Valid Regions of Formulas of Sound Speed in Bubbly Liquids

There are numerous formulae relating to the predictions of sound wave in the cavitating and bubbly flows. However, tile valid regions of those formulae are rather unclear from the view point of physics. In this work, the validity of the existing formulae is discussed in terms of three regions by employing the analysis of three typical lengths involved （viscous length, thermal diffusion length and bubble radius）. In our discussions, viscosity and thermal diffusion are both considered together with the effects of relative motion between bubbles and liquids. The importance of relative motion and thermal diffusion are quantitatively discussed in a wide range of parameter zones （including bubble radius and acoustic frequency）, The results show that for large bubbles, the effects of relative motion will be prominent in a wide region.

Some Aspects of Ray Representation Running Sound Waves in Liquid Spaces

Work is devoted to the analysis of errors meeting in literature in treatment of a spatial part of a phase of running sound waves. In some cases, it is not taken into consideration that this part of a phase is formed by scalar product of vectors which does not depend on a choice of system of co-ordinates. Taking into account the necessary corrections in record of a phase of plane waves, it is shown that the decision of the homogeneous wave equation in the form of “belated” potentials is simultaneously and the decision of the equations of movement of a liquid, and “outstripped” potentials does not satisfy them. The analysis of coefficients of reflection and passage of running waves in non-uniform space is carried out. It is shown that on boundary of spaces with different sound speeds, a turning point of a sound wave is the point of full internal reflection. The way of calculation of coefficients of reflection and passage is offered by consideration of all three waves on boundary of spaces as vectors with the set directions and amplitude of a falling wave. Calculation of coefficients of reflection and passage of a sound wave in a wave-guide of canonical type along the chosen trajectory by two methods—under traditional formulas and a vector method is carried out. Results of calculation practically coincide.

To the Question of Sound Waves Propagation in Liquid

This paper is proposed to consider the propagation of sound waves in the liquid as a result of special deformation of the medium. Mechanical vibrations of the membrane, (diaphragm) creating a sound wave, transfer from layer to layer in medium without causing synchronous oscillations of the fluid particles. It can be assumed that the deformation of the liquid is similar to the driving force (pressure) in the direction perpendicular to the plane of the vibrating membrane. Usually, the running wave functions are used to describe the sound waves, but they do not contain the direction of propagation. It is proposed to consider that the amplitude of the wave is a vector coinciding with the vector tangent to the path of the wave. This would allow for a change of direction of propagation without changing its phase, in which the direction of wave is not present. It proposed a method of calculating a vector of amplitudes of the reflected and transmitted sound waves based on the laws of conservation of impulse and energy of the waves and the boundary conditions defined by Snell’s law. It is shown that one of the two solutions of the wave equation does not apply to real physical process of sound wave’s propagation in the liquid.

A New Concept of Calculation Coefficietns of Reflection and Passage Sound Waves on the Boundary of Liquid Spaces

It is consider that, from the standpoint of the law of conservation of energy, the process of converting sound wave falls on the boundary between two spaces in two, leaving the boundary, reflected and passage. It is assumed that the simultaneous presence of three waves is impossible, and that the process of converting one wave in two waves occurs instantaneously. Based on this concept, enter the following boundary conditions for the calculation of amplitudes (coefficients) of the reflected and passage waves. The initial phases of the reflected and passage waves coincide with the phase of the falling wave. The energy of the falling wave is equal to the sum of the energies of the reflected and passage waves. The normal component velocity amplitude of the particle of the liquid under the influence of the falling wave is equal to the sum of the normal component of particle velocity amplitudes of the reflected and passage waves. It was found that the character of dependence of the reflection coefficient on the angle of departure of the initial wave is the same as in the traditional formulas, but the coefficient of passage does not exceed unity. Calculations of reflection and passage coefficients for different values of the refractive coefficient at the boundary between two homogeneous spaces as well as the canonical form of the waveguide, wherein the speed of sound which is minimum at predetermined depth is carried out.

Properties of sound attenuation around a two-dimensional underwater vehicle with a large cavitation number

Due to the high speed of underwater vehicles, cavitation is generated inevitably along with the sound attenuation when the sound signal traverses through the cavity region around the underwater vehicle. The linear wave propagation is studied to obtain the influence of bubbly liquid on the acoustic wave propagation in the cavity region. The sound attenuation coefficient and the sound speed formula of the bubbly liquid are presented. Based on the sound attenuation coefficients with various vapor volume fractions, the attenuation of sound intensity is calculated under large cavitation number conditions. The result shows that the sound intensity attenuation is fairly small in a certain condition. Consequently, the intensity attenuation can be neglected in engineering.

New Method in Calculating the Trajectory of Sound Waves at Stratified Ocean

There is a new method of calculating the trajectory of sound waves (rays) in layered stratified speed of sound in ocean without dispersion. A sound wave in the fluid is considered as a vector. The amplitudes occurring at the boundary layers of the reflected and refracted waves are calculated according to the law of addition of vectors and using the law of conservation of energy, as well as the laws that determine the angles of reflection and refraction. It is shown that in calculating the trajectories, the reflected wave must be taken into account. The reflecting wave’s value may be about 1 at certain angles of the initial wave output from the sours. Reflecting wave forms the so-called water rays, which do not touch the bottom and the surface of the ocean. The conditions of occurrence of the water rays are following. The sum of the angles of the incident and refracted waves (rays) should be a right angle, and the tangent of the angle of inclination of the incident wave is equal to the refractive index. Under these conditions, the refracted wave amplitude vanishes. All sound energy is converted into the reflected beam, and total internal reflection occurs. In this paper, the calculation of the amplitudes and beam trajectories is conducted for the canonical type of waveguide, in which the speed of sound is asymmetric parabola. The sound source is placed at the depth of the center of the parabola. Total internal reflection occurs in a narrow range of angles of exit beams from the source 43° - 45°. Within this range of angles, the water rays form and not touch the bottom and surface of ocean. Outside this range, the bulk of the beam spreads, touching the bottom and the surface of the ocean. When exit corners, equal and greater than 77°, at some distance the beam becomes horizontal and extends along the layer, without leaving it. Calculation of the wave amplitudes excludes absorption factor. Note that the formula for amplitudes of the sound waves applies to light waves.

PMMA多孔微球改性制备隔声材料研究

以甲基丙烯酸甲酯、偶氮二异丁腈、聚乙二醇、明胶以及钠化、有机化处理后的蒙脱土为原料,制备了聚甲基丙烯酸甲酯/蒙脱土(PMMA/MMT)多孔微球,并将其作为填料其加入液体硅橡胶泡沫材料中,制备出一种隔声材料。通过扫描电子显微镜、BET测试、激光粒度测试、阻抗管法等分析方法,研究了PMMA/MMT多孔微球的结构与性能,以及其掺入对所制备隔声材料对不同频段噪声的隔声性能的影响。结果表明:包覆MMT后的PMMA多孔微球的比表面积、孔容和孔径都得到提高,粒径均一性较好,将其掺入液体硅橡胶泡沫后,材料的中低频隔声性能显著提升,微球掺量为10%的复合材料对500~2000Hz中频段噪声的隔声量(TL)比未掺微球时提高了44%。

部分浸没充液无限长圆柱壳声辐射特性研究

本文旨在研究圆柱壳的浸没和充液对其声辐射特征的影响,为界面附近充液壳体目标声学性能的评估和测量提供理论依据和研究方法。通过有限元数值仿真方法计算得到半充液无限长圆柱壳辐射声压的频率-浸没深度谱和半浸没无限长圆柱壳辐射声压的频率-充液高度谱,结果均呈现出两种明显的共振现象,分别由弯曲波和低阶流体附加波激发。根据相速度频散曲线推导出共振频率的预报公式,能够准确地预报辐射声场中出现的共振现象,可为系泊状态内部液舱结构振动声辐射线谱特征控制与评估提供理论支撑。

气井环空液面下泄漏声场模拟

气井油套管环空液面下泄漏声波的产生及传播机理一直备受关注。为研究液面下泄漏声波声源特性,建立了井下油套管环空泄漏物理模型,联合STAR-CCM+软件对环空液面下气体泄漏状态进行了流场及声场的仿真分析,得到了泄漏流场的压力和相态云图及不同泄漏孔径、泄漏位置和泄漏速度下的声压频率曲线。研究结果表明:随着泄漏速度升高,泄漏气流冲击管壁且液面震荡剧烈,液面下泄漏声源主要以四极子声源为主;液面上泄漏声源主要由液面震荡破裂及液面下四极子声源共同产生,泄漏声波能量的主要频率分布在0~100 Hz区间;在单一变量条件下,泄漏声压级随泄漏孔径、泄漏速度及泄漏位置距底部距离的增大而增大。研究结果可为在井口应用声波法检测液面下泄漏奠定理论基础。

水平管气液两相流流型变化诱导噪声特性研究

为探究水平管内气液两相流流型变化激励流动噪声特性,结合VOF(volume of fluid)多相流模型与Lighthill声类比理论开展数值计算研究。结果表明,随着气相和液相流速增加,气液两相流呈现弹状流–层状流–泡状流的演变规律,进而导致噪声呈现不同变化趋势。随着频率增加,弹状流噪声呈现先减小后增大的趋势,而层状流和泡状流噪声分别呈现逐渐减小和增大的趋势。此外,在不同工况下,泡状流诱导噪声最大,弹状流噪声次之,层状流噪声最小。研究成果对于气液两相流噪声控制技术研究具有重要指导作用。

中央空调多联机液流噪音影响因素研究及对策

家用多联机使用过程中出现的噪音问题,是目前多联机售后投诉的重中之重,但由于多联机空调的控制逻辑复杂性、安装规范性、系统可靠性因素,带来了问题处理的高难度。多联机噪音问题多种多样,其中多联机内机的液流噪音,是所有噪音问题里最难解决的。本文调研了现有主流造成多联机内机液流噪音的各种因素,结合实际处理过程的有效方法经验,分析了各类液流噪音的形成机理、控制关键因素,总结形成有效的系统解决策略。

基于电磁式声波发射的环空液面连续监测技术研究与应用

钻遇井漏失返后,井筒内液柱压力长时间低于地层压力后易引发漏转喷,而当前钻井现场主要采用气枪式测距仪对环空钻井液液面高度进行监测,受该测距仪氮气瓶储量的限制,无法连续监测井筒环空液面高度,不便于现场作者人员及时发现漏转喷的井控风险。针对该测距仪的缺陷,文章将电磁式声波发射器引入到井漏后环空液面高度的监测技术中,从环空声波衰减特性研究入手,优化发声器结构设计,提升其低频响应特性,研发了一套基于电磁式声波发射器的环空液面高度自动识别监测系统,该系统具有自动连续监测、测量误差小(测量误差小于2%)、体积小、易操作等优点,便于现场作业人员及时掌握环空液面高度,分析漏层的漏失情况,预判是否存在漏转喷的井控风险,为快速处理井漏复杂、降低井控风险提供技术支撑。

超声波液体密度传感器

介绍了超声波密度传感器的工作原理和超声波探头的选择与制作工艺要点。所设计的硬件电路包括发射电路、放大接收电路和检波整形电路。超声波传播时间的测量是通过ATMEGA16L单片机内部的高速计数器实现的。针对环境温度对密度的测量有较大的影响,采用集成温度传感器AD590与单片机共同完成温度补偿。经测试证明:传感器的准确度达到±0.25%。

气液两相流中的声速研究

气液两相流在工业各领域中广泛存在,而声速是描述其声学性质的一个重要参数。本文从流体的体积弹性模量的定义出发,推导了气液两相流中的声速随含气率的变化关系式,即混合流体的Wood声速公式,将其声速的部分计算结果和其他作者的实验数据进行了比较,吻合良好。并通过COMSOL有限元模拟软件得到不同气体分布下圆管谐振腔最低阶模式的共振频率,间接数值模拟研究了含气率对声速的影响。模拟结果与理论计算结果一致,当气液两相流中含气率较低时,声速随含气率的增大急剧减小。本研究结果为确定声速与气液两相流中的含气率间的关系提供了参考依据。

多通道肺音采集系统设计

目的:设计一种多通道肺音采集系统。方法:系统采用增强型的32位基于ARM核心的微控制器STM32F103ZET6作为核心控制芯片。电容传声器将采集到的肺音信号转换为电信号,设计多路放大滤波电路对肺音电信号进行处理,微控制器通过控制4通道串行输出AD转换芯片ADS8341实现多通道数据采集,采用SD卡作为存储介质用以存储所采集的肺音信号,采用液晶显示器作为人机界面,显示操作提示信息或系统工作状态。结果:可以同时采集1-4通道的肺音数据,采样频率为8789 Hz,数据采样精度为16位,单次可连续存储30s^60s的肺音数据。结论:系统操作简便,体积较小,肺音数据以WAV格式的音频文件存储于SD卡中。计算机可以方便地读取SD卡中肺音数据,进行肺音音频播放,还可以对肺音数据进行进一步的分析处理。系统能准确地采集多通道肺音数据,数据存储快速、可靠,数据读取方便,能满足临床医生采集肺音数据的需求。

基于FPGA的超声波液体密度传感器

液体密度是工业生产中一个重要的参数,尤其是在医药、化工等领域。本文采用双探头结构,利用声速法测量液体密度,其关键是准确测量超声波在液体中传播时间。传统电路设计由于受到芯片时钟频率的影响,测量效果往往不够理想。为了能够得到精确的测量时间,采用内部时钟频率较高的FPGA来设计高精度的计数器。同时,为了减少外围电路,避免电子器件之间的电磁干扰,系统中的控制和计算模块也都由FPGA来完成。经过实验,结果表明本方法具有较高的可靠性和速度上的优越性。

船用超声液位传感器的分析与设计

介绍了一种船用某型超声液位传感器的基本结构和工作原理。在对脉冲式超声探头的轴向声压分布特点及其声透射强度分析研究的基础上,给出了该传感器的超声信号发射端与接收端之间距离d和压电晶片保护膜的壁厚δ值的确定方法。最后设计了一套超声液位传感器性能测试实验平台,对上述理论研究结论进行了实验验证。

透明液体中激光致声特性

研究透明液体的特性阻抗、激光声的传播距离和激光焦斑半径对激光声信号的影响.通过实验和数值计算发现,在一定范围内,随着特性阻抗的增加,声波的峰值声压、主频和声能也相应增加;随着激光声传播距离的增加,激光声的主频从急速下降变为相对稳定;在保证光击穿的条件下,选择较大的激光焦斑半径,可提高光声能量转换效率.

液体性质与吸收能量对激光致声特性的影响

建立了激光致声的产生和测量系统,对蒸馏水、酒精和甘油中的激光致声进行测量分析,分别计算了这3种透明液体在体积模量（0.2-7.0 GPa）、动力粘性系数（0.001-30.000 Pa.s）和所吸收激光脉冲能量（10-400 mJ）变化时对应的激光致声的相关数值。实验和数值计算结果表明：激光致声的主频、峰值声压和声能随着透明液体体积模量的增加而增加;激光致声的峰值声压和声能随着动力粘性系数的增加而减小,随着击穿区所吸收的激光脉冲能量的增加而增加;动力粘性系数和击穿区所吸收的激光脉冲能量对主频的影响不明显。

矩形声化学反应器空化场分布的研究

文章研究了分析反应器尺寸及液体深度对矩形声化学反应器空化场分布的影响。在刚性边界条件下,理论分析得出了纵向声压分布公式。用MATLAB仿真分析了纵向声压分布情况,并用染色法进行了实验验证。结果表明:声场中声压有多种简正声波和高次同相振动叠加而成。近场区总声压幅值以高次同相振动为主,声压幅值随液体深度的增大而迅速衰减;远场区则以简正声波为主,声压幅值随液体深度的增大而起伏变化。当满足一定条件时,在槽体可发生长度共振。