声悬浮无容器处理的实验研究及数值模拟分析

介绍了一种自行研制的单轴式超声悬浮装置，用此装置实现了密度为7．9g／cm。钢球的稳定悬浮，并采用有限元方法对声场进行了数值模拟，分析了试验中常见的小球沿凹球面壁运动的现象，为进一步研究声悬浮的稳定性打下一定的理论基础。     

驾驶室外声场分析的边界元法与无限元法

车外噪声是产生环境噪声的重要因素,驾驶室外声场的数值分析能够为控制噪声提供理论参考。介绍外声场分析的边界元法和无限元法两种数值方法的基本理论,研究声固耦合问题分析的流程,包括无限元法与有限元法耦合、有限元法与边界元法耦合。以拖拉机驾驶室模型为例,对驾驶室外声场进行数值分析,分析结果表明两种方法计算的声场结果基本一致,都能有效地分析驾驶室外声场,指导驾驶室结构设计。     

理想声源辐射声场的数值分析

通过声场的特性和规律分析可以识别和定位噪声源,对噪声控制以及声源的设计提供参考。数值方法是求解有源声场的重要工具,复杂的声辐射一般可分解为简单的声辐射叠加。研究了单极子、偶极子、活塞等几种理想声源辐射声场的解析解,并用有限元法计算数值解,得到相应的辐射声场,包括声压、速度、指向性等量,有限元法得到的数值结果与解析解吻合;利用有限元法计算了点声源的线性阵列与平面阵列等典型的叠加声场。对各种声源的特性和辐射声场的规律以及在工程领域中的应用进行了归纳。     

声振耦合对薄壁圆柱结构动力特性的影响

声振耦合是航空航天飞行器在运行过程中备受关注的问题.针对具有代表性的薄壁圆柱结构,建立声场-结构直接耦合的三维动力学模型,其中结构和声场分别采用实体有限元和三维声单元剖分,并且采用无限元模拟自由声场边界.通过理论和数值分析研究声场中薄壁圆柱结构的模态、幅频响应、相频响应等振动特性的变化规律,讨论声振动对结构动力特性的影响及机理.研究发现声场在大多数情况下降低了结构的固有频率,在低频段声振动相当于给结构增加了附加质量,但是在高频段,声振动和结构阻尼的影响比较相似.随着声场流体密度增大,结构的大多数固有频率值明显减小,结构响应幅值在低频段增大,在高频段减小.声速对声场模态有显著影响,但是对结构模态频率的影响不大.     

驾驶室结构振动及其声固耦合噪声响应分析

利用有限元分析软件ANSYS和声学分析软件SYSNO ISE对卡车驾驶室的振动与内部声场耦合做了数值计算分析研究。介绍了振动频响分析方法,动力学计算与声学边界元模型耦合的具体步骤。通过计算分析,分别研究了驾驶室结构的声固耦合模型与非耦合模型对室内声场的影响,从而找出在不同的壁板厚度条件下,声固耦合作用对室内噪声的影响,以及驾驶室内声场的变化规律。     

球阀气体内漏的声场数值模拟及实验研究

以Lighthill气动力声学方程作为控制方程,采用有限差分法,对不同内漏度和压力差下的球阀气体内漏喷流声场进行了数值模拟。得出它们对球阀气体内漏喷流声场强度和传播特性的影响,确定了球阀气体内漏声场强度最高的位置。数值模拟表明,二次截流处附近的内漏噪声最强,噪声能随着内漏度和压力差的增大而增强,这为球阀气体内漏声学检测与定量分析提供了理论依据。同时采用声学方法对球阀的内漏发声进行了实验研究。实验结果也验证了数值模拟的正确性。     

时域有限差分法在超声波声场特性分析中的应用

超声波无损检测结果与超声波换能器的声场特性密切相关,运用数值方法可以有效地进行超声波声场特性分析。介绍时域有限差分法(Finite difference time domain method,FDTD),分析二维流体运动方程并建立相关有限差分模型,使时域宽带超声波信号的分析更易于实现;应用完全匹配层(Perfect matched layer,PML)方法对FDTD计算的边界进行吸收处理,取得了理想的边界吸收效果;通过数值计算和仿真,研究超声波声场传播特性及圆盘声源声场分布特性,与相关文献的对比表明该算法有效可行;对脉冲波信号激励的聚焦超声波换能器分别进行有限差分法数值仿真和实际测量试验,声束轴向切面的声场分布试验结果表明两者的分布特性有很好的一致性。研究结果为超声波声场特性分析提供一种新方法。     

开口薄壁结构声固耦合问题的计算方法

对于开口薄壁结构的声辐射问题,很难用解析法直接计算,可采用多种数值方法进行仿真分析。文中研究了有限元法、边界元法与无限元法几种数值方法及其耦合的理论基础,研究了求解不封闭声腔声辐射问题的几种数值方法。在考虑声固耦合的前提下,分析了间接边界元法、直接边界元内外声场耦合法、有限元与边界元耦合法、有限元与无限元耦合法4种方法求解开口结构声场问题的系统方程及求解过程,以具体开口薄壁结构为实例采用4种方法进行了模拟计算,并对结果进行了分析比较,得出相关结论。     

圆筒型非接触式压电作动器的设计与试验研究

 提出了一种基于超声悬浮和驱动的非接触式压电作动器,该作动器中的转子呈完全悬浮状态。转子的悬浮由兰杰文换能器提供,自身旋转与定位由圆筒型定子提供。通过分别对换能器和定子的压电陶瓷片施加电压,使得换能器悬浮端面激发出一阶弯曲振动模态,而定子激发出两相B(0,3)驻波并合成一高声强行波,进而诱发高声强声场来驱动转子。分别建立了非接触式压电作动器中兰杰文换能器和定子的有限元模型,对换能器和定子进行了分析、设计、扫频以及定频试验,确定了结构方案, 最后加工、制造了样机。搭建了整个样机的测试系统,对其悬浮和驱动特性进行了分析,测得转子转速可达4261r/min。结果表明转子在近声场的作用下成功地实现了完全悬浮式的高速旋转。      

基于近场声悬浮的非接触式直线型压电作动器

针对近场声悬浮(NFAL)传输在航空航天、高纯度材料加工以及微机电系统装配操作等领域的良好应用前景,设计出了非接触式直线型压电作动器。该作动器依靠兰杰文振子的振动,产生高声强声场来悬浮并驱动物体沿行波方向运动。先通过动力学分析和结构设计,试制出了一对兰杰文振子样机,并通过实验获得了其动态特性参数;然后,成功制造出了基于NFAL的非接触式直线型压电作动器,此作动器可悬浮传输的最大单位面积质量为3.06g。     

微操作中球基对象的近场声悬浮与旋转驱动研究

针对微操作中圆球类对象的悬浮与操纵问题,从推导圆球的超声波近场声悬浮高度公式入手,确定了影响悬浮高度的主要因素。制作了带有凹球面工具端的专用换能器,实现了圆球的近场声悬浮。进而构建偏心式气动驱动系统,进行了转速与气压、偏心距、悬浮高度及扰动关系的实验。结果表明：出气孔气压是影响转速的主要因素,而偏心距对转速的影响较小;随着悬浮圆球转速增加,悬浮高度降低,扰动加大。     

轴/径向耦合式非接触型压电作动器的研究

提出了一种基于近场声悬浮机理的球转子压电作动器,特别设计了可分别沿轴向和径向辐射超声近场的作动器,其目的是为了实现球转子的稳定、可控悬浮和高速旋转,可将其应用到航空航天的高速电机、球轴承传动或姿态传感领域。该新型压电作动器通过轴向与径向悬浮装置的不同耦合形式来提供超声悬浮力并以非接触的方式驱动球转子,实现对球转子的灵活控制。介绍了轴/径向耦合式非接触型压电作动器的结构和工作原理,通过仿真得到了悬浮装置的声场分布形式,深入分析和阐释了球转子的悬浮和驱动机制,加工了样机,搭建了轴/径向耦合式超声悬浮型压电作动器的特性测试系统,通过非接触式激光位移传感器得到了球转子的悬浮特性,并获得了691.5r/min的转速。     

The near-field acoustic levitation for spheres by transducer with concave spherical radiating surface

To levitate ICF target spheres in the near-field acoustic levitation, a transducer with concave spherical radiating surface and a nearfield acoustic levitation system is established. The concave spherical radiating surface of the transducer is designed by the finite element parametric method. Then the levitation height and levitation perturbation of spheres with different mass and diameters in the near-field acoustic levitation system are tested and discussed in the driving voltage at 400V, 500V and 600V, respectively, when the levitation system is under the resonant frequency. Finally, based on the experimental results, the height formula of the near-field acoustic levitation for spheres is deduced by introducing a coupling coefficient.     

Analysis of the particle stability in a new designed ultrasonic levitation device

The use of acoustic levitation in the fields of analytical chemistry and in the containerless processing of materials requires a good stability of the levitated particle. However, spontaneous oscillations and rotation of the levitated particle have been reported in literature, which can reduce the applicability of the acoustic levitation technique. Aiming to reduce the particle oscillations, this paper presents the analysis of the particle stability in a new acoustic levitator device. The new acoustic levitator consists of a piezoelectric transducer with a concave radiating surface and a concave reflector. The analysis is conducted by determining numerically the axial and lateral forces that act on the levitated object and by measuring the oscillations of a sphere particle by a laser Doppler vibrometer. It is shown that the new levitator design allows to increase the lateral forces and reduce significantly the lateral oscillations of the levitated object.     

NFAL Prototype Design and Feasibility Analysis for Self-Levitated Conveying

In order to avoid friction and scratching when conveying object, an acoustic levitation prototype was designed to verify the feasibility. The modal shapes and the forced harmonic shapes of the prototype are obtained by an ANSYS coupled field computation with a one-quarter symmetry model and the levitation capacity was assessed by the use of groups of simulation and physical testing. The simulation results showed that the pure flexural and mixed flexural wave shapes with different wave numbers existed at some specific frequency. The amplitude in the central point of an aluminum plate having four piezo-electric discs glued to the bottom surface was simulated for a frequency spectrum. The experimental results confirmed the theoretical results and the feasibility of the prototype and confirm that objects can be floated at several resonant frequencies under forced vibrating condition. The system can provide largest bearing capacity when both the piezoelectric disc and the plate resonances coincide.     

超声波马达的真空和温度特性研究

研究了超声波马达在非常状态下的驱动行为,选取了5种工程塑料作为转子摩擦材料,利用真空试验机和自制的与其相匹配的超声波马达模拟试验台,采用对比试验方法,研究了接触预紧力、真空度和环境温度等对行波型超声波马达的驱动特性的影响。结果表明,随着预紧力和真空度的增加,马达的堵转力矩增加而空载转速下降;随着环境温度的增加马达的空载转速下降。运用声学理论分析了真空度对接触状态的影响,得出声悬浮作用使定子和转子的动态接触力减小的结论。在真空状态下,超声波马达的堵转力矩比常态下提高的主要原因是声悬浮作用降低引起定子和转子的动态接触力增加所致。     

Effect of Surface Grooves on the Characteristics of Noncontact Transportation Using Near-Field Acoustic Levitation

ABSTRACT

Near-field acoustic levitation is a novel noncontact handling method. However, low load-carrying capacity and low transportation speed limit its application. This study proposes a novel method in which bar-type grooves are machined on the plate surface to increase load-carrying capacity and transportation speed. An experimental rig with a flexural rail vibrated by piezoelectric transducers is developed to transport the rigid plate and measure the levitation height and transportation speed. The flexural vibration mode of the rail and the dynamic position of the rigid plate are coupled with groove characteristics to determine the gas film thickness between the rail and plate. The Reynolds equation is linearized by using Green's formula and then solved by using an eight-node discrete grid finite difference method. The effects of groove direction, depth, number, width, and length on the load-carrying capacity and transportation speed are also discussed. Numerical results are consistent with the experiment results. The load-carrying capacity and transportation capability can be significantly improved with groove length direction vertical to the rail wave transportation direction. Predicted results show that optimum groove depth, number, width, and length can be used to increase load-carrying capacity and transportation capability.     

Non-contact handling in microassembly: Acoustical levitation

Microassembly is currently of the utmost importance in industry. Nevertheless, the classical assembly processes are no longer usable for very small components, typically ranging from 10  m to 10 mm, since usually neglected surface forces disturb the handling task by inducing adhesion between the component and the gripper. A promising alternative to tackle surface forces consists in levitating the handled component. The various advantages of this contactless handling method are reviewed here and justify the choice of this approach. Consequently, the numerous physical principles suitable for contactless handling are briefly described together with their limitations. The evaluation shows that acoustic levitation is best fitted in the case of microassembly. A classification of literature applications is presented hereafter with special focus on acoustic levitation. Finally, the most common models of acoustical levitation are inspected in a general way. The described models come within the scope of non-linear acoustics.     

Influence of nonlinear characteristics of electromagnet and normal force of a linear induction motor on a magnetically levitated vehicle

In the literature related to maglev vehicles, most studies have primarily discussed the trade-off between a levitation system and guideway smoothness, such as deflection and surface roughness, and the optimization of a levitation controller. A dynamic model integrated with a kinematic vehicle, electromagnetic suspension system, guideway profile, and levitation controller model has been widely used for this purpose. However, in addition to guideway smoothness and stiffness, the normal force of a Linear induction motor (LIM) that is installed in the same bogie frame and drives the maglev vehicle can be regarded as a disturbance element affecting a levitation system. In addition, a linear model of an electromagnetic force is usually used in linear approximations around the nominal equilibrium point, in spite of its nonlinear characteristics. In this study, to analyze the interaction between electromagnetic and normal forces of the LIM, a dynamic model coupled with the normal force calculated from finite element analysis was developed. In addition, to comparatively analyze levitation stability by considering the linear and nonlinear characteristics of electromagnets, the non-linear electromagnetic forces measured in the experiment are coupled to the dynamic model. From the simulation results, it was confirmed that although a slight increase in current was observed with the LIM model when compared to without the LIM model, it produced no adverse effect on levitation stability. In simulation, considering the non-linear characteristics of an electromagnet, it was confirmed that the nominal current of the linear model converged to a higher value than the designed nominal current when the vehicle was standing still, whereas the nominal current of the non-linear was similar to the designed one.