Wave disturbances in transonic separated flows

The results of an investigation of the nature and role of wave disturbances in transonic separated flows are presented. The effect of these disturbances on flow formation and stability, as well as on the characteristics of the pressure fluctuations and the time-average flow parameters, is considered.     

Uniform stabilization of a nonlinear structural acoustic model with a Timoshenko beam interface

This paper is concerned with a nonlinear model which describes the interaction of sound and elastic waves in a two‐dimensional acoustic chamber in which one flat ‘wall’, the interface, is flexible. The composite dynamics of the structural acoustic model is described by the linearized equations for a gas defined on the interior of the chamber and the nonlinear Timoshenko beam equations on the interface. Uniform stability of the energy associated with the interactive system of partial differential equations is achieved by incorporating a nonlinear feedback boundary damping scheme in the equations for the gas and the beam. Copyright © 2006 John Wiley & Sons, Ltd.     

有限温度下二维Heisenberg铁磁系统的横向声频支声子激发

在二维正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型.利用Matsubara格林函数理论研究了系统的横向声频支声子激发，计算了布里渊区的主要对称点线上的横向声频支声子色散曲线，发现在第一布里渊区的Σ线上，小波矢区(Γ附近k_xa＜0.2)横向声频支声子有硬化现象，但是在软化区(0.25＜k_xa＜0.7)有横向声频支声子有软化现象，在M附近(0.75＜k_xa)横向声频支声子有硬化现象.在Δ线上没有发生横向声频支声子有软化与硬化现象.在Z线上小波失区(X附近k_xa＜0.65)横向声频支声子有软化现象，但是在M附近横向声频支声子有硬化现象.并且又讨论了各项参数对横向声频支声子激发的影响，发现磁振子-声子耦合与自旋波劲度常数对横向声频支声子软化起很大的作用. 关键词： 磁振子-声子相互作用 横向声频支声子软化 Matsubara格林函数理论 铁磁系统     

An analytical method for the electro-acoustic performance of the underwater transducer

A finite element-Helmholtz integral hybrid method has been developed to calculate the electro-acoustic performance of a finite length cylindrical transducer immersed in water. The numerical study concerned with electrical impedances and beam patterns of the transducer is presented. Experimental data are shown to support the numerical study.     

Simple estimation of electron correlation energy for multi-atomic strong ionic compounds KX and (KX)2 (X=OH, NC)

On the basis of the calculations and analyses of the intrapair and interpair correlation energy of KX (X = OH, NC) molecules and the results of the transferability of both the innermost intrapair correlation energy and the inner core effect of K and X in KX molecules, we defined and calculated the K^δ+ and X^δ-correlation contributions to the total correlation energy of KX molecules. With the comparison of the pair correlation energy of K⁺, X^- and KX systems, we present a simple estimation method to estimate the electron correlation energy of strong ionic compound by summarizing the correlation energy of its constituent ion and ionic group. By using this simple method, the reasonable estimation results of the correlation energy of (KOH)₂ and (KNC)₂ have been obtained at mp2/6-311++G(d) level with Gaussian98 program, and the deviations are very small. Applying the scheme of “Separate Large System into Smaller Ones” to the calculation of electron correlation energy of large ionic compounds, it can not only save lot of computation work but also reach the chemical accuracy.     

光声信号的声透镜层析成像研究

提出了一种用声透镜实现光声层析成像的新模式。从理论上计算出了声透镜的响应，测出了已知声场中标准物像面处的声场分布。考虑到圆形活塞振源的指向性，对代表物成像进行了理论修正，并与实验结果做了对比分析。研究表明，利用声透镜可以实现光声层析成像，并经图像重构得到了生物组织中异物的光声图像，横向、纵向分辨力较高。     

Surface self-diffusion of quench condensed hydrogen films

The annealing behaviour of quench condensed H₂-, HD- and D₂-films has been investigated using acoustic surface waves. Upon annealing at temperatures far below the triple point we observe drastic changes of sound velocity and attenuation which can be attributed to a considerable rearrangement of the film structure via surface diffusion. These findings are in good agreement with recent experiments using surface plasmons. From the temperature dependence of the speed of the structural changes we deduce the activation energies for surface self-diffusion as 23 K, 35 K, and 47 K for H₂, HD, and D₂, respectively.     

Acoustic gas slip induced by surface waves

A boundary kinetic effect has been predicted on the basis of a model of interaction between Rayleigh surface acoustic waves (SAW) and a gas. The effect resembles some classic boundary effects such as thermal or diffusion gas slip. The functional dependence of the effect on gas and SAW parameters is presented. The slip phenomenon takes place due to angular restrictions of the scattered gas molecules because of the deformation of the solid surface.     

不同路面激励下车内噪声预测与板件声学贡献量分析

利用有限元模拟计算的方法对不同路面激励下车内噪声进行了预测, 并分析了板件对声 学的贡献量. 使用MATLAB软件生成了B级和C级路面谱. 由NASTRAN软件计算 出车身结构在不同路面谱激励下1$\sim$200\,Hz的频率响应结果, 在LMS Virtual. Lab声学软件中, 根据声传递向量技术预测驾驶员和乘客耳旁声压级响应. 还探讨了 声腔结构表面阻抗特性对车内噪声的影响. 并针对C级路面谱激励, 通过车身各板件对 驾驶员右耳声压的面板贡献量分析, 找出了结构优化的重点区域, 为降低车内声压检测点噪 声进行相关的声学处理提供参考依据.     

Determination of nonlinear medium parameter B/A using model assisted variable-length measurement approach

This work addresses the difficulties in the measurements of the nonlinear medium parameter B/A and presents a modification of the finite amplitude method (FAM), one of the accepted procedures to determine this parameter. The modification is based on iterative, hybrid approach and entails the use of the versatile and comprehensive model to predict distortion of the pressure–time waveform and its subsequent comparison with the one experimentally determined. The measured p–t waveform contained at least 18 harmonics generated by 2.25 MHz, 29 mm effective diameter, single element, focused PZT source (f-number 3.5) and was recorded by Sonora membrane hydrophone calibrated in the frequency range 1–40 MHz. The hydrophone was positioned coaxially at the distal end of the specially designed, two-section assembly comprising of one, fixed length (60 mm), water-filled cylindrical container and the second, variable length (60–120 mm) container that was filled with unknown medium. The details of the measurement chamber are described and the reasons for this specific design are analyzed. The data were collected with the variable length chamber filled with 1.3-butanediol, which was used as a close approximation of tissue mimicking phantom. The results obtained provide evidence that a novel combination of the FAM with the semi-empirical nonlinear propagation model based on the hyperbolic operator is capable of reducing the overall uncertainty of the B/A measurements as compared to those reported in the literature. The overall uncertainty of the method reported here was determined to be ±2%, which enhances the confidence in the numerical values of B/A measured for different, clinically relevant media. Optimization of the approach is also discussed and it is shown that it involves an iterative procedure that entails a careful selection of the acoustic source and its geometry and the axial distance over which the measurements need to be performed. The optimization also depends critically on the experimental determination of the source surface pressure amplitude.