Modification of the ultrasound induced activity by the presence of an electrode in a sono-reactor working at two low frequencies (20 and 40 kHz). Part II: Mapping flow velocities by particle image velocimetry (PIV)

Sonoelectrochemical experiments differ from sonochemical ones by the introduction of electrodes in the sonicated reaction vessel. The aim of the study is to characterize the changes in the ultrasonic activity induced by the presence of an electrode located in front of the transducer. The scope of our investigations concerns two low frequency vibration modes: 20 and 40 kHz. For this purpose, two laser visualization techniques have been used. The first part of the study, described in a previous paper (Part I), deals with the laser tomography technique which provides an accurate picture of the reactor active zones, related to numerous cavitation events. The second part of the paper (Part II) will describe the particle image velocimetry (PIV) technique used to measure the velocity vector field in the fluid portion between the horn and the electrode. As for the previous study, two parameters were studied: the electrical power supplied to the transducer and the electrode/transducer distance. The velocity vector fields show a main flow in the reactor axis. This flow seems to correspond to the conical cavitation bubbles structure which is observed on the laser tomography pictures. When an electrode is introduced into the reactor, two additional symmetric transversal flows can be quantified on both sides of the electrode.     

Built-up edge investigation in vibration drilling of Al2024-T6

Adding ultrasonic vibrations to drilling process results in an advanced hybrid machining process, entitled “vibration drilling”. This study presents the design and fabrication of a vibration drilling tool by which both rotary and vibrating motions are applied to drill simultaneously. High frequency and low amplitude vibrations were generated by an ultrasonic transducer with frequency of 19.65 kHz. Ultrasonic transducer was controlled by a MPI ultrasonic generator with 3 kW power. The drilling tool and workpiece material were HSS two-flute twist drill and Al2024-T6, respectively. The aim of this study was investigating on the effect of ultrasonic vibrations on built-up edge, surface quality, chip morphology and wear mechanisms of drill edges. Therefore, these factors were studied in both vibration and ordinary drilling. Based on the achieved results, vibration drilling offers less built-up edge and better surface quality compared to ordinary drilling.     

The complex-mode vibration of ultrasonic vibration systems

The longitudinal-flexural and torsional-flexural vibrations are studied for the ultrasonic solid horn and the ultrasonic vibration system comprised of a sandwich transducer and a solid horn. The discussed solid horn is of arbitrary non-uniform cross-section. The analysis on flexural-mode vibration is based on Timoshenko theory. The theoretical results are verified by experiment.     

铜微颗粒碰撞阻尼特性

碰撞阻尼在机床、机器人、透平机械、飞机以及运载火箭等领域具有重要的应用价值. 在碰撞阻尼器中加入微颗粒材料, 可以利用颗粒的细化和塑性变形而有效地吸收振动能量, 为碰撞阻尼的研究和发展开辟了一条新途径. 本文讨论了带有中值粒度为50 μm的铜颗粒碰撞阻尼器在96 h内对正弦激励悬臂梁的阻尼减振特性. 研究表明, 在所考察的时间段内, 主系统的响应经历了先上升、再下降和再上升的过程. 这三个阶段的响应对应着铜颗粒微观结构变化的三个阶段. 在初始阶段, 铜颗粒主要表现为弹性变形, 能耗较低, 而钢球的次谐波共振可能将部分能量返回给主系统, 使主系统响应随时间呈现近似线性的上升; 在第二阶段, 当主系统响应增加到一定程度时, 钢球对铜粉的冲击力超出铜颗粒的屈服应力, 铜颗粒发生屈服, 不可逆能耗使主系统的响应震荡下降; 到了第三阶段, 铜颗粒在钢球冲击下发生硬化, 其应变和层错概率上升, 应变能和层错能下降, 主系统的响应再次持续震荡上升. 本文的结果对振动的被动控制以及材料塑性变形机理研究具有参考 意义. 关键词： 振动控制 碰撞阻尼 颗粒减振剂 微结构分析     

Equivalent circuits and directivity patterns of air-coupled ultrasonic transducers

Air-coupled transducers for producing ultrasonic radiation in gases are studied. The transducer consists of a circular thin plate in flexural vibration and a sandwich longitudinal electromechanical vibrator that is attached to the center of the plate. The lowest-order axially symmetric flexural vibrational mode of a circular thin plate is analyzed. The equivalent circuits of the circular plate in flexural vibration and the compound transducer are presented and the frequency equation is derived. The radiated ultrasonic field of the circular thin plate in flexural vibration is calculated and the directivity pattern is obtained theoretically. Some transducers of this type are designed according to the frequency equation, and their resonance frequencies are measured. The measured resonance frequencies are in good agreement with the theoretical results, and the calculated radiation ultrasonic field is also in good agreement with the measured results of a previous work.     

Optimization design of high power ultrasonic circular ring radiator in coupled vibration

This paper presents a new high power ultrasonic (HPU) radiator, which consists of a transducer, an ultrasonic horn, and a metal circular ring. Both the transducer and horn in longitudinal vibrations are used to drive a metal circular ring in a radial-axial coupled vibration. This coupled vibration cannot only generate ultrasound in both the radial and axial directions, but also focus the ultrasound inside the circular ring. Except for the radial-axial coupled vibration mode, the third longitudinal harmonic vibration mode with relative large vibration amplitude is also detected, which can be used as another operation mode. Overall, the HPU with these two vibration modes should have good potential to be applied in liquid processing, such as sonochemistry, ultrasonic cleaning, and Chinese herbal medicine extraction.     

Forced vibrations of two nonlinearly connected solid waveguides under static load

Forced impact oscillations in nonlinearly coupled solid waveguides with nearly equal natural frequencies are examined using the harmonic balance method. A dynamic model is used to describe the process of ultrasonic micro-forging where the material to be worked is considered as a nonlinear connecting-link between the ultrasonic transducer and passive waveguide-reflector. The influence of the material properties (yield stress, stiffness of tool-workpiece contact, striker and blank geometries) and the processing conditions (amplitude of vibration, static compressive force, work rate) on the resonance characteristics of the vibratory system is taken into account. The resonance and antiresonance frequencies, boundaries of response stability, ranges of inphase and antiphase oscillations of impacting waveguides, and some other features of strongly coupled vibrators under impact loading are determined.It is shown also that the largest amplitude of impact oscillations can be attained only if the natural frequency of the ultrasonic transducer exceeds that of the waveguide-reflector. By measuring the dynamic drift in the unfastened ultrasonic unit, it is possible to control, directly in the course of ultrasonic micro-forging, the thickness of the metal workpiece. Calculated data are compared with the experimental results.     

Study on the high power air-coupled ultrasonic compound transducer

The high power air-coupled compound ultrasonic transducer in flexural vibration is studied. The transducer consists of a sandwich longitudinal piezoelectric transducer and a circular thin plate in flexural vibration. The resonance frequency equation and the equivalent circuit of a circular radiator with clamped boundary condition are derived. The resonance frequency equation and the equivalent circuit of the compound transducer are also obtained. The radiated acoustic field of the circular thin plate radiator is analyzed and the directional pattern is calculated. It can be seen that when the vibrational order of the circular thin plate in flexural vibration is increased, the radiated acoustic field becomes complex.     

Ultrasonic particle size fractionation in a moving air stream

Identification of bio-aerosol particles may be enhanced by size sorting before applying analytical techniques. In this paper, the use of ultrasonic acoustic radiation pressure to continuously size fractionate particles in a moving air stream is described. Separate particle-laden and clean air streams are introduced into a channel and merged under laminar flow conditions. An ultrasonic transducer, mounted flush to one wall of the channel, excites a standing ultrasonic wave perpendicular to the flow of the combined air stream. Acoustic radiation forces on the particles cause them to move transverse to the flow direction. Since the radiation force is dependent upon the particle size, larger particles move a greater transverse distance as they pass through the standing wave. The outlet flow is then separated into streams, each containing a range of particle sizes. Experiments were performed with air streams containing glass microspheres with a size distribution from 2-22 μm, using a centerline air stream velocity of approximately 20 cm/s. An electrostatic transducer operating at a nominal frequency of 50 kHz was used to drive an ultrasonic standing wave of 150 dB in pressure amplitude. The microsphere size distributions measured at the outlet were compared with the predictions of a theoretical model. Experiments and theory show reasonable correspondence. The theoretical model also indicates an optimal partitioning of the particle-laden and clean air inlet streams.     

大负载超声振动磨削系统的设计

设计了一种大负载超声振动磨削系统,超声系统由换能器、圆柱圆锥形变幅杆和轮辐式砂轮组成.首先将轮辐式砂轮等效成轮毂为圆柱杆、辐板与轮缘为中厚板的复合模型,利用各接触面边界连续的条件推导系统的频率方程,完成了超声磨削系统的设计,制作了实验装置并分析验证了其声学振动特性.实验结果表明:利用轮辐式砂轮复合模型求解系统频率方程,...     

A model-based inverse method for positioning scatterers in a cladded component inspected by ultrasonic waves

Nondestructive methods aim at detecting, locating and identifying defects. Inversion of ultrasonic measurements obtained by inspecting a steel component of regular geometry with an immersed transducer leads to accurate location of defects. When the component is cladded, the irregular geometry of the surface and the anisotropic nature of the cladding material lead to aberrations of the radiated field (e.g., beam distortions, splitting and defocusing, these varying with the transducer scanning position). As a consequence, defect location may be inaccurate and defects (e.g., cracks) sizing impossible. In the present paper, a model-based inverse method is developed to solve this problem. It relies on the time-dependent simulation of ultrasonic propagation in this material of complex geometry and structure, in order to determine a set of probable positions for the defect at the origin of the measured ultrasonic echo-structure. The most probable position is determined by minimizing a cost-function of likeness between the simulated and measured ultrasonic images. The overall scheme shall generally apply to inverse measured ultrasonic echo-structures as soon as the simulation of the forward problem is tractable. To validate the method, examples of application are given dealing with actual measurements obtained in the real configuration of pressure vessel inspection.     

An analogy between free vibration of a plate and of a particle of mass

In this paper, the free flexural vibration of an elastic circular thin plate with an initial imperfection is investigated. Approximate solution of the problem for the fundamental frequency of vibration, of large amplitude and with the plate imperfection, leads to a non-linear ordinary differential equation with time as the independent variable. It is shown that this equation also represents the free vibration of a particle of mass on a shallow curve of fourth degree.. With this similarity in view, it is possible to draw an analogy between these two vibrations. A numerical analysis is made with particular reference to this analogy and the results are given in various figures which represent the vibratory motion and the period of vibration versus the initial amplitude of the plate or of the particle of mass.     

高功率超声脉冲激励下金属板的非线性振动现象研究

对高功率超声脉冲作用下金属板中的超谐波、次谐波、准次谐波以及混沌等非线性振动现象进行了实验和理论研究.在实验中,高功率超声换能器产生脉冲调制的高频振动激励金属板产生非线性振动,利用激光测振技术测量不同尺寸和不同固定方式下金属板复杂的非线性振动情况,并对其进行了时序分析、频谱分析以及相空间分析.根据实验条件,提出包含非线性接触阻尼的振动-碰撞动力学模型,用以研究强超声振动-碰撞作用下的板非线性振动机制,并进行了相应的理论计算.计算结果表明,超声换能器的变幅杆与金属板之间的间歇性高频碰撞作用是金属板强非线性振 关键词： 非线性板振动 强超声脉冲激发 振动-碰撞动力学     

声子晶体结构在功率超声换能器中的应用

该文提出了一种二维声子晶体结构模型,并将该模型应用于横向尺寸较大的功率超声换能器的前盖板中,避免了形成耦合振动对换能器的影响,从而优化了该类换能器的工作性能.首先设计了一种具有近周期性结构的圆柱形孔的前盖板,然后研究了声子晶体结构前盖板散射体的半径大小和高度对换能器共振频率以及前盖板带隙的影响.结果表明,随着散射体半径...     

超声辐照及辐照环境对液体中流场分布特性的影响

研究了超声辐照下液体中声压场分布,模拟了流场分布的特性,模拟结果与利用粒子成像测速仪得到的实验结果相符。进一步研究了声学参数及容器几何环境对流场分布的影响。研究发现,增大超声功率和频率可使流场速度变大:在30~60W范围内,超声功率与流场中最大流速间存在线性关系;在频率为100~472kHz范围内,流场速度大小随频率的升高而增加:在层流区,流速与频率的平方成正比;在湍流区,流速与频率的1/2次方成正比。进一步研究发现,随着换能器到容器壁间距离的增加,流场速度减小。      

Granular layers on vibrating plates: effective bending stiffness and particle-size effects

Acoustic methods of land mine detection rely on the vibrations of the top plate of the mine in response to sound. For granular soil (e.g., sand), the particle size is expected to influence the mine response. This hypothesis is studied experimentally using a plate loaded with dry sand of various sizes from hundreds of microns to a few millimeters. For low values of sand mass, the plate resonance decreases with added mass and eventually reaches a minimum without particle size dependence. After the minimum, a frequency increase is observed with additional mass that includes a particle-size effect. Analytical nondissipative continuum models for granular media capture the observed particle-size dependence qualitatively but not quantitatively. In addition, a continuum-based finite element model (FEM) of a two-layer plate is used, with the sand layer replaced by an equivalent elastic layer for evaluation of the effective properties of the layer. Given a thickness of sand layer and corresponding experimental resonance, an inverse FEM problem is solved iteratively to give the effective Young's modulus and bending stiffness that matches the experimental frequency. It is shown that a continuum elastic model must employ a thickness-dependent elastic modulus in order to match experimental values.     

Biodiesel production from palm oil using combined mechanical stirred and ultrasonic reactor

This paper investigates the production of biodiesel from palm oil using a combined mechanical stirred and ultrasonic reactor (MS–US). The incorporation of mechanical stirring into the ultrasonic reactor explored the further improvement the transesterification of palm oil. Initial reaction rate values were 54.1, 142.9 and 164.2 mmol/L min for the mechanical-stirred (MS), ultrasonic (US) and MS–US reactors, respectively. Suitable methanol to oil molar ratio and the catalyst loading values were found to be 6 and 1 of oil, respectively. The effect of ultrasonic operating parameters; i.e. frequency, location, and number of transducer, has been investigated. Based on the conversion yield at the reactor outlet after 1 h, the number of transducers showed a relevant role in the reaction rate. Frequency and transducer location would appear to have no significant effect. The properties of the obtained biodiesel (density, viscosity, pour point, and flash point) satisfy the ASTM standard. The combined MS–US reactors improved the reaction rate affording the methyl esters in higher yield.     

压电瞬态响应在换能器声功率测量中的应用

探索一种简便的聚焦超声功率测量方法,利用压电陶瓷片直接接收超声信号,通过机电类比得到压电瞬态响应由压电片在声波作用力下引起受迫振动产生的电压响应与固有振动产生的高频衰减响应叠加而成,分析输出压电信号与换能器声功率之间的换算关系。对输出压电信号进行二次包络提取,获得表征声功率变化的电压幅度曲线,分别找出不同换能器驱动电压下包络曲线的最大峰值电压,将其平方值与声功率计所测声功率进行线性拟合,并对理论关系式中的比例系数进行标定。实验结果所得线性拟合度较高,且标定后所得声功率与声功率计所测值相对误差低于8.7%,证明了通过压电瞬态响应测量换能器声功率具有可行性。      

Microfeeding with different ultrasonic nozzle designs

Microfeeding of dry powder excited by ultrasonic vibration makes use of relatively simple equipment and can be applied to solid freeforming and pharmaceutical dosing. The nozzle was a vertical glass capillary and four configurations for ultrasonic actuation were investigated: Type I had a piezoelectric transducer ring bonded to the base of a cylindrical water-containing vessel containing an axial nozzle; Type II had a piezoelectric transducer ring attached to the sidewall of the vessel; Type III used direct mechanical connection to the glass wall of the capillary to give nominally longitudinal vibration; and Type IV also used direct connection to the glass tube but arranged to give progressive wave vibration. The experimental results show that all four configurations realized powder microfeeding and dosing but the characteristics, in terms of minimum flow rate, dependence on voltage amplitude and uniformity of dose varied considerably. The discharge of particles was observed by a high-speed camera.     

幂函数型环形聚能器径向振动的等效电路

基于机电类比原理和变厚度薄圆环的平面应力方程,推导了幂函数型环形聚能器径向振动的等效电路、共振频率方程和位移放大系数。讨论了第一、二阶径向共振频率及相应的位移放大系数随圆环半径比的变化关系。结果表明,幂函数型环形聚能器径向振动的等效电路是一种非互易二端口等效网络;一阶和二阶共振频率随圆环内外半径比的增大而增大;一阶径向共振模式下位移放大系数随圆环半径比的增大先降低后升高,二阶径向共振模式下位移放大系数随圆环半径比的增大而降低,但二阶时的位移放大系数整体大于一阶,因此二阶径向共振模式具有更好的径向振动性能。用COMSOL有限元软件对解析理论分析结果进行了验证,仿真模拟结果与解析理论符合良好。根据幂函数型环形聚能器的等效电路模型,进一步设计了一种压电环形换能器,计算了第一、二阶径向共振频率、反共振频率及有效机电耦合系数,通过与COMSOL有限元软件模拟结果对比,符合良好。本文研究结果为幂函数型环形聚能器及压电环形换能器的工程应用提供了简明设计理论,文中研究结论可作为一种径向超声切割刀在超声工程中获得重要应用。