基于波叠加方法的水下声源辐射声场预报及实验研究

根据基于波叠加方法的声全息技术研究了水下声源的辐射声场预报问题,通过水听器阵列测得的复声压预报三维空间声场的声特性。数值仿真分析了一有限长圆柱壳模型在不同频率力激励作用下的声场预报精度,发现测量阵列尺寸与结构尺寸相近即可准确预测声场。水池和湖上实验分别对柱形换能器声源和加肋双层圆柱壳受激辐射声场进行了预测并和实测值进行了对比,结果表明该方法是一种稳健有效的声场预报方法。不同频率下,二者误差一般在3dB以内,能够满足工程需要。为实际水下大型结构的空间声场预报和降噪性能预估提供了工程参考。     

珊瑚型环礁斜坡地形水下声传播特性分析

从岛礁斜坡地形条件下的声信号衰减和地形阻断效应分析出发,重点针对水下声场分布规律及其对声传播造成的影响开展研究。利用水声模型理论,结合某礁实测地形以及水文数据,建立岛礁斜坡地形下的多途声信道模型,基于Bellhop与RAM声学仿真方法,对不同地形下的声线轨迹、声传播损失以及信号时延等声场特性进行仿真分析,得出岛礁斜坡地形下的声场分布特征。研究结果表明：（1）岛礁斜坡地形是影响其声传播模式的关键因素;（2）斜坡外缘浅海区域的目标不易被岛礁斜坡顶端的声呐所探测; （3）陡坡地形对浅海声源的声传播有利,当声源深度足够大时,缓坡地形下的本征声线数目能够达到在陡坡地形下的5倍,对声传播有利。以上研究结果可为岛礁区水下声场的特性分析以及水下声学对抗等实践应用提供理论基础和技术参考。     

浅海负跃层海底单参数模型研究

海底反射特性在浅海声传播中起着决定性的影响。用小掠射角下海底反射损失随掠射角变化率Fd B构建单参数模型可很好地描述浅海海底特性。对单参数模型进行深入研究和改进,建立了在浅海负跃层条件下描述水下声场的海底单参数模型,并利用数值仿真和海上实验数据,对浅海负跃层海底单参数模型水下声场预报的正确性进行了验证。     

薄壳目标的多基地声散射特性研究

文章对水中薄壳目标的多基地声散射特性进行了理论仿真与试验测量研究。首先采用有限元耦合边界元和基尔霍夫(Kirchhoff)近似积分两种不同的数值计算方法对内部充气球冠圆柱壳的多基地声散射特性进行建模仿真,然后通过目标在消声水池的散射声场试验测量验证仿真结果的有效性。采用相同的数值计算方法对Benchmark模型的多基地散射声场进行仿真计算,分析多基地(全向)声散射特性及散射机理。结果表明,水中目标多基地散射的回波强度与回波结构与多基地分置角相关,且回波亮点的主瓣宽度也随多基地分置角变化而变化;Benchmark模型的艇体和指挥舱之间存在强烈的干涉作用,使多基地(全向)散射声场的竖状条纹发生倾斜。研究为水下目标的多基地探测提供理论支持。     

用快速场(FFP)分析空气中声源在水下产生的声场

本文介绍了基于传捅矩阵的快速场(FFP)模型,并用该模型开发出相应的计算机程序,用于对空气中声源在水下产生的声场进行分析.研究了空气中声源高度对于水下声场的影响.计算结果表明,在不考虑空气声吸收的情况下,在远场,声源的高度变化对水下声场强弱影响不大,而在声源正下方区域,随着声源的高度增加,声场减弱.     

热声热机的网络模型与仿真研究

介绍了热声热机的网络模型和其仿真计算方法。所开发的计算程序能预测热声系统的声场、回热器等元件及系统的阻抗、以及包括制冷量、制冷温度、热流、声功和ＣＯＰ等的性能参数。本模型的仿真研究将为热声系统的优化设计提供前提和依据。     

敷设粘弹性材料的多层吸声模型阻抗匹配

研究敷设粘弹性材料多层结构的阻抗匹配方法对水下目标隐身具有重要意义。文中利用多层介质声传播理论,推导了简洁的任意多层结构模型声场特性计算公式,并结合粘弹性材料的动态特性,应用所推公式计算了水下敷设吸声材料多层模型的声场特性。借助数值分析方法,对多层结构模型各层材料特性阻抗与模型声学性能间的关系进行了仿真,探索利用模型各层特性阻抗设计模型阻抗匹配的方法。通过分析模型各层特性阻抗比例关系对模型声场特性的影响,得出其实现阻抗匹配的最优取值范围。研究结果对设计、选取吸声材料具有重要意义。     

纹影法在超声场成像中的应用

纹影法成像系统具有分辨率高、成像速度快等特点,可以实现稳态声场分布以及声波传播的瞬态过程快速成像。将纹影法应用于瞬态声传播特性以及声子晶体声场的成像研究。在瞬态成像时,记录了单脉冲辐照固体表面产生的泄漏瑞利波和泄漏纵波的传播过程,并且与仿真结果进行比较,两者的泄漏波辐射角较一致。在声子晶体声场的成像中,通过改变入射频率,观察到了声子晶体在其工作频率时背表面的稳态声场,为其俘获颗粒能力的研究与分析提供了直观的实验依据。     

基于介尺度曳力模型双组分颗粒混合的CFD模拟

为了对鼓泡流化床内双组分颗粒混合过程进行更精准的计算流体力学(CFD)数值模拟,结合颗粒动力学理论和欧拉多流体模型,建立以气泡为介尺度的双组分曳力模型,在三维鼓泡流化床反应器中模拟了双组分颗粒的分离和混合过程,并通过实验数据验证该模型的准确性,分析外界操作条件和颗粒物性参数对双组分颗粒的分离和混合过程的影响。结果表明:固相颗粒直径的减小、气体入口表观速度的增大以及床层温度的升高都将会加大两相间曳力的非均质性,固相颗粒混合程度逐渐加大;随着颗粒直径和入口气体表观速度的减小,两相颗粒分离程度加大,混合指数随之减小;颗粒物性和外界操作条件的合理匹配有利于双组分颗粒的分离。     

封闭空间中结构声辐射的有源力控制研究

推导了在初级力源和次级力源共同作用下的弹性结构振动声辐射公式,对封闭空间中的有源结构声控制（ＡＳＡＣ）建立了有源力最优控制模型。模拟实验研究了弹性结构由力源激励所产生的封闭空间声场的特点、有源控制力向量的位置、幅值和次级力源个数的选择等问题。结果表明,弹性结构在力源激励下的封闭声场,是由激励力大小、结构模态和空腔模态间的耦合决定的;对于单模态振动声辐射,应选取振幅最大处作为次级力源的位置,同时优化力的大小;另外,合理选取次级力源个数可有效控制多模态振动声辐射。这些结论为建立封闭空间中结构声辐射有源力控实验系统提供了理论基础。     

The Effect of Frequency Sweeping and Fluid Flow on Particle Trajectories in Ultrasonic Standing Waves

Particle concentration and separation in ultrasonic standing waves through the action of the acoustic radiation force on suspended particles are discussed. The acoustic radiation force is a function of the density and compressibility of the fluid and the suspended particles. A two-dimensional theoretical model is developed for particle trajectory calculations. An electroacoustic model is used to predict the acoustic field in a resonator, driven by a piezoelectric transducer. Second, the results of the linear acoustic model are used to calculate the acoustic radiation force acting on a particle suspended in the resonator. Third, a particle trajectory model is developed that integrates the equation of motion of a particle subjected to a buoyancy force, a fluid drag force, and the acoustic radiation force. Computational fluid dynamics calculations are performed to calculate the velocity field that is subsequently used to calculate fluid drag. For a fixed frequency excitation, the particles are concentrated along the stable node locations of the acoustic radiation force. Through a periodic sweeping of the excitation frequency particle translation is achieved. Two types of frequency sweeps are considered, a ramp approach and a step-change method. Numerical results of particle trajectory calculations are presented for two configurations of flow-through resonators and for two types of frequency sweeping. It is shown that most effective particle separation occurs when the fluid drag force is orthogonal to the acoustic radiation force.     

微构件所受超声辐射力理论研究

为了将超声波俘获技术应用到微机电系统中,以达到对微构件进行无损、非接触遥操纵的目的,开展了微构件在超声波场中所受辐射力的理论研究．计算机仿真结果表明：微构件的材料与尺寸、介质的密度、超声波的声学参数等都对微构件所受辐射力产生影响,同时,利用超声驻波场技术实现对微构件的操纵是可行的．     

Massively Multiplexed Submicron Particle Patterning in Acoustically Driven Oscillating Nanocavities

Nanoacoustic fields are a promising method for particle actuation at the nanoscale, though THz frequencies are typically required to create nanoscale wavelengths. In this work, the generation of robust nanoscale force gradients is demonstrated using MHz driving frequencies via acoustic‐structure interactions. A structured elastic layer at the interface between a microfluidic channel and a traveling surface acoustic wave (SAW) device results in submicron acoustic traps, each of which can trap individual submicron particles. The acoustically driven deformation of nanocavities gives rise to time‐averaged acoustic fields which direct suspended particles toward, and trap them within, the nanocavities. The use of SAWs permits massively multiplexed particle manipulation with deterministic patterning at the single‐particle level. In this work, 300 nm diameter particles are acoustically trapped in 500 nm diameter cavities using traveling SAWs with wavelengths in the range of 20–80 µm with one particle per cavity. On‐demand generation of nanoscale acoustic force gradients has wide applications in nanoparticle manipulation, including bioparticle enrichment and enhanced catalytic reactions for industrial applications.     

Effects of various parameters on ultrasonic separation of inclusions from magnesium alloy melt

The acoustic radiation force generated by ultrasonic standing wave in the flow media can make solid particles suspending in the liquid agglomerate at the nodal planes of the waves and then realize their separation, which is also known as ultrasonic agglomeration in chemical industry. In this paper, ultrasonic waves were employed to promote and accelerate the separation of inclusions from magnesium alloy melt, and the effect of acoustic radiation forces on oxide inclusions removal from magnesium alloy melts were studied by numerical calculation. The agglomeration behavior of the inclusions was also obtained by solving the equations of motion for inclusions. Finally, parametric studies, usually very helpful for continued optimization and design efforts, were carried out to evaluate the effects of various parameters such as ultrasonic power, ultrasonic treating time, particle size and density difference between particle and melt on the inclusions distribution. The results indicate that when a moderate ultrasonic power was applied, most of inclusions could agglomerate at wave nodes in a short time which finally enhanced and accelerated the separation of inclusions from magnesium alloy melt.     

Matrix method for acoustic levitation simulation

A matrix method is presented for simulating acoustic levitators. A typical acoustic levitator consists of an ultrasonic transducer and a reflector. The matrix method is used to determine the potential for acoustic radiation force that acts on a small sphere in the standing wave field produced by the levitator. The method is based on the Rayleigh integral and it takes into account the multiple reflections that occur between the transducer and the reflector. The potential for acoustic radiation force obtained by the matrix method is validated by comparing the matrix method results with those obtained by the finite element method when using an axisymmetric model of a single-axis acoustic levitator. After validation, the method is applied in the simulation of a noncontact manipulation system consisting of two 37.9-kHz Langevin-type transducers and a plane reflector. The manipulation system allows control of the horizontal position of a small levitated sphere from -6 mm to 6 mm, which is done by changing the phase difference between the two transducers. The horizontal position of the sphere predicted by the matrix method agrees with the horizontal positions measured experimentally with a charge-coupled device camera. The main advantage of the matrix method is that it allows simulation of non-symmetric acoustic levitators without requiring much computational effort.     

水中板声辐射的声功率模态分析

由于水中结构的振动声辐射要考虑流体加载效应,因此水中结构声辐射的模态分析也与空气中的有所不同。基于辐射声功率的二次型表达式,采用有限元和Rayleigh积分耦合方法,对板结构的水下声功率模态进行了计算分析研究,通过辐射效率、模态振型和辐射声功率等探讨了其特点。结果表明以激励力为变量、考虑了结构阻抗的水下声功率模态具有各阶模态声辐射独立、低频时前几阶模态(特别是第1阶模态)的声辐射占主导地位、模态辐射效率峰值和模态振型物理意义清楚等特点,在水下结构振动声辐射的分析和控制方面有一定实用价值。     

Noninvasive acoustic cell trapping in a microfluidic perfusion system for online bioassays

Techniques for manipulating, separating, and trapping particles and cells are highly desired in today's bioanalytical and biomedical field. The microfluidic chip-based acoustic noncontact trapping method earlier developed within the group now provides a flexible platform for performing cell- and particle-based assays in continuous flow microsystems. An acoustic standing wave is generated in etched glass channels (600x61 microm2) by miniature ultrasonic transducers (550x550x200 microm3). Particles or cells passing the transducer will be retained and levitated in the center of the channel without any contact with the channel walls. The maximum trapping force was calculated to be 430+/-135 pN by measuring the drag force exerted on a single particle levitated in the standing wave. The temperature increase in the channel was characterized by fluorescence measurements using rhodamine B, and levels of moderate temperature increase were noted. Neural stem cells were acoustically trapped and shown to be viable after 15 min. Further evidence of the mild cell handling conditions was demonstrated as yeast cells were successfully cultured for 6 h in the acoustic trap while being perfused by the cell medium at a flowrate of 1 microL/min. The acoustic microchip method facilitates trapping of single cells as well as larger cell clusters. The noncontact mode of cell handling is especially important when studies on nonadherent cells are performed, e.g., stem cells, yeast cells, or blood cells, as mechanical stress and surface interaction are minimized. The demonstrated acoustic trapping of cells and particles enables cell- or particle-based bioassays to be performed in a continuous flow format.     

细颗粒物声波团聚的微观机理研究

为拓展声波团聚机理,对声波团聚过程中的声流与声涡作用进行了理论和实验研究。利用声流测试系统,发现在0～1 kHz低频与5 kHz高频时,团聚室内声流现象较为明显;并通过可视化测试,在7 kHz高频时观察到明显的漩涡。结果表明,流场中的声流与声涡对颗粒团聚会产生很大的影响,声流或声涡越强,团聚效果越好。在0～1 kHz低频与5 kHz高频时,声流产生的切应力带动气溶胶颗粒发生碰撞团聚;高频时声涡力矩较大,其产生的轨道角动量带动粒子发生圆周和自旋运动;当声压级大于132 dB时,声涡团聚开始发挥作用,与声流一起促进颗粒团聚,且声压级越大团聚效果越强;与波节相比,波腹处的声流速度更大,声涡现象更明显,团聚效果也更好。     

声凝并中颗粒间相互作用研究进展

声凝并是细颗粒物(PM2.5)排放控制的重要技术途径,其通过外加声场作用促进PM2.5发生碰撞凝并,使得颗粒数目减少、粒径增大,从而提高后续除尘装置的效率。对声凝并中颗粒间的相互作用机理,包括同向相互作用、声尾流效应、互辐射压力效应、互散射效应的相关研究进行总结和评述,结合声凝并技术在PM2.5排放控制中的应用,指出已有研究在理论模型和实验观测上存在的问题,进而提出今后的研究应在实验方法上进行创新,发展出能够跟踪微米和亚微米尺度PM2.5颗粒或颗粒团相互作用过程细节信息的实验手段,为理论模型的实验验证提供数据支撑;同时应进一步发展理论模型,从而在模型验证的基础上,充分发挥数值模拟的优势,全面识别声凝并中颗粒间相互作用的动力学行为。     

脉冲波声场的数值计算与测试研究

针对超声检测中影响缺陷定量准确性的声场问题进行了深入讨论,研究了脉冲波声场的计算方法,设计了相应的计算软件并绘制出实用换能器声轴线上的声压分布曲线,分析了不同材料和厚度的采样回波对频谱的影响,比较了连续波声场和脉冲波声场的分布特性及异同点。对脉冲波声场的测试结果表明,数值计算和实测结果有较好的一致性。本研究结果为提高超声检测中缺陷定量的准确性和科学性提供了依据。