Parameter measurement of the cylindrically curved thin layer using low-frequency circumferential Lamb waves

The characteristic parameters of a cylindrically curved thin layer include its elastic constants, thickness and curved radius. A layer is considered thin if the echoes from the front and back surfaces of the layer cannot be separated in the time domain, and/or that the wave arrivals corresponding to longitudinal and shear wave part cannot be identified in the time or space domain. This paper describes a low-frequency circumferential Lamb wave method to characterize those parameters of a cylindrically curved thin layer. The technique is based on the measurement of circumferential Lamb wave phase velocity and the unknown parameter is estimated through minimizing the mean square error obtained by comparing theoretical and experimental phase velocities. The sensitivity and accuracy of the proposed technique to different parameters are analyzed. Using the present technique, a cylindrically curved thin layer with thickness down to ten percent of the longitudinal wavelength can be successfully measured with an average relative error less than two-percent in our experiment.     

海底沉积物声速与物理性质的理论关系

为建立海底沉积物声速与物理性质的关系,引入密度变化比和弹性模量变化比为参数描述海底沉积物声速。密度变化比是描述声速的一个复合参数,由孔隙率、固相密度和海水密度三个物理参数表示;弹性模量变化比是描述声速的另一个复合参数,由孔隙率、固相体积模量和海水体积模量三个物理参数表示;声速公式可展开为这两个复合参数的泰勒多项式。两个复合参数的变化构成声速曲面,声速曲面包含了声速特性与沉积物性质的完整信息;而单参数声速公式是声速曲面上的一条曲线。数值计算与测试结果对比表明:把孔隙率-声速经验公式变换为参考声速乘以一个调制函数的标准形式,各个海区的孔隙率-声速经验公式的调制函数是相当接近的。论文导出的声速公式与Wood声速公式的区别在于弹性模量的模型不同。      

Acoustical analysis of pipes with flow using invariant field functions

An analysis of the pressure field within a pipe is carried out using simplified formulations of pipe acoustics. The fluid contained within the pipe is considered non-viscous, while the flow velocity of the fluid is assumed to be smaller than the speed of sound.The analysis is limited to frequencies which are well below the pipe ring frequency, i.e., at which only simple waves can propagate. Expressions and diagrams are given which specify the applicable frequency range in each particular case.Three invariant functions of the internal pressure field are evaluated. These functions allow for the determination of the following quantities: base pressure spectrum (spatial mean r.m.s. value), lower and upper bounds of the pressure spectrum for the entire pipe, pressure spectrum at an arbitrary position, speed of sound in the contained fluid and fluid flow velocity.Experimental identification of these quantities requires simultaneous measurement at three points. A few measurements carried out on one air-filled and one water-filled pipe have demonstrated the potential of pipe invariant functions for acoustical analysis.     

稠密可压缩气粒两相流动中的等熵声速计算建模及物理规律

气体相与颗粒相混合流场的声速研究, 由于具有重要的基础理论价值与广泛的工程应用背景, 逐渐受到人们重视. 针对稠密可压缩气粒两相流动, 综合考虑颗粒相所占空间体积以及颗粒间相互作用, 推导给出了新的等熵声速计算公式; 新公式包含了已有的纯气体、稀疏气粒两相流情形的计算公式作为其特例, 一方面验证了公式推导的正确性, 另一方面说明新公式更具有通用性; 分析了不同颗粒质量分数条件下的声速变化规律, 相应结果与普朗特的理论分析符合, 特别对于稠密气粒两相流动工况得到了一些新的物理认识; 开展了颗粒间相互作用建模参数的物理分析, 揭示了其对气粒两相流动声速的影响机理. 本文取得的成果为稠密可压缩气粒两相流动研究以及相关工程应用提供理论支撑.     

椭偏光谱测量中椭偏参数的灵敏度分析

在对椭圆偏振测量的基本原理进行了简单介绍和推导后,讨论了椭圆偏振测量中椭偏参数关于薄膜参数的灵敏度以及入射角对椭偏参数的影响,并进行了具体的仿真分析,得到如下结论：椭偏参数Delta对薄膜光学常数和薄膜厚度变化的灵敏度明显高于椭偏参数Psi。在椭偏数据处理中,椭偏参数Delta的测量精度直接影响薄膜光学常数和薄膜厚度的拟合精度。为了提高椭偏参数Delta的测量精度,可以选择入射角在膺布儒斯特角附近。所得结论对高精度椭偏测量具有指导意义。     

超声吸收体物理参数对红外热成像测量高强度聚焦超声声场的影响

超声吸收体的物理参数对利用水听器和红外热成像技术的高强度聚焦超声(High-Intensity Focused Ultrasound,HIFU)声场测量结果具有重要影响。为了探索超声吸收体的物理参数(密度、声速、衰减系数、热扩散系数、定压比热容)对测量结果的影响规律,本文根据层状模型计算出相同声源功率输出时不同物理参数对应的超声吸收体内部声场和热场,利用有限差分法计算出超声吸收体表面在辐照过程中的温度变化;利用基于水听器和红外热成像技术的聚焦声场测量方法测量出焦域内不同位置上声场特征值(轴线声强和-6 dB声束宽度),与通过理论计算得到的声源在纯水中声场特征值进行比较,分析了不同物理参数对测量结果的影响。超声吸收体的声、热学参数中除了声速外,其它物理参数的变化引起声场特征值的测量造成最大相对差异率小于15%。因为声波传播速度的改变会导致超声吸收体内部热场分布变化,使测量结果与理论计算值有较大偏差,其中-6 dB声束宽度和轴线声强最大相对差异率为95.37%和69.97%。因此在选择超声吸收体的声、热学参数时应重点关注声波在吸收体内声速的影响。超声吸收体的声学参数与水的声学参数相近时,可以在焦域内获得较好的测量结果。      

A novel method for the measurement of acoustic speed

Traditional methods for measuring acoustic speed require knowledge of either the specimen thickness or the distances between the transducers and the specimen. In general, the accuracy in measuring these quantities determines the accuracy of the experimental technique for measuring speed. This problem is particularly acute in measuring sound speed in biological specimens. A new method for measuring acoustic speed of materials, which eliminates the need for determining these quantities, has been developed. The technique, which necessitates the use of only one transducer, requires measurement of four times of flight of a sound pulse and the knowledge of the speed of sound in a reference fluid medium in which the specimen is placed. Ultrasonic speed in stainless steel and Plexiglas was measured using this method to verify its validity. Results on measurements on porcine liver, myocardium, and soft fat are also reported.     

Theoretical relationship between sound velocity and the physical properties of submarine sediment

Density and elastic modulus change ratios are introduced to describe the sound velocity of submarine sediment.The density change ratio is a composite parameter describing the sound velocity.It is expressed by three physical parameters:porosity,solid phase density and seawater density.The elastic modulus change ratio is also a composite parameter of sound velocity.It is expressed by three physical parameters,including porosity,solid phase modulus and seawater bulk modulus.The sound velocity formula can be developed into a Taylor polynomial formula of these two composite parameters.The change in the two composite parameters constitutes the sound velocity surface,which contains the complete information regarding velocity properties and sediment characteristics.The one-parameter velocity formula is a curve on the velocity surface.Each porosity-velocity empirical formula,which represents various sea locations and conditions,is transformed to a standard form.This result is the product of a reference velocity and a modulation function.Comparisons of the numerical calculation and measurements show that the derived modulation functions yield similar results.The difference between the velocity formula derived in this paper and the Wood velocity formula is due to the elastic modulus models.     

一种基于单水听器的浅海水下声源被动测距方法

针对浅海波导中宽带脉冲声源的被动测距问题,本文在群延迟理论的基础上,与warping变换处理相结合,提出了一种适用于浅海波导中宽带声源的单水听器被动测距方法.利用warping变换可以实现对脉冲声源接收信号各阶简正波的分离提取,对分离后的简正波进行时频分析处理可以得到各阶简正波到达时刻和频率之间的关系,即各阶简正波的频散曲线,从而得到任意两阶简正波到达接收水听器的时延差.海底相移参数P是描述海底地声参数的一个重要参量,包含了海底地声参数信息,在海底环境参数未知而P已知的情况下,利用P和简正波水平波数之间的关系可以求得任意两阶简正波的?S_(g,mn)(群慢差).根据群延迟理论,利用得到的任意两阶简正波的时延和?S_(g,mn)可实现利用单水听器对水下声源进行被动测距.本文提出的测距方法测量简单、计算方便,具有较强的实用意义.数值仿真和海上实验数据处理结果的测距误差都在10%以内,证明了该方法的有效性.     

Determination of the inhomogeneous structure of a medium from its plane wave reflection response,part II: A numerical approximation

This paper is concerned with a standard one dimensional inverse scattering problem: given the reflection response of an unknown inhomogeneous medium for plane waves under normal or oblique incidence, determine its sound speed and density structures. The problem is solved by means of a simple numerical technique which involves only fast Fourier transform operations and numerical integration of ordinary differential equations. Three cases are specifically considered: (a) sound speed is unknown, density is known; (b) sound speed is known, density is unknown; (c) sound speed and density are to be determined simultaneously. Numerical simulations performed on reflection coefficients computed in Part I for a limited band of frequencies lead to accurate reconstructions of the original structures of various media.     

Acoustic attenuation, phase and group velocities in liquid-filled pipes II: simulation for Spallation Neutron Sources and planetary exploration

This paper uses a finite element method (FEM) to compare predictions of the attenuation and sound speeds of acoustic modes in a fluid-filled pipe with those of the analytical model presented in the first paper in this series. It explains why, when the predictions of the earlier paper were compared with experimental data from a water-filled PMMA pipe, the uncertainties and agreement for attenuation data were worse than those for sound speed data. Having validated the FEM approach in this way, the versatility of FEM is thereafter demonstrated by modeling two practical applications which are beyond the analysis of the earlier paper. These applications model propagation in the mercury-filled steel pipework of the Spallation Neutron Source at the Oak Ridge National Laboratory (Tennessee), and in a long-standing design for acoustic sensors for use on planetary probes. The results show that strong coupling between the fluid and the solid walls means that erroneous interpretations are made of the data if they assume that the sound speed and attenuation in the fluid in the pipe are the same as those that would be measured in an infinite volume of identical fluid, assumptions which are common when such data have previously been interpreted.     

Geoacoustic inversion based on reflection model of effective density fluid approximation

In order to obtain the physical and geoacoustic properties of marine sediments,an inverse method using reflection loss of different grazing angles is presented.The reflection loss is calculated according to the reflection model of effective density fluid approximation.A two-step hybrid optimization algorithm combining differential evolution and particle swarm optimization along with Bayesian inversion is employed in estimation of porosity,mean grain size,mass density and bulk modulus of grains.Based on the above physical parameters,geoacoustic parameters,including sound speed and attenuation,are further calculated.According to the numerical simulations,we can draw a conclusion that all the parameters can be well estimated with the exception of bulk modulus of grains.In particular,this indirect inverse method for bottom geoacoustic parameters performs high accuracy and strong robustness.The relative errors are 0.092%and 17%,respectively.Finally,measured reflection loss data of sandy sediments at the bottom of a water tank is analyzed,and the estimation value,uncertainty and correlation of each parameter are presented.The availability of this inverse method is verified through comparison between inverse results and part of measured parameters.     

圆孔非线性声阻抗三维时域仿真与特性分析

为研究有限振幅声波作用下圆孔的非线性声学特性,提出了基于三维时域计算流体动力学(CFD)仿真的圆孔非线性声阻抗提取方法,通过求解层流方程来模拟声信号在圆孔及上下游的传播,以及采用横向周期性边界条件来考虑高穿孔率时圆孔之间相互作用的影响。研究了不同幅值声波作用下孔径、厚度和穿孔率对声阻抗的影响规律,通过对质点振速幅值、频率和板厚等组成的无量纲参量进行非线性回归分析,得到了圆孔非线性声阻抗的拟合公式,并将其转换为可考虑多频声波影响的时域模型。最后结合声阻抗时域模型和有限差分方法计算了直通穿孔管消声器在小振幅和有限振幅声波作用下的传递损失,通过与实验测量结果的比较,验证了拟合公式的准确性和实用性。     

基于等效密度流体近似反射模型反演海底参数

为了获取海底沉积物的物理和地声特性,根据等效密度流体近似反射模型得到的不同掠射角下的海底反射损失,利用差分进化算法和粒子群算法相结合的两级混合优化算法以及Bayesian反演方法对海底沉积物的孔隙度、平均颗粒粒度、颗粒质量密度以及颗粒体积弹性模量进行反演,再根据这4个物理参数的估计值进一步计算出海底地声参数,包括声速和衰减。通过反演结果与仿真真值的比较可以看出,除颗粒体积弹性模量外,得到的估计结果是令人满意的,特别是这种间接反演海底地声参数的方法对地声参数的估计具有较高的精确性和较强的稳健性,相对误差分别为0.092%和17%。最后,对实验室水池池底沙质沉积物的反射损失数据进行处理,给出了沙质沉积物各参数的估计值、不确定性和相关性,并通过反演结果与部分实测参数值的比较验证了反演方法的可行性。      

Hybrid geoacoustic inversion of broadband Mediterranean Sea data

This paper describes an acoustic experiment (PROSIM'97) carried out to investigate inversion for seabed properties at a site off the west coast of Italy where previous acoustic and geophysical studies have been performed. Acoustic fields were measured at a vertical hydrophone array due to a swept-frequency source towed over weakly range-dependent bathymetry. Based on the known geology, the seabed is modeled as a sediment layer overlying a semi-infinite basement with unknown model parameters consisting of the sediment thickness, sediment and basement sound speeds, source range and depth, water depth at the source and array, and array tilt. A hybrid inversion algorithm is applied to determine the model values that minimize the mismatch with the measured acoustic fields. Multiple data sets are analyzed to examine the consistency of the inversion results. It is found that the low sound speed of the sediment layer, together with a large uncertainty in bathymetry, leads to strong correlations between the water depths and sediment thickness. This precludes reliable estimation of these parameters individually; however, the total depth to the basement can be estimated reliably. In addition, the basement speed and geometric parameters are estimated consistently, and all parameters compare favorably with the geophysical ground-truth information and with previous inversion results.     

浅海环境下数据同化声层析方法研究

讨论了适用于浅海的基于声速局部测量模型、声传播模型及声压场局部测量模型的声学数据同化方法,并给出了具体的执行算法。该算法根据最优化准则把局部声速和声压场的先验测量信息,以及声传播模型进行了有效地融合,提高了海洋环境参数估计的精度,为浅海声层析提供了新思路。同时,利用实验浅海声速测量数据,通过经验正交函数对实际海洋声速剖面进行了估计,并分析了各类噪声对水体声速场及海底声学参数估计精度的影响,验证了该执行算法的有效性。      

海底沉积物压缩波速度与切变波速度的关系

基于连续介质假设,根据无吸收各向同性弹性介质通用方程分析沉积物声波传播关系,提出应用弹性结构分布因子表达的声速通用模型(GMSS,General Model of Sound Speed)分析海底沉积物的声速特性;通过研究Willey时间平均模型、Wood方程、Gassmann方程、Buckingham模型、Biot-Stoll模型和EDFM模型,可以表述成GMSS通用模型中的弹性结构分布因子的具体表达形式,得出GMSS通用模型在解释压缩波速度和切变波速度特性上具有一致性的特点。GMSS通用模型具有弹性结构分布因子、孔隙度、孔隙海水的等效密度和等效弹性模量、固相颗粒的等效密度、固相颗粒的等效体积弹性模量和等效切变弹性模量共7个参数,为研究海底沉积物压缩波和切变波速度提供了一种模型简单、参数少、通用性强的方法。但也需要从物理结构上以及应力应变关系上开展更为深入的分析和探寻GMSS模型的物理意义和参数测量的方法。      

传统笙的物理模型及声音合成方法

为研究传统笙的物理结构与音色之间的关系,提出了传统笙的物理模型及声音合成方法。在簧舌振动模型的基础上,结合指孔和音窗的传输矩阵计算方法,建立了笙管的等效电路,并将二者结合,得到笙的完整物理模型。为了验证模型的有效性,设计了一套笙的实验系统,实现了对笙管发声过程中特征量的多通道同步测量。通过对比实验和模型仿真结果的时频域特点以及与音色相关的特征量,分析了模型的性能.结果表明,该模型可较好地模拟传统笙管的发声过程,合成笙样本能够较准确的反映真实笙样本的音色特征。      

海底沉积物压缩波声速比与物理特性的关系

海底沉积物因组成结构复杂导致声学特性复杂多样,多种理论解释模型存在参数较多且各具适用性现象·通过运用体积平均和等效参数的方法对海底沉积物声波传播机理进行研究,提出一种少参数的海底沉积物与底层海水的压缩波声速比通用模型(General Model of Sound Speed Ratio,GMSSR).GMSSR模型包含弹性结构分布因子、孔隙度、等效密度比、等效弹性模量比4个物理特性参数。分析海底沉积物两相介质结构的串联和并联两种极限情况分析,基于弹性结构分布因子和串并联结构的体积平均分布建立一般情况下海底沉积物的等效弹性模量表达式·应用GMSSR合理地分析各海域测量的海底沉积物声速比经验模型的共性和解释南海实测数据分散的范围,表明:(1)表层海底沉积物主要是以串联结构为主,接近于悬浮液状态或者体积分量很少的并联堆积状态;(2)等效弹性模量比的影响因素大于等效密度比,结构变化往往通过影响弹性结构分布因子而影响等效弹性模量比,从而引起声速比的变化;(3)不同研究海域的声速比-孔隙度经验关系具有相似性,可以通过GMSSR模型分析得出;(4)基于弹性结构分布因子的差异,可以合理解释南海海域测量表层海底沉积物声速比较大的分散性。      

探究用比较法测液体粘滞系数

采用间接比较法,就是利用已知的标准量作为参考,通过比较公式,来测量某未知量.该方法可使实验操作过程大为简化,不仅减少了测量量,且单位不必国际化,计算更简单,有效数字位数只由已知标准量来确定,从而提高了测量的精度,使比较公式的物理意义更加明确.该方法使学生的视野大为开阔,为很多的实验,提供了多选方案,为进一步拓展学生的思...