Determination of the parameters of a linear-viscoelastic thin layer using the normally-incident ultrasonic waves

This paper proposes a method of simultaneous determination of the four layer parameters （mass density, longitudinal velocity, the thickness and attenuation） of an immersed linear-viscoelastic thin layer by using the normally-incident reflected and transmitted ultrasonic waves. The analytical formula of the layer thickness related to the measured trans- mitted transfer functions is derived. The two determination steps of the four layer parameters are developed, in which acoustic impedance, time-of-flight and attenuation are first determined by the reflected transfer functions. Using the derived formula, it successively calculates and determines the layer thickness, longitudinal velocity and mass density by the measured transmitted transfer functions. According to the two determination steps, a more feasible and simplified measurement setups is described. It is found that only three signals （the reference waves, the reflected and transmitted waves） need to be recorded in the whole measurement for the determination of the four layer parameters. A study of the stability of the determination method against the experimental noises and the error analysis of the four layer parameters are made. This study lays the theoretical foundation of the practical measurement of a linear-viscoelastic thin layer.

An Efficient Three-Dimensional Coupled Normal Mode Model and Its Application to Internal Solitary Wave Problems

We present an efficient three-dimensional coupled-mode model based on the Fourier synthesis technique. In principle, this model is a one-way model, and hence provides satisfactory accuracy for problems where the forward scattering dominates. At the same time, this model provides an efficiency gain of an order of magnitude or more over two-way coupled-mode models. This model can be applied to three-dimensional range-dependent problems with a slowly varying bathymetry or internal waves. A numerical example of the latter is demonstrated in this work. Comparisons of both accuracy and efficiency between the present model and a benchmark model are also provided.

Selection of Reference Genes in Equine White Blood Cells for Real Time PCR Normalization Following Extracorporeal Shock Wave Therapy

Selection of proper reference genes (RGs) is an essential step needed for accurate normalization of results from genomic studies. Expression of RGs is regulated by many factors such as species, age, gender, type of tissue, the presence of disease, and the administration of therapeutic treatment. The aim of the present study was to identify optimal RGs in a set of blood samples collected at different time points (0, 24, 48, 72 h) from horses following administration of extracorporeal shock wave therapy (ESWT). The mRNA expression of twelve RGs: HPRT1, ACTB, HSP90A, SDHA, GUSB, B2M, UBC, NONO, TBP, H6PD, RPL32, GAPDH was determined using real time quantitative polymerase chain reaction (qPCR). An SAS program developed on the algorithm of geNorm, SASqPCR, was used to determine stability of the expression and the number of optimal RGs. The results showed that the range of quantification cycle (Cq) values of the evaluated genes varied between 17 and 26 cycles, and that one optimal RG, ACTB, was sufficient for normalization of gene expression. Results of stability of expression demonstrated that ACTB was the optimal choice for all the samples studied. Notably, in samples collected at 72 h post ESWT, TBP showed a significant change in the expression level, and was not suitable for use as a RG. These results substantiate the importance of validating and selecting an appropriate RG.

基于时间线性拟合的地缆架空混合线路的行波故障定位

目的研究n段地缆架空混合输电线路中行波故障定位问题,提出一种基于时间线性拟合的行波故障定位方法。方法首先对故障区域进行判断,确定故障所在的区域,其次再将不同波阻抗线路进行归一化处理,减少因波速不同而产生的测距误差,最后使用时间线性拟合的方法对故障进行精确定位。结果解决了初始行波波头识别困难的问题,也减小了行波速度随传输距离变化而变化带来的测距误差问题。结论在MATLAB/Simulink中搭建一个500 kV的地缆架空混合输电线路仿真模型,实验的验证结果表明此故障定位方法能够有效地解决因行波速度不同而导致的双端行波测距方法不适用问题,最终实现对故障点的精确定位。

Interaction of Streamwise and Wall-Normal Velocities in Combined Wave-Current Motion

The aim of this paper is to present an analytical expression for the streamwise velocity distribution in a non-uniform flow in the presence of waves; the correlation between the horizontal and vertical velocity components has been compreheusively examined. Different from previous researches which attributed the deviation of velocity from the classical log-law to the wave Reynolds stress, i.e. - ρ uv^- only, this study demonstrates that the momentum flux caused by mean velocities, i.e., u^- and v^-, is also responsible for the velocity deviation, and it is found that the streamwise velocity for a flow in the presence of non-zero wall-normal velocity does not follow the classical log-law, but the modified log-law proposed in this study based on simplified mixing-length theorem. The validity of the modified log-law has been verified by use of available experimental data from published sources for combined wave-current flows, and good agreement between the predicted and observed velocity profiles has been achieved.

浅海粗糙海底声散射建模及声场特性

声散射是海洋声学的重要内容,海底表面的不平整性形成的声散射是海洋中引起声传播起伏的原因之一.针对海底表面粗糙度声散射问题,建立了水平分层浅海波导中海底散射声场模型.该模型将简正波理论与Lambert定律相结合.基于该模型获得了散射声场声压的振幅与相位的统计分布,并数值模拟了海底散射声场的强度及其空间相关系数,实现了粗糙界面条件下海底散射声场预报,揭示了散射声场空间特性随海底粗糙度的变化规律.结果表明,使用Lambert定律描述粗糙界面声散射时,在海底粗糙度小于波长情况下,随着空间距离的增大,空间两个不同位置的散射声场的空间相关系数具有周期性振荡衰减的变化规律,并且在垂直方向上,振荡周期更大,衰减更慢.当粗糙度增大时,水平和垂直相关系数振荡幅度逐渐增大,水平相关系数振荡周期数逐渐减少,在接收点逐渐靠近海底时,垂直相关系数不再发生衰减,这是海底声散射减弱的结果.本文模型理论亦可推广到粗糙海面的声散射建模中.对于非水平海底情况,采用耦合简正波或绝热简正波理论进行声传播建模,可以得到距离有关波导中粗糙界面的散射声场.

Performance Evaluation of Bottom-Standing Submerged Breakwaters in Regular Waves Using the Meshless Singular Boundary Method

In this paper, the improved version of the meshless singular boundary method (ISBM) is developed for analyzing the hydrodynamic performance of bottom-standing submerged breakwaters in regular normally incident waves. Both the single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. Only the impermeable breakwaters are considered in this study. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with the appropriate mixed-type boundary conditions, and it is solved numerically using the ISBM. The numerical results are presented in terms of the hydrodynamic quantities of reflection and transmission coefficients. The values are first validated against the data of previous studies, computed, and discussed for a variety of structural conditions, including the height, width, and spacing of breakwater submergence. An excellent agreement is observed between the ISBM results and those of other methods. The breakwater width is found to feature marginal effects compared with the height. The present method is shown to accurately predict the resonant conditions at which the maximum reflection and transmission occur. The trapezoidal breakwaters are found to generally present a wide spectrum of reflections, suggesting that they would function better than the rectangular breakwaters. The dual breakwater systems are confirmed to perform much better than single structures.

基于主动超声激励的岩石节理刚度分布测量研究

Goodman提出采用节理刚度表征复杂岩石节理面的拓扑行为并为其提供定量值,而无需对节理面的粗糙度、接触面积等参数进行详细测量分析。然而目前对岩石节理刚度的测量仍存在局限,因此,在试验室环境下采用压电陶瓷换能器对完整平板试件和含节理平板试件进行弹性波激励,同时采用三维扫描激光多普测振仪监测平板内弹性波的传播数据。将采集的波场信号数据进行滤波、插值、积分等一系列处理,并基于Schoenberg线性滑移模型计算节理刚度分布,实现岩石节理接触行为的全局参数表征,同时进一步验证了岩石节理全场超声表征的可行性。全场波形数据清晰地揭示了岩石节理界面接触行为,为后续深入探索岩石节理几何形状、孔径、界面性质及其地震特征之间的相互关系奠定了基础。

“圆规”台风后海口铺前湾沙滩恢复效率与主控因素研究

在台风期间滩肩缩窄和后滨坡度变陡是砂质海滩的重要特征,而在常浪期间海滩剖面的恢复效率与近岸动力-泥沙-地貌的互馈密切相关。本研究基于海南岛铺前湾在超强台风“圆规”前后以及后续常浪恢复期间的海滩剖面实测数据,同时结合XBeach数学模型试验,分析了砂质海滩风暴后的恢复特征与影响恢复效率的主控因素。结果表明:台风浪造成了海滩剖面潮上带的侵蚀和潮间带的淤积,滩肩脊两侧的坡度在台风的影响下变缓。在台风后恢复期连续常浪的向岸堆积作用下,潮上带泥沙量呈增加趋势,滩肩脊两侧的坡度又会逐渐变陡,同时滩肩脊的位置有所抬高且向陆域一侧移动。滩肩高程的恢复效率高于滩肩宽度的恢复效率,潮间带滩面的恢复效率高于平均高潮位以上滩面的恢复效率。波浪对于浪控沙滩恢复效率的主导作用主要体现在波高峰值和波浪非对称引起的泥沙输运通量,恢复期间涨潮期的底床切应力和回流速度大于落潮期,促进底砂起动后向岸净输运落淤。

基于正态分布的一种岩石(岩块)弹性纵波速度取值方法

新鲜完整岩石(岩块)波速(Vpr)是计算岩体完整性系数的重要参数,岩石弹性纵波速度取值对岩体完整性评判具有重要作用,但其取值具有较强人为随意性的缺点,对同一类型岩石原位测试进行统计分析,得到了岩石弹性纵波速度分布的概率分布模型。通过不同概率保证率,可以利用概率分布模型得到完整岩体波速的上限值,得到岩石弹性纵波速度参数取值范围。以某抽水蓄能电站中花岗岩试验数据为例,通过实际工程算例表明,所提出的基于正态分布的岩体弹性波参数取值的方法可为实际工程中确定岩体完整性评价提供参考。

基于变分模态分解和波速归一的配电网混架线路故障精确定位

随着城市现代化进程的不断推进,配电网输电线路开始由单一形式的架空线路全面向电缆-架空混架线路发展。配电网混架线路由于结构复杂,发生故障时难以精确定位,现有故障定位方法可靠性不高。为此,提出一种基于变分模态分解和波速归一的配电网混架线路故障精确定位方法,其使用变分模态分解和峰度校准进行行波波头时间标定,使用波速归一法进行混架线路的故障点精确计算。该方法经PSCAD/EMTDC仿真分析验证具有可行性。

基于正态分布的双差波速比方法研究——以山东长岛震群为例

对于震源位置相对集中的震群活动,首先应用双差波速比法对台站到时数据进行2次差分,该方法充分利用不同台站纵横波的到时数据,无需地震发震时刻及位置信息,且将计算波速比范围限定在震源区附近,消除了震源区到台站传播路径的影响;然后运用正态分布的组合去除误差分布的影响,得到关于去除误差分布后的纵横波到时二维正态分布,通过公式推导确定了二维正态分布的相关系数;最后,通过计算置信椭圆长轴斜率得到长岛震群整体波速比。研究结果表明,长岛震群整体波速比为1.7275,等地震数滑动(60个)计算得到的波速比区间为[1.4887,3.0541];2017、2018年长岛震群波速比变化与震群活动过程密切相关,同时反映了震源区介质流体饱和度、裂隙密度和状态变化。

T接-混架配电线路故障定位技术研究及应用

针对现有T接-混架配电线路故障定位可靠性不高的问题,提出一种基于分布式故障行波测距的T接-混架配电线路定位方法。先以模量分解法实现T接线上的故障精确定位,即通过凯伦布尔变换将相量行波分量分解成模分量,通过ICEEMDAN和TEO算子标定模分量的波头时间,以线模、零模波速和波头时间计算故障位置。再以波速归一法实现混架线路的故障精确定位。PSCAD/EMTDC仿真分析验证了所提出方法的可行性。

A novel method for internal wave monitoring based on expansion of the sound speed profile

For acoustic detection of internal waves, the core issue is to obtain the temporal and spatial distribution of the sound speed profile(SSP). In the inversion process, the SSP is usually expressed by a few parameters through expansion. However, information about internal waves may sometimes be hard to read directly from the inversion results. The aim of this paper is to characterize the internal waves directly though expansion coefficients. By deducing the dynamic equations of the internal waves, an orthogonal basis called the hydrodynamic normal modes(HNMs) can be extracted from a certain number of SSP samples. Unlike the existing widely used empirical orthogonal functions(EOFs), the HNMs have a more explicit physical meaning that is directly related to internal wave activity. The HNMs are then used to expand the SSP time series, and the expansion coefficients are derived.Eventually, information about internal waves can be read directly from the time derivative of the expansion coefficients of the first two modes. In this study, this method is applied to thermistor string profiles from the northern shelf of the South China Sea, where the SSP shows evident spatial and temporal variations due to internal waves. The results show that the SSP can be described approximately by the first two modes with adequate precision. The special oscillation structure of the time derivative of the expansion coefficients can be used to detect internal solitary waves. The expansion coefficients can also give information on internal solitary wave amplitude and width. According to theoretical and experimental analysis, it can be concluded that the internal waves monitoring method introduced in this paper is effective. The HNMs method is simple to apply and depends less on sample data than EOFs. It could be used as an efficient alternative to EOFs to expand the use of the SSP in highly variable areas, where internal waves are intensive.

4D毫米波雷达稀疏点云下的连续帧隐空间法线估计

针对毫米波连续调频雷达在室外运动场景下点云数据稀疏和空间配准精度低的问题,本文提出了一种轻量级空间配准方法。该方法适用于室外运动场景下毫米波雷达连续多帧之间的点云处理,能在没有位姿传感器辅助的情况下,通过时空图神经网络准确估计相邻多帧点云的隐空间法线,并将每帧雷达点云数据转换到统一的观测坐标系中,从而实现四维点云的多帧融合与场景配准。实验结果表明,该方法不仅能准确评估四维点云的空间姿态,还能有效校正和融合每帧点云的坐标,在运动及震动过程中实现点云坐标的精准配准。此外,该算法还能显著提高点云成像的密度,增强图像的精度和可读性,同时适用于静态和动态目标的成像,为毫米波雷达在室外运动场景的应用提供了有力支持。

Biomechanical modeling for the response of human thorax to blast waves

A simplified finite element model of a human thorax had been developed for probing into the mechani- cal response in simple and complex blast environments. The human thorax model was first created by CT images with blast loading applied via a coupled arbitrary Lagrangian- Eulerian method, allowing for a variety of loads to be considered. The goal is to analyze the maximum stress distri- butions of lung tissue and peak inward thorax wall velocity and to know the possible regions and levels of lung injury. In parallel, a mathematical model has been modified from the Lobdell model to investigate the detailed percentage of lung injury at each level. The blast loadings around the human tho- rax were obtained from the finite element model, and were then applied in the mathematical model as the boundary con- ditions to predict the normalized work of the human thorax lung. The present results are found in agreement with the modified Bowen curves and the results predicted by Axels- son＇s model.

Analytical Solution for Acoustic Waves Propagation in Fluids

This paper presents a mathematical model of linear acoustic wave propagation in fluids. The benefits of a mathematical model over a normal mode analysis are first discussed, then the mathematical model for acoustic propagation in the test medium is developed using computer simulations. The approach is based on a analytical solution to the homogeneous wave equation for fluid medium. A good agreement between the computational presented results with published data.

Synthetic seismograms for finite sources in spherically symmetric Earth using normal-mode summation

Normal-mode summation is the most rapidly used method in calculating synthetic seismograms. How- ever, normal-mode summation is mostly applied to point sources. For earthquakes triggered by faults extending for as long as several 100 km, the seismic waves are usually simulated by point source summation. In this paper, we attempt to follow a different route, i.e., directly calculate the excitation of each mode, and use normal-mode sum- mation to obtain the seismogram. Furthermore, we assume the finite source to be a ＂line source＂ and numerically calculate the transverse component of synthetic seismo- grams for vertical strike-slip faults. Finally, we analyze the features in the Love waves excited by finite faults.

钢轨中超声导波模式激励方法研究

超声导波具有传播距离长、探测范围大的优点,可应用于铁路快速、远距离的检测。较为单一导波模式的激发和传播有利于信号处理和损伤识别。本文基于正交模式展开方法对钢轨中较单一波模式的激励方法开展研究,给出考虑切向激励的横截面振幅因子经验公式,分析不同位置激励时钢轨中不同导波模式的振幅因子;通过有限元仿真对激励方法进行验证,使用上述激励方法对轨头和轨底缺陷进行检测,结果表明该激励方法激励的波模式较为单一,可明显识别伤损回波信号。该方法可用于开发适用于损伤识别的单一波模式激励策略,显示无损检测和结构健康监测应用的潜力。

Observation of double pseudowaves in an ion-beam-plasma system

Pseudowaves, known as burst-ion signals, which are different from plasma normal modes, exist frequently in ion- wave excitation experiments when launching the waves by applying a pulsed voltage to a negatively biased grid. In previous experiments, only one kind of the pseudowave was observed. In this paper, we report the observation and identification of double pseudowaves in an ion-beam-plasma system. These pseudowaves originate from two ion groups： the burst of the beam ions and the burst of the background ions. It was observed that the burst of the background ions was in the case of high ion beam energy, while the burst of the beam ions was in the case of low ion beam energy. By observing the dependence of the signal velocities on the characteristics of the excitation voltage, these pseudowaves can be identified. It was also observed that the burst ion signal originating from the background ions can interact with slow beam mode and that originating from the beam ions can interact with fast beam mode.