Microstructure Features and the Macroscopic Acoustic Behavior of Gassy Silt in the Yellow River Delta

The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.

Acoustic wireless communication based on parameter modulation and complex Lorenz chaotic systems with complex parameters and parametric attractors

As the competition for marine resources is increasingly fierce,the security of underwater acoustic communication has attracted a great deal of attention.The information and location of the communicating platform can be leaked during the traditional underwater acoustic communication technology.According to the unique advantages of chaos communication,we put forward a novel communication scheme using complex parameter modulation and the complex Lorenz system.Firstly,we design a feedback controller and parameter update laws in a complex-variable form with rigorous mathematical proofs(while many previous references on the real-variable form were only special cases in which the imaginary part was zero),which can be realized in practical engineering;then we design a new communication scheme employing parameter modulation.The main parameter spaces of the complex Lorenz system are discussed,then they are adopted in our communication scheme.We also find that there exist parametric attractors in the complex Lorenz system.We make numerical simulations in two channels for digital signals and the simulations verify our conclusions.

Molecular structure dependence of acoustic nonlinearity parameter B/A for silicone oils

Exploring new acoustic parameters is essential to develop a noninvasive imaging technique for the surgery of silicone oil tamponades. In this study, the acoustic nonlinearity parameters B/A of varied silicone oil samples （e.g., linear or hyper-branched） are experimentally measured by using a modified thermodynamic method. The results show that： （i） when the concentration of the silicone oil with a molecular weight of 5 × 10^4 increases from 0.5 g/100 ml to 8 g/100 ml, the corresponding B/A value increases by about 18%, but the acoustic velocity only increases by about 0.1%; （ii） when the molecular weight of the hyper-branched silicone oil is enhanced from 2 × 10^5 to 1 × 10^6, the B/A value increases by about 22%, while the acoustic velocity is only raised by about 0.2%. This study suggests that the B/A parameter of the silicone oil is more sensitive to the change in its molecular structure than that of the acoustic velocity. Thus, the B/A parameter might be utilized as an effective index for the development and optimization of the noninvasive imaging of the surgery of silicone oil tamponades.

Novel Method for Selection of Regularization Parameter in the Near-field Acoustic Holography

Because of the ill-posedness of the near-field acoustic holography（NAH）,the regularization method is required to stabilize the computational process of NAH.The regularization effect is related to how to select the parameter correctly and effectively.However the L-curve method commonly used for the selection of regularization parameters has the disadvantages of wrong selection and incorrect selection,which influences the application of NAH.For the purpose of solving the problems existed in the L-curve method,the （？）-curve method is introduced into the field of NAH,and the performance applied to NAH directly is analyzed on the basis of equivalent source method-based NAH.However,it is found out via investigations that the（？）-curve method in NAH also has the problem of wrong selection and is unable to choose the regularization parameter correctly.In order to select the parameter correctly and effectively,a novel method for selecting regularization parameters is proposed based on the original（？）-curve method,which can be called improved （？）-curve method.In the proposed method the regularization parameters are discretized linearly between the largest singular value and the smallest singular value,and the solution norm and the residual norm corresponding to these regularization parameters are also described in a linear coordinate instead of in a lg-lg coordinate,which are the two main differences compared with the L-curve and with the original（？）-curve method.In linear coordinate and using the linearly discretized regularization parameters,the solution norm is a monotonically decreasing function of the residual norm as the increase of the regularization parameter,moreover the curve is convex everywhere.So the regularization parameters can be selected correctly and effectively based on the improved（？）-curve method.Then a numerical simulation is done with a simply supported plate to verify the validity of the proposed method.Experiments with two actual sources,a clamped plate and the double speakers,are carried out to do a further demonstration.The simulation result as well as the experimental result shows that the improved（？）-curve method is efficacious and has some advantages over the L-curve method and the original（？）-curve method.The proposed novel method is able to avoid the problem of wrong selection and to select the regularization parameter correctly even if the curve is smooth.

Relation between welding parameter and acoustic emission information during laser deep penetration welding

In laser non penetration deep penetration welding process, welding material will vaporize, metal vapor and ambient gas will produce a higher degree ionization, which forms plasma of high concentration. In the case of forming a small hole, plasma will eject from the hole, and form acoustic emission (AE) signals. Because AE information has many advantages such as non contact measuring, fast response, and high ratio of signal to noise, it can be used as a monitor variable for in process control. By studying AE information, information of welding pool and small hole can be obtained. According to characteristic of AE information, this paper reveals the correlation between welding parameters and AE signals, and provides a good base for further quality control.

A new acoustic model used in Chinese order recognition system for space teleoperating manipulator

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Measurements of the Cosmological Parameters &Omega;_mand <i>H</i>₀

From Baryon Acoustic Oscillation measurements with Sloan Digital Sky Survey SDSS DR14 galaxies, and the acoustic horizon angle measured by the Planck Collaboration, we obtain Ωm=0.2724±0.0047, and h+0.020&sdot;∑mv=0.7038±0.0060, assuming flat space and a cosmological constant. We combine this result with the 2018 Planck “TT, TE, EE + lowE + lensing” analysis, and update a study of ∑mv with new direct measurements of σ8, and obtain ∑mv=0.27±0.08 eV assuming three nearly degenerate neutrino eigenstates. Measurements are consistent with Ωk=0, and Ωde(a)=ΩΛ constant.

The Third-Order Viscoelastic Acoustic Model Enables an Ice-Detection System for a Smart Deicing of Wind-Turbine Blade Shells

The present work is based on the third-order partial differential equation (PDE) of acoustics of viscoelastic solids for the quasi-equilibrium (QE) component of the average normal stress. This PDE includes the stress-relaxation time (SRT) for the material and is applicable at any value of the SRT. The notion of a smart deicing system (SDS) for blade shells (BSs) of a wind turbine is specified. The work considers the stress in a BS as the one caused by the operational load on the BS. The work develops key design issues of a prospective ice-detection system (IDS) able to supply an array of the heating elements of an SDS with the element-individual spatiotemporal data and procedures for identification of the material parameters of atmospheric-ice (AI) layer accreted on the outer surfaces of the BSs. Both the SDS and IDS flexibly allow for complex, curvilinear and space-time-varying shapes of BSs. The proposed IDS presumes monitoring of the QE components of the normal stresses in BSs. The IDS is supposed to include an array of pressure-sensing resistors, also known as force-sensing resistors (FSRs), and communication hardware, as well as the parameter-identification software package (PISP), which provides the identification on the basis of the aforementioned PDE and the data measured by the FSRs. The IDS does not have hardware components located outside the outer surfaces of, or implanted in, BSs. The FSR array and communication hardware are reliable, and both cost- and energy-efficient. The present work extends methods of structural-health/operational-load monitoring (SH/OL-M) with measurements of the operational-load-caused stress in closed solid shells and, if the prospective PISP is used, endows the methods with identification of material parameters of the shells. The identification algorithms that can underlie the PISP are computationally efficient and suitable for implementation in the real-time mode. The identification model and algorithms can deal with not only the single-layer systems such as the BS layer without the AI layer or two-layer systems but also multi-layer systems. The outcomes can be applied to not only BSs of wind turbines but also non-QE closed single- or multi-layer deformable solid shells of various engineering systems (e.g., the shells of driver or passenger compartments of ships, cars, busses, airplanes, and other vehicles). The proposed monitoring of the normal-stress QE component in the mentioned shells extends the methods of SH/OL-M. The topic for the nearest research is a better adjustment of the settings for the FSR-based measurement of the mentioned components and a calibration of the parameter-identification model and algorithms, as well as the resulting improvement of the PISP.

加载速率影响下板裂化脆性岩石失稳破坏试验研究

深部脆性岩体开挖常发生板裂破坏,并可能进一步发生片帮剥落、岩爆等工程灾害,严重威胁深埋隧(巷)道施工安全。在深部岩体工程中,受构造应力、开挖条件和工程扰动等因素的影响,岩体开挖后应力重分布的速率、来压快慢均存在差别。为探究加载速率对板裂围岩失稳破坏的影响,采用脆性岩石加工成的板裂试样进行单侧限单轴压缩试验,对不同加载速率下试样宏观破裂、强度特性、声发射(AE)特征以及能量机制进行综合研究。结果表明:(1)低加载速率下试样发生大块剥落,整体失稳并发生分离,高加载速率下试样未发生大块分离,但有小块动力弹射现象;(2)低频、高幅信号的增多及b值的变化表明试样产生了突发式的裂纹失稳扩展,且这个过程中大小尺度破裂不断交替产生;(3)在平稳加载阶段,高加载速率使试样AE活动更加剧烈,而临近失稳及失稳破坏阶段则相反,且低加载速率下低频信号、大尺度破裂事件占比更大。因不同开挖方案、施工方法导致的围岩应力重布快慢差异,在工程上会导致围岩发生板裂后,进一步诱发不同模式破坏。

基于单矢量水听器时频声强法的非合作水声跳频信号多维参数估计

针对传统方法对水下非合作跳频信号的多维参数估计效果不佳的问题,提出一种基于单矢量水听器时频声强法的非合作水声跳频信号空时频参数估计方法。利用矢量水听器声压通道与振速通道的接收信号建立时频域的短时互谱分布,分析噪声与信号在时频域分布的差异,通过迭代去噪法与连通域方法,对噪声进行抑制并平滑每跳的能量分布;采用复声强法对短时互谱矩阵进行处理,得到清晰稳定的跳频信号空时频分布;提取空时频分布的脊线并利用Haar小波变换对脊线进行奇异点检测,估计出信号的多维参数。仿真和水池试验结果表明,当信噪比大于-5 dB时,所提方法得到的参数估计归一化均方根误差小于0.05。

泥岩卸荷力学行为、声发射特征及能量演化研究

为了更好地探究水利水电工程地下开挖施工时泥岩损伤演化,利用四川大学MTS 815混凝土与岩石力学试验系统开展泥岩三轴卸荷试验,试验共设置3种围压(10,20,25 MPa),采用加围压-恒围压加轴压-加轴压卸围压的方式加载,同步进行声发射数据采集,从力学行为、声发射特征和能量演化的角度分析试验结果.结果表明:围压越高,卸载后对试样的影响越大,泥岩的体积膨胀特性更显著,试样破坏时的卸荷比更小,弹性应变能和耗散能的增速越快.随着卸荷比增大,泥岩的变形模量会先增大后减小,内摩擦角、黏聚力、剪胀角增大,弹性应变能增大,耗散能先增大后趋于稳定甚至下降.在峰值应力出现前会出现声发射振铃计数率的高值,围压的增大会延缓声发射活跃期的出现,同时声发射累计计数与能量会增加.

基于声发射参数分析的红层泥岩高周循环加卸载损伤及变形特性

为研究不同应力上限及加载频率条件下软弱红层泥岩的损伤及变形特性,基于声发射损伤监测手段开展高周循环加卸载试验,系统分析应力上限与加载频率对红层泥岩损伤及裂纹扩展模式的影响。结果表明:当应力上限低于屈服临界动应力值时,泥岩经历先剪缩后缓慢剪胀的过程,岩样中微裂隙的发展与黏土矿物的膨胀逐渐占据主导地位;低频AE信号产生于静载阶段,而高频AE信号主要出现在循环加载阶段,且随加载频率的增大,超过300 kHz的超高频声AE信号占比逐渐增大;红层泥岩循环荷载下所产生的裂纹总体以张拉裂纹为主,但第I阶段剪切裂纹占比相对其他阶段较大,且随着动应力幅值减小或加载频率的增大,剪切裂纹所占比例减小;在裂隙自愈合效应下,泥岩中由动载引起的损伤裂隙会被逐渐修复,且随着放置时间的增加,声发射Kaiser效应逐渐减小甚至消失。

基于声传播损失的南海海域地声参数敏感性分析

以中国南海地声-水声联合调查实验数据为基础,利用多道地震数据偏移成像以及浅地层剖面数据反演获取了一个分层地声模型。通过设定该模型各层地声参数的参考值和变化区间,结合实测的水体声学参数,利用Krakenc耦合简正波模型计算了不同地声参数下的声传播损失;分析了理论与实测声传播损失均方根误差随地声参数的变化规律以及均方根误差的区间分布情况。研究结果表明:对于频率100 Hz的声传播,地声模型第一层和第二层沉积层的声速对声传播损失影响最为显著;第一层和第二层沉积层衰减系数、厚度对声场的影响次之;基底对声场的影响最小。本文在接近真实海底的环境下研究了海底各分层结构中地声参数对声场的影响,可为建立海洋环境地声模型提供一定的依据。

基于Kriging代理模型的水下目标模型几何参数识别方法

[目的]水下目标参数识别可为目标分类识别提供依据,为此,提出一种基于Kriging代理模型的水下目标参数识别方法。[方法]首先,对敷设声学覆盖层的水下目标模型在螺旋桨和主辅机激励情况下的结构表面低频振动声辐射与声辐射灵敏度进行分析;然后,基于分析结果建立低频声辐射功率代理模型,并基于该代理模型构造由低频声辐射响应特征和目标参数组成的样本空间;最后,基于所构建的样本空间,建立目标参数识别代理模型并选取测试点进行模型验证。[结果]结果显示,测试样本的实际目标参数值与所构建代理模型的目标参数预测值吻合良好;利用有限元法和边界元方法可以实现考虑阻尼材料频变特性的黏弹性阻尼结构的低频声辐射分析,并能解决商业软件无法大批量处理振动结果文件的问题;影响水下目标模型低频振动声辐射的主要目标参数为目标长度、最大半径、基层壳厚度和声学覆盖层厚度。[结论]基于Kriging代理模型的水下目标参数识别方法可以通过声辐射线谱特征准确预测水下目标模型的主要目标参数值。

聚焦换能器声场特性的快速检验方法

高强度聚焦超声(HIFU)已在无创肿瘤治疗方面展示出巨大的应用潜力,而换能器聚焦性能的优劣对疗效起到至关重要的作用,因此声场的精确测量成为实际应用的重要保障.由于加工工艺和安装精度的限制,聚焦换能器的实际声场和理想声场可能存在一定偏差.针对传统三维扫描测量存在速度慢和精度低的问题,提出了一种基于双平面双精度测量的聚焦换能器声场特性快速检验方法.通过沿理想z轴的高精度一维扫描确定换能器倾斜角范围,在声压极值点所在横截面内利用低精度和高精度变邻域搜索法实现最大声压点的精准定位,进一步通过焦域内双平面最大声压点构建声场的实际轴线,完成实际声场焦点的精确定位,最后基于实际焦平面内轴向与径向的高精度测量结果,计算获得焦域尺寸、旁瓣大小、分布对称性和声功率等性能参数.利用构建的声场扫描实验系统对聚焦换能器声场进行三维扫描和快速测量,结果表明在相同的测量精度(0.1 mm)下可以有效提高测量速度百倍以上,具有测量速度快、测量精度易于调节和性能分析全面等优点.方法为聚焦换能器检验提供一种高精度的快速声场测量新技术,在超声治疗仪器的检验中具有重要的指导意义与应用价值.

水产养殖智能投饵技术研究进展

在水产养殖中,投喂成本占总养殖成本的40%~80%,是影响水产养殖效益的主要因素。因此,如何做到科学投喂是降低养殖成本、增加养殖经济效益的关键。智能投饵就是利用各类传感器获取鱼群摄食过程中的全局信息,结合相关算法与模型将信息反馈给控制系统动态调整投饵策略的投喂方式,是做到科学投喂、提高配合饲料利用率的有效手段。近年来,水产养殖智能投饵研究取得了一定成果,但由于实际养殖存在诸多不确定因素,实现智能投饵仍面临挑战。文章介绍了自动投饵机与自动投饵系统的研究现状,主要综述了基于机器视觉、声学、水质参数和生物模型等技术的智能投饵方法,指出了各方法的优缺点并进行总结。今后,应加强对水产养殖动物摄食过程中的图像、声音、环境因子、生物模型等信息的综合分析与运用,以提高智能投饵系统对摄食强度评估的准确性以及与养殖环境的匹配度。

三维可视化言语康复训练在脑卒中后构音障碍患者中的应用效果分析

目的探讨三维可视化言语康复训练在脑卒中后构音障碍患者中的应用效果。方法选取2022年7月至2023年10月首都医科大学附属北京天坛医院收治的80例脑卒中后构音障碍患者为研究对象,在组间基线特征可比的原则上,采用随机数字表法分为对照组(41例)和观察组(39例)。对照组患者给予常规康复训练,观察组患者给予常规康复训练联合三维可视化言语康复训练,两组患者均连续治疗2周。比较分析两组患者治疗前后的构音障碍严重程度[Frenchay构音障碍评估量表(FDA)评分]、语音清晰度以及声学参数[共振峰F1、共振峰F2、音高、音强、元音空间面积(VSA)、元音清晰度指数(VAI)、共振峰集中率(FCR)、下颌距]。结果治疗前,两组患者的FDA评分、语音清晰度、共振峰F1、共振峰F2、音高、音强、VSA、VAI、FCR、下颌距比较差异均无统计学意义(P>0.05);治疗2周后,两组患者的FDA评分、语音清晰度、共振峰F2、音高、音强、VAI与治疗前比较均显著升高,且观察组优于对照组,差异均有统计学意义(P<0.05);两组患者的FCR与治疗前比较均降低,且观察组低于对照组,差异均有统计学意义(P<0.05)。结论三维可视化言语康复训练可显著减轻患者的构音障碍严重程度,提高语音清晰度,改善声学参数,从而促进患者的康复。

高频聚焦超声声场和温度场的仿真研究

为探究临床常用的7 MHz高频聚焦超声在多层生物组织中的声传播以及毫秒级时间内的生物传热规律问题,基于Westervelt方程和Pennes传热方程,使用有限元方法建立高频聚焦超声辐照多层组织的非线性热黏性声传播及传热模型。首先分析了线性模型和非线性模型之间的差异,然后在非线性模型下探究换能器的参数对声场和温度场的影响。仿真结果显示:在7 MHz频率下,当换能器输出声功率超过5 W时,声波传播的非线性效应不可忽视(p<0.05);当声功率从5 W增大到15 W时,非线性模型与线性模型预测的温度偏差从20%增加到34.703%;高频聚焦超声波的非线性行为比低频更加显著,基频能量向高次谐波转移的程度增大,声功率为10 W和15 W时4次谐波与基波之比分别达到7.33%和12.12%;高频换能器参数的改变对组织中声场和温度场分布的影响较大,换能器焦距从12 mm减小到11.2 mm,焦点处最高温度增加了77%。结果表明,7 MHz聚焦超声的非线性声传播需要考虑到4次谐波的影响。该文提出的多层组织非线性仿真模型可为高频聚焦超声换能器参数优化及制定安全、有效的术前治疗方案提供理论参考。

基于参数搜索的水声定位时标跳变改正方法

利用水声定位技术可将全球卫星导航系统(GNSS)维持的位置基准传递至海洋内部。国内GNSS-声学海底定位实验通常采用多种硬件设备相互配合完成,但不同设备输出的观测数据可能存在时标跳变的问题。一般可通过冗余观测解决时标跳变问题,但对于无冗余观测的情况,尚无有效的解决办法。本文提出基于参数搜索的时标跳变改正方法,构建时标偏差的搜索空间,以水声定位结果的单位权方差为判定指标,通过数值方式搜索观测数据的时标跳变。利用实测海试数据对提出的方法进行验证,结果表明,参数搜索方法成功探测到声学设备数据约1 s的时标跳变,并通过改正时标将水声定位精度从dm级提升至mm级。

基于阻抗模型的玻璃棉声学参数反演方法研究

为了能准确获取玻璃棉材料的声学参数,文章对玻璃棉声学参数在不同阻抗模型下的声学参数进行了反演。采用了厚度分别为22 mm和44 mm的玻璃棉样本实测吸声曲线及各声学参数,选取四种常用阻抗模型,通过遗传算法(Genetic Algorithm,GA)对玻璃棉材料进行声学参数的反演,并选择反演效果最优的模型进行敏感性分析。比较各参数反演结果的误差比,并对比不同模型描述的吸声曲线与测试曲线的一致性,最后量化并比较Johnson-Champoux-Allard(JCA)模型中各参数对吸声系数的影响程度。研究表明,使用GA结合JCA模型或Johnson-Champoux-Allard-Lafarge(JCAL)模型反演的参数值与测试值误差较小;JCA模型适用于玻璃棉材料的声学参数反演,模型中流阻率和曲折度的敏感性较高,反演过程需保证其精确度。