measured by the indirect method, which makes use of the Kohlrausch relationship. The microprobes are used in this case to measure the conductance ratio between leading and following solutions. The detector is described in detail along with a suitable power supply. A sheared cell is introduced in which the boundary is formed initially with the aid of a pipet and a flowing system. The apparatus is tested thoroughly on systems whose transference numbers are known.     

Experimental Investigations into Laser Generation of Surface Acoustic Waves in Ferromagnetics

The effect of magnetic phase transition on the parameters of high-temperature conversion of pulse laser radiation into the acoustic field of surface waves (SAWs) was studied. For this purpose, an experimental setup was designed and assembled.     

圆柱形谐振管内非线性驻波的有限体积计算方法

提出一种用于求解圆柱形谐振管内非线性驻波的有限体积计算方法。谐振管内初始为自由状态的流体被整体谐振激励,当激励频率与谐振管内声场固有频率一致时,谐振管内将产生非线性驻波。建立整体振动条件下谐振管内瞬态可压缩热粘性牛顿流体的一维Navier-Stokes模型方程的积分方程;在时域上,通过SIMPLEC方法(以压力为基础的有限体积法)和交错网格技术推导出离散化代数方程组,并进行求解。当谐振管内的流体为R-12气体,在整体振动的条件下,利用提出的方法对谐振管内的非线性驻波进行求解,通过与现有文献中伽辽金方法的计算结果进行对比,所得到的非线性驻波声压在波形和幅值方面都与这些结果非常吻合,从而验证了该方法的可行性。得到谐振管左端处的绝对压力波形、温度波形和声压频谱响应等物理特性分布;同时得到谐振管内不同位置处的速度变化,发现在谐振管两端出现了速度钉状波形;有限体积计算方法为解决强声密封的非线性驻波的数值计算奠定了良好基础。     

谐振管内非线性驻波的二维间断Galerkin计算方法

基于柱坐标下的二维瞬态可压缩Navier-Stokes方程、理想气体状态方程以及保强稳定的Runge-Kutta方法,提出了求解谐振管内非线性驻波的二维间断Galerkin计算方法。通过处理边界条件以及采取局部时间步长,利用所提出的二维间断Galerkin计算方法对圆柱形谐振管内非线性驻波进行求解,得到了谐振管内压力空间分布以及压力波形、速度波形、密度波形等物理特性,证明时间域、空间域内均产生激波,从而使压力幅值和密度幅值无法进一步提升;同时研究了激励加速度幅值对谐振管内非线性驻波压力波形及非稳态进程的影响。     

基于电磁超声换能器阵列的管道螺旋导波传播规律研究

螺旋导波因在管道超声导波层析成像中的巨大应用价值,近年来受到研究者们的重视。阐述管道螺旋导波的激发/接收条件、传播路径和波前形状等规律。建立FE模型,研究由圆环波前S₀模态兰姆波在管道上形成螺旋导波的过程。组建了双环24阵元的电磁超声换能器阵列及试验系统,170 kHz下激发圆环波前S₀模态兰姆波在管道中产生螺旋导波,试验研究了激励源所在圆周及管段上的波动场信号特征。仿真和试验结果表明,管道螺旋导波实质上是兰姆波在曲面上的传播形态,可由管道某处点源激发兰姆波产生,主要存在于波动场的近场。由于管道结构的封闭性,兰姆波的波前在管道上反复交叉前行,形成了螺旋传播路径。从波源到管道上任意一点的螺旋导波传播路径有无数条,各阶螺旋角不连续。利用螺旋导波进行管段检测提供了缺陷的多角度入射信息,对缺陷高分辨率检测具有重要意义。     

水中运动声源的声全息参数选取研究

针对水中运动噪声源难以识别问题,采用声全息技术建立运动噪声源的声全息动态识别方法,详细推导全息重构公式,建立测量系统和重构声源的坐标系关系,利用采集到含有多普勒效应的声信号构造出全息数据完成重建,对运动声源的信号采集和多普勒消除等方法进行研究.利用所编制的程序进行仿真验证,分析重构参数的选取原则,给出重构频率、重构距离...     

二维声学数值计算的梯度最小二乘加权

针对传统有限元法求解声学问题由于刚度矩阵过硬导致较大的色散误差,以及在较高波数和网格扭曲时计算精度过低甚至错误的问题,采用移动最小二乘权函数对传统有限元法的声压梯度进行加权重构,推导了梯度移动最小二乘加权(Gradient weighted by moving least-squares,GW-MLS)的二维声学计算公式。对声压梯度的加权重构使得GW-MLS模型的刚度相对于FEM模型得以软化,刚度更接近真实模型刚度。采用与有限元法相同的方式构造质量矩阵和边界积分矢量,保证质量矩阵和边界条件的正确施加和积分精度。通过二维管道声腔模型和二维车内声腔模型算例对所提出的算法进行验证,数值分析结果表明,GW-MLS有效地减少了色散误差的影响,提高了计算精度,尤其是对较高波数和网格扭曲时表现出良好的适应性。     

Effect of Surface Waves from a Moving Object on Its Image During Reconstruction using Aperture Synthesis

The reconstruction of an image of the cross section of a thin wire obtained by an ultrasonic detector in an aqueous medium at a frequency of 1.3 MHz with a monochromatic probing signal is considered. The image was reconstructed using a synthesized aperture by correlation processing of a trajectory Doppler signal with calculated reference trajectory signals from point objects. The disturbing effect of the ultrasonic wave reflected from the surface wave generated by the moving wire on the image reconstruction is taken into account. The results of reconstruction of the image of the wire cross-section from model and experimental trajectory signals in the presence of a surface wave are given.     

基于模态声发射和小波变换的薄板中导波传播特性的实验研究

基于小波变换和模态声发射理论。通过声发射实验的方法确定了薄板中导波传播的弥散特性。通过分析声发射信号的Gabor小波变换幅度在时频空间分布特点，确定某一频率下某一模态导波到达传感器的时间，从而确定该频率下该模态导波的群速度，进而确定其弥散曲线。实验确定薄板弥散曲线与理论计算曲线较好吻合，证明小波变换是分析弥散波时频特性的有效工具。     

基于边界控制的Gn连续过渡曲面的构造

讨论了基于重新参数化局部基曲面线性组合构造G^n连续过渡曲面时重新参数化局部基曲面的形状对于过渡曲面的边界和形状的影响；提出了采用能量最小法使过渡曲面的边界弯曲最小来确定重新参数化局部基曲面参数域的方法，并提出相应的重新参数化局部基曲面的确定方法，从而构造较好的过渡曲面。     

Characterization of Transducer Performance and Narrowband Transient Ultrasonic Fields in Metals by Rayleigh-Sommerfeld Backpropagation of Compression Acoustic Waves Measured with Double-Pulsed Tv Holography

This article presents a method aimed at the characterization of the narrowband transient acoustic field radiated by an ultrasonic plane transducer into a homogeneous, isotropic and optically opaque prismatic solid, and the assessment of the performance of the acoustic source. The method relies on a previous technique based on the full-field optical measurement of an acoustic wavepacket at the surface of a solid and its subsequent numerical backpropagation within the material. The experimental results show that quantitative transversal and axial profiles of the complex amplitude of the beam can be obtained at any plane between the measurement and excitation surfaces. The reconstruction of the acoustic field at the transducer face, carried out on a defective transducer model, shows that the method could also be suitable for the nondestructive testing of the performance of ultrasonic sources. In all cases, the measurements were performed with the transducer working under realistic loading conditions.     

Rarefied Gas Flow through Passages with Static Boundaries

A resume of the current state-of-knowledge concerning rarefied gas flow through passages with static boundaries is presented. A brief development of the theoretical gas flow models which have been used for long tubes and annuli is included. These theoretical models have been developed to cover the flow regime extending from laminar continuum flow to free molecular flow. The analysis required to use these models is simple and straightforward. Experimental data are presented for the flow of argon through a long tube and for the flow of argon and xenon through annuli. The experimental values of mass flow rate per unit pressure drop as a function of Knudsen number are graphically presented for a long tube and for two annuli. Also presented on the same figures are the values predicted by the theoretical models. The agreement between theory and experiment for the complete regime between continuum and free molecular flow is very good.     

一种基于瞬时频率的多普勒畸变声信号校正方法

运动声源信号中广泛存在多普勒效应影响,针对其引起的频移、频带扩展问题提出了一种校正方法。信号的频率非平稳性的还原通常使用重采样方法,而建立一组重采样时间序列就是该方法的核心。对于多普勒畸变信号,瞬时频率与原信号频率有着密切的关系。仿真信号和实验信号处理结果显示,多普勒效应带来的频带扩展问题得到了较好的解决,畸变信号得到了有效校正。     

Acoustic levitation with self-adaptive flexible reflectors

Two kinds of flexible reflectors are proposed and examined in this paper to improve the stability of single-axis acoustic levitator, especially in the case of levitating high-density and high-temperature samples. One kind is those with a deformable reflecting surface, and the other kind is those with an elastic support, both of which are self-adaptive to the change of acoustic radiation pressure. High-density materials such as iridium (density 22.6 gcm(-3)) are stably levitated at room temperature with a soft reflector made of colloid as well as a rigid reflector supported by a spring. In addition, the containerless melting and solidification of binary In-Bi eutectic alloy (melting point 345.8 K) and ternary Ag-Cu-Ge eutectic alloy (melting point 812 K) are successfully achieved by applying the elastically supported reflector with the assistance of a laser beam.     

带边界约束叶片的螺旋加工轨迹规划

通过采用通道加工原理实现的螺旋加工方法成功解决了叶片螺旋加工中刀具与叶片橼板之间的干涉问题,讨论了确定走刀步长的保证条件,求证出相邻两刀具切触点法矢夹角与刀轴摆角之间的关系。结果表明,采用提出的方法能够有效解决叶根处的干涉问题,为提高叶片的加工效率找到了一种新的解决方案。     

Abrasive-assisted Nickel Electroforming Process with Moving Cathode

In traditional electroforming process for revolving parts with complex profiles, the drawbacks on surface of deposits, such as pinholes and nodules, will lead to varying physical and mechanical properties on different parts of electroformed components. To solve the problem, compositely moving cathode is employed in abrasive-assisted electroforming of revolving parts with complicated profiles. The cathode translates and rotates simultaneously to achieve uniform friction effect on deposits without drawbacks. The influences of current density and translation speed on the microstructure and properties of the electroformed nickel layers are investigated. It is found that abrasive-assisted electroforming with compound cathode motion can effectively remove the pinholes and nodules, positively affect the crystal nucleation, and refine the grains of layer. The increase of current density will lead to coarse microstructure and lower micro hardness, from 325 HV down to 189 HV. While, faster translational linear speed produces better surface quality and higher micro hardness, from 236 HV up to 283 HV. The weld-ability of the electroformed layers are also studied through the metallurgical analysis of welded joints between nickel layer and 304 stainless steel. The electrodeposited nickel layer shows fine performance in welding. The novel compound motion of cathode promotes the mechanical properties and refines the microstructure of deposited layer.     

水声换能器的随机噪声绝对校准

本文利用Ｐｒｏｎｙ参数模型进行水声换能器随机噪声绝对校准技术的研究。在研究Ｐｒｏｎｙ参数估计的基础上利用一定带宽的滤波器进行换能器校准的模拟实验，结果表明了利用随机噪声互相关的方法可以有效地排除水声换能器校准过程中由水域边界引起的反射干扰，突破由水域有限尺寸引起的可校准的低频限。最后进行换能器实际校准研究，表明了随机噪声校准技术是换能器低频绝对校准的一种有效方法。     

Excitation of Elastic Waves in Half-Space with Periodic Surface Undulations

The components of the displacement of elastic waves excited by a normal transducer in half-space with periodic surface undulations is calculated by the perturbation method within the framework of the two-dimensional model. The numerical examples of the calculation results obtained for a surface described by harmonic functions are given. The phenomenon of transformation of longitudinal waves into transverse waves on periodic surface undulations, which has been revealed earlier, is confirmed. As a result of this phenomenon, transverse waves are emitted in the direction of the normal to the plane of the transducer at its center.